An Efficient Silver-Metal Oxide Hybrid Bifunctional Catalyst for Alkaline Air-Electrodes: DEMS and RRDE Study

In order to develop a commercial catalyst for metal-air batteries, stability, good round-trip efficiency, high activity and fast kinetics for OER/ORR should be satisfied. Since the high cost of Pt limits its industrial application, several metal oxides of the perovskite and spinel type such as Co₃O₄ have been tested as bifunctional catalysts.[1] Silver is a non-precious and active catalyst for ORR. Thus, coupling of silver and metal oxide like Co₃O₄ revealed to be a promising catalyst for both ORR and OER. This carbon-free mixed catalyst showed high activity and good stability in alkaline media. 10% and 20% of Co₃O₄ was found to be optimum for ORR and OER, respectively. RRDE data showed that ORR follow the direct 4-electron pathway with negligible peroxide formation. About 60mV shift in half wave potential of ORR for the 10% catalyst compared to pure silver was achieved. DEMS results monitored the OER onset. Tafel slopes of about 80 mV/dec at low overpotentials were obtained for the mixed catalysts.

In further model experiments we studied the activity of the spinel on smooth Ag and also other metal electrodes confirming the synegetic effect. Experiments with a variety of perovskites yielded similar results.

References:

[1] F.H.B. Lima, J.F.R. de Castro, E.A. Ticianelli, Journal of power sources 161(2006)806