A novel cathode for alkaline fuel cells based on a porous silver membrane

Porous silver membranes were investigated as potential substrates for alkaline fuel cell cathodes and as an approach for studying pore size effects in alkaline fuel cells. The silver membrane provides both the electrocatalytic function, mechanical support and a means of current collection. Relatively high active surface area (∼0.6 m2 g−1) results in good electrochemical performance (∼200 mA cm−2 at 0.6 V and ∼400 mA cm−2 at 0.4 V) in the presence of 6.9 M KOH. The electrode fabrication technique is described and polarization curves and impedance measurements are used to investigate the performance. The regular structure of the electrodes allows parametric studies of the performance of electrodes as a function of pore size. Impedance spectra have been fitted with a proposed equivalent circuit which was obtained following the study of impedance measurements under different experimental conditions (electrolyte concentration, oxygen concentration, temperature, and pore size). The typical impedance spectra consisted of one high frequency depressed semi-circle related to porosity and KOH wettability and one low-frequency semi-circle related to kinetics. A passive air-breathing hydrogen–air fuel cell constructed from the membranes in which they act as mechanical support, current collector and electrocatalyst achieves a peak power density of 50 mW cm−2 at 0.40 V cell potential when operating at 25 °C.