Electro-catalysis of the Cu/carbon cathode for the reduction of O2 during fuel-cell reactions

To develop a new cathode without using Pt for a H2/O2 polymer-electrolyte-membrane-fuel-cell, we studied the possibility of using a Cu/carbon cathode for the reduction of O2. The plan for development of the Cu/carbon cathode is: (i) formation of redox functional groups on carbon to promote electron-transfer reaction, (ii) deposition of phosphorous groups on carbon to promote proton diffusion and (iii) loading Cu on the modified carbon support. The electro-catalytic activity of the Cu/carbon cathode was not so excellent as that of the Pt/carbon cathode, but it was fairly good at lower P(O2). To clarify the Cu function for the acceleration of the O2 reduction, we characterized the Cu/carbon electro-catalyst with XRD, SEM and CV measurements. When the oxidation state of Cu was 2+ at higher cell voltages, the reduction of O2 was accelerated. On the other hand, when metallic Cu was formed at lower cell voltages, the enhancing effect of Cu disappeared. The CV data strongly suggested that Cu2+ species functioned as an adsorption site of O2, not as a redox mediator. On the basis of the experimental results, a suitable model of the reduction mechanism of O2 over the Cu/carbon cathode was proposed.