N. A. Kapustina

Direct ethanol oxidation fuel cell with anionite membrane and alkaline electrolyte

A number of cathode catalysts were synthesized from nitrogen-containing organic complexes on XC-72R carbon black for an alkaline electrolyte. The catalysts were studied by the rotating disc electrode (RDE) technique. The polyacrilonitrile (PAN), phthalocyanine (Pc), and cobalt tetra(methoxyphenyl)porphyrin (CoTMPP) systems showed the highest activity. The slope of the oxygen polarization curves in the first region in 1 M KOH was 35–40 mV; this corresponds to concentration polarization in an alkaline solution in the O2-HO2− system. A cyclic voltammetry study demonstrated that the catalytic systems with the highest corrosion stability were Pc + Co + Fe/XC-72R and CoTMPP/XC-72R pyropolymer. The activity of the catalysts decreased by 20–25% compared with the initial current densities on average. An ethanol-oxygen fuel cell with a Fumasep FAA anionite membrane and nonplatinum catalysts was tested. The maximum power density was 32 mW/cm2 at 40°C. The stability test of the fuel cell showed that the materials used for the membrane-electrode assembly allowed more than 100 h of continuous operation with constant working characteristics.

Kinetics and mechanism of oxygen electroreduction in acidic and neutral solutions on carbon black XC-72R modified by products of pyrolysis of cobalt 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin

AbstractCathodic oxygen reduction on the XC-72R carbon black modified by the products of pyrolysis of cobalt 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin (CoTMPP) (XC-72M) was studied in acidic and neutral electrolytes. Formation of new active centers on XC-72M is confirmed by voltammetric curves (specific charge density grows as compared to the XC-72R carbon black by 2–2.5 times) using the methods of rotating disk electrode (a shift in half-wave potential E1/2 by 600 mV) and rotating ring-disk electrode (the fraction of the direct reaction increases to 70%). Herewith, the

Cathodic reduction of oxygen on PdCo/C catalyst synthesized based on commercial Pd/C catalyst

\frac{{\partial E_{1/2} }} {{\partial pH}}

Corrosion stability of nanosize Pd/C, PdCo/C, and PdCoCr/C catalytic systems in acidic media for fuel cell cathodes

value in the range of pH 0.3–8.5 is −60 mV. It is shown that proton necessarily participates in the slow stage of the first electron transfer for the further occurrence of the direct reaction to water. At a transition from acidic solutions to neutral ones, the polarization curves converge for XC-72M and XC-72R, which is due to a decrease in the concentration of proton in the solution and variation of the mechanism of the oxygen reduction slow stage.

Kinetics and mechanism of oxygen electroreduction in alkaline solutions on xc-72r carbon black modified by products of pyrolysis of cobalt 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin

The data on the cathodic PdCo/C catalyst prepared by high-temperature synthesis from 20 wt % Pd/C (E-TEK) are shown. According to XRD data, the catalyst represents an alloy with the preferential composition of Pd2Co. The kinetics and mechanism of oxygen reduction on the PdCo/C catalyst are studied by the methods of rotating disk electrode, rotating ring-disk electrode, and electrochemical impedance. It is shown that oxygen is reduced preferentially to water (k1) but in the potential range more negative than 0.6 V, the ratio of constants k1/k2 decreases, which suggests that the contribution of the reaction that proceeds through the formation of H2O2 (k2) increases. The activity of PdCo/C catalyst under model conditions in 0.5 M H2SO4 was assessed to be 15 mA/mgcat at a potential of 0.7 V.

Kinetics and mechanism of oxygen reduction reaction at CoPd system synthesized on XC72

An express method for determining the corrosion stability of palladium-based cathodic catalytic systems was developed. The method consists of cycling the electrode potential with a thin catalyst layer in 0.5 M H2SO4 in the range of potentials of the fuel cell operation and a subsequent comparison of the characteristics of catalytic systems (specific surface area and activity in the oxygen reduction reaction) before and after the corrosion action. The suggested method was used to characterize the corrosion behavior of the Pd/C commercial catalyst, as well as the PdCo/C and PdCoCr/C catalysts synthesized at the Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences. According to the XRD data, they correspond to systems with a high level of alloy formation. It is shown that the PdCo/C and PdCoCr/C catalysts are considerably more stable towards corrosion action than 20% Pd/C (E-TEK). The results were compared with the stability data obtained using a chronoamperometric method.

Development of platinum-free catalyst and catalyst with low platinum content for cathodic oxygen reduction in acidic electrolytes

Cathodic oxygen reduction on XC-72R carbon black modified by products of pyrolysis of cobalt 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin (CoTMPP) (XC-72M) was studied. When XC-72R carbon black is modified, new active centers (ACs) are formed on the surface of the carbon support, on which the direct reaction to OH- occurs, as shown using the rotating ring-disk electrode technique. The process of oxygen reduction on nonmodified carbon black occurs via the serial path. At low polarizations, the dependence of potential on pH corresponds to the slope of ∼30 mV both for the carbon material and modified carbon black. This value is close to the coefficient in the Nernst equation for H2/HO2−. The slow stage of oxygen reduction is the transfer of the first or second electron to the adsorbed molecule. Herewith, the difference in the kinetics and mechanism of oxygen reduction on XC-72R and XC-72M is related to a stronger adsorption interaction of oxygen and ACs on XC-72M. The {ie1113-1} value in the pH range of 12–14.6 is −15 to −20 mV both for XC-72R and XC-72M. In the case of the second halfwave potential on XC-72R, it is −50 to −60 mV. The observed effects are explained by a change in the surface state of catalysts at an increase in adsorption of OH− ions at an increase in pH.