The surface phosphorization of NiCo2S4 make it exhibit superior electrochemical activity, which is ascribed to the modulation of electronic structure, the rise of conductivity, the promotion of electrochemical surface area and the active sites.

No abstract

The next-generation energy storage focuses on sustainability and renewability, facilitating the process of metal-air batteries and fuel cells. Nevertheless, their performances are suffering from the tardy development of the elaborate design and large-scale synthesis strategy of cost-efficient electrocatalysts. In this work, a convenient strategy for facile synthesizing electroactive material is proposed. As a result, a trifunctional Co/C catalyst is fabricated via a convenient calcination process, utilizing the pyrolysis of cobalt acetate and melamine. The prepared Co/C sample delivers a positive half-wave potential of 0.75 V in oxygen reduction reaction (ORR). Furthermore, the low overpotentials at 10 mA cm −2 are shown in alkaline conditions for oxygen evolution reaction (OER, 388 mV) and hydrogen evolution reaction (HER, 202 mV). The improved activity is mainly due to the interaction between Co and the in situ formed carbon carrier. The promising trifunctional activities endow the Co/C sample with a bright prospect in metal-air batteries and overall water splitting.

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.