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, NiSe2, Ni3Se2, and Ni3Se4) and their composites with HCSs for the alkaline hydrogen evolution reaction (HER). The HCSs/NixSey composites exhibited significantly improved HER performance compared to pure nickel selenides, with overpotentials of 211 mV (HCSs/NiSe), 267 mV (HCSs/NiSe2), 242 mV (HCSs/Ni3Se2), and 280 mV (HCSs/Ni3Se4) at −10 mA/cm2. These composites also demonstrated higher electrochemical active surface areas such as 120 cm2 for HCSs/Ni3Se4 vs. 57.5 cm2 for pure Ni3Se4, 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 NixSey 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.