Investigation of Activity of Sputtered Transition-Metal (TM)–C–N (TM = V, Cr, Mn, Co, Ni) Catalysts for Oxygen Reduction Reaction

Variations with heat-treatment temperature of the structure and the electrocatalytic activity of sputtered transition-metal (TM)–C–N ( , Cr, Mn, Co, and Ni) films for the oxygen reduction reaction (ORR) in acid and alkaline electrolytes were studied. The films prepared were all originally amorphous. At a critical heat-treatment temperature ( , different for each composition) substantial nitrogen release occurred and the films transformed to a heterogeneous N-containing carbon structure with either , Co, Ni, , or , depending on the TM used. In acid electrolyte, heat-treated , , and films began to show oxygen reduction activity at , while and films showed little or no activity for ORR in acid electrolyte for all temperatures studied. However, all of the heat-treated ( , Cr, Mn, Co, and Ni) films showed oxygen reduction activity in alkaline electrolyte even when heated to temperatures below . Because all the films heated above contained N-containing carbon, the activity of heat-treated sputtered and C films, as well as graphite powder, were studied for comparison. Their activities were much lower in acid electrolyte than those of the , , and films heat-treated at the same temperatures. films, C films, and graphite powder all showed activity in alkaline electrolyte but were less active than some heated and films. The choice of TM and the heat-treatment temperature played important roles in determining the activity of the sputtered films for ORR in acid and alkaline electrolytes. The corrosion stability of the heat-treated libraries was studied as well. Heat-treated libraries showed good passivation against corrosion.