Non-linear and pulse phenomena during H2O2 reduction at chalcopyrite (photo)cathodes

The current-voltage curves of H2O2 reduction in alkaline medium recorded at CuFeS2 and CuInSe2 cathodes show non-monotonic profiles, with a pronounced current wave and a region of negative i/U slope. In the latter region, photocurrents inverted in sign are observed at CuInSe2 electrodes. XP spectra taken on CuFeS2 electrodes after polarization experiments show products of surface corrosion and-depending on emersion potential-changes in the oxidation state of copper. On the basis of electrochemical and spectroscopic results, the current wave is attributed to activation of a catalytic mechanism of H2O2 reduction involving copper species. Current oscillations are observed when the polarization conditions are properly set. An "electrical" analysis of the oscillatory phenomena is proposed, focused on the conditions of polarization control and resulting circuit (in)stability. At CuInSe2, illumination may be used as a key parameter to switch the oscillatory regime on and off or to trigger individual oscillations. The system may be considered a simple model device of a light sensor based on an electrode/electrolyte junction.