Amorphous–Crystalline Heterostructure with Ample Oxygen Vacancy In Situ Evolved from Heterojunction Ni(OH)2@V–Ni3S2/NF toward Efficient Water Electrolysis

Water electrolysis is a green and efficient way to generate pure hydrogen energy for the alleviation of the energy crisis. Non-noble metal compounds, like Ni-based (oxy)hydroxides and sulfides, have become competitive candidates to substitute for the noble metal catalysts toward water electrolysis. Construction of heterojunction catalysts works as an effective approach to improve the performance of water electrolysis. However, it remains a challenge to explore the structure evolution of heterojunction transition metal electrocatalysts during water electrolysis and uncover its effect. In this work, we curated and synthesized V-doped Ni3S2 nanorods decorated with Ni(OH)2 nanosheet in situ growth on nickel foam (Ni(OH)2@V–Ni3S2/NF), composed of the shell of Ni(OH)2 and the core of V–Ni3S2. Evolution of Ni(OH)2@V–Ni3S2/NF occurred during the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) courses and resulted in an amorphous–crystalline heterostructure with oxygen vacancies, which acted as the real catalyst. Profited from the core–shell structure with enhanced active surface area, excellent conductivity, and amorphous heterostructure with ample oxygen vacancies, the optimized catalyst exhibited excellent properties with overpotentials of 231 mV for the OER and 114 mV for the HER to attain 10 mA cm–2 with outstanding long-term durability. The asymmetrical two electrodes constructed by Ni(OH)2@V–Ni3S2/NF required 1.57 V to drive 10 mA cm–2. This research provides a new chance to explore the dynamic evolution of an electrocatalyst and applies a reference for the design of an effective catalyst.