The synthesis of novel Pt-containing catalysts to achieve the high electrocatalytic activity in methanol oxidation reaction is the one of important directions in modern direct methanol fuel cells research and design. However, the comparison of results of electrochemical experiments shown in various works for different compositions of catalyst is practically impossible due to various conditions of experiments used by different authors’ groups. Hence, the importance of the methodology in study of electrochemical properties of Pt-containing catalysts discussed in the current work becomes evident. The Pt/C and PtRu/C commercial catalysts and also model systems with Pd, Rh, Ru, PtRu particles electrodeposited on glassy carbon electrode surface were used to specify the methodological aspects of comparative characterization of catalysts with various composition. The role of several important factors such as the methodology of electroactive surface area estimation, the nature of model acid electrolyte, polarization mode (potential range using in CV), polarization regime used for modeling of catalyst work in DMFC, medium pH and influence of methanol oxidation intermediates was discussed. It is shown that CO desorption is more appropriate method (with proposed modifications) for ECSA estimation; HClO4 is more favorable electrolyte for model experiments with catalysts when Nafion suspension is used as a binding agent. The polarization in CV mode in the potential range including the hydrogen adsorption region leads to local (near the electrode) pH changes, which results in increase in concentration (correlates with forward peak current density) of main electroactive species, gem-diolate, in methanol solution. The use of diluted methanol solutions allows to increase the efficiency of fuel consumption and decrease the overpotential of methanol oxidation reaction due to more favorable ratio of concentrations of electroactive and oxygen species adsorbed on the electrode surface.

Herein, the impact of the chemical stability of RedOx mediator ferricyanide, K3[Fe(CN)6] (FC), a type of buffer solution used for bioreceptor preparation, gel composition (carboxymethylcellulose, CMC, Aerosile, AS, and alginate, ALG) on the long term stability of glucose test-strips and their analytical performance was examined. By simple addition of ALG to the functional gel aiming to improve its viscosity, we managed to enhance the sensitivity of conventional CMC-containing amperometric glucose test-strips from 3.3 µA/mM to 3.9 µA/mM and extend their shelf life from 8 months to 1.7 years. Moreover, during the course of investigations, it was revealed that the activity of enzyme in dependence with the used buffer did not linearly correlate with its activity in a dried functional layer, and the entire long-term electrochemical signal of glucose test-strips was determined by RedOx mediator FC chemical stability. The most stable and sensitive test-strips were obtained by the screen-printing approach from a gel containing 24 mg/mL GOx prepared in citrate buffer with pH 6, 200 mg/mL of FC and 10 mg/mL of CMC supplemented with 25 mg/mL of ALG.

PdRh/C catalyst and electrodeposited Pd, Rh and PdRh particles on glassy carbon electrode were studied in methanol and ethanol oxidation reactions in comparison with Pt-containing catalysts. Some features of this process have been described: (1) the appearance of oxidation peak in acidic and neutral media is possible only when polarization on CV is prolonged to hydrogen adsorption region where the surface OH-group formation occurred and surface oxides are reduced; (2) the CV-responses of model systems (electrodeposited Pd, Rh, PdRh) corresponding to alcohol oxidation increase and deform even during relaxation period when polarization is switched off; (3) experiments with addition of corresponding aldehydes (formaldehyde, acetaldehyde) to alcohol solution with stabilized CV responses showed that only increase in currents but not deformation of CV occurred. The addition of acid residue did not change the response noticeably. The formation of the same electroactive species, gem-diolate, for both alcohol and aldehyde electrooxidation mechanisms was supposed.

Selective electrochemical oxidation of acetaldehyde in aqueous alkaline ethanol solutions on the silver-containing electrodes has been presented. Several types of silver-containing electrode were used: the smooth silver disk electrode, rough silver electrode and the glassy carbon electrode modified with the silver-polypyrrole composite ink. Silver-polypyrrole (Ag-PPy) composite was synthesized via single-step chemical oxidation with the use of diluted aqueous solutions of silver nitrate and pyrrole in molar ratio 1:50. It has been shown that acetaldehyde is oxidized selectively on silver in the presence of ethanol in alkaline solutions. The influence of various factors (pH, the presence of molecular oxygen, ethanol and acetate anions, surface area extension and polypyrrole presence) on the aldehyde electrooxidation process has been studied. It was shown that for the silver-polypyrrole composites the aldehyde electrooxidation peak potential is shifted to negative direction in comparison with the silver electrode. However, the sensitivity of the silver-polypyrrole composite modified electrode is lower than for smooth or rough silver electrode. The addition of nitrate anions in alkaline solution permits to increase the peak currents for Ag-PPy modified electrode.

Low chemical durability of proton exchange membranes is one the main factors limiting their lifetime in fuel cells. Ceria nanoparticles are the most common free radical scavengers. In this work, hybrid membranes based on Nafion-117 membrane and sulfonic or phosphoric acid functionalized ceria synthesized from various precursors were prepared by the in situ method for the first time. Ceria introduction led to a slight decrease in conductivity of hybrid membranes in contact with water. At the same time, conductivity of membranes containing sulfonic acid modified ceria exceeded that of the pristine Nafion-117 membrane at 30% relative humidity (RH). Hydrogen permeability decreased for composite membranes with ceria synthesized from cerium (III) nitrate, which correlates with their water uptake. In hydrogen-air fuel cells, membrane electrode assembly fabricated with the hybrid membrane containing ceria synthesized from cerium (IV) sulfate exhibited a peak power density of 433 mW/cm2 at a current density of 1080 mA/cm2, while operating at 60 °C and 70% RH. It was 1.5 times higher than for the pristine Nafion-117 membrane (287 mW/cm2 at a current density of 714 mA/cm2).

Catalytic layers of low temperature fuel cell with various nanoscale platinum loading (40% Pt/C catalyst) catalyst loading have been designed by different methods. Membrane electrode assemblies with these electrodes were studied in hydrogen-air PEMFC. It was shown that the use of platinum loading 0.2 mg/cm2 leads to the highest utilization. Analytical modeling of cathode catalytic layer of PEMFC was carried out and the role of its main properties in current-voltage characteristics was shown.

The possibility of modifying the nafion direct alcohol fuel cell proton-exchange membrane by monolayer graphene by hot pressing has been demonstrated. It is shown that this modification can reduce the permeability of the membrane on methanol while maintaining a high proton conductivity membrane, but with the long operation of the membrane without additional protection of the barrier layer formed in this way, it is detached. With a Nafion/graphene/Nafion membrane, the formed graphene layer is sufficiently protected to reduce the methanol crossover and increase the power of the single methanol fuel cell by 2 times.

In this work, a comparative study was carried out of the transport properties and performance in a hydrogen-air fuel cell of the membranes based on polymethylpentene (PMP) with grafted sulfonated polystyrene and the standard Nafion (R) 212 membrane. Grafted cation-exchange membranes (GCM) were obtained by radiation graft post-polymerization of styrene onto UV-exposed PMP film followed by sulfonation with chlorosulfonic acid. The proton-conductivity of the GCM membrane with an ion-exchange capacity of 2.9 +/- 0.1 meq/g reaches 21 +/- 1 mS cm(-1) at room temperature and 95% relative humidity, which is twice higher the conductivity of the Nafion (R) under the same conditions. The GCM-1 H-2-permeability of 2.06.10(-7) cm(2) s(-1) even slightly lower than that of the Nafion (R) 212 (2.14.10(-7) cm(2) s(-1)). A comparison of these membranes in the membrane electrode assemblies (MEA) of hydrogen-air fuel cells (FC) shows that the use of the grafted membranes with the high ion-exchange capacity is highly promising. The maximum performance of FC with grafted and Nafion (R) 212 membrane are both close to 180 mW/cm(2) at the current density of 400 mA/cm(2). At the same time, the high degree of crosslinking of sulfonated polystyrene leads to a decrease in conductivity and does not give an advantage in gas permeability. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

The kinetics of bioelectrocatalytic oxidation of glucose by protein extracts—supersonic-destruction products of Escherichia coli BB cells—is studied in the presence of [Fe(CN)6]3– as the mediator system. The effect of the concentration of mediator, glucose, and protein extract is studied by electrochemical methods. The results are used in determination of effective parameters: the rate constant of glucose biooxidation, the constant of substrate-induced inhibition, and the activation energy. It is shown that the activation energy of this reaction falls into the interval of activation energies of dehydrogenase reactions. The voltammetric characteristics of a model asymmetrical biofuel cell which employs the protein extract as the anodic catalyst are determined. The maximum specific power of such model biofuel cell is found to be 400 µW/cm2 (4 W/m2).

A brief analysis of the publications on the synthesis of polyphenylquinoxalines, their sulfonation, and the study of their thermal stability and proton conductivity is presented. Polyphenylquinoxaline is synthesized based on 3,3',4,4'-tetraaminodiphenyl oxide and 1,4-bis(phenylglyoxalyl) benzene and sulfonated. Films of sulfonated polyphenylquinoxaline with sulfur contents of 0.6, 1.7, 6.0, and 8.0% are obtained, and their thermal stability, proton conductivity, and testing as a proton-conducting membrane in a membrane electrode block of a fuel cell are investigated.

Platinum-containing bimetallic nanoparticles manifest high functional characteristics as electrocatalysts. To use PtCu/C catalysts in low-temperature fuel cells, it is necessary to minimize selective copper dissolution, as copper cations can pollute the polymer membrane and decrease its proton conductivity. The work determines the composition, measures the electrochemically active surface area, and studies the electrochemical behavior of PtCu/C catalysts containing nanoparticles with a “core–shell” structure in the initial state (as-prepared) and after pretreatment in solutions of different acids. The comparative determination of catalyst activity in an electrochemical cell and their testing in a membrane-electrode assembly of fuel cells showed that pretreated PtCu/C materials with a much better stability as compared to Pt/C were also noninferior to the latter as regards their activity in the oxygen electroreduction reaction.

A protein extract of microbe cells is studied as a bioelectrocatalyst for glucose oxidation. The microbial protein extract prepared from Escherichia coli BB, which comprises all enzymes of the life cycle of these bacteria, is considered here as a model system. This system demonstrates the mediator mechanism of interaction with an inert glassy-carbon electrode in a buffer containing glucose as the substrate. The efficiency of the bioelectrocatalytic process was shown to depend on the type of mediator system and also on the nature of buffer, its temperature, pH, and ionic strength. The protein extract is shown to contain NAD-dependent Fe-glucosodehydrogenase and demonstrate the current densities in mediator-assisted glucose oxidation well comparable with the known data for pure dehydrogenase enzymes and E. coli microbial systems. The prospects for further studies and practical applications of this new bioelectrocatalyst type are outlined.

AbstractThe influence of pulsed activation on the electrochemical characteristics of fuel cells based on the Nafion proton-conducting membrane is studied. The activation was a repeated pulsed operation of the membrane–electrode assembly (MEA), which was characterized by alternating a constant load of the MEA near a short-circuit current at voltage U _L = 0.1 V and its “idle time” corresponding to the open circuit voltage of the MEA, U _OCV ≈ 0.95 V. It is shown that there is an optimal ratio of the time parameters of the pulsed load at which the activation is much more efficient than in the case of constant potentiostatic or galvanostatic regimes often used in practice.

The influence of pulsed activation on the electrochemical characteristics of fuel cells based on the Nafion proton-conducting membrane is studied. The activation was a repeated pulsed operation of the membrane–electrode assembly (MEA), which was characterized by alternating a constant load of the MEA near a short-circuit current at voltage UL = 0.1 V and its “idle time” corresponding to the open circuit voltage of the MEA, UOCV ≈ 0.95 V. It is shown that there is an optimal ratio of the time parameters of the pulsed load at which the activation is much more efficient than in the case of constant potentiostatic or galvanostatic regimes often used in practice.

The electrochemical noise of a polymer membrane hydrogen-air fuel cell operating at different load currents was measured in serial experiments. Spectral power densities of the noise are shown to be divided into three regions. At frequencies greater than 3–10 Hz, the spectrum dependence has a constant slope of − 2 in the bilogarithmic coordinates. At frequencies 0.3–5 Hz, there is a horizontal plateau in which length is determined by the value of a load. At frequencies less than 0.3 Hz, the dependence of spectral power density has a slope of − 2. Medium-frequency plateau and high-frequency slope of spectral power densities of the noise were approximated by model RC circuits. The values of Faradic resistance and double-layer capacitance connected in parallel were obtained from the electrochemical impedance data. At load voltages higher 0.5 V, the height of the plateau was shown to be proportional to the 2.68 power of the load current value.