Delineating the roles of Co3O4 and N-doped carbon nanoweb (CNW) in bifunctional Co3O4/CNW catalysts for oxygen reduction and oxygen evolution reactions†
While many synthesis methods have been reported for Co3O4–carbon nanocomposites as a bifunctional electrocatalyst for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in alkaline solutions, the individual contributions of Co3O4 and CNW towards ORR and OER are still not clear. Here, we report the individual functionality of Co3O4 and the N-doped carbon nanoweb (CNW) in ORR and OER. The Co3O4/CNW bifunctional catalysts were synthesized by an in situ growth of Co precursors onto CNW followed by a controlled heat treatment. The specific functions of Co3O4 and CNW were delineated by rotating disk electrode measurements. It was found that Co3O4 alone exhibited poor ORR catalytic activity. However, in the presence of CNW, Co3O4 assisted the selective four-electron oxygen reduction over the two-electron pathway. Analyses of the Tafel slope and reaction order suggested that Co3O4 acted as the primary catalytic site for OER. CNW improved the electronic conduction between Co3O4 and the current collector. CNW underwent serious degradation at the high potential of the OER but its stability improved greatly upon the deposition of Co3O4. Two possible mechanisms for the improved catalytic stability are discussed. The findings demonstrate the specific functions of Co3O4 and CNW in catalyzing the OER and ORR and further establish an understanding of the synergy of the composite in electrocatalysis.