Recent Progress and Prospective of Nickel Selenide-Based Electrocatalysts for Water Splitting

Hydrogen economy based on electrochemical water splitting is one of the most prospective strategies to circumvent the rapid consumption of traditional fossil fuels. The development of efficient and durable electrocatalysts for water splitting plays a crucial role in the energy conversion and storage process. Nickel selenide (NixSey), as a typical multifunctional electrocatalyst, has attracted great consideration owning to its component diversity, high conductivity, and regulated morphology/electronic structures. In NixSey, nickel has a unique valence electron configuration (3d84s2) and acts as the main catalytic activity site. Compared with S and O, Se in NixSey not only has the same valence electrons and oxidation number but also has excellent intrinsic metal properties, which means better electrical conductivity and electrocatalytic activity. In addition, Ni and Se could form stoichiometric compounds (NiSe, NiSe2, Ni3Se2, Ni3Se4) and nonstoichiometric compounds (Ni0.85Se), which is ascribed to the electronegativity difference between Ni (1.9) and Se (2.4). In this review, the crystal structure, preparation methods, and practical applications of NixSey-based electrocatalysts are summarized. The merits and limitations of nickel selenide are discussed in terms of structure and composition. Finally, the challenges and opportunities faced by NixSey-based electrocatalysts in water splitting are discussed.