Delineating the roles of Co3O4 and N-doped carbon nanoweb (CNW) in bifunctional Co3O4/CNW catalysts for oxygen reduction and oxygen evolution reactions

Abstract

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.