Crafting amorphous VO2–crystalline NiS2 heterostructures as bifunctional electrocatalysts for efficient water splitting: The different cocatalytic function of VO2

The rational design of bifunctional electrocatalysts is essential to achieve efficient hydrogen production from water splitting. Here, inspired by cocatalysts widely utilized in photocatalysis, we designed a heterostructure comprising amorphous VO2 and crystalline NiS2, aiming at using VO2 cocatalyst to boost activity of NiS2 for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Intriguingly, we found that VO2 displayed different co-catalytic function in boosting the OER and HER. Specifically, the VO2 optimized the binding energy of hydrogen intermediate on NiS2 and thus improved the HER activity. As for the OER, the amorphous VO2 was easily dissolved in the KOH electrolyte, resulting in the generation of abundant oxygen vacancies in the in-situ generated active phase of NiOOH from NiS2, thereby drastically enhancing the OER activity. Consequently, the obtained VO2–NiS2@CC displayed excellent performance for overall water splitting, with a low voltage of 1.53 V at 10 mA cm−2.