Robust Electronic Structure: Uncovering the Origins of Fast Oxygen Reduction Kinetics of the NiCo Nanoalloys@N-Doped Carbon

Abstract

The non-noble nanoalloy family is one of the promising catalysts for oxygen reduction reactions and zinc–air batteries. However, the complex reconstruction behavior is not clear enough for guiding the design of alloy catalysts. The origins of reaction kinetics during drastic aging require further investigation. Hence, we prepare several NiCo nanoalloys@NC with tunable electronic structures. Among them, Ni2Co4@NC displays a suitable electronic structure, in which the interacted Ni and Co sites accelerate oxygen reduction and evolution reactions. It delivers an ultralow Tafel slope of 46.3 mV dec–1 for the oxygen reduction reaction and 65.0 mV dec–1 for the oxygen evolution reaction and releases an excellent power density of 162.9 mW cm–2 in the zinc–air battery. With ex situ Raman and other characterizations, we subsequently deduce the reconstruction behavior of these NiCo nanoalloys@NC samples. The suitable surface oxyhydroxide–hydroxide–oxide shell accounts for the excellent stability and reaction kinetics of Ni2Co4@NC. With density functional theory simulations, we further discover its robust electronic structure during the drastic reconstruction so that it displays rapid kinetics after aging. In the experiment, its oxygen reduction reaction (ORR) Tafel slope merely increased from 46.3 to 48.6 mV dec–1. We highlight the decisive role of the surface electronic structure in electrochemical kinetics and explain how to achieve excellent stability.