A greener approach: microwave-assisted synthesis of nickel selenides anchored on hollow carbon spheres for hydrogen production in alkaline solutions

A rapid, microwave-assisted hydrothermal method was used to synthesize four distinct nickel selenide phases (NiSe, NiSe 2 , Ni 3 Se 2 , and Ni 3 Se 4 ) and their composites with HCSs for the alkaline hydrogen evolution reaction (HER). The HCSs/Ni x Se y composites exhibited significantly improved HER performance compared to pure nickel selenides, with overpotentials of 211 mV (HCSs/NiSe), 267 mV (HCSs/NiSe 2 ), 242 mV (HCSs/Ni 3 Se 2 ), and 280 mV (HCSs/Ni 3 Se 4 ) at −10 mA/cm 2 . These composites also demonstrated higher electrochemical active surface areas such as 120 cm 2 for HCSs/Ni 3 Se 4 vs. 57.5 cm 2 for pure Ni 3 Se 4 , lower Tafel slopes (41–61 mV/dec), and reduced charge-transfer resistance (61 Ω for HCSs/NiSe vs. 123 Ω for pure NiSe). The enhanced performance was attributed to the synergistic interaction between Ni x Se y and the conductive-defect-rich HCSs, which facilitated electron transport, exposed active sites, and modulated interfacial electronic structure. This green synthesis approach supports sustainable hydrogen production and aligns with SDGs 7 and 13.