Comments on the ideal polarisability of electrodes displaying cpe-type capacitance dispersion

Composite layers consisting of a polyaniline (PANI) matrix and a molybdenum-doped ruthenium selenide (MRS) dispersed phase have been tested as cathodes for O2 reduction in 0.5 M H2SO4. The investigation, carried out on rotating disc electrodes using steady-state techniques, shows that a 4-electron reduction of O2 is efficiently carried out on PANI+MRS composites. The onset potential is close to 0.5 V (SCE) and a current plateau is observed at E<0.1 V (SCE). The overall process is under mixed control. Besides the charge transfer and mass transport in solution, either O2 diffusion in the film or partial blockage of the electrode are possible limiting factors. The performance of PANI+MRS electrodes becomes better than that of Pt in 0.5 M H2SO4 in the presence of methanol. Diminished current densities are obtained at higher pH due to a decreased O2 solubility, the conductivity of the PANI matrix being always good at pH<3.