A Highly Efficient Bifunctional Catalyst for Alkaline Air-Electrodes Based on a Ag and Co3O4 Hybrid: RRDE and Online DEMS Insights

Enhanced catalytic activity towards oxygen reduction (ORR) and evolution (OER) reactions has been achieved by combination of spinel Co3O4 nanoparticles with Ag particles. Quasi-stationary polarization curves showed that the mixed catalyst, Ag + Co3O4 (10 wt%), outperformed its components. Rotating ringdisc electrode (RRDE) measurements revealed a negligible peroxide species formation and a 4-electron pathway for ORR. A tafel slope of ca. 75 mV dec(-1) has been observed. The overpotential for ORR at 10% Co3O4 catalyst is ca. 70 mV lower than that of Ag and only ca. 80 mV higher than that of the commercial Pt catalyst. DEMS technique provided a direct evidence for oxygen evolution at these bimetallic catalysts. This hybrid is therefore one of the (or even the) most active, carbon-free, durable, non-precious ORR and OER electrocatalysts reported to date. (C) 2014 Published by Elsevier Ltd.