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Results of experiments and modeling of a compact (800 cm3) membrane reformer module for the production of 0.25–0.30 Nm3/h hydrogen by methane steam reforming are reported. The module consists of a two-sided composite membrane disc with a 50 μm PdAg layer and two adjacent 4 mm thick Ni foam discs (60 ppi). A nickel catalyst and a porous support were deposited on the foam discs to give the final composition of 10%Ni/10%MgO/Ni-foam. Membrane permeability by pure hydrogen was investigated, and coefficients of transverse hydrogen transport across the Ni foam to the membrane in the case of inlet binary N2H2 mixture were refined in order to account for concentration polarization effect into the model. Activity of the catalytic discs was measured in a differential laboratory scale reactor at a pressure of 1 bar and temperature of 400–600 °C. Modules were tested at a 8–13 bar pressure of the mixture in the reforming zone and at 1 bar of pure hydrogen under the membrane, H2O/C = 2.5–3 and a module temperature of 550–680 °C (with and without hydrogen removal). Two modifications of the module were tested: consecutive (I-type) and parallel (II-type) flow of the reaction mixture around two sides of the membrane disc. In order to optimize construction of the module, calculations were made for revealing the effect of thickness of the PdAg membrane layer (5–50 μm), thickness of the Ni foam discs (0.5–8 mm) and temperature (600–700 °C) on the hydrogen output of the module. A comparison of the values obtained in our experiments (>1 MW/m3 and >0.7 kg(H2)/h/m2) with the literature data reported by other authors showed that the developed modules are promising for practical application as components of a fuel processor section for mobile applications. [ABSTRACT FROM AUTHOR]

HiSPEC 13100-monoplatinum-catalyst-based cathode for hydrogen-air (hydrogen-oxygen) fuel cell with proton-conducting polymer membrane is studied. The cathodes of membrane-electrode assemblies with different platinum load were subjected to accelerated stress-tests for the purpose of the revealing of peculiarities of the cathode degrading and its electrochemical parameters' changing, depending on the platinum load in active layers. The cathodes with lower platinum load were shown to have better characteristics, such as the mass activity and platinum utilization coefficient. However, they are much more prone to degradation and increased transport losses at limiting currents as compared with high-platinum-loaded cathodes. A degradation mechanism is suggested, which basically allows for the platinum nanoparticles coalescence. [ABSTRACT FROM AUTHOR]

Electrochemical and structure characteristics of PtCoCr/C-catalyst with platinum content 50 wt % under model conditions and in cathode of membrane-electrode assembly (MEA) of hydrogen-oxygen fuel cell are studied. The metal-phase nanoparticles are shown to represent a PtCo alloy with partial inclusion of chromium, the nanoparticles surface being enriched with platinum. The platinum mass activity and the PtCoCr/C-catalyst high corrosion resistance do not depend on the amount of platinum deposited onto XC72 carbon black (20 or 50 wt %). Herewith the platinum surface area decreases in the same way as the carbon black specific surface area (measured with the BET method); the latter is 227, 169, and 105 m/g for pure carbon black and that containing 20 and 50 wt % Pt, respectively. Testing of the 50PtCoCr/C-catalyst in the MEA cathode active layer in hydrogen-oxygen fuel cell showed performance not inferior to MEAs with pure-platinum systems, the catalyst being more stable. [ABSTRACT FROM AUTHOR]

Degrading of membrane-electrode assemblies of hydrogen-air fuel cells during their long-term and accelerated stress testing is analyzed by complex of electrochemical and structural methods. In both testing types, the principal degrading factor is the cathode catalyst destruction accompanied by the active surface loss due to the platinum oxidation, its particles' coarsening, and platinum ion transfer to polymer electrolyte. The approach to membrane-electrode-assembly state evaluation during the long-term testing on basis of the accelerated stress testing is validated. A method of the lifetime prediction for fuel cells operating in various conditions, differing in temperature, current load and regime, as well, as the membrane-electrode assembly architecture, is suggested. [ABSTRACT FROM AUTHOR]

The degradation processes of HiSPEC 9100 (60% Pt/C) and 13100 (70% Pt/C) cathodic monoplatinum catalysts, which were tested under the model conditions and in the composition of membrane-electrode assemblies (MEA) of hydrogen-air and hydrogen-oxygen fuel cells, are studied. It is shown that, in all cases, the main reason for a decrease in the catalyst activity was a decrease in its surface area, which was caused by the coarsening of platinum nanoparticles, irreversible oxidation of a fraction of active centers, and the destruction of the catalyst due to the carbon support oxidation. The results of electrochemical measurements are supplemented with the structural investigations by the methods of transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), and X-ray photoelectron spectroscopy (XPS). It is found that the degradation processes of MEA in the accelerated stress tests (AST) are similar to those in the long-term life tests. With respect to a decrease in the catalyst active surface area, the application of 2500 cycles in the voltage range of 0.6 to 1.2 V in the AST is equivalent to the life tests for 1010 h. During the fuel cell operation, the destruction of polymer electrolyte proceeds along with the catalyst degradation. This leads to a decrease in the ion-exchange capacity of the membrane and ionomer in the composition of cathode active layer. [ABSTRACT FROM AUTHOR]

A cathodic catalyst, which can replace monoplatinum commercial catalyst, is developed and investigated. New catalyst combines a smaller consumption of platinum with a higher mass activity and corrosion resistance. A method of fabrication of ternary (PtCoCr/C) catalyst is improved in order to obtain the catalytic system containing 45-50 wt % platinum. This is necessary to form thinner active layers of cathodes of membrane-electrode assemblies of hydrogen-air fuel cells. The activity of the synthesized PtCoCr/C catalyst is by 1.2-1.5 times higher than that of the monoplatinum catalyst containing 60-70 wt % Pt. According to the accelerated-test data, the corrosion resistance of PtCoCr/C catalyst is also higher than that of Pt/C system. [ABSTRACT FROM AUTHOR]