_Applied_  
_sciences_  
_Article_  
_Ni\({}_{3}\)Se\({}_{4}\)@MoSe\({}_{2}\) Composites for Hydrogen_  
_Evolution Reaction_  
_[PERSON] 1,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,19,18,19,19,19,18,19,19,18,19,19,19,18,19,19,19,19,18,19,19,1  
is water. These properties make it a highly efficient and environmentally friendly energy and enable its potential to replace the current traditional fossil fuels. Its production from electrolytic water is an important key to realize industrialization because this path for conversion of electricity to chemical energy has many advantages, such as low cost, being friendly to the environment, high efficiency, and good safety [8; 9; 10]. To achieve the best efficiency, this conversion process largely demands the assistance of a highly active hydrogen evolution reaction (HER) electrocatalyst [11; 10]. To date, platinum is considered as the most efficient catalyst for hydrogen evolution [12; 13; 14; 15]. However, its scarcity on earth and high price make it unsuitable for widespread adoption. A few recent works have demonstrated high catalytic activity using less Pt on electrodes [16]. Nevertheless, it is still necessary to explore earth-abundant and inexpensive electrocatalysts for hydrogen production [17; 18; 19; 20]. Among the catalyst candidates, layered transitional metal dichalcogenides MX, where M represents a transition metal (e.g., Mo, W, V) and X is a chalcogenide (e.g., S, Se, Te), have drawn great attention due to their attractive electrocatalytic properties towards HER, as well as their low cost compared to noble metals and stability in acid [21; 22; 23; 24]. However, only the edges, rather than the basal planes within the material structure, are catalytically active to HER [23; 25; 26; 27; 28]. In order to expose more active edges, intense efforts have been made on active edge engineering by hybridizing with other materials, such as carbon nanotubes, graphene, and noble metals, to improve their conductivity and accelerate the electron transfer rate between the electrocatalyst and the working electrode [11; 29; 30; 31]. Recently, some studies have reported that Ni-based materials, such as NiSe nanofiber [32; 33; 34], Ni-Mo alloy [35; 36; 37], and transition metal dichalcogenides (TMDs) integrated with Ni components [5; 37; 38], exhibited great catalytic activity and long-term stability for water splitting. Inspired by this viewpoint, we consciously chose one of the selenides of nickel as a candidate for structuring Ni-based components/MoSe\({}_{2}\) hybrid composites for hydrogen production. Among all nickel selenides, Ni\({}_{3}\)Se\({}_{2}\) has been intensively studied and hybrid materials based on them have been extensively reported [39; 40; 41]. However, the common methods employed to obtain nickel selenides, such as hydrothermal technique or electrodeposition, are either time-consuming or energy-consuming processes. Therefore, it is imperative to use a facile preparation method for these compounds and facilitate their integration with other materials and make it applicable to large-scale HER catalysts. In this study, we presented a Ni\({}_{3}\)Se\({}_{4}\)/MoSe\({}_{2}\) composites catalyst fabricated by a facial two-step synthesis method for the first time. The Ni\({}_{3}\)Se\({}_{4}\) was prepared in a simple way as a template and the MoSe\({}_{2}\) was grown in situ on as-prepared Ni\({}_{3}\)Se\({}_{4}\) using the colloid synthesis method. The Ni\({}_{3}\)Se\({}_{4}\) nanosheets are expected to support the nucleation and formation of MoSe\({}_{2}\), which can improve the quality of the MoSe\({}_{2}\) nanosheets and prevent the agglomeration issue associated with Ni\({}_{3}\)Se\({}_{4}\) and MoSe\({}_{2}\). The simplification of preparing Ni\({}_{3}\)Se\({}_{4}\) makes it easier to tune and control the proportion of the components in Ni\({}_{3}\)Se\({}_{4}\)/MoSe\({}_{2}\) composites.