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The urge for carbon-neutral green energy conversion and storage technologies has invoked the resurgence of interest in applying brucite-type materials as low-cost oxygen evolution reaction (OER) electrocatalysts in basic media. Transition metal layered hydroxides belonging to the brucite-type structure family have been shown to display remarkable electrochemical activity. Recent studies on the earth-abundant Fe3+ containing mossbauerite and Fe3+ rich Co-Fe layered oxyhydroxide carbonates have suggested that grafted interlayer anions might play a key role in OER catalysis. To probe the effect of such interlayer anion grafting in brucite-like layered hydroxides, we report here a systematic study on the electrocatalytic performance of three distinct Ni and Co brucite-type layered structures, namely, (i) brucite-type M(OH)2 without any interlayer anions, (ii) LDHs with free interlayer anions, and (iii) hydroxynitrate salts with grafted interlayer anions. The electrochemical results indeed show that grafting has an evident impact on the electronic structure and the observed OER activity. Ni- and Co-hydroxynitrate salts with grafted anions display notably earlier formations of the electrocatalytically active species. Particularly Co-hydroxynitrate salts exhibit lower overpotentials at 10 mA cm-2 (η=0.34 V) and medium current densities of 100 mA cm-2 (η=0.40 V) compared to the corresponding brucite-type hydroxides and LDH materials.

The complex interplay of restricted mass transport leading to local accumulation or depletion of educts, intermediates, products, counterions and co-ions influences the reactions at the active sites of electrocatalysts when electrodes are rough, three-dimensionally mesoporous or nanoporous. This influence is important with regard to activity, and even more to selectivity, of electrocatalytic reactions. The underlying principles are discussed based on the growing awareness of these considerations over recent years.

Water electrolysis is a promising technology for sustainable hydrogen production; however, its commercialisation is limited by sluggish kinetics of the oxygen evolution reaction (OER). A potential alternative to the OER is hence required and is seen in the electrocatalytic glycerol oxidation reaction (GOR) as it offers concomitant value-added product generation from a cheap and abundant feedstock. Here, we show a facile solid-state synthesis method to obtain Ni-boride, a non-noble metal-based catalyst subsequently used in an in-depth study of the GOR product distribution as a function of key electrolysis parameters. Highly crystalline, mixed-phase Ni borides were obtained, and their synthesis was successfully optimised regarding GOR activity. Long-term chronoamperometry was conducted in a circular flow-through cell and samples were analysed by HPLC. It is shown that the formation of lactic acid, one of the most valuable GOR products, can be enhanced by optimising the electrolyte composition and the applied potential.

Bimetallic silver-copper electrocatalysts are promising materials for electrochemical CO2 reduction reaction (CO2RR) to fuels and multi-carbon molecules. Here, we combine Ag core/porous Cu shell particles, which entrap reaction intermediates and thus facilitate the formation of C2+ products at low overpotentials, with gas diffusion electrodes (GDE). Mass transport plays a crucial role in the product selectivity in CO2RR. Conventional Hcell configurations suffer from limited CO2 diffusion to the reaction zone, thus decreasing the rate of the CO2RR. In contrast, in the case of GDE-based cells, the CO2RR takes place under enhanced mass transport conditions. Hence, investigation of the Ag core/porous Cu shell particles at the same potentials under different mass transport regimes reveals: (i) a variation of product distribution including C3 products, and (ii) a significant change in the local OH- activity under operation.

Die Nutzung erneuerbarer Energie mittels elektrochemischer Techniken durch Konversion von H2O, CO2 und N2 in chemische Energieträger und Rohstoffe, ist die Basis zur Sicherung einer zukünftigen nachhaltigen „grünen“ Energieversorgung. Es werden einige Schwächen und Inkohärenzen in der Praxis der Bestimmung der elektro-katalytischen Leistung diskutiert, die ein rationales Bottom-up-Katalysatordesign verhindert. Große Diskrepanzen in den Materialeigenschaften sowie hinsichtlich der elektrokatalytischen Aktivität und Stabilität werden offensichtlich, wenn Materialien unter den Bedingungen ihres geplanten Einsatzes im Gegensatz zu den üblichen Laborbedingungen getestet werden. Es wird für einheitliche Aktivitäts-Stabilitäts-Korrelationen bei anwendungsrelevanten Bedingungen plädiert, und es wird die Notwendigkeit zur eindeutigen Darstellung der elektrokatalytischen Leistung durch Kontextualisierung in Bezug auf die funktionelle Untersuchung oder den Fortschritt in RichtungAnwendung betont.

Es wird eine universelle, auf Nanokapillaren basierende Methode zur Probenabscheidung auf der Siliziumnitridmembran von LCTEM-Chips (liquid cell transmission electron microscopy) vorgeschlagen. Sie ist auf alle Substanzen anwendbar, die in einem Lösungsmittel dispergierbar und für eine Tropfenimmobilisierung geeignet sind, einschließlich Katalysatoren, biologische Proben und Polymere. Am wichtigsten ist, dass diese Methode die Einschränkungen bezüglich der Probenimmobilisierung aufgrund der Zerbrechlichkeit der ultradünnen Glaskohlenstoffelektrode/Siliziumnitridmembran, die für die Elektronenübertragung erforderlich ist, überwindet. Somit wird ein einfacher Weg vorgestellt, um das Forschungsgebiet des LCTEM auf jede Probe zu erweitern, die zuvor extern abgeschieden werden kann. Mit dieser Methode werden NixB-Nanopartikel auf der Arbeitselektrode des LCTEM-Chips im mm-Maßstab deponiert und die In-situ- Beobachtung einzelner Katalysatorpartikel während der Ethanoloxidation erstmals erfolgreich mithilfe von TEM-Filmen durchgeführt.

To investigate the conduction properties of ionic liquid crystal electrolytes and to correlate them to their molecular structure, two electrolytes based on imidazolium iodides have been chosen for a comparative study: one ionic liquid crystal (1-dodecyl-3-methylimidazolium iodide) (C12) and one ionic liquid (1-hexyl-3-methylimidazolium iodide) (C6). For the electrical characterization of the samples the electrochemical impedance spectroscopy technique (EIS) has been used in the frequency range 1 MHz ÷ 10 mHz. For both electrolytes three frequency domains have been singled out. At large frequencies a hopping mechanism ensures the relative high conductivity of ionic liquids. A good fit of the conductivity data with respect to temperature with a Vogel-Tamman-Fulcher (VTF) equation has been done. The interesting result is that although C12 has a higher viscosity than C6 and thus a smaller conductivity was expected the observed conductivity is actually larger, this fact being attributed to the smectic A liquid crystal order of C12. At medium frequencies and especially at low frequencies the buildup of double layers by the electrodes is well observed. Assuming that in this region (10 Hz ÷ 10 mHz) the cell is equivalent to an electric circuit formed by the parallel of a resistance, R0, and a capacitance, C0, the simple Debye relaxation model, characterized by one relaxation time, has been modified taking into account the adsorption phenomenon in the Langmuir approximation. A theoretical interpretation of the experimental results based on the double layer model is presented.

Enzymes are characterized by an active site that is typically embedded deeply within the protein shell thus creating a nanoconfined reaction volume in which high turnover rates occur. We propose nanoparticles with etched substrate channels as a simplified enzyme mimic, denominated nanozymes, for electrocatalysis. We demonstrate increased electrocatalytic activity for the oxygen reduction reaction using PtNi nanoparticles with isolated substrate channels. The PtNi nanoparticles comprise an oleylamine capping layer that blocks the external surface of the nanoparticles participating in the catalytic reaction. Oxygen reduction mainly occurs within the etched channels providing a nanoconfined reaction volume different from the bulk electrolyte conditions. The oxygen reduction reaction activity normalized by the electrochemically active surface area is enhanced by a factor of 3.3 for the nanozymes compared to the unetched nanoparticles and a factor of 2.1 compared to mesoporous PtNi nanoparticles that possess interconnecting pores.

The determination of the intrinsic properties of nanomaterials is essential for their optimization as electrocatalysts, however it poses great challenges from the standpoint of analytical tools and methods. Herein, we report a novel methodology that allows for a binder-free investigation of electrocatalyst nanoparticles. The potential-assisted immobilization of a non-noble metal catalyst, i.e., nickel-iron layered double hydroxide (NiFe LDH) nanoparticles, was employed to directly attach small nanoparticle ensembles from a suspension to the surface of etched carbon nanoelectrodes. The dimensions of this type of electrodes allowed for the immobilization of the catalyst material below the picogram scale and resulted in a high resolution towards the faradaic current response. In addition the effect of the electrochemical aging on the intrinsic activity of the catalyst was investigated in alkaline media by means of continuous cyclic voltammetry. A change in the material properties could be observed, which was accompanied by a substantial decrease in its intrinsic activity.

Mossbauerite is investigated for the first time as an "iron-only" mineral for the electrocatalytic oxygen evolution reaction in alkaline media. The synthesis proceeds via intermediate mixed-valence green rust that is rapidly oxidized in situ while conserving the layered double hydroxide structure. The material catalyzes the oxygen evolution reaction on a glassy carbon electrode with a current density of 10 mA cm-2 at 1.63 V versus the reversible hydrogen electrode. Stability measurements, as well as post-electrolysis characterization are presented. This work demonstrates the applicability of iron-only layered double hydroxides as earth-abundant oxygen evolution electrocatalysts. Mossbauerite is of fundamental importance since as an all Fe3+ material its performance has no contributions from unknown synergistic effects as encountered for mixed valence Co/Ni/Fe LDH.

Hydroxyapatite powders characteristics need to be determined both for quality control purposes and for a proper control of microstructural features of bone reconstruction products. This study combines bulk morphological and compositional analysis methods (XRF, SEM-EDS, FT-IR) with surface-related methods (XPS, contact angle measurements) in order to correlate the characteristics of hydroxyapatite powders derived from bovine bone for its use in medical applications. An experimental approach for correlating the surface and volume composition was designed based on the analysis depth of each spectral method involved in the study. Next, the influences of powder particle size and forming method on the contact angle between water drops and ceramic surface were evaluated for identifying suitable strategies of tuning hydroxyapatite’s wettability. The results revealed a preferential arrangement of chemical elements at the surface of hydroxyapatite particles which could induce a favourable material behaviour in terms of sinterability and biological performance.

In order to design more powerful electrocatalysts, developing our understanding of the role of the surface structure and composition of widely abundant bulk materials is crucial. This is particularly true in the search for alternative hydrogen evolution reaction (HER) catalysts to replace platinum. We report scanning electrochemical cell microscopy (SECCM) measurements of the (111)‐crystal planes of Fe4.5Ni4.5S8, a highly active HER catalyst. In combination with structural characterization methods, we show that this technique can reveal differences in activity arising from even the slightest compositional changes. By probing electrochemical properties at the nanoscale, in conjunction with complementary structural information, novel design principles are revealed for application to rational material synthesis.\ud \ud

Um leistungsfahigere Elektrokatalysatoren zu entwickeln, ist es notwendig, den Einfluss der Oberflachenstruktur und -zusammensetzung von Materialien mit hoher lokaler Auflosung besser zu verstehen. Dies trifft insbesondere auf die Entwicklung geeigneter Alternativen fur Platin bei der elektrokatalytischen Wasserstofferzeugung zu. Elektrochemische Rasterzellmikroskopie (scanning electrochemical cell microscopy, SECCM) wurde benutzt, um die lokale elektrochemische Aktivitat der Wasserstoffbildung an einkristallinen (111)-Oberflachen von Fe4.5Ni4.5S8, einem hochaktiven Elektrokatalysator fur die Wasserstofferzeugung, zu untersuchen. In Kombination mit strukturaufklarenden Methoden zeigen wir, dass kleinste Veranderungen der chemischen Zusammensetzung die Aktivitat signifikant verandern konnen. Somit stellen die auf der Nanoskala durchgefuhrten elektrochemischen Messungen, erganzt mit lokalen strukturellen Messungen sowie Kenntnis der lokalen Zusammensetzung ein wichtiges Hilfsmittel fur das rationale Design neuer Katalysatoren dar.

Inspired by our recent finding that Fe4.5Ni4.5S8 rock is a highly active electrocatalyst for HER, we set out to explore the influence of the Fe:Ni ratio on the performance of the catalyst. We herein describe the synthesis of (FexNi1–x)9S8 (x = 0–1) along with a detailed elemental composition analysis. Furthermore, using linear sweep voltammetry, we show that the increase in the iron or nickel content, respectively, lowers the activity of the electrocatalyst toward HER. Electrochemical surface area analysis (ECSA) clearly indicates the highest amount of active sites for a Fe:Ni ratio of 1:1 on the electrode surface pointing at an altered surface composition of iron and nickel for the other materials. Specific metal–metal interactions seem to be of key importance for the high electrocatalytic HER activity, which is supported by DFT calculations of several surface structures using the surface energy as a descriptor of catalytic activity. In addition, we show that a temperature increase leads to a significant...

A novel electrochemical approach aimed at developing biosensing platforms based on polypyrrole/sulfonated graphene nanocomposites is reported. Specifically, nanocomposite layers are deposited onto platinum electrodes through the electrochemical polymerization of pyrrole monomer in the presence of reduced graphene oxide bearing phenylsulfonyl groups. Thus, the functionalized graphene nanofiller acts as dopant and balances the positive charges on the polymer chains, leading to an enhancement of the polymer's electrical conductivity and concomitantly increasing the electrode surface area. The polypyrrole/graphene nanocomposite films are further modified with carboxyphenyl groups via electrochemical reduction of 4-carboxyphenyl diazonium tetrafluoroborate. Grafting carboxyphenyl functionalities serves a dual purpose: it permits the covalent immobilization of glucose oxidase via carbodiimide chemistry and also forms an electrode blocking layer which hinders the oxidation of interfering substances. The feasibility of this strategy is demonstrated by the preparation of a glucose biosensor which exhibited an improved performance: wide linear range (0.02–12 mM), good sensitivity (0.56 μA mM−1 cm−2) and adequate selectivity towards common interferents including ascorbic acid, paracetamol, uric acid, and cysteine.

The present work is aimed to develop new composite films based on pectin and functionalized graphene oxide (GOf) by using a simple casting method. The non-covalent functionalization of graphene oxide (GO) was performed by using a non-ionic surfactant (Tergitol NP9) and therefore the interaction between GO and the polymer matrix was significantly enhanced. X-ray diffraction (XRD), X-ray photoelectron spectrometry (XPS) and Fourier-transform infrared (FT-IR) were used to prove the GO functionalization. The functionalization was evidenced also by Raman spectrometry and thermogravimetric analysis (TGA). According to the mechanical tests, an improvement of the Young’s modulus was recorded even at low loading of GOf within the pectin matrix which indicates a strong interaction between the polymer and GOf. By incorporation of GOf within pectin a modification of the morphology of the composite materials was observed by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) analysis.

Bifunctional oxygen electrocatalysts were fabricated following a three-step synthesis method which consisted of i) liquid phase exfoliation of graphite in the presence of nitrogen-containing manganese macro¬cyclic complexes and using DMF as the dispersion medium under formation of few-layer graphene sheets. Subsequently, ii) solvent re¬moval by vacuum-filtration and drying, and iii) pyrolysis of the resulting composites under an inert gas atmosphere with subsequent mild calcination yielded manganese oxides embedded within a graphitic carbon matrix (MnOX/G). We further demonstrate that traces of iron impurities in the used graphite result in enhanced electrocatalytic acti¬vity of the MnOX/G towards both the oxygen reduction and the oxygen evolution reactions owing to synergistic interaction of the iron impuri¬ties with the species formed upon thermal decomposition of manga¬nese macrocyclic complexes.

Monocrystalline, yet porous mosaic platelets of cobalt ferrite, CoFe2O4, can be synthesized from a layered double hydroxide (LDH) precursor by thermal decomposition. Using an equimolar mixture of Fe2+, Co2+, and Fe3+ during co-precipitation, a mixture of LDH, (FeIICoII)2/3FeIII1/3(OH)2(CO3)1/6·mH2O, and the target spinel CoFe2O4 can be obtained in the precursor. During calcination, the remaining FeII fraction of the LDH is oxidized to FeIII leading to an overall Co2+:Fe3+ ratio of 1:2 as required for spinel crystallization. This pre-adjustment of the spinel composition in the LDH precursor suggests a topotactic crystallization of cobalt ferrite and yields phase pure spinel in unusual anisotropic platelet morphology. The preferred topotactic relationship in most particles is [111]Spinel‖ [001]LDH. Due to the anion decomposition, holes are formed throughout the quasi monocrystalline platelets. This synthesis approach can be used for different ferrites and the unique microstructure leads to unusual chemical properties as shown by the application of the ex-LDH cobalt ferrite as catalyst in the selective oxidation of 2-propanol. Compared to commercial cobalt ferrite, which mainly catalyzes the oxidative dehydrogenation to acetone, the main reaction over the novel ex-LDH cobalt is dehydration to propene. Moreover, the oxygen evolution reaction (OER) activity of the ex-LDH catalyst was markedly higher compared to the commercial material.

Engineering stable electrodes using highly active catalyst nanopowders for electrochemical water splitting remains a notorious challenge. We report an innovative and general approach for attaining highly stable catalyst films with self-healing capability based on in-situ self-assembly of catalyst particles during electrolysis. The catalyst particles are added to the electrolyte forming a suspension that is pumped through the electrolyzer. Particles with negatively charged surfaces stick onto the anode, while particles with positively charged surfaces stick to the cathode. The self-assembled catalyst films possess self-healing properties as long as a sufficient amount of catalyst particles are present in the electrolyte. The proof-of-concept was demonstrated in a non-zero gap alkaline electrolyzer using NiFe LDH and NixB catalyst nanopowders for anode and cathode, respectively. Steady cell voltages were maintained for at least three weeks during continuous electrolysis at 50-100 mA cm-2

Graphene and graphene-related materials exhibit switchable charge-carrier mobility induced by applying a potential or by interaction with molecules. The short review summarizes concepts for the development of solution-gated field effect transistors using graphene or related substances as gate material focusing on applications in biosensors.

Prompted by the impact of Ni-based support materials on the intrinsic activity of electrocatalysts, we investigated the influence of partial Co substitution by Ni during the reductive thermal synthesis of cobalt-cobalt phosphide nanoparticles from triphenylphosphine complexes. The obtained catalysts were characterised by X-ray diffraction and electrochemistry. Increasing the amount of Ni in the precursor complexes leads to materials with lower overpotential for the OER at low current densities, and lower Tafel slopes. Co nanoparticles, which are only formed in materials with low Ni content, increase the intrinsic material conductivity and reduce the OER overpotential at high current densities. Keywords: Electrocatalysis, Oxygen evolution reaction, Co phosphide, Ni phosphide, Transition metal phosphide

The reproducible immobilization of enzymes represents a key requirement in developing sensitive and fast responding amperometric microbiosensors. A microbiosensor for the detection of glucose and adenosine-5'-triphosphate (ATP), respectively, is presented using a poly(benzoxazine) derivative for entrapment of the enzymes glucose oxidase (GOD) and hexokinase (HEX) at platinum microelectrodes (MEs). For glucose, a sensitivity of 123.05 ± 10.78 pA/mM (n = 5) was obtained, which shows twice as high sensitivity compared to microbiosensors using electrophoretic paints as immobilization matrix for the same size of ME (radius: 25 μm). For the determination of ATP, a sensitivity of 48.47 ± 5.12 pA/µM, and a signal-to-noise ratio of 40 at physiological pH values were obtained. Apart from their enhanced sensitivity, a significant improvement of these sensors is related to their improved mechanical stability. The applicability of these poly(benzoxine)-based microbiosensors for ATP detection was demonstrated with measurements at receptor protein tyrosine phosphatase zeta (PTPRζ) osteoblastic cells during mechanical stimulation.

A universal nano‐capillary based method for sample deposition on the silicon nitride membrane of liquid‐cell transmission electron microscopy (LCTEM) chips is demonstrated. It is applicable to all substances which can be dispersed in a solvent and are suitable for drop casting, including catalysts, biological samples, and polymers. Most importantly, this method overcomes limitations concerning sample immobilization due to the fragility of the ultra‐thin silicon nitride membrane required for electron transmission. Thus, a straightforward way is presented to widen the research area of LCTEM to encompass any sample which can be externally deposited beforehand. Using this method, NixB nanoparticles are deposited on the μm‐scale working electrode of the LCTEM chip and in situ observation of single catalyst particles during ethanol oxidation is for the first time successfully monitored by means of TEM movies., A novel universal method of single catalyst nanoparticle immobilization on the working electrode without damaging the fragile membrane allows single NixB nanoparticle catalysts to be monitored in situ during ethanol oxidation by means of TEM movies.

Layered double hydroxides (LDHs) are presently among the best-performing oxygen evolution reaction (OER) electrocatalysts in alkaline media. The high activity of LDHs is due to synergistic effects between two transition metals as well as the layered structure which facilitates electron transfer. Because of a perfect match with the size of interlayer carbonate a ratio of 2:1 for the di- and tri-valent octahedral cations is energetically preferred. Here we present a strategy, where first mixed valent (Co2+1-zFe2+z)4 Fe3+2 - LDHs, with z values between 0 and 0.75 are synthesized, which are subsequently oxidized to Co2+Fe3+ LDH-type layered (oxy)hydroxides with an unusual high trivalent Fe content. Characterization of the chemically oxidized materials using bulk and surface techniques demonstrated the successful synthesis of LDH-like trivalent iron rich (Co2+)4-4z (Fe3+)2+4z (oxy)hydroxides with a final Fe content ranging from 33.3 to 83.3%. Current densities of up to 200 mA cm−2 were obtained at potentials lower than 1.7 V vs. RHE for (Co2+)4-4z (Fe3+)2+4z (oxy)hydroxides containing a maximum of 80% Fe.

Carbon is a frequently used electrode material and an important additive in catalyst films. Its corrosion is often reported during electrocatalysis at high anodic potentials, especially in acidic electrolyte. Investigation of the carbon corrosion in alkaline environment is difficult due to the CO\(_{2}\)/CO\(_{3}\)\(^{2}\)− equilibrium. We report the on-line determination of electrolysis products generated on Ni\(_{x}\)B/C hybrid electrocatalysts in alkaline electrolyte at anodic potentials using differential electrochemical mass spectrometry (DEMS). Ni\(_{x}\)B/C catalyst films were obtained from mixtures containing different ratios of NiXB and benzoxazine monomers followed by polymerization and pyrolysis. The impact of the composition of the electrocatalyst on the dominant electrolysis process allows to distinguish between the oxygen evolution reaction and carbon corrosion using DEMS results as well as the catalyst surface composition evaluated from X-ray photoelectron spectra. At the imposed highly oxidative conditions, an increasing amount of Ni\(_{x}\)B in the electrocatalyst leads to a suppression of carbon corrosion.

In vitro synthesis of ATP catalyzed by the ATP-synthase requires membrane vesicles, in which the ATP-synthase is present within the bilayer membrane. Inverted vesicle prepared from Gram negative cells (e.g., Escherichia coli or Pseudomonas putida) can be readily obtained and used for in vitro ATP-synthesis. Up to now, quantification of ATP synthesized by membrane vesicles has been mostly analyzed via bioluminescence-based assays. Alternatively, vesicle respiration and the associated ATP level can be determined using biosensors, which not only provide high selectivity, but allow ATP measurements without the sample being illuminated. Here, we present a microbiosensor for ATP in combination with scanning electrochemical microscopy (SECM) using an innovative two-compartment electrochemical cell for the determination of ATP levels at E.coli or P. putida inverted vesicles. For a protein concentration of 22 mg/ml, a total amount of 0.29 ± 0.03 μM/μl ATP per vesicle was determined in case of E.coli; in turn, P. putida derived vesicles yielded 0.48 ± 0.02 μM/μl ATP per vesicle at a total protein concentration of 25.2 mg/ml. Inhibition experiments with Venturicidin A clearly revealed that the respiratory chain enzyme complex responsible for ATP generation is effectively involved.

Determination of the intrinsic electrocatalytic activity of nanomaterials by means of macroelectrode techniques is compromised by ensemble and film effects. Here, a unique "particle on a stick" approach is used to grow a single metal-organic framework (MOF; ZIF-67) nanoparticle on a nanoelectrode surface which is pyrolyzed to generate a cobalt/nitrogen-doped carbon (CoN/C) composite nanoparticle that exhibits very high catalytic activity towards the oxygen evolution reaction (OER) with a current density of up to 230 mA cm-2 at 1.77 V (vs. RHE), and a high turnover frequency (TOF) of 29.7 s-1 at 540 mV overpotential. Identical location transmission electron microscopy (IL-TEM) analysis substantiates the "self-sacrificial" template nature of the MOF, while post-electrocatalysis studies reveal agglomeration of Co centers within the CoN/C composite during the OER. "Single-entity" electrochemical analysis allows for deriving the intrinsic electrocatalytic activity and furnishes insight into the transient behavior of the electrocatalyst under reaction conditions.

We propose a method for the formation of highly active bifunctional oxygen electrocatalysts, by exploiting the unique features of nitrogen-rich metallo-macrocyclic complexes and the structural and electronic properties of few-layer graphene. The precursors of the electrocatalysts were synthesized by sonication of graphite in DMF leading to exfoliation and the formation of few-layer graphene sheets in the presence of a suitable transition metal macrocyclic complex. After pyrolysis and subsequent mild calcination metal oxide nanoparticles as well as metal-nitrogen (MN x ) moieties embedded within a N-doped graphitic carbon matrix are obtained. The formation, in-depth characterization and electrochemical performance of two different catalysts derived from Co and Ni containing precursor complexes are demonstrated.

We report a simple, facile, and safe route for preparation of cobalt–cobalt phosphide (Co/Co2P) nanoparticles and demonstrate their application as efficient low-cost catalysts for electrochemical water splitting. The catalyst achieves good performance in catalyzing both the cathode and anode half-cell water-splitting reactions in 1.0 M KOH and the hydrogen evolution reaction in an acidic electrolyte, 0.5 M H2SO4. For the oxygen evolution reaction in 1.0 M KOH, a current of 10 mA cm–2 was attained at 0.39 V overpotential on a glassy carbon electrode, while an overpotential of 0.19 V was attained at 50 mA cm–2 when the catalyst was supported on nickel foam.

Although oxidases are selective and specific biocatalysts frequently used in enzyme biosensors, amperometric detection methods can hardly distinguish the current response of enzymatic reaction products from the currents generated by other electroactive species commonly encountered in complex matrices. Therefore, various methods have been developed in order to improve the overall selectivity of enzyme-based biosensors. Here, we employ substituted polyaryl films grafted on platinum electrodes via the electrochemical reduction of a variety of diazonium tetrafluoroborates as blocking layers. Electron transfer kinetics of three redox probes at the bare and modified Pt electrodes were investigated in order to evaluate the blocking effect of the grafted layers. Further, the effect of surface modification on the voltammetric responses of commonly encountered interferents for glucose determination were examined. As proof of concept, interference-free amperometric biosensors employing glucose oxidase were constructed using aryl modified Pt electrodes.

Green biobased polymeric membranes are rapidly emerging as materials of choice for a number of biomedical applications. In this work, we report our preliminary studies on the covalent immobilization of sericinon to green cellulose membranes for potential biomedical applications such as in the osseointegration field. Initially, the surface of the cellulose acetate membrane was immobilized with the amino-propyl-triethoxysilane (APTS) functional group, while the protein was immobilized through glutaraldehyde that was used as a linker between amino-propyl-triethoxysilane and sericin. The functionalized membranes were thoroughly characterized by different characterization techniques such as infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA/DTG). All these techniques confirmed the successful functionalization and uniform immobilization of the protein onto the membrane surface. Subsequently, the perfo...

A future widespread application of electrochemical energy conversion and storage technologies strongly depends on the substitution of precious metal-based electrocatalysts for the high-overpotential oxygen reduction and oxygen evolution reactions. We report a novel Co/Co–Fe nanoparticles/N-doped carbon composite electrocatalyst (Co/CoxFey/NC) obtained by pyrolysis of CoFe layered double hydroxide (CoFe LDH) embedded in a film of a bisphenol A and tetraethylenepentamine-based polybenzoxazine poly(BA-tepa). During pyrolysis poly(BA-tepa) forms a highly conductive nitrogen-doped carbon matrix encapsulating Co/Co–Fe nanoparticles, thereby circumventing the need of any additional binder material and conductive additives. Optimization with respect to pyrolysis temperature, the CoFe LDH/BA-tepa ratio, as well as of the gas atmosphere used during the thermal treatment was performed. The optimized Co/CoxFey/NC composite material catalyst exhibits remarkable bifunctional activity towards oxygen reduction (ORR) and oxygen evolution (OER) reactions in 0.1 M KOH represented by a potential difference of only 0.77 V between the potentials at which current densities of −1 mA cm−2 for the ORR and 10 mA cm−2 for the OER were recorded. Moreover, the Co/CoxFey/NC composite material pyrolyzed in ammonia atmosphere exhibits promising stability during both the ORR and the OER.

The increasing amount of residual pharmaceutical contaminants in wastewater has a negative impact on both the environment and human health. In the present study, we developed new cellulose acetate/Mg-Al layered double hydroxide (Mg-Al LDH) nanocomposite membranes as an efficient method to remove pharmaceutical substances from wastewater. The morphology, porosity, surface properties and thermal stability of nanocomposite membranes containing various amounts of nanofiller were evaluated by scanning electron microscopy (SEM), X-ray microtomography (μCT), contact angle measurements and thermogravimetric analysis (TGA). The Mg-Al LDH nanofiller showed a high degree of exfoliation in the polymer matrix, evidenced by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The hydrodynamic properties and adsorption capacity were evaluated with pure water and aqueous solutions of two common drugs, diclofenac sodium (DS) and tetracycline (TC), and the nanocomposite membranes showed an improved permeability compared with neat cellulose acetate. The membrane prepared with 4 wt.% Mg-Al LDH loading exhibited the highest water flux compared with the pure polymer one (529 vs 36 L·m−2·h-1) and a tenfold increase in adsorption capacity for DS. This enhancement is attributed to electrostatic interactions between the negatively charged drug molecule and positively charged Mg-Al LDH layers. Conversely, in the case of TC, the increase in adsorption capacity was smaller and was assigned to hydrogen bonding interactions between the drug molecule and the nanofiller.

Electrochemical dopamine-sensing surfaces were fabricated by deposition of graphene sheets modified with cobalt tetrasulfonated phthalocyanine on glassy carbon electrodes (CoTSPc/Gr-GC) using differential pulse amperometry. Differential pulse stripping voltammetry was used to detect dopamine (DA) and the influence of pH value, scan rate, accumulation potential and time as well as dopamine concentration on the performance of CoTSPc/Gr-GC electrodes was investigated. The modified electrodes were successfully used as sensors for the selective and high sensitive determination of DA in presence of high concentrations of ascorbic acid (AA) and uric acid (UA) with a detection limit of 0.87 nM over the dynamic linear range of 20 nM to 220 nM.

“Single entity” measurements are central for an improved understanding of the function of nanoparticle‐based electrocatalysts without interference arising from mass transfer limitations and local changes of educt concentration or the pH value. We report a scanning electrochemical cell microscopy (SECCM) investigation of zeolitic imidazolate framework (ZIF‐67)‐derived Co−N‐doped C composite particles with respect to the oxygen evolution reaction (OER). Surmounting the surface wetting issues as well as the potential drift through the use of a non‐interfering Os complex as free‐diffusing internal redox potential standard, SECCM could be successfully applied in alkaline media. SECCM mapping reveals activity differences relative to the number of particles in the wetted area of the droplet landing zone. The turnover frequency (TOF) is 0.25 to 1.5 s−1 at potentials between 1.7 and 1.8 V vs. RHE, respectively, based on the number of Co atoms in each particle. Consistent values at locations with varying number of particles demonstrates OER performance devoid of macroscopic film effects., The oxygen evolution reaction (OER) activity of single and multiple ZIF‐derived Co/N−C nanocomposite particles was examined by high‐throughput scanning electrochemical cell microscopy. Through the use of an Os complex as an internal reference standard, the intrinsic activity of the catalyst with respect to the OER activity as well as the turnover frequency could be determined.

Earth‐abundant transition‐metal‐based catalysts are attractive for alkaline water electrolysis. However, their catalytic properties are often limited by their poor electrical conductivity. Here, we present a strategy for enhancing the electrical conductivity of NiFe layered double hydroxide (LDH) in order to further improve its properties as an electrocatalyst for the oxygen evolution reaction (OER) in alkaline media. We show that NiFe LDH containing metal tetrasulfonate phthalocyanine in the interlayers between the NiFe oxide galleries can be coupled with graphene during liquid‐phase exfoliation by taking advantage of their π‐π stacking capabilities. A substantial enhancement in the electrocatalytic activity of NiFe LDH with respect to the OER was observed. Moreover, the activity and selectivity of the catalyst materials towards the oxygen reduction reaction were investigated, demonstrating that both the metal hydroxide layer and the interlayer species contribute to the electrocatalytic performance of the composite material., Stack the odds! A strategy is presented for boosting the activity of NiFe layered double hydroxide (LDH) towards the oxygen evolution reaction. The strategy consists of enhancing its electrical conductivity by π‐π stacking graphene (G) with phthalocyanine ligands present at the LDH interlayer through liquid‐phase exfoliation. The resulting NiFe LDH/G composites exhibit remarkably higher activities than their separate components.

NiFe layered double hydroxide (LDH) is inarguably the most active contemporary catalyst for the oxygen evolution reaction under alkaline conditions. However, the ability to sustain unattenuated performance under challenging industrial conditions entailing high corrosivity of the electrolyte (≈30 wt. % KOH), high temperature (>80 °C) and high current densities (>500 mA cm-2 ) is the ultimate criterion for practical viability. This work evaluates the chemical and structural stability of NiFe LDH at conditions akin to practical electrolysis, in 30 % KOH at 80 °C, however, without electrochemical polarization, and the resulting impact on the OER performance of the catalyst. Post-analysis of the catalyst by means of XRD, TEM, FT-IR, and Raman spectroscopy after its immersion into 7.5 m KOH at 80 °C for 60 h revealed a transformation of the structure from NiFe LDH to a mixture of crystalline β-Ni(OH)2 and discrete predominantly amorphous FeOOH containing minor non-homogeneously distributed crystalline domains. These structural and compositional changes led to a drastic loss of the OER activity. It is therefore recommended to study catalyst stability at industrially relevant conditions.

In this paper we report a new strategy for obtaining conducting azopolymers having pendant azobenzene moieties via functionalization of polypyrrole by electrochemical reduction of 4-[(4′-nitrophenyl)azo]benzenediazonium tetrafluoroborate (NABDBF4−). The functionalization of polypyrrole films with 4′-nitroazobenzene (NAB) groups has been evaluated by cyclic voltammetry and by spectroscopic techniques such as XPS, Raman and UV–vis spectroscopy. Moreover, the third-order nonlinear optical response of NAB-functionalized polypyrrole has been investigated using the optical third-harmonic generation technique. All these investigations confirmed the presence at the polymeric films surface of the functional groups introduced by the electrochemical reduction of diazonium salt. The versatility of this methodology allows not only the functionalization of polypyrrole-type materials with chromophore groups, but can also be successfully applied to other conjugated polymer systems in order to create various photoresponsive materials.

Benzoxazine oligomers synthesized by a Mannich type reaction of bisphenol A, tetraethylenepentamine and formaldehyde were electrochemically crosslinked in presence of both an Os-complex modified poly(methacrylate) polymer and glucose oxidase. The crosslinking led to the formation of a biocatalytically active layer on an electrode surface exhibiting a swelling process after immersion in an electrolyte solution containing glucose most likely due to the local decrease of the pH value upon glucose oxidation. Optimization of the poly(benzoxazine) to Os-complex modified poly(methacrylate) ratio was performed leading to a reagentless glucose biosensor with improved stability.

The synthesis of a benzoxazine (BZ) monomer inside the montmorillonite (MT) layers was done using a diamino-modified MT as the amine component, phenol, and formaldehyde. The formation of the BZ rings within the MT layers was investigated by thermogravimetric analysis, X-ray photoelectron spectroscopy, proton nuclear magnetic resonance spectroscopy, and X-ray diffraction, this being enhanced when dioxane was used as the solvent. The morphology of the hybrid BZ monomer was investigated by scanning electron microscopy.

Highly active electrocatalysts for the oxygen evolution (OER) reaction are in most cases powder nanomaterials, which undergo substantial changes upon applying the high potentials required for high-current-density oxygen evolution. Owing to the vigorous gas evolution, the durability under OER conditions is disappointingly low for most powder electrocatalysts as there are no strategies to securely fix powder catalysts onto electrode surfaces. Thus reliable studies of catalysts during or after the OER are often impaired. Herein, we propose the use of composites made from precursors of polybenzoxazines and organophilically modified NiFe layered double hydroxides (LDHs) to form a stable and highly conducting catalyst layer, which allows the study of the catalyst before and after electrocatalysis. Characterization of the material by XRD, SEM, and TEM before and after 100 h electrolysis in 5 m KOH at 60 °C and a current density of 200 mA cm−2 revealed previously not observed structural changes.

The aim of this study was to obtain membranes with antimicrobial activity presenting a complex sandwich-type structure. The outer layers are comprised of poly(methyl methacrylate) membranes, whereas the inner active layer consists of a modified commercial membrane to achieve antimicrobial properties. This activity arises due to the presence of silver nanoparticles in a material with a hybrid composition deposited on a commercial membrane. This hybrid material consists of polymer colloids and multiwall carbon nanotubes used for both the stabilization of the active layer by the interconnections of the polymer particles and as active component. The filtration tests revealed a good stability of the materials and an increased hydrophilicity of the hybrid membranes. The antimicrobial properties have been evaluated using Staphylococcus aureus and Escherichia coli, and have been correlated with the content and migration rate of silver ions.

We successfully synthesized tin dioxide nanoparticles with polyhedral morphology via an ethylene glycol assisted sol-gel approach. The structural characteristics of three tin dioxide samples were investigated after being thermally treated at 400°C, 600°C and 800°C. X-ray diffraction (XRD) patterns clearly show the formation of single phase tin dioxide nanoparticles, with crystallite size of 6–20 nm, in good correlation with Fourier transform infrared (FTIR) spectra. Transmission electron microscopy (TEM) analysis confirms the formation of 6nm polyhedral nanoparticles for the 400°C sample. Ultraviolet-visible (UV-Vis) and photoluminescence (PL) spectra suggest a high concentration of oxygen vacancies. The oxygen vacancy concentration increases with temperature, due to the combined action of the formation of VO and the energetic O compensation. X-ray photoelectron spectroscopy (XPS) analysis also confirms the formation of single phase tin dioxide and the presence of oxygen vacancies in good agreement with UV-VIS and PL data.

New polybenzoxazine/LDH nanocomposites were synthesized using three types of LDH (layered double hydroxides) and various LDH concentrations (1, 5, 10 and 30% wt.). Microcomposites were obtained if unmodified LDH (LDH A or LDH B) was used, while exfoliated nanocomposites were produced if modified LDH with sodium dodecyl sulfate (SDS) was employed. The influence of LDH on the benzoxazine polymerization was investigated by DSC showing a catalytic effect on the polymerization process, which is quite significant if LDH–SDS is used, a decrease with ∼20° of the temperature corresponding to the maximum rate of polymerization being noticed. XRD, SEM and TEM were employed to determine the morphology of the composite materials. Thus high exfoliation degree was revealed for 5% LDH–SDS. The introduction of LDH in the polybenzoxazine matrix decreases the thermostability of the neat resin considering the value of the temperature at which the mass loss is 1% (T d1% ), but stabilizes the composite material at higher degradation stages promoting the residual char formation. The best thermal properties were achieved for the exfoliated nanocomposites containing 5% LDH–SDS, a good interaction between LDH–SDS and polybenzoxazine being the key factor for the overall properties of the nanocomposites.

Water-soluble benzoxazine oligomers were synthesized by reacting bisphenol A, tetraethylenepentamine and formaldehyde. The pre-formed benzoxazine oligomers can be further electropolymerized from aqueous suspensions under formation of poly(benzoxazine)-based films on electrode surfaces. Integration of glucose oxidase in a poly(benzoxazine) film let to highly reproducible and stable biosensors. Poly(benzoxazines) are proposed as a new family of stable polymers for the design of enzyme electrodes. Keywords: Poly(benzoxazine), Electrodeposition, Amperometric biosensor, Enzyme immobilization, Potential pulse deposition

In this paper we report the functionalization of conductive polypyrrole (PPY) films via electrochemical reduction of the aryl di-azonium salts in a manner that is similar to the one employed for other conductive surfaces. To understand the general trendsof the grafting behavior of diazonium salts and to establish the optimal conditions for the covalent functionalization of the PPYfilms, we have compared the grafting behavior of four

The synthesis of 3,3′-(hexane-1,6-diyl)bis-(3,4-dihydro-2 H -1,3-benzoxazine) was done in the absence and in the presence of 10, 30, 50 and 100 wt.% montmorillonite (MMT). The MMT exhibits a significant catalytic effect on the ring-opening reaction of the benzoxazine monomer, increasing of MMT amount influences the oligomeric structures in the polybenzoxazine precursor composition according to 1 H NMR, 13 C NMR and SEC data. The influence of solvent polarity and temperature was also studied especially in correlation with possible interactions between solvent and MMT. The influence of the polybenzoxazine precursor composition on the polymerization behaviour was investigated by DSC. The thermostability of the obtained polybenzoxazines was studied by TGA and DMA method was involved to determine the glass transition temperature.