Polyoxometalate@ZIF Induced CoWO₄/WS₂@C-N Nanoflower as a Highly Efficient Catalyst for Zn–Air Batteries

Abstract

It is crucial to cultivate competent and stable bifunctional electrocatalysts for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). In this work, a high-performance and long-lasting electrocatalyst of CoWO4/WS2@C-N nanocomposite with the unique hierarchical flowerlike superstructure is achieved by sulfuration of porous polyoxometalate@ZIF-67 precursor, in which the polyoxometalate acts as both template and acidic etching agent. The introduction of polyoxometalate also plays a key role in forming the binary CoWO4/WS2 active center during the sulfuration process. CoWO4/WS2@C-N electrocatalyst shows higher electrocatalytic activity than commercial noble-metal catalysts under the same conditions. DFT calculations indicate that both the high adsorption energy for the OH– group and low adsorption energy for O2 on the surface of CoWO4/WS2 sites result in high OER and ORR activity. When CoWO4/WS2@C-N is assembled in a lab-made Zn–air battery as cathode material, the battery shows a higher discharge plateau voltage of 1.46 V and a specific capacity of 664 mA h gZn–1, the behavior of which is comparable to the reported non-noble-metal materials. The synthetic strategy presented in this work not only opens a polyoxometalate-etching-ZIF way to constructing a nanosized heterojunction catalyst but also provides a cost-effective and robust electrocatalyst potentially used in practical Zn–air batteries.