Co9S8@MoS2 Core-Shell Heterostructures as Trifunctional Electrocatalysts for Overall Water Splitting and Zn-Air Batteries.

The development of efficient non-noble-metal electrocatalysts is of critical importance for clean energy conversion systems, such as fuel cells, metal-air batteries, and water electrolysis. Herein, uniform Co9S8@MoS2 core-shell heterostructures have been successfully prepared via a solvothermal approach, followed by an annealing treatment. Transmission electron microscopy, X-ray absorption near-edge structure, and X-ray photoelectron spectroscopy measurements reveal that the core-shell structure of Co9S8@MoS2 can introduce heterogeneous nanointerface between Co9S8 and MoS2, which can deeply influence its charge state to boost the electrocatalytic performances. Besides, due to the core-shell structure that can promote the synergistic effect of Co9S8 and MoS2 and provide abundant catalytically active sites, Co9S8@MoS2 exhibits a superior hydrogen evolution reaction performance with a small overpotential of 143 mV at 10 mA cm-2 and a small Tafel slope value of 117 mV dec-1 under alkaline solution. Meanwhile, the activity of Co9S8@MoS2 toward oxygen evolution reaction is also impressive with a low operating potential (∼1.57 V vs reversible hydrogen electrode) at 10 mA cm-2. By using Co9S8@MoS2 catalyst for full water splitting, an alkaline electrolyzer affords a cell voltage as low as 1.67 V at a current density of 10 mA cm-2. Also, Co9S8@MoS2 reveals robust oxygen reduction reaction performance, making it an excellent catalyst for Zn-air batteries with a long lifetime (20 h). This work provides a new means for the development of multifunctional electrocatalysts of non-noble metals for the highly demanded electrochemical energy technologies.