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Engineering the surface chemistry of carbon-based materials is of crucial importance in tuning their intrinsic properties, including electrical conductivity, wettability, electroactivity, adsorption potential, reactivity, physical and chemical stability. Intense research has recently focused on understanding the role of surface oxygen functional groups when carbon materials are in contact with an electrolyte or solvent in order to tailor and improve them for technological applications. For this purpose, their synthesis method and/or further oxidation treatments should be carefully selected, since they can substantially influence not only the oxygen content, but also the nature of the oxygen moieties, which could be decisive in determining the surface properties of the resulting material. The combined use of different chemical, spectroscopic and electrochemical techniques, provides unique and reliable information about the contribution of a specific oxygen-containing group in the surface (electro)chemistry of carbon-based materials. This paper provides a discussion of the role of oxygen heteroatoms in the surface electrochemistry of a carbon material as they relate to their influence on both its electroactivity and reactivity. G.A.M. and B.M.S thanks Ministerio de Universidades (grant number: FPU18/05127 and FPU20/03969). The authors would like to thank PID2019-105923RB-I00 and PID2021-123079OB-I00 projects funded by MCIN/AEI/10.13039/501100011033 and “ERDF A way of making Europe”.

Covalent functionalization of multi-walled carbon nanotubes (MWCNTs) and oxidized MWCNTs (o-MWCNTs) with chlorodiphenylphosphine (Ph2PCl) has been studied by cyclic voltammetry in organic medium. Depending the upper potential limit used in the electrochemical functionalization, different amount of phosphorus incorporation n is obtained, as result of the formation of radical species during the electrochemical oxidation of the Ph2PCl. The electrochemical oxidation of Ph2PCl promotes the covalent attachment of diphenylphosphine-like structure on the carbon nanotube surface. At the same time, the incorporation of Cl on the carbon nanotubes is observed during the functionalization. Furthermore, the presence of oxygen surface groups on the MWCNTs provides a favorable attachment of the Ph2P ∙ + species, which has promoted preferentially the formation of C-P bonds, whereas the amount of Cl is reduced. The authors would like to thank MINCIN (PID2019-105923RB-I00) for the financial support.

Pt nanoparticles were incorporated on carbon black (Vulcan XC-72R) and an activated carbon (F400) using a fast and efficient microwave method. For the preparation, a Pt solution was contacted with the corresponding carbon sample and heated up to 110°C in a microwave oven using an optimised heating rate. TEM images revealed that the carbon-supported Pt nanoparticles had a small average particle size and high dispersion. These Pt-based electrocatalysts showed both high electrocatalytic activity and selectivity towards the 4-electron pathway for the oxygen reduction reaction (ORR) in acid and alkaline media. In addition, they presented excellent stability and resistance to CO poisoning. Moreover, the as-prepared electrocatalysts exhibited outstanding electrocatalytic behaviour for the hydrogen evolution reaction (HER). It should be highlighted that, even though our Pt-based electrocatalysts have much lower loadings than that of the commercial Pt/C sample (used as reference), the electroactive surface areas of as-prepared electrocatalysts were higher compared to the reference electrocatalyst. Such small and well-dispersed Pt NPs with an enhanced electroactive surface area and strong interaction with the carbon support, led to an improvement of the current density normalised by Pt loading (A gPt−1). The authors would like to thank PID2019-105923RB-I00 and PID2021-123079OB-I00 projects project funded by MCIN/AEI/10.13039/501100011033 and “ERDF A way of making Europe”, the Generalitat Valenciana (GRISOLIA/2020/114) and CONACYT project SEP-CB-2014-01-237118 and FORDECYT-2018-8-297525 for their financial support.

This work describes the development and characterization of fluorescent nanocomposite hydrogels, with high swelling and absorption capacity, and prepared using a green protocol. These fluorescent materials are obtained by incorporating, for the first time, polyfluorenes-based nanoparticles with different emission bands—poly[9,9-dioctylfluorenyl-2,7-diyl] (PFO) and poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(1,4-benzo-{2,1,3}-thiadiazole)] (F8BT)—into a three-dimensional polymeric network based on polyacrylamide. To this end, two strategies were explored: incorporation of the nanoparticles during the polymerization process (in situ) and embedment after the hydrogel formation (ex situ). The results show that the combination of PFO nanoparticles introduced by the ex situ method provided materials with good storage stability, homogeneity and reproducibility properties, allowing their preservation in the form of xerogel. The fluorescent nanocomposite hydrogels have been tested as a transportable and user-friendly sensing platform. In particular, the ability of these materials to specifically detect the enzyme alkaline phosphatase (ALP) has been evaluated as a proof-of-concept. The sensor was able to quantify the presence of the enzyme in an aqueous sample with a response time of 10 min and LOD of 21 nM. Given these results, we consider that this device shows great potential for quantifying physiological ALP levels as well as enzyme activity in environmental samples. This work was funded by the Spanish Ministry of Science and Innovation (TED2021-129894B-I00). The study forms part of the Advanced Materials programme and was supported by MCIN with funding from European Union NextGenerationEU (PRTR-C17.I1) and Generalitat Valenciana (MFA/2022/058). DLS, FESEM and Fluorescence lifetime spectrometer equipment acquisition funded by Generalitat Valenciana–Conselleria d’Educació Investigació Cultura i Esport and EUFEDER “Una forma de hacer Europa” (GVA-IDIFEDER/2018/020 and GVA-IDIFEDER/2021/036).

Graphene-based materials were synthesized by electrochemical exfoliation method (cathodic method) starting from a graphite sheet. In the established methodology, an initial immersion in H2SO4 was applied, followed by cathodic expansion in potassium sulphate, where the effect of the applied voltage was studied. Finally, by ultrasound treatment, the exfoliation was achieved to produce a dispersion of few layer graphene material. Once the optimum procedure was established, Pt nanoparticles were incorporated using H2PtCl6.6H2O. This incorporation was studied at each stage of the graphene-based material synthesis to determine which was the most adequate to obtain the highest Pt dispersion and the best distribution of the Pt nanoparticles. In this sense, the incorporation of Pt in the graphene-based material colloidal dispersion by stirring for 3 h and sonication for 1 h, results in Pt nanoparticles with an average size of around 1 nm with an excellent distribution in the carbon material. The performance of this catalyst was compared with the commercial Pt/C electrocatalyst, showing a great oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) activity, exceeding it by far when comparing the mass-specific activity (A gPt−1) In addition, it presents excellent stability and selectivity toward the 4-electron pathway in ORR, which is the most energy-efficient, and using half of the platinum loading compared to the commercial material. The authors would like to thank PID2019-105923RB-I00 and PID2021-123079OB-I00 projects funded by MCIN/AEI/10.13039/501100011033 and “ERDF A way of making Europe”, and the Generalitat Valenciana (GRISOLIA/2020/114) for the financial support.

Biphasic interfacial electron transfer (IET) reactions at polarisable liquid|liquid (L|L) interfaces underpin new approaches to electrosynthesis, redox electrocatalysis, bioelectrochemistry and artificial photosynthesis. Herein, using cyclic and alternating current voltammetry, we demonstrate that under certain experimental conditions, the biphasic 2-electron O2 reduction reaction can proceed by single-step IET between a reductant in the organic phase, decamethylferrocene, and interfacial protons in the presence of O2. Using this biphasic system, we demonstrate that the applied interfacial Galvani potential difference ΔwoØ provides no direct driving force to realise a thermodynamically uphill biphasic IET reaction in the mixed solvent region. We show that the onset potential for a biphasic single-step IET reaction does not correlate with the thermodynamically predicted standard Galvani IET potential and is instead closely correlated with the potential of zero charge at a polarised L|L interface. We outline that the applied ΔwoØ required to modulate the interfacial ion distributions, and thus kinetics of IET, must be optimised to ensure that the aqueous and organic redox species are present in substantial concentrations at the L|L interface simultaneously in order to react. M.D.S. acknowledges funding from Science Foundation Ireland (SFI) under grant no. 13/SIRG/2137 and the European Research Council through a Starting Grant (agreement no. 716792). A.G.-Q. acknowledges funding received from an Irish Research Council (IRC) Government of Ireland Postdoctoral Fellowship Award (grant number GOIPD/2018/252) and a Marie Skłodowska-Curie Postdoctoral Fellowship (Grant Number MSCA-IF-EF-ST 2020/101018277).

Electrocatalysis at the interface between two immiscible electrolyte solutions (ITIES) is an emerging field of research, which allows the separation of reactants according to their lipophilicity. Electrocatalysts of various nature (noble metals, carbon-based and inorganic nanomaterials, enzymes and supramolecular ensembles) are assembled at the ITIES, either spontaneously or following the application of an interfacial Galvani potential difference. While primarily used for the electrocatalysis of the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER), recent work has focused on the electrocatalysis of the oxygen evolution reaction (OER) and the electrocatalytic oxidation of elemental sulfur (S8) and an organosulfur compound. Protocols to compare electrocatalytic performances at the ITIES call for careful data analysis and a detailed knowledge of the catalysts morphological parameters (e.g., active surface area and catalyst loading). However, standardisation of such protocols at the ITIES has yet to be implemented and is required to allow better comparison of the results from individual biphasic systems. M.D.S. acknowledges funding from the European Research Council through a Starting Grant (agreement no. 716792). A.G.-Q. acknowledges funding received from an Irish Research Council (IRC) Government of Ireland Postdoctoral Fellowship Award (grant no. GOIPD/2018/252) and a Marie Skłodowska-Curie Postdoctoral Fellowship (grant no. MSCA-IF-EF-ST 2020/101018277). P.P. acknowledges funding from the European Research Council through a Starting Grant (agreement no. 950038), the Academy Research Fellow funding and project funding by the Academy of Finland (Grants No. 315739 and 334828).

Life Cycle Assessment (LCA) is applied to eco-design the H3PO4-assisted hydrothermal carbonization (HTC) process converting biomass residue into high-value products. The main innovation of the process relies on the combination of the H3PO4-assisted HTC with the activation treatment of the obtained hydrochar, resulting in activated carbon that is then functionalized. In addition, the liquid phase obtained from HTC is eventually purified to extract levulinic acid. Under average conditions at the laboratory scale (reference), the LCA showed that electricity consumption is the main contributor (45–70%) to impacts on climate change, photochemical ozone formation, acidification, freshwater eutrophication, freshwater ecotoxicity and fossil resources use. Pyridine, the main chemical used in the functionalization stage, contributes to impacts on human toxicity and on marine eutrophication respectively by 77.3% and 47.3%. Building on these results, two further scenarios were studied, one considering the maximum capacity of each equipment and another one assuming the potential improvements once the process will be upscaled. The scenarios were validated in a series of laboratory scale tests. Depending on the environmental impact category chosen, the results showed a reduction potential of 30–65% as compared to the reference scenario. These findings confirm the added value of LCA in the ecodesign of technologies and pave the way to further improvements of the technology itself but also of the LCA methodology used for the assessment. This research was partially supported by the MICINN, FEDER (RTI2018-095291-B-I00). JCG thanks for her predoctoral scholarships (GRISOLIA/2018/105) and (BEFPI/2020/067) funded by the Generalitat Valenciana and DST thanks MICINN for the “Juan de la Cierva” contract (IJCI-2016-27636).

LaNi1-xCoxO3 perovskite materials were synthesized by a sol-gel method for use in electrochemical reactions which involve molecular oxygen. The metal oxides were characterized by different physicochemical techniques and it was observed that the incorporation of Co induces some changes in the surface of the materials that affect the electrocatalytic activity. The different perovskite metal oxides were mixed with carbon black (Vulcan) to improve their electrocatalytic performance. The results from TPR and TPD techniques supported the XPS interpretation suggesting that a stronger interaction between carbon material and metal oxides can be obtained by physically mixing the two materials. This interaction improves the electron transfer and enhances the catalytic activity. Among the as-prepared materials, it was observed that the electrocatalytic performance of LaNi1-xCoxO3 perovskite/Vulcan materials is higher than that of LaNiO3/Vulcan for ORR, but similar towards OER. It is claimed that Co3+ is more catalytic for ORR, while Ni3+ favors the OER. Moreover, the presence of Co stimulates the formation of chemisorbed oxygen species, which also favor the electron transfer. Metal oxides containing both cations show higher stability, being this effect more notorious for OER. LaNi0.5Co0.5O3/Vulcan seems a suitable bifunctional catalyst for both electrochemical reactions. The authors thank to the Ministerio de Ciencia e Innovación (PID2019-105923RB-I00) for financial support. J.X.F.-L. gratefully acknowledges MINECO for financial support through an FPI contract (BES-2017-081598).

This paper explores the synthesis, characterization and electrocatalytic behavior of a new ferrocenyl-substituted tetradentate Nickel Schiff base complex. The complex, N,N-Bis[5-(N,N-ferrocenmethylaminophenyl)methylsalicylidyne]-1,2-diaminoethane of nickel(II) ((Fc-Me-Ani)2-LNiII), was prepared by heating the tetradentate Schiff base ligand ((Fc-Me-Ani)2-H2L) in the presence of a stoichiometric amount of tetrahydrate nickel(II) acetate salt, dissolved in a mixture of ethanol and methylene chloride at 50°C under N2 atmosphere. The molecular structure of the complex was deduced from elemental analysis, FT-IR, UV-Vis and mass spectrometry. The electrochemical characterization was investigated by cyclic voltammetry on a glassy carbon electrode and the effect of the solvent (methylenechloride (DCM), dimethylformamide (DMF) and dimethylsulfoxide (DMSO)) was analyzed. The electrochemical characterization of the nickel complex reveals the electron-transfer capability of the two electroactive redox moieties, ie. the ferrocenyl moieties (Fc+‏/Fc) and the metallic centre (Ni2+/Ni+). The diffusion coefficient (D) and the standard rate constant (K0) have also been calculated from the cyclic voltammetry and the polarization curves of ferrocenyl redox process. So, they are influenced by both used method and medium. Cyclic voltammetry has also been performed to examine the performances of the electrocatalytical reduction reaction towards two alkylhalides like ethyl chloroacetate and ethyl bromoacetate in DMF solution. The current increase and the cathodic shift of the Ni2+→Ni+ reduction process in the presence of increasing concentrations of these alkyl halides evidence the catalytic effect of the (Fc-Me-Ani)2-LNiII complex in the reduction of these compounds. The authors would like to thank the MESRS and DG-RSDT (Ministère de l'Enseignement Supérieur et de la Recherche Scientifique et la Direction Générale de la Recherche et du Développement Technologique-Algérie) for their financial support. Financial support from the Ministerio de Ciencia e Innovacion funds (PID2019-105923RB-I00, RYC-2017-23618) is also gratefully acknowledged.

The organosulfur compound 2,5-dimercapto-1,3,4-thiadiazole (DMcT) finds widespread applications in batteries, lubricant fluids, heavy metal ion sensors, waste-water purification and as a biocide. In this article, we demonstrate the untapped versatility inherent to using biphasic systems for electrosynthesis by showcasing several successful approaches to the electrosynthesis of poly(DMcT) films at a polarised interface between two immiscible electrolyte solutions (ITIES) by cyclic voltammetry (CV) cycling using either I2, Hg2+ or O2 as the oxidising agents. AC voltammetry is demonstrated as an effective in situ method to monitor poly(DMcT) film formation by I2 or Hg2+ as a function of the aqueous electrolyte anion and pH. DMcT is further shown to act as a binder molecule to promote interfacial gold nanoparticle (AuNP) assembly into floating films at an immiscible liquid|liquid (L|L) interface. Exploiting the electrocatalysis of DMcT oxidation by O2 in the presence of adsorbed interfacial AuNPs yields AuNP/poly(DMcT) composite films. Raman spectroscopy suggests the latter were a coordination polymer of poly(DMcT) with AuNPs and surface enhanced Raman spectroscopy (SERS) active. The dielectric nature of the poly(DMcT) films suppresses the capacitance at the ITIES, yet the AuNP/poly(DMcT) films show a very high interfacial capacitance, with an ability to efficiently adsorb cations. Thus, these films open opportunities to selectively modulate the interfacial capacitance, potentially forming the basis of novel “soft” capacitors at a polarised L|L interface. M.D.S. acknowledges Science Foundation Ireland (SFI), under Grant No. 13/SIRG/2137 and the European Research Council Through a Starting Grant (Agreement No. 716792). A.G.-Q. acknowledges funding received from an Irish Research Council (IRC) Government of Ireland Postdoctoral Fellowship Awards (Grant No. GOIPD/2018/252). M.F.S.-H. acknowledges the “Universidad Nacional de Colombia” for allowing his sabbatical leave and the “Fundación Banco de la República” through the grant 4.562.

The interest for the electrodes based on conductive boron-doped diamond powder (BDDP) is increasing in recent years due to their excellent physical and chemical stability, the wide potential window in both aqueous and organic electrolytes, the relatively large specific surface area, and their versatility in comparison to boron-doped diamond thin film electrodes. These materials have been proposed as alternative cathode catalyst support due to their high corrosion resistance when subjected to the highly positive potentials originated during the start-stop operations in fuel cells, especially in automobiles. In this work, we present three BDDP supports with different particle sizes and different surface oxygen contents as supports of different iron species for oxygen reduction reaction in alkaline solution. BDDP supports were modified with carbon nitride (C3N4) or phthalocyanines (Pc) as anchoring points for iron. The different electrocatalytic performance observed confirmed the strong influence of the surface chemistry of the BDDP supports on the activity of the metallic sites for FePc samples while, for Fe-C3N4 samples, the determining effect was the particle size of the BDDP support. Additionally, DFT calculations were used to obtain some insights about the interaction of the FePc with the diamond surface. The authors would like to thank PID2019-105923RB-I00 and PID2021-123079OB-I00 projects funded by MCIN/AEI/10.13039/501100011033 and “ERDF A way of making Europe”. B. Martínez-Sánchez and G. Alemany-Molina thank Ministerio de Universidades for the FPU18/05127 and FPU20/03969 grants, respectively.

Hybrid materials consisting of aniline (ANI) and/or 2‐aminodiphenylamine (PD) in the presence of V2O5 nanoparticles were synthesized by in‐situ chemical oxidative polymerization in one‐step. Physicochemical and electrochemical characterization confirmed that in the structure of the composites, intercalation between the polymer chains and the V2O5 slabs occurs. Optical properties study shows that the optical band gap of poly(ANI‐co‐PD)/V2O5 is lower than poly‐PD/V2O5. Thermal stability of the composites by thermogravimetric analysis was evaluated. Composites showed electrochemical activity with improved electron‐transfer of the redox species in the polymer observed by cyclic voltammetry. These results highlight the great influence of the V2O5 sheets and the polymer composition on the hybrid materials formation and properties. The authors wish to acknowledge the directorate General of Scientific Research and Technological Development (DGRSDT) (Algeria). Financial support from the Spanish Ministerio de Ciencia e Innovación (PID2019-105923RB-I00) is gratefully acknowledged. A.F.Q.J. gratefully acknowledges Generalitat Valenciana for the financial support through Santiago Grisolía grant (GRISOLIA/2016/084).

Iron(II) phthalocyanines (FePc) supported on functionalized nanostructured carbon materials have been studied as electrocatalysts for the oxygen reduction reaction (ORR) in an alkaline medium. Herein, two types of carbon nanotubes (CNTs) have been explored as support, Single-Walled Carbon Nanotubes and Herringbone Carbon Nanotubes (SWCNTs and hCNTs, respectively), both electrochemically modified with ortho- aminophenylphosphonic acid (2APPA), which provides phosphate axial coordinating ligands for the immobilization of FePc molecules. All the catalysts were prepared via a facile incipient wetness impregnation method. Comprehensive experimental analysis together with density functional theory (DFT) calculations has demonstrated both the importance of the five-coordinated Fe macrocycles that favor the interaction between the FePc and the carbon support, as well as the effect of the CNT structure in the ORR. FePc axial coordination provides a better dispersion, leading to higher stability and a favorable electron redistribution that also tunes the ORR performance by lowering the stability of the reaction intermediates. Interestingly, such improvement occurs with a very low content of metal (∼1 wt% Fe), which is especially remarkable when hCNT support is employed. This work provides a novel strategy for the development of Fe-containing complexes as precious metal-free catalysts towards the ORR. B.M.-S. thanks the Ministry of Science, Innovation and Universities of Spain for the FPU grant (FPU18/05127). The authors would like to thank MCI/AEI and FEDER, UE (PID2019-105923RB-I00, RTI2018-095291-B-I00 projects) for the financial support.

One of the biggest challenges in producing fuel cells at affordable prices is to synthesize carbon materials selectively doped with graphitic nitrogen, as it is considered the most active nitrogen species for the oxygen reduction reaction (ORR). So far, all strategies focus on the use of nitrogen-containing carbon precursors, which limits the functionalization of commercially available carbon materials. Here, we present a post-functionalization method to boost the catalytic properties of carbon materials for the ORR by selectively enriching activated carbons with nitrogen graphitic species. A commercial high-surface area activated carbon was post-functionalized by a two-step procedure. First, the commercial carbon was mixed with different carbon/urea weight ratios and heated in air at 350 °C. Then, the functionalized materials were heat-treated at high temperature (from 700 to 1300 °C) to tailor the amount and distribution of the different nitrogen species in the resulting carbon structure. Nitrogen functionalization using a carbon to urea weight ratio of 1:2 and heat-treatment at 1100 °C led to highly selective doping in graphitic nitrogen species, which provided the tools to individually asses the catalytic activity of these nitrogen species. In addition, this study presents a low-cost and easily feasible synthesis route to improve the catalytic activity of carbon materials, leading to an onset potential of almost 0.9 V compared to reversible hydrogen electrode for ORR in an alkaline electrolyte. Moreover, this study provides significant evidence for the key role of graphitic nitrogen. The French research team thanks ANR-15-IDEX-04-LUE and the TALiSMAN project (2019-000215), financed by the European Regional Development Fund (ERDF). The authors from UA thank MICINN and ERDF (project RTI2018-095291-B-I00) for financial support.

[EN] Transition metal oxide-based materials are an interesting alternative to substitute noble-metal based catalyst in energy conversion devices designed for oxygen reduction (ORR), oxygen evolution (OER) and hydrogen evo-lution reactions (HER). Perovskite (ABO3) and spinel (AB2O4) oxides stand out against other structures due to the possibility of tailoring their chemical composition and, consequently, their properties. Particularly, the elec-trocatalytic performance of these materials depends on features such as chemical composition, crystal structure, nanostructure, cation substitution level, eg orbital filling or oxygen vacancies. However, they suffer from low electrical conductivity and surface area, which affects the catalytic response. To mitigate these drawbacks, they have been combined with carbon materials (e.g. carbon black, carbon nanotubes, activated carbon, and gra-phene) that positively influence the overall catalytic activity. This review provides an overview on tunable perovskites (mainly lanthanum-based) and spinels featuring 3d metal cations such as Mn, Fe, Co, Ni and Cu on octahedral sites, which are known to be active for the electrochemical energy conversion., The authors thank to the Ministerio de Ciencia e Innovacion/AEI (PID 2019-105923RB-I00) for financial support. J.X.F.-L. gratefully acknowledges MINECO for financial support through an FPI contract (BES- 2017-081598).

This paper describes the synthesis and properties of a new nitro-substituted bidentate Schiff base ligand (HL) and its nickel complex (Ni(II)-2L). Its ligand was derived from the condensation of 2′-methoxyphenyl-2-ethylamine with 5-nitro-2-hydroxybenzaldehyde. This ligand and its nickel complex were characterized through elemental analysis, UV–Vis, IR, 1H NMR and 13C NMR. The molecular structure of the nickel complex was confirmed using single-crystal X-ray diffraction. This complex crystallizes in dichloromethane in triclinic system, space group of P-1 with a = 6.6803 (2), b = 9.6702 (2), c = 12.1836 (3) and 1 formula unit in the cell. The obtained data revealed that the Ni(II) center is tetra-coordinated by two oxygen and two nitrogen atoms involving two ligands. Cyclic voltammograms of the nickel complex, recorded in DMF solutions, showed one quasi-reversible redox couple related to the Ni(II)/Ni(I) couple, demonstrating its electro-activity. This indicates a slow redox transition and/or electron exchange process, which implies that this electrochemical process is mainly diffusion-controlled. The antioxidant activity of the synthesized compounds was evaluated from the reactivity with the free radical DPPH, showing IC50 values between 0.4 and 4.5 mg/mL. The authors thank the Algerian Ministry of Higher Education and Scientific Research (MESRS) and the Directorate General of Scientific Research and Technological Development (DGRSDT) for their financial support. The authors also gratefully acknowledge the financial help (MAT2016-76595-R) of the Ministerio de Economía y Competitividad and FEDER. Special thanks are owed to the Spanish Ministry of Economy and Competitiveness (MINECO) for the granting of a “Ramón y Cajal” contract (RYC-2017-23618).

Zn-air batteries (ZABs) are promising electrochemical devices to store energy. Metal oxide perovskites mixed with carbon materials are highlighted as interesting materials for this application because of their appropriate bifunctional performance in oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The interaction between both components of the electrocatalyst is important in the bifunctional electrocatalytic activity, and the mixing method plays an important role in this interaction. Then, different mixing methods have been studied in this work (ball-milling, mortar and manual shaking). The use of different physicochemical techniques such as temperature programmed desorption (TPD), temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS) in the materials characterization, allows us to conclude that the mixing method strongly influences the particle size and the interaction between both components, which determine the final electrocatalytic activity. The materials prepared by ball-milling displayed the best performance. Herein, the experimental conditions were optimized to obtain electrocatalysts with enhanced electrocatalytic activity for ORR and OER. Low rotating speed, air atmosphere and low ball-milling time generate electrocatalysts with a small nanoparticle size, more homogeneous and with a higher interaction between both components, which enhances electron transfer, and consequently, the overall oxygen-involved reactions. The best electrocatalyst obtained was studied as air-electrode in a Zn-air battery and it was compared to a commercial Pt/C electrocatalyst, obtaining higher cyclability (55.2 vs. 51.7%) for 30 h, and higher energy density at 5 mA/cm2 (764 mAh/g vs. 741 mAh/g). The authors would like to thank PID2019-105923RB-I00 project funded by MCIN/AEI/10.13039/501100011033. J.X. Flores-Lasluisa thanks the MICINN for the FPI contract (BES-2017-081598 for). M. García-Rodríguez thanks for the funding of the Research Initiation Scholarship from Vicerrectorado de Investigación y Transferencia de Conocimiento of the University of Alicante (AII-20-14) and Ministerio de Universidades for the FPU20-01746 grant.

Oxygen reduction reaction (ORR) is one of the most important electrochemical reactions for fuel cells. However, commercial Pt-based catalysts used have important limitations such as their deactivation by carbon monoxide and Pt scarcity. In the present work, small and highly-dispersed copper and iron clusters were anchored onto composite supports based on carbon nitride (C3N4) nanostructures and a highly porous carbon material. Catalysts with a moderate carbon nitride content showed an interesting catalytic behaviour because of the combination of the metallic active sites and the availability of micropores, which play an active role in ORR. The presence of either Fe or Cu in the synthesis affected the structure of the resulting composite materials, as well as their electrocatalytic activity. Copper-based materials showed superior catalytic activity, which is supported by the information obtained from the evaluation of the system using DFT computational calculations. This work was financed by the MCI/AEI/FEDER, UE (RTI2018-095291-B-I00). G.A.M thanks the Research Initiation Scholarship from Vicerrectorado de Investigación y Transferencia de Conocimiento of the University of Alicante and Ministerio de Universidades (grant number: FPU20/03969). M.N.G. thanks the Plan GenT project (CDEIGENT/2018/027) for the financial support.

N-doped carbon materials have been considered one of the most promising options for the replacement of platinum-based electrocatalysts towards the oxygen reduction reaction (ORR). This work provides insights into the deactivation routes of N-doped carbon materials. The changes occurring in the active sites of N-doped carbon catalysts have been analyzed in detail through pre- and post-ORR characterization by XPS of selectively N-doped carbon materials. Moreover, computational modelling was used to deepen into the deactivation mechanism of N-doped carbon materials in the ORR. From XPS and computational modelling, it can be concluded that the deactivation of graphitic-type nitrogen species, during the ORR in both acidic and alkaline environments, occurs through oxidation and tautomerization reactions that result in the formation of N–C–O-type groups. In acidic environment, the reaction kinetics is slower due to the high stability of the ORR intermediates. In alkaline electrolyte, the N–C–O-type groups can be easily formed due to the interaction of graphitic-type N species and the OH− anions from the electrolyte. In this case, the catalytic activity is due to the contribution of both graphitic nitrogen groups and N–C–O species. The authors would like to thank MICINN and FEDER (projects PID2019-105923RB-100 and RTI2018-095291-B-I00) for the financial support.

Firstly, Polyaniline-derived@poly(styrene sulfonate) (PANI-derived@PSS) hydrogel materials have been prepared by supramolecular self-assembly between positively charged poly(aniline-co-piperazine) (poly(Ani-co-Pip) chain and negatively-charged PSS chain by oxidative polymerization method. The study of the monomer ratio (X) (aniline:piperazine) has been analyzed. Afterwards, symmetric capacitors based on poly(ANI-co-Pip)@PSS-X mixed with Vulcan (Vu) have been studied. A combination of different techniques like cyclic voltammetry, Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and Thermogravimetric analyses (TGA) were applied to characterize both the chemical structure and the behavior of the hydrogels. The different hydrogels have exhibited electrical conductivity and electroactivity in acid conditions. Moreover, the effects of Vulcan on the structure and properties of poly(ANI-co-Pip)@PSS have been investigated. Additionally, supercapacitors based on as-prepared poly(ANI-co-Pip)/Vu@PSS displayed an improvement of capacitor performance compare to that of conventional hydrogels-based capacitors. This study offers valuable hints for achieving the preparation of supramolecular materials. The authors wish to thank the Management Algerian Ministry of Higher Education and Scientific Research for providing facilities for this work. The authors thank also to the Generalitat Valenciana (project Prometeo2018/087).

Two analytical methods based on miniaturized electrochemical sensors, voltammetric and amperometric sensors, have been developed for the determination of 6-methyl-2-thiouracil (MTU) in meat consumption samples (beef liver and foie). A multivariate approach has been considered to optimize the experimental procedure including extraction and electrochemical detection. Under optimal conditions and at a typical working potential of 1.55 V (vs Ag pseudo-reference electrode), response is linear in the range 0 to 20 µg L−1 MTU concentration range. The empirical limit of detection is 0.13 µg L−1, lower than the maximum concentration established by legislation. The electrochemical methods have been used to analyze MTU-spiked meat samples, and recovery values varying between 85 and 95% with coefficients of variation

[EN] The redox transitions of PANI in acidic medium have been monitored by a combination of cyclic voltammetry, in situ conductance and in situ FTIR spectroscopy. The results of the semiquantitative analysis strongly suggest that the classical tetrameric model of PANI does not satisfactorily describe the actual structures of the polymer at different redox states. An octameric model is revisited, with the inclusion of essential resonant structures, to provide an appropriate prediction of the relative IR intensity changes of the aromatic Csingle bondC stretching (at around 1520 cm¿1) and the quinoid Cdouble bondC stretching (at around 1590 cm¿1) vibrations observed by FTIR, which are difficult to interpret by considering only 4 aniline rings. Particularly, it is found that the emeraldine state is better described as a resonance hybrid of the classical bipolaronic and semiquinoid (polaron lattice) structures, while most of the charge transferred at the onset of the second voltammetric peak comes from the additional oxidation of this hybrid, which becomes unstable in the electrochemical environment producing mineralization to CO2 and release of soluble quinones., This work was financed by the Spanish Ministerio de Ciencia e Innovacion (project PID2019-105923RB-I00) and by Generalitat Valenciana (Conselleria de Educacion, Investigacion, Cultura y Deporte through project PROMETEO/2018/087). The authors of this work are deeply grateful to Prof. Jose Luis Vazquez Pico (Pepe, nowadays retired) for his mentorship, which was the seed to develop this work. We appreciate the wise advice he gave us during our careers which served us to deepen the science contained in this article, as well as for the friendship with which he honored us over the years.

Large-scale environmental applications of microbial electrochemical technologies (MET), such as wastewater treatment, bioremediation, or soil improvement, would be more feasible if bioelectrodes could be fabricated with simpler materials. Biochar with potentially improved electroactive properties (e-biochar) can be an ideal candidate for this scope, being at the same time widely available, biocompatible, and fully recyclable at its end-of-life as a soil amendment. Here we review the application of biochar to MET, to set benchmarks aimed at tuning the electroactive properties of such materials from the point of view of MET. The precursor biomass, thermochemical process conditions, and pre-, in situ-, and/or post-treatments should tailor optimized combinations of electrical conductivity, capacitance, superficial redox-active and electroactive functional groups, porosity distribution, and capacity to host electroactive microbial communities. We also discuss methods to rigorously characterize e-biochar properties and the most relevant multidisciplinary research challenges toward its application in large-scale MET. This work has been financed by the Italian Ministry of University and Research (MIUR), within the SIR2014 Grant, project RBSI14JKU3. Dr. R. Berenguer also thanks the Spanish Ministerio de Economía y Competitividad and FEDER funds (RYC-2017-23618 and CTM2015-71520-C2-1-R) for financial support. Ricardo Louro and Catarina Paquete thank Fundação para a Ciência e a Tecnologia (FCT) Portugal [PTDC/BBBBQB/4178/2014 and PTDC/BIA-BQM/30176/2017], by Project LISBOA-01-0145-FEDER-007660 (Microbiologia Molecular, Estrutural e Celular) funded by FEDER funds through COMPETE2020 - Programa Operacional Competitividade e Internacionalização (POCI), and by ITQB research unit GREEN-it “Bioresources for sustainability” (UID/Multi/04551/2013). This work has also received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 810856. This investigation has also received funding from the European Union’s Horizon 2020 research and innovation programme under the grant agreement No. 642190 (Project “iMETLAND”; http://www.imetland.eu).

P-postmodified polyaniline was obtained by reacting phosphorus trichloride (PCl3) and chlorodiphenylphosphine (PPh2Cl) and polyaniline (PANI), under mild conditions. The reaction was found to be very selective, as only the imine groups were involved in the P-functionalization, and efficient as well, affording a P-loading of 3 at.% and 5 at.% for PPh2Cl and PCl3, respectively. All the polymers were characterized by different techniques and the results were endorsed by theoretical calculations. Experimental and Density Functional Theory results proved that the reaction occurs through the imine groups and the phosphorus atoms, generating NP bonds. The electrochemical properties of the NP modified materials were evaluated and the catalytic activity towards oxygen reduction reaction was measured. It was found that a high concentration of phenyl groups from PPh2Cl (about 3 at.%) affected negatively the activity of the catalyst since they prevented the access of the oxygen molecules to the catalytic active sites. However, a lower amount of PPh2 groups (1 at.%) or the use of PCl3 avoided this hindrance and resulted in an improved catalytic activity with respect to pristine PANI. The authors thank MINECO, MICIUNIN, FIS2015-64222-C2-2-P and FEDER (RTI2018-095291-B-I00 and MAT2016-76595-R) for the financial support.

Knowledge of the carbon active sites for Oxygen Reduction Reaction (ORR) remains confusing and controversial and thus the detailed mechanism is still not clarified. Considering the nature of the carbon-oxygen interaction in active sites during the gasification reaction, it could be inferred that the sites for this reaction are the same as those participating in the ORR. Herein, the relationship between carbon-oxygen gasification properties and ORR activities was elucidated. Carbon materials including different structures and porosities were selected and extensively characterized in terms of structural and electrochemical properties. Regarding gasification properties, active surface area (ASA) and reactivity for carbon-oxygen reaction were determined. A good linear correlation is found between ORR activity and carbon-oxygen gasification reactivity. Interestingly, similar correlation is found between ORR activity or gasification reactivity and ASA, although two different slopes are observed for the analyzed samples, being higher for the carbon nanotubes (CNT) based samples. The results suggest that the active sites participating in the gasification reaction can be catalytic sites for ORR although the specific catalytic activity is determined by the carbon structure. Thus, active sites in CNT show higher activities toward ORR and carbon gasification reactivities than others. The authors gratefully acknowledge the financial support by MINECO (CTQ2015-66080-R MINECO/FEDER) and HEIWA NAKAJIMA FOUNDATION.

Synthesizing high-activity metal/heteroatom-co-doped carbon (M/H–C) electrocatalysts for the oxygen reduction reaction (ORR) is critical for the commercialization of fuel cells, but remains challenging because of the difficulty in making highly dispersed (M/H–C) electrocatalysts. Herein, a commercial ion-exchange resin, Amberlyst 15, is used as a support, and Co/2-methylimidazole is anchored on the ion-exchange site of the support to obtain Co/N/Amb as the precursor of the M/H–C electrocatalyst. After the precursor is pyrolyzed and converted into Co/N/C materials, it is activated with CO2, and the obtained material (act-Co/N/C) exhibits remarkable ORR activity with a high onset potential of 0.943 V (vs. the reversible hydrogen electrode) and an excellent kinetic current density comparable to commercial 5 wt% Pt/C in an alkaline medium. The favorable activity is mainly attributed to the ultra-dispersed CoNx and high porosity of act-Co/N/C. Our synthetic strategy could be applied to the preparation of other well-dispersed M/H–C materials. This work opens a new direction in the synthetic strategy of carbon materials. Financial support from MINECO (CTQ2015-66080-R) and HEIWA NAKAJIMA FOUNDATION is acknowledged.

The present work describes the development of an easy-to-use portable electrochemical biosensor based on alkaline phosphatase (ALP) as a recognition element, which has been immobilized in acrylamide-based hydrogels prepared through a green protocol over disposable screen-printed electrodes. To carry out the electrochemical transduction, an electroinactive substrate (hydroquinone diphosphate) was used in the presence of the enzyme and then it was hydrolyzed to an electroactive species (hydroquinone). The activity of the protein within the matrix was determined voltammetrically. Due to the adhesive properties of the hydrogel, this was easily deposited on the surface of the electrodes, greatly increasing the sensitivity of the biosensor. The device was optimized to allow the determination of phosphate ion, a competitive inhibitor of ALP, in aqueous media. Our study provides a proof-of-concept demonstrating the potential use of the developed biosensor for in situ, real-time measurement of water pollutants that act as ALP inhibitors. This research was funded by Ministerio de Ciencia e Innovación (projects PID2019-105923RB-I00, PDC2021-120884-I00, European Union NextGenerationEU PRTR-C17.I1) and Generalitat Valenciana (project GVA-THINKINAZUL/2021/015 and PROMETEO/2018/087).

METland® technology consists of a bioengineering strategy for treating wastewater by integrating microbial electrochemical concepts into constructed wetland systems to enhance pollutants removal. In this context, we have constructed planted (Iris sibirica) biofilters to assess the impact of different electrically conductive bed materials (electroconductive coke, electroconductive biochar, non-electroconductive biochar and gravel) by analyzing the (i) wastewater treatment efficiency (COD and nitrogen removal), (ii) bioelectrochemical response, and (iii) diversity of microbial communities. Electrically conductive materials outperformed non-conductive ones allowing removal rates as high as 175-180 gCOD/bed*m3 day capable to support footprint as low 0.4 m2/pe. In contrast, the highest nitrogen removal rates were achieved with non-conductive biochar in presence of plants (80 %) regardless the anoxic conditions of the assay. This was confirmed by the presence of annamox bacteria like Planctomycetes. Furthermore, the presence of a marked electric potential profile along the bed height in electroconductive materials together with redox pairs (cyclic voltammetry analysis) demonstrated an effective electron flow from bottom to uppermost layers of the bed (geoconductor mechanism). In electroconductive biochar, such effective conductivity-based model co-exists with a geobattery mechanism due to presence of electroactive phenolic and carbonyl/quinone groups and/or microporosity. Microbial biodiversity analysis revealed the impact of plants just at the upper layers of the biofilters where roots and Rhizobium predominate. Bacteria from genus Clostridium were dominant in gravel inert material; in contrast, bacteria from genus Geobacter (12%) and Trichococcus (30%) outcompete the rest of communities for an effective colonization of carbonaceous beds, suggesting their main role as part of the electrosyntrophies mechanism after METland®. The authors thank the MINECO and FEDER (RYC-2017-23618) for financial support. This investigation has received funding from the European Union's Horizon 2020 research and innovation programme under the grant agreements No. 826244 (Project “ELECTRA”; http://www.electra.site). Amanda Prado de Nicolás was funded by the “Formación de Personal Investigador (FPI)” PhD fellowship programme from the University of Alcalá.

The occurrence of hypoxic muddy sediments on shallow beaches and other sheltered areas is a well-known environmental problem, which negatively affects coastal areas, tourism potential, the public use of beaches and sediment biodiversity. The usual solution is limited to dredging and removal of sludge to a landfill site. In this study, a laboratory-scale experiment was performed to determine the effectiveness of two technologies: a modification of air sparging and a new approach based on injecting oxygen-saturated seawater in hypoxic muddy sediments (oxygen-saturated seawater injections method), for remediating sludge in coastal sediments, minimizing environmental impact respect to dredging. Our results showed that both technologies significantly increased dissolved oxygen content in pore water, facilitating the oxidation of more than 90% of the organic matter, and other reduced inorganic compounds such as sulphide, with the consequent increase in sulphate concentration from 0.3 to 3.0 g·L−1. Moreover, a rise of redox potential from − 258 mV to above 200 mV, and a dramatic drop in chemical oxygen demand were also indicators that oxic conditions had been restored. After 65 days, soft, black, muddy and hypoxic sediment with high organic matter content and a characteristic foul odour was transformed into well-oxygenated sediment, which had a low organic matter content and had lost its initial shiny black colour and odour. The main difference between both technologies was the depth influenced by sediment remediation; oxygen-saturated seawater injections affected deeper areas than clean pressurized air injections. This work was supported by Own Research Program to MC and CB of the University of Alicante (Grant Number [PC15-05]) and Route Pont SL.

Chemical hydrogen storage stands as a promising option to conventional storage methods. There are numerous hydrogen carrier molecules that afford satisfactory hydrogen capacity. Among them, ammonia borane has attracted great interest due to its high hydrogen capacity. Great efforts have been devoted to design and develop suitable catalysts to boost the production of hydrogen from ammonia borane, which is preferably attained by Ru catalysts. The present review summarizes some of the recent Ru-based heterogeneous catalysts applied in the hydrolytic dehydrogenation of ammonia borane, paying particular attention to those supported on carbon materials and oxides. This work was financed by the MICINN, FEDER (RTI2018-095291-B-I00). MNG thanks the Plan GenT project (CDEIGENT/2018/027) for their financial support. DST thanks MICINN for the “Juan de la Cierva” contract (IJCI-2016-27636) and the Vicerrectorado de Investigación y Transferencia de Conocimiento de la Universidad de Alicante (GRE19-16).

This work evaluates the feasibility of electrochemical regeneration of granular activated carbon used in drinking water treatment plants as a real alternative to thermal regeneration. Two pilot-plant-scale reactors, with a capacity of 10−15 kg, have been designed using two different configurations, parallel plate electrodes and concentric cylindrical electrodes. The optimization of the anode material has also been studied and Pt/Ti, RuO2/Ti and IrO2/Ti have been used. After the regeneration and, thus, recovery of the porosity the samples were tested in the adsorption of bisphenol A. In the electrochemical regeneration, recovery of the porosity of spent activated carbon until 100 % and 96 % with respect to the pristine activated carbon using Pt/Ti anode after 3 h of treatment, has been achieved. The regeneration process produces a small increase in the number of surface oxygen groups. No important differences have been observed among the tested anodes and RuO2/Ti and IrO2/Ti can be an economic alternative to Pt/Ti. Bisphenol A adsorption kinetics was slower in regenerated activated carbons probably due to the formation of surface oxygen groups. However, the adsorption capacity was similar in the regenerated samples and the pristine one. This work was supported by the European Union-Horizon 2020 (PORTABLECRAC - SPIRE09 - 2017 Nº 768905).

The adsorption and electroadsorption of bromide from natural water has been studied in a filter-press electrochemical cell using a commercial granular activated carbon as the adsorbent. During electroadsorption experiments, different voltages were applied (2 V, 3 V and 4 V) under anodic conditions. The presence of the electric field improves the adsorption capacity of the activated carbon. The decrease in bromide concentration observed at high potentials (3 V or 4 V) may be due to the electrochemical transformation of bromide to Br2 . The anodic treatment produces a higher decrease in the concentration of bromide in the case of cathodic electroadsorption. Moreover, in this anodic electroadsorption, if the system is again put under open circuit conditions, no desorption of the bromide is produced. In the case of anodic treatment in the following adsorption process after 24 h of treatment at 3 V, a new decrease in the bromide concentration is observed as a consequence of the decrease in bromide concentration after the electrochemical stage. It can be concluded that the electroadsorption process is effective against the elimination of bromide and total bromine in water, with a content of 345 and 470 µg L−1 , respectively, reaching elimination values of 46% in a single-stage electroadsorption process in bromide and total bromine. The application of the electric field to the activated carbon with a positive polarization (anodic electroadsorption) increases the adsorption capacity of the activated carbon significantly, achieving a reduction of up to 220 µg L−1 after 1 h of contact with water. The two stage process in which a previous electrochemical oxidation is incorporated before the electroadsorption stage significantly increased the efficiency from 46% in a single electroadsorption step at 3 V, to 59% in two stages.

The electrochemical performance of nitrogen-doped and non-doped superporous activated carbons as electrodes for supercapacitors was assessed in organic and ionic liquid-based electrolytes. The nitrogen functionalization was carried out through post-modification treatments at mild conditions to produce N-doped activated carbons that preserve the microporosity of the pristine carbon material. The electrodes based on these materials provide large capacitance values (up to 150–180 F/g) in both 1 M Pyr14TFSI/PC and 1 M Pyr14BF4/PC due to their tailored porous texture, given by their well-developed microporosity and low mesopore volume. The electrochemical double layer capacitors based on these materials displayed outstanding capacitance (37–40 F/g and 14 F/cm3) and energy values (44–48 Wh/kg and 16–17 Wh/L). The nitrogen-doped activated carbons evidence high stability at positive and negative polarization potentials due the presence of specific N functionalities. The results prove that surface chemistry of carbon materials plays a key role on their degradation under high operation voltage conditions. The durability of the devices can be improved by doping carbon electrodes with selected nitrogen groups, such as nitrogen heterocycles and amine-like surface functionalities. The authors thank MICINN, FEDER (RTI2018-095291-B-I00 and ENE2017-90932-REDT). MJML acknowledges financial support through VALi+d grant (ACIF/2015/374) and mobility grant (BEFPI/2017/036).

An enzymatic metal-free electrochemical biosensor based on immobilized glucose oxidase on a N-doped porous carbon material has been studied for the detection of glucose in different real samples. The N-doped carbon material, which contains quaternary nitrogen groups, has been obtained by heat treatment of polyaniline. These functionalities promote the electrocatalytic activity to oxygen reduction reaction. The electrochemical biosensor presents a remarkable electrochemical activity towards oxygen reduction reaction, being able to detect changes in oxygen concentration generated by the enzymatic oxidation of glucose, allowing the indirect detection of this compound in phosphate buffered solution (0.1 M PB solution, pH=7.2). The metal-free electrochemical biosensor shows an outstanding performance, with a linear detection range between 5 µM and 5 mM and a high sensitivity of 23.57±1.77 µA mM−1 cm−2 at -0.4 V vs. Ag/AgCl. At these conditions, the addition of ascorbic acid, dopamine, uric acid and l-gluconic acid does not interfere with glucose determination. The method has been successfully applied to human urine and commercial sugary drink samples, without significant matrix effects, providing an alternative for glucose detection. The authors would like to thank MINECO and FEDER (RTI2018–095291-B-I0 0 and PID2019–105923RB-I0 0) for the financial sup- port. A.F.Q.J. gratefully acknowledges Generalitat Valenciana for the financial support through Santiago Grisolia grant (GRISO- LIA/2016/084).

This work studies the removal of o-cresol from wastewater by using ozonation followed by adsorption onto sodium natural bentonite (Na-Bent). The degradation of o-cresol was followed by UV-Vis. During ozonation, 2-methylbenzoquinone (2-mBQ) and 2-methylhydroquinone (2-mHQ) were identified as two of the main by-products, while the pH decrease suggested the breakage of aromatic compounds into smaller organic acids. After 30 min treatment, the o-cresol degradation for 250–62.5 mg/L solutions was found between 64–85%, respectively. Next, the wastewater containing persistent o-cresol and by-products was contacted with Na-Bent adsorbent. The solutions and physicochemical properties of Na-Bent were analysed, before and after adsorption, by UV-Vis, FTIR, XRD and N2 adsorption-desorption. Moreover, equilibrium and kinetic experiments were carried out to study the adsorptive properties of the Na-Bent. While sole ozonation or adsorption failed on the remediation of o-cresol solutions, the obtained results show that the contact of ozonated solutions with Na-Bent led to almost total removal of the o-cresol initial concentrations (between 96% and 99%). This excellent performance is assigned to the high volume of interlayer micropores and the suitable surface chemistry of this natural adsorbent. The authors would like to thank the Algerian Directorate General of Scientific Research and Technological Development (DGRSDT) and the Ministry for Higher Education and Scientific Research for the financial support for this work. In addition, the Spanish Ministerio de Economía y Competitividad and FEDER funds (RYC-2017-23618) are gratefully appreciated.

In this study, we developed Pd nanoparticles-based catalysts supported on composites formed by multi-walled carbon nanotubes (MWCNTs) and graphitic carbon nitride (g-C3N4) in various proportions, for their use in the dehydrogenation of formic acid in the liquid phase. It was observed that the composition of the support determined the average size of the Pd nanoparticles as well as their electronic properties, which ultimately affected the performance of Pd/MWCNT-C3N4 catalysts. Among assessed, the catalyst with 63 wt.% of C3N4 exhibited the best activity, with an initial TOF value of 4258 h-1 calculated based on the surface Pd atoms. The present work was financed by the MICINN, FEDER (RTI2018-095291-B-I00). MNG thanks the Plan GenT project from GV (CDEIGENT / 2018/027) for the financial support. DST thanks MICINN for the “Juan de la Cierva” contract (IJCI-2016-27636), and the Vicerrectorado de Investigación y Transferencia de Conocimiento de la Universidad de Alicante (GRE19-16).

In this work, a bidentate Schiff base ligand (HL) containing N and O as donor heteroatoms has been used to synthesize series of new stable metal complexes of general composition of M(L)2 with M = Mn, Ni and VO. This ligand was obtained from condensation of 2-methoxybenzylamine on 2,3-dihydroxybenzaldehyde in methanolic solutions in which its complexes were obtained by mixing the corresponding metal acetate salt and the ligand in 1:2 molar ratio. The resulting three complexes have been characterized by different analytical techniques like FT-IR, UV-Vis, mass spectroscopy, thermogravimetry and cyclic voltammetry, to identify their molecular structures and redox/electrochemical properties. Moreover, the effect of the metal on the complexes electronic properties with their reactivity has also been studied by Density Functional Theory (DFT). The stable structures were optimized by using the hybrid B3LYP/6–31 G method. The spectroscopic data obtained suggest that the metal is bonded to the ligand through the phenolic-like oxygen and the imine-type nitrogen atoms. Electronic and vibrational absorption spectra of the nickel complex was found to be of square-planar geometry while square-pyramidal and octahedral geometries have been proposed for VO(IV) and Mn(II) complexes, respectively. The thermogravimetric analyses of these complexes confirmed the presence of water molecules in their structures and thermal decomposition led to the formation of metal oxides as the latest residues. The voltammogram of the Ni(II) complex suggests the existence of quasi-reversible redox system in DMSO solution. The authors would like to thank the MESRS and DG-RSDT (Ministère de l’Enseignement Supérieur et de la Recherche Scientifique et la Direction Générale de la Recherche et du Développement Technologique-Algérie) for their financial support. Financial support from the Ministerio de Economía y Competitividad (Spain) and FEDER (MAT2016-76595-R and RYC-2017-23618) is also gratefully acknowledged.

Biomass upgrading is a promising approach to face the current energy consumption and chemicals production. Lignocellulosic biomass residues have taken the lead in this field. In this study, hemp residue-based activated carbons (ACs) were prepared by H3PO4-assisted hydrothermal carbonization (HTC) using a low concentration of H3PO4 (25 wt%). ACs with a high porosity development were obtained (SBET > 1200 m2 g−1), and they were subsequently functionalized with nitrogen groups using mild conditions. As-synthesized ACs were also heat-treated to enhance the electrical conductivity, improving the electrochemical performance. As a proof of concept, electrochemical capacitors (ECs) based on as-prepared ACs in aqueous and organic electrolytes, showing energy densities comparable to those of a capacitor based on an AC used in commercial capacitors. The most attractive outcome of this study is the straightforward, cost-effective, and sustainable methodology to prepare high added-value functional ACs with great potential for energy and environmental applications. This research was partially supported by the MICINN, FEDER (RTI2018-095291-B-I00). JCG thanks for her predoctoral scholarship (GRISOLIA/2018/105) funded by the Generalitat Valenciana and DST thanks MICINN for the “Juan de la Cierva” contract (IJCI-2016-27636).

The validation study of the electrochemical regeneration process of activated carbons (AC) used in water treatment plants saturated under real conditions has been carried out. The study has been performed using a bench-scale electrochemical reactor and the recovery of the porous texture has been analysed. Saturated AC from different brands and manufacturing methods have been studied. The results showed that it is easier to recover the porosity of the AC prepared by agglomeration than those produced by direct activation process. In addition, it is shown that the larger the surface area of the spent AC, the better is the regeneration efficiency achieved. Specifically, to reach a good regeneration efficiency, the SBET of the spent sample should be higher than 600 m2/g. This is a similar value as that requested by the thermal regeneration companies for a successful regeneration of the AC. El estudio de validación del método electroquímico a escala de banco para la regeneración de carbones activados (CA) utilizados en condiciones reales en plantas de tratamiento de agua se ha realizado empleando CAs de distinta procedencia y forma de fabricación. Los resultados mostraron que los CAs preparados mediante aglomeración presentaron una mayor facilidad para la recuperación de la textura porosa que los fabricados mediante el proceso de activación directa. Además, se pone de manifiesto que, a mayor área superficial del CA usado, mayor es la eficiencia de la regeneración electroquímica. En concreto, se ha determinado que, para lograr una buena eficiencia de regeneración, el SBET del CA gastado debe ser superior a 600 m2/g. Este valor es el mismo que piden las empresas de regeneración térmica para que la regeneración del CA tenga éxito. This work was supported by the European Union-Horizon 2020 (PORTABLECRAC - SPIRE09 – 2017 No768905).

Electrochemical functionalization of Single-Walled Carbon Nanotubes and Herringbone Carbon Nanotubes (SWCNTs and hCNTs, respectively) has been successfully performed with aminophenylphosphonic acid isomers by potentiodynamic treatment in oxidative conditions. Exceptional selectivity and control of the functional species embedded into the Carbon Nanotubes (CNTs) have been achieved by carefully optimizing the electrochemical conditions in the functionalization. X-ray photoelectron spectroscopy (XPS) analysis determined a maximum heteroatom incorporation of ca. 2.3-2.6 at. % N and 1.4-1.6 at. % P when 2-aminophenylphosphonic acid (2APPA) is used with both carbon materials, probably because of the linear polymeric growth comparable to that of oligomers derived from aniline (ANI). However, the polymeric product obtained with 4-aminophenylphosphonic acid (4APPA) is much more limited, giving rise to a branched structure. In addition, electrochemical characterization, Raman spectroscopy and electron microscopy suggest that SWCNTs structure facilitates the oligomerization of longer but less stable chains through π-π interactions with the walls of CNTs, while hCNTs promote a more stable attachment according to their heterogeneity and higher reactivity. Computational calculations have confirmed the experimental results obtained, which allow us to shed more light on the mechanisms of the electrochemical functionalization of CNT with phosphorus and nitrogen-containing polymers. B.M.-S. thanks the Ministry of Science, Innovation and Universities of Spain for the FPU grant (FPU18/05127). The authors would like to thank MICINN and FEDER (projects PID2019-105923RB-100 and RTI2018-095291-B-I00) for the financial support.

Authors from the Universidad de Alicante acknowledge to the Ministerio de Ciencia e Innovacion (PID2019-105923RB-I00) for financial support. J.X.F.-L. gratefully acknowledges (MINECO for the financial support through an FPI contract (BES-2017-081598) . D.S.-T. thanks MICINN for the "Juan de la Cierva" contract (IJCI-2016-27636) . M.V.L.-R. and C.M.-C. acknowledge to Junta de Andalucia, projects RNM366 and RNM172, respectively., In this study, we synthesized MnFe2O4 solid nanospheres (MSN) calcined at different temperatures (200–500 ◦C) and MSN-based materials mixed with carbon black, for their use as electrocatalysts in the oxygen reduction reaction (ORR) in alkaline medium (0.1 M KOH). It was demonstrated that the calcination temperature of MSN material determined its chemical surface composition and microstructure and it had an important effect on the electrocatalytic properties for ORR, which in turn was reflected in the performance of MSN/CB-based electrocatalysts. The study revealed that the presence of Mn species plays a key role in the ORR activity. Among tested, MSN200/CB and MSN350/CB exhibited the best electrochemical performances together with outstanding stability., Instituto de Salud Carlos III Spanish Government European Commission PID2019-105923RB-I00, MINECO BES-2017-081598, Spanish Government European Commission IJCI-2016-27636, Junta de Andalucia RNM366 RNM172

La estrategia de aprendizaje en la que se ha centrado este trabajo es el método POGIL (Process Oriented Guided Inquiry Learning), el cual está orientado a mejorar el trabajo del alumnado en grupo haciendo uso de diferentes roles participativos. Este método de carácter cooperativo se aplicó en diferentes asignaturas impartidas en la Facultad de Ciencias, tanto de grado como de postgrado, obteniendo resultados que reflejan la aceptación del método POGIL por parte del alumnado y una mejora en la adquisición de los conceptos en comparación con las clases tradicionales. En esta experiencia se ha planteado el desafío de implementar este método en clases en formato no presencial (online), ya que la situación sanitaria acaecida ha limitado la asistencia del alumnado. A partir de las encuestas realizadas por el alumnado y comparando con los resultados de las encuestas de años anteriores, se puede afirmar que este método se ha aplicado de manera satisfactoria tanto en clases presenciales como en clases online. Adicionalmente, se observó que el contraste entre clases POGIL online y las clases expositivas clásicas es aún mayor que en años anteriores cuando se aplicaba el método POGIL en clases presenciales.

Development of effective direct electron transfer is considered an interesting platform to obtain high performance bioelectrodes. Therefore, designing of scalable and cost-effective immobilization routes that promotes correct direct electrical contacting between the electrode material and the redox enzyme is still required. As we present here, electrochemical entrapment of pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH) on single-wall carbon nanotube (SWCNT)-modified electrodes was carried out in a single step during electrooxidation of para-aminophenyl phosphonic acid (4-APPA) to obtain active bioelectrodes. The adequate interaction between SWCNTs and the enzyme can be achieved by making use of phosphorus groups introduced during the electrochemical co-deposition of films, improving the electrocatalytic activity towards glucose oxidation. Two different procedures were investigated for electrode fabrication, namely the entrapment of reconstituted holoenzyme (PQQ-GDH) and the entrapment of apoenzyme (apo-GDH) followed by subsequent in situ reconstitution with the redox cofactor PQQ. In both cases, PQQ-GDH preserves its electrocatalytic activity towards glucose oxidation. Moreover, in comparison with a conventional drop-casting method, an important enhancement in sensitivity was obtained for glucose oxidation (981.7 ± 3.5 nA mM-1) using substantially lower amounts of enzyme and cofactor (PQQ). The single step electrochemical entrapment in presence of 4-APPA provides a simple method for the fabrication of enzymatic bioelectrodes. The authors would like to thank MICINN (PID2019-105923RB-I00) for the financial support. A.F.Q.J. gratefully acknowledges Generalitat Valenciana for the financial support through Santiago Grisolia grant (GRISOLIA/2016/084), to the University of Alicante for the support in the mobility program through the Escuela de Doctorado (EDUA).

The production of hydrogen from liquid organic hydrogen carrier molecules stands up as a promising option over the conventional hydrogen storage methods. In this study, we explore the potential of formic acid as a convenient hydrogen carrier. For that, soft-biomass-derived carbon-supported Pd catalysts were synthesized by a H3PO4-assisted hydrothermal carbonization method. To assess the impact of the properties of the support in the catalytic performance towards the dehydrogenation of formic acid, three different strategies were employed: (i) incorporation of nitrogen functional groups, (ii) modification of the surface chemistry by performing a thermal treatment at high temperatures (i.e., 900 °C), and (iii) combination on both thermal treatment and nitrogen functionalization. It was observed that the modification of the carbon support with these strategies resulted in catalysts with enhanced performance and outstanding stability even after six consecutive reaction cycles, thus highlighting the important effect of tailoring the properties of the support.

According to UNESCO Institute for Statistics (UIS) data (UIS fact sheet, 2019), less than 30% of researchers worldwide are women. Long-standing biases and gender stereotypes are discouraging girls and women away from science related fields. In particular, STEM (science, technology, engineering and mathematics) research is traditionally male dominated and women remain underrepresented. As UNESCO has highlighted, both science and gender equality are, however, essential to ensuring sustainable development. In order to change traditional mindsets, gender equality must be promoted, stereotypes defeated, and girls and women should be encouraged to pursue careers in STEM. Throughout history, the contributions of female researchers to scientific progress have been extremely important. Yet, whereas the extraordinarily talented Nobel laureate Marie Sklodowska-Curie is often mentioned as a role model, it is nowadays well established that countless women such as Lise Meitner have received less recognition and acknowledgement for their research findings than their male counterparts (so-called Matilda effect (Rossiter, 1993)). Also, women traditionally publish less than men according to the European Commission She Figures, the ratio of women to men among authors of scientific publications in the EU being on the average one to two (EU, 2018), and recent surveys are highlighting a further drop in academic submissions from female scientists since the start of the Covid-19 pandemic early 2020. Role models are definitely extremely important to show to younger generations the growing impact of female researchers to science. Therefore, continuing the spirit of the International Day of Women and Girls in Science, Frontiers in Materials is proud to offer this platform to promote the work of female scientists, across the breadth of materials science and engineering. This inaugural ‘Women in Science: Materials’ collection (Fig.1) aims to highlight the impact of women researchers working in materials science and engineering. It gathers a selection of original articles with the lead author and/or corresponding author being a woman. 32 contributions (3 reviews, 1 brief research report and 28 original research articles) present advances in theory, experiment and methodology with applications to compelling problems, across almost all sections of the journal:  Mechanics of materials (Bouquerel et al., Jeong et al., TerMaath et al., Zhu et al.);  Smart materials (Duc et al.);  Polymeric and composite materials (Badji et al., Berzin et al., Brunella et al., Hostettler et al., Martins and Gil, Mirbaha et al., Padhan et al., Quintana et al., Raj et al., Saffar et al.);  Carbon-based materials (Kato et al., Moulefera et al., Xu et al., Zhang et al.);  Structural materials (Bonoli et al., Boyer et al., Korat and Ducman, Manzi et al., Masi et al.);  Colloidal materials and interfaces (Garcia-Hernando et al., Pucci et al.);  Energy materials (Castro-Gutierrez et al.);  Ceramics and glass (Giosue et al.);  Environmental materials (Bassi et al.);  Biomaterials (Criado-Gonzalez et al., Kebaili et al.); The Guest Editorial team hope that this collection of papers will be the foundation of an international network of women researchers working in materials science and engineering, and a starting point for future collaborations and discussions.

High-quality performance of catalysts is increasingly required to meet industry exigencies. However, chemical synthesis is often insufficient to maximize the potential properties of the catalysts. On the other hand, electrochemical synthesis has arisen as a promising alternative to overcome these limitations and provide precise control in the preparation of catalysts. In this sense, this work involved the well-controlled electrochemical synthesis of a catalyst based on platinum nanoparticle deposition on carbon nanotubes using only electrochemical treatments. Thin films of functionalized carbon nanotubes were cast onto the surface of a glassy carbon electrode using potential pulsed electrodeposition, resulting in a better distribution of the carbon nanotubes on the electrode when comparing with traditional methods. Then, platinum nanoparticles were electrodeposited on the carbon nanotube-modified electrode. To check the performance of the catalyst and the relevance of the electrochemical synthesis treatments, the samples were analyzed as electrocatalysts towards methanol electrooxidation, showing an important improvement in the catalytic activity in comparison with electrodes that were prepared by traditional methodologies. This research was funded by MICINN and FEDER (RTI2018-095291-B-I00 and PID2019-105923RB-I00), “Juan de la Cierva” contract (IJCI-2016-27636), and the Vicerrectorado de Investigación y Transferencia de Conocimiento de la Universidad de Alicante (GRE19-16).

[EN] Manganese-based materials can catalyze the oxygen reduction reaction (ORR), although their activity is known to depend on the crystalline phases and on the concentration of surface-active species. In the present study, we have optimized these two parameters to obtain improved catalysts for ORR. A sol-gel method was used to synthesize LaMnO3-manganese oxides composites with different lanthanum-to- manganese atomic ratios. The synthesized materials, which can be described as La1-xMnOz, were tested under ORR conditions and characterized by several physicochemical techniques such as SEM, XPS, EDX or XRD. It was found that the concentration of lanthanum governs the formation of different crystal phases and determines the crystallite size. Besides, high values of x tend to increase the surface concentration of manganese and therefore to produce more active sites for ORR. Among the materials analysed, La0.6MnOz mixed with carbon black (Vulcan) showed the best electrocatalytic performance. The high tolerance to methanol makes this electrocatalyst a promising alternative to substitute Pt-based materials in alkaline electrolytes., The authors thank to the Ministerio de Ciencia e Innovacion (PID2019-105923RB-I00) for financial support. J.X.F.-L. gratefully acknowledges MINECO for financial support through an FPI contract (BES-2017-081598).

Metal-free carbon-based catalysts have gained much attention during the last 15 years as an alternative toward the replacement of platinum-based catalysts for the oxygen reduction reaction (ORR). However, carbon-based catalysts only show promising catalytic activity in alkaline solution. Concurrently, the most optimized polymer electrolyte membrane fuel cells use proton exchange membranes. This means that the cathode electrode is surrounded by a protonic environment in which carbon materials show poor performance, with differences above 0.5 V in EONSET for nondoped carbon materials. Therefore, the search for highly active carbon-based catalysts is only possible if we first understand the origin of the poor electrocatalytic activity of this kind of catalysts in acidic conditions. We address this matter through a combined experimental and modeling study, which yields fundamental principles on the origin of the pH effects in ORR for carbon-based materials. This is relevant for the design of pH-independent metal-free carbon-based catalysts. The authors thank Ministerio de Ciencia, Innovación y Universidades, and FEDER for the financial support (projects RTI2018-095291-B-I00 and ENE2017-90932-REDT) and the Portuguese Foundation for Science and Technology (FCT) under the projects IF/00894/2015 and CICECO-Aveiro Institute of Materials, UIDB/50011/2020 and UIDP/50011/2020, financed by national funds through the FCT/MCTES.

[EN] The need for improving the energy harvesting from Microbial Fuel Cells (MFCs) has boosted the design of new materials in order to increase the power performance of this technology and facilitate its practical application. According to this approach, in this work different poly(3,4-ethylenedioxythiophene)-polystyrenesulfonate (PEDOT-PSS) modified electrodes have been synthesised and evaluated as anodes in urine-fed MFCs. The electrochemical synthesis of PEDOT-PSS was performed by potentiostatic step experiments from aqueous solution at a fixed potential of 1.80 V (vs. a reversible hydrogen electrode) for different times: 30, 60, 120 and 240 s. Compared with other methods, this technique allowed us not only to reduce the processing time of the electrodes but also better control of the chemical composition of the deposited polymer and therefore, obtain more efficient polymer films. All modified anodes outperformed the maximum power output by MFCs working with the bare carbon veil electrode but the maximum value was observed when MFCs were working with the PEDOT-PSS based anode obtained after 30 s of electropolymerisation (535.1 µW). This value was 24.3 % higher than using the bare carbon veil electrode. Moreover, the functionality of the PEDOT-PSS anodes was reported over 90 days working in continuous mode., M.J. Salar-Garcia is supported by Fundacion Seneca (Ref: 20372/PD/17). I. Ieropoulos is grateful to the Gates Foundation (Ref: OPP1149065) for the financial support of parts of this work. The other authors also thank the support of Generalitat Valenciana (Ref: PROMETEO/2018/087).