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

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 O-2 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 g(Zn)(-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.