Strongly Cooperative Nano-CoO/Co Active Phase in Hierarchically Porous Nitrogen-Doped Carbon Microspheres for Efficient Bifunctional Oxygen Electrocatalysis

Abstract

The development of highly efficient, non-noble-metal-based bifunctional oxygen electrocatalysts with low cost for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is the key for the commercialization of rechargeable metal-air batteries and regenerative fuel cells. In this work, a non-noble-metal-based, hierarchically porous CoO/Co@N-C microsphere electrocatalyst with low cost and earth-abundance was created by directly reducing carbonized glucose-coated urchin-like Co3O4 microspheres through the carbon-thermal processing with NH3 reducing environment. Urchin-like Co3O4 microspheres provided a Co source for the creation of nano-CoO/Co active phase and served as the template without a removal requirement for the creation of hierarchically porous N-doped carbon microsphere matrix with abundant macropores and mesopores for efficient mass diffusion. Among its three major components, CoO played the leading role to provide both ORR and OER active sites, a porous N-doped carbon microsphere matrix mainly provided the conductive catalyst support, and the metallic Co component mainly acted as a "bridge" between CoO and graphic carbon to reduce the electron transfer resistance for the enhancement of its conductivity. Thus, their synergetic effect within its unique structure endowed a superior bifunctional performance toward both ORR and OER to the CoO/Co@N-C electrocatalyst over the commercially available Pt/C and Ir/C electrocatalysts.