Search

3 figures, 1 table.-- Work presented at the EHEC 2022, European Hydrogen Energy Conference, 18-20 May, 2022. Madrid, Spain., The development of active and inexpensive non-precious metal catalysts is a necessary and essential requirement to replace currently used Pt-based catalysts, in order to reduce the cost of polymer electrolyte fuel cells(PEFC). [1] Catalysts based on the Fe-N-C structure develop high electroactivity towards the oxygen reduction reaction (ORR), the limiting reactionin fuel cells. To increase the catalysts activity, Fe must be dispersedin acarbon material with a high surfacearea.In this context, carbon xerogels are excellent candidates, as their main properties can be easily tailored: porosity, electrical conductivity and surface chemistry. [2] The meso/macroporosity of carbon xerogels can be designed by modifying the conditions of the synthesis process, while microporosity can be generated by subsequent carbonization/activation treatments [3].In the present work, on the basis of carbon xerogels with an optimal ratio of micro/meso/macroporosity, we investigate the effect of two different methods of nitrogen-doping in the catalytic activity of Fe-N-C catalysts. Catalysts are evaluated both in half-cell and single-cell configurations and their activity is correlated to their physical-chemical features., The authors wish to thank the Ministry of Science and Innovation and the AEI(MCIN/AEI/10.13039/501100011033) for the funding received with the reference project PID2020-115848RB-C21 and the Government of Aragon for funding the T06-20R group. L. Álvarez-Manuel wish to thank the Government of Aragon for her pre-doctoral contract.

6 figures, 3 tables., In this work, carbon xerogels (CXGs) doped with nitrogen or sulfur have been investigated as DSSC counter electrodes. CXGs have been prepared by a sol–gel method from resorcinol and formaldehyde and subsequent carbonization. Nitrogen doping has been carried out by introducing melamine into the synthesis process along with resorcinol and formaldehyde, while sulfur has been incorporated by direct reaction of the carbon material with elemental sulfur. The counter electrodes for DSSCs have been prepared by airbrushing on conductive glass (fluorine-doped tin oxide, FTO), and their electrochemical behavior has been evaluated, observing that the introduction of heteroatoms such as nitrogen or sulfur leads to an improvement in efficiency compared to the undoped material thanks to a decrease in charge transfer resistance., This research was funded by PON Ricerca e Innovazione 2014–2020-PROGETTO ARS01_00334 NAUSICA-NAvi efficienti tramite l’Utilizzo di Soluzioni tecnologiche Innovative e low Carbon-Area di Specializzazione: Mobilità Sostenibile. CSIC authors wish to thank the Government of Aragon for funding the T06-20R group.

11 figures.-- Supplementary information available., Bifunctional oxygen electrocatalysts are essential in the development of low-temperature unitized regenerative fuel cells (URFCs), as a promising alternative for storing energy via hydrogen. TiO2, as a semiconductor material, is commonly not established as an active electrocatalyst for oxygen reduction and oxygen evolution due to its poor electrical conductivity and low reactivity. Here, we demonstrated that composites composed of TiO2 and N-doped graphene can be active in oxygen reduction and evolution reactions in an alkaline environment. Combination factors such anatase/rutile interaction, N-doping graphene, and the presence of Ti3+/Ti–N species raise the active sites and improve the electrochemical activity. Our results may afford an opportunity to develop a non-noble and promising electrocatalyst in energy storage technology., This research was funded by the Ministry of Science, Innovation and Universities and FEDER, grant number ENE2017-83976-C2-1-R

11 figures, 4 tables.-- Información suplementaria., Biomass from agricultural by-products is gaining increasing interest as cheap and abundant precursor in the development of active materials for efficient and environmentally friendly devices like fuel cells. Herein, we investigated iron and nitrogen co-doped nanoporous carbons derived from aronia, peach stones and coal tar pitch/furfural as electrocatalysts for the electrochemical oxygen reduction reaction (ORR) in alkaline media. Urea was used as nitrogen precursor and two annealing steps with intermediate acid leaching served to activate the catalysts. Within the series, the peach stone-derived catalyst exhibited a catalytic activity for the ORR close to the benchmark Pt/C, with a 60 mV dec−1 Tafel slope upon the incorporation of 0.57 wt% Fe and proper combination of N-Fe species (20%) with pyridinic/pyridonic moieties (49%). We concluded that the microporosity and a certain content of meso/macro-pores of the activated carbon, together with the creation of graphitic domains result in a high relative amount of Fe-N4 and nitrogen functionalities, which determine the electrocatalytic performance., The authors gratefully acknowledge financial support given by the project BLOW UP "Balkans Waste to Products: transfer of NoI model to Balkan area: de-siloing new waste-derived raw materials and developing new applications" from EIT RAW MATERIAL EIT16320, Horizon 2020. D. Sebastián and C. Alegre acknowledge the Ministry of Economy, Industry and Competitiveness for their Ramón y Cajal (RyC-2016-20944) and Juan de la Cierva Incorporación (IJCI-2017-32354) research contracts, respectively.

4 figures.-- Supporting information available on the website of the publisher., Graphene oxide (GO) is reduced by Joule heating using in-situ transmission electron microscopy (TEM). The approach allows the simultaneous study of GO conductivity by electrical measurements and of its composition and structural properties throughout the reduction process by TEM, electron diffraction and electron energy-loss spectroscopy. The small changes of GO properties observed at low applied electric currents are attributed to the promotion of diffusion processes. The actual reduction process starts from an applied power density of about 2 × 1014 Wm−3 and occurs in a highly uniform and localized manner. The conductivity increases more than 4 orders of magnitude reaching a value of 3 × 103 Sm−1 with a final O content of less than 1%. We discuss differences between the reduction by thermal annealing and Joule heating., S.H. and R.A. acknowledge funding by German Research Foundation (DFG project He 7675/1-1). Research supported by the Spanish MINECO and MICINN (MAT2016-79776-P,AEI/FEDER, EU; PID2019-104739GB-100/AEI/10.13039/501100011033; ENE2016-79282-C5-1-R, AEI/FEDER, EU and PID2019-104272RB-C51/AEI/10.13039/501100011033), Government of Aragon (projects DGA E13-17R (FEDER, EU); DGA T03-17R (FEDER, EU) and DGA T03-20R) and European Union H2020 programs “ESTEEM3” (823717), Flag-ERA GATES (JTC - PCI2018-093137), ITN Enabling Excellence (MSCA-ITN) and Graphene Flagship (881603).

8 figures, Polymer electrolyte fuel cells with alkaline anion exchange membranes (AAEMs) have gained increasing attention because of the faster reaction kinetics associated with the alkaline environment compared to acidic media. While the development of anion exchange polymer membranes is increasing, the catalytic layer structure and composition of electrodes is of paramount importance to maximize fuel cell performance. In this work, we examine the preparation procedures for electrodes by catalyst-coated substrate to be used with a well-known commercial AAEM, Fumasep® FAA-3, and a commercial ionomer of the same nature (Fumion), both from Fumatech GmbH. The anion exchange procedure, the ionomer concentration in the catalytic layer and also the effect of membrane thickness, are investigated as they are very relevant parameters conditioning the cell behavior. The best power density was achieved upon ion exchange of the ionomer by submerging the electrodes in KCl (isopropyl alcohol/water solution) for at least one hour, two exchange steps, followed by treatment in KOH for 30 min. The optimum ionomer (Fumion) concentration was found to be close to 50 wt%, with a relatively narrow interval of functioning ionomer percentages. These results provide a practical guide for electrode preparation in AAEM-based fuel cell research., This research was funded by the Ministry of Economy, Industry and Innovation (MICINN) and FEDER, grant number ENE2017-83976-C2-1-R and by the Government of Aragón and FEDER for supporting ‘Grupo de Conversión de Combustibles’, grant number T06_17R. D.S. and J.M.L.-C. acknowledge also MICINN for their Ramón y Cajal research contract (RyC-2016-20944) and Ph.D. grant, respectively. G.L. acknowledges as well Aragón Government for his Ph.D. grant.

5 figures., Carbonaceous materials have always played an important role in history of electrochemical processes, from the fabrication of solid electrodes to the development of porous matrixes in the conversion and storage of energy and chemicals. This book chapter provides a general overview of emerging carbon nanostructures potentially used in electrochemistry. One-dimensional carbon nanofilaments, such as carbon nanotubes and carbon nanofibers, two-dimensional graphene, and three-dimensional materials, such as carbon gels and ordered mesoporous carbons, are reviewed. The chapter focuses on the physicochemical properties and synthesis methodologies of these carbon nanostructures together with their application to cutting-edge technologies for electrochemical energy conversion and storage, such as fuel cells, electrolyzers, supercapacitors, or batteries. The major challenges and directions for future research are also discussed to guide the design of efficient carbon-based electrodes and catalysts for electrochemical devices., Authors acknowledge financial support given by Spanish Ministry of Science, Innovation and University (MICINN) through project ENE2017-83976-C2-1-R (cofounded by FEDER). C. Alegre and D. Sebastián acknowledge also MICINN for their Juan de la Cierva (IJCI-2017-32354) and Ramón y Cajal (RyC-2016-20944) research contracts, respectively.

Comunicación oral presentada en de IV Encuentro de Jóvenes Investigadores de la SECAT, "Jóvenes y catálisis, CLAVES PARA UN FUTURO SOSTENIBLE”, celebrado en Bilbao del 21 al 23 de septiembre de 2020, y organizado por la Sociedad Española de Catálisis y los Cursos de Verano de la Universidad del País Vasco.

4 figures, 1 table., In order to decrease the cost of direct methanol fuel cells (DMFCs), allowing the market penetration of these devices, it is necessary to reduce the costs of the components, in particular the cathode catalysts based on platinum. Another issue of these fuel cells is related to methanol crossover through the polymeric membrane, which creates a mixed potential at the cathode and decreases the overall efficiency. For this reason the development of methanol-tolerant cathode catalysts that are cheaper than Pt are of great importance in this field. In this chapter a short review analysis on Pt-free catalysts, mainly based on Pd and platinum group metal-free compounds with the general formula M–N–C (M being a transition metal such as Fe or Co) for the cathode, with good methanol-tolerance characteristics, has been carried out. Preparation procedures for the catalysts and physicochemical characteristics are reported and discussed in correlation with the DMFC performance., Introduction.-- Palladium as oxygen reduction reaction catalyst in direct methanol fuel cells.-- Non platinum-group-metal electrocatalysts based on M–N–C.-- Conclusion

of the poster presented at the Giornate dell’Elettrochimica Italiana, GEI 2019, 8-12 September 2019 Padova, Italy, organized by the Società Elettrochimica Italiana, Divisione di Elettrochimica., Dye-sensitized solar cells (DSSCs) are well known as potentially low-cost photovoltaic devices [1] and are attracting great attention for their capability to provide low cost power. DSSC components include a photoanode composed of a dye-sensitized wide-bandgap semiconductor, a redox electrolyte (e.g. iodide/triiodide), and a counter electrode (CE) for reducing oxidized species in the electrolyte, generally based on a noble metal thin film. The CE collects the electrons from the external circuit to reduce the redox species used as a mediator in regenerating the sensitizer after electron injection into the photoanode. Platinum is well known as benchmark CE due to its high catalytic activity [2]. Efforts are nowadays directed to decrease the fabrication cost through alternative CE formulations. Metal-Nitrogen-Carbon (M-N-C) materials represent an attractive alternative to platinum in DSSC counter electrodes to contribute to an efficient conversion of solar energy into electricity. Despite the slower kinetics of these carbon-based materials for the reduction of triiodide compared to platinum, they are characterized by low cost. Various Fe-N-C catalysts were prepared by the so-called sacrificial support method (SSM) [3], consisting of the use of a templating agent based on silica, which is removed by hydrofluoric acid (HF) after a thermal treatment. The influence of the Fe-precursor, used for the synthesis, on the electrochemical behavior as counter electrodes in DSSC is analysed. The fabricated DSSCs were investigated by polarization experiments and electrochemical impedance spectroscopy, and compared with a cell equipped with a benchmark CE.

Work presented at the CARBON 2019 conference, The World Conference on Carbon, 14th-19th july 2019, Lexington, Kentucky (U.S.A.).

1 figure.-- Abstract of the poster presented at the VII International Symposium SRUK/CERU (2019), organized by the Society of Spanish Researchers in the United Kingdom. 28th-30th June 2019, Liverpool (United Kingdom)., Graphene oxide nanomaterials, specifically reduced few-layer graphene oxide (rFLGO) sheets and reduced graphene oxide quantum dots (rGOQD), were explored as active and cost-effective counter electrodes for dye-sensitized solar cells (DSSCs). The synthesis strategy adopted in this work for these materials is based on an economic and easily scalable route of exfoliation of multi-wall carbon nanotubes (Top-Down approach). This allows the easy tailoring of rFLGO/rGOQD size and oxidation degree for their use as bulk material in counter electrodes, having a significant influence on the photovoltaic performance and stability. Despite the slower kinetics of carbon for the reduction of triiodide compared to platinum, they are characterized by low cost and promising stability. The electrochemical performance of DSSC assembled with either rFLGO or rGOQD at the counter electrode is correlated to their most important physico-chemical features. The domain size of graphene sheets had an important effect on the performance at the counter electrode, with quantum dots performing 13% higher efficiency than rFLGO, correlated with a higher density of active sites. Both graphene nanostructures exhibited a better stability behavior upon electrochemical cycling and seasoning of the cells as compared to Pt counter electrode., ICB-CSIC authors acknowledge the Raw Materials Network of Infrastructure ITO substitution in opto-electronic devices (European Union), and the funding of the FEDER and the Spanish Economy and Competitiveness Ministry (MINECO) (ENE2011-28318-C03-01 and ENE2014-52189-C02-01-R). JLP and DS thank MINECO for their Ramon y Cajal research contracts (RyC-2013-12494 and RyC-2016-20944). CNR-ITAE authors acknowledge the financial support from the FotoH2 project. This project has received funding from the European Union s Horizon 2020 research and innovation programme under Grant Agreement n° 760930.

9 Figuras. 4 Tablas. Datos suplementarios pueden encontrarse en la versión en línea del editor., This work reports a study of the electrocatalytic properties and stability of nanostructured carbon electrodes by on-line differential electrochemical mass spectrometry (DEMS). A wide electrochemical characterization in 0.1 M NaHCO3 involving anodic (carbon corrosion and oxygen evolution reaction, OER) and cathodic (CO2 reduction and hydrogen evolution reaction, HER) key reactions in energy-conversion devices was performed. DEMS studies showed that the faradaic current from 1.3 to 1.6 V vs. RHE of carbons was only associated to CO2 formation by corrosion and not to OER, the stability being improved by the graphitic character of carbon. H2 evolution was also enhanced with graphitic carbon nanofilaments, even though metal traces might positively influence their catalytic activity. By comparison of the faradaic currents and the H2 formation signals, in the absence and presence of CO2, a high inhibition of the HER was established for all carbon electrodes due to the species adsorption from CO2 reduction., The authors gratefully acknowledge financial support given by Spanish MINECO (CTQ2011‐28913‐C02‐01 and 02). S. Pérez-Rodríguez acknowledges Gobierno de Aragón for the DGA grant.

Pt-Sn catalysts supported on carbon, with different Pt-Sn atomic ratios (3:1, 1:1, 1:3), were prepared through the formic acid method (FAM) and supported on different carbon supports (nanofibers and carbon blacks) to study their behavior toward CO stripping and ethanol oxidation reaction (EOR). PtSn/C catalysts and supports were physicochemically characterized by XRD, EDX, XPS, TEM and TPD. Good particle dispersion onto the carbon support, similar particle sizes (around 4-5 nm) and the presence of tin oxides were observed in all cases. Sn insertion favored the development of the Pt3Sn1 phase and the presence of higher oxidation states of both metals in the catalyst. Ethanol and adsorbed CO oxidation was studied at these materials both in acid and alkaline media, by linear sweep voltammetry and chronoamperometry. Higher EOR current densities were obtained with the increase in the amount of Sn in the samples, been those materials supported on CNF the ones with the best CO tolerance and catalytic activity toward this reaction. As expected, a great improvement of the EOR activity was found in alkaline media compare with sulfuric acid media, providing good expectative for these materials as catalysts for alkaline direct ethanol fuel cells., This work has been supported by Fundación Cajacanarias (project BIOGRAF) and the Ministry of Economy and Competitiveness (MINECO) through the projects CTQ2011-28913- C02-02 and ENE2014-52158-C2-2-R. R.R. is also indebted with the MINECO for the pre-doctoral grant.

7 Figuras, 2 Esquemas, Tandem photoelectrochemical cells, formed by two photoelectrodes with complementary light absorption, have been proposed to be a viable approach for obtaining clean hydrogen. This requires the development of new designs that allow for upscaling, which would be favored by the use of transparent polymer electrolyte membranes (PEMs) instead of conventional liquid electrolytes. This article focuses on the photoelectrochemical performance of a water-splitting tandem cell based on a phosphorus-modified α-Fe2O3 photoanode and on an iron-modified CuO photocathode, with the employment of an alkaline PEM. Such a photoelectrochemical cell works even in the absence of bias, although significant effort should be directed to the optimization of the photoelectrode/PEM interface. In addition, the results reveal that the employment of polymer electrolytes increases the stability of the device, especially in the case of the photocathode., A.C. acknowledges the University of Alicante for a predoctoral grant (FPU-UA) and also thanks the Vicepresidency of Research, Development and Innovation of University of Alicante for a mobility grant. Authors are also grateful to Dr. Teresa Lana-Villarreal for the acquisition of Raman spectra.