Deactivation studies on the porous Ni-gas diffusion electrode in H₂/O₂ alkaline fuel cell

Long term performance tests were carried out potentiostatically for the Cu-impregnated Ni-gas diffusion electrode at various temperatures. To measure the deactivation with time, the voltage between the working electrode and the reference electrode was kept constant and the fall of current density (i.e. the reaction rate) was monitored as a function of time. At almost every temperature there was a decay of activity. The higher the temperature the faster the observed deactivation rate was. The deactivation model assumed a first order reactant-gas-concentration-independent deactivation. The spherical flooded grain model was used for the determination of the deactivation rate constants (k_ds) at different conditions. Deactivation is attributed to: (a) dissolution of promoter Cu and Ni, hence reducing the electronic contact: (b) formation of Ni(OH)₂ which passivates the electrode; (c) the change in the hydrophobicity of PTFE; and (d) dissolution of atmospheric CO₂ in the KOH, forming K₂CO₃.