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 (Ni_xSe_y), as a typical multifunctional electrocatalyst, has attracted great consideration owning to its component diversity, high conductivity, and regulated morphology/electronic structures. In Ni_xSe_y, nickel has a unique valence electron configuration (3d⁸4s²) and acts as the main catalytic activity site. Compared with S and O, Se in Ni_xSe_y 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 (Ni_0.85Se), 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 Ni_xSe_y-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.

中文翻译：

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硒化镍基水分解电催化剂的研究进展与展望

基于电化学水分解的氢经济是规避传统化石燃料快速消耗的最有前景的策略之一。开发高效耐用的水分解电催化剂在能量转换和存储过程中起着至关重要的作用。硒化镍（Ni _x Se _y）作为一种典型的多功能电催化剂，由于其组分多样性、高导电性和可控的形态/电子结构而备受关注。在Ni _x Se _{y 中}，镍具有独特的价电子构型（3d ⁸ 4s ²）并作为主要的催化活性位点。与 S 和 O 相比，Ni _{x 中的}SeSe _y不仅具有相同的价电子和氧化数，而且具有优异的本征金属性质，这意味着更好的导电性和电催化活性。此外，Ni和Se可以形成化学计量化合物（NiSe、NiSe ₂、Ni ₃ Se ₂、Ni ₃ Se ₄）和非化学计量化合物（Ni _0.85 Se），这是由于Ni（1.9）和Se（ 2.4)。在这篇综述中，Ni _x Se _y的晶体结构、制备方法和实际应用基于的电催化剂进行了总结。从结构和组成方面讨论了硒化镍的优点和局限性。最后，讨论了基于 NixSey 的电催化剂在水分解中面临的挑战和机遇。