Controllable synthesis and phase-dependent catalytic performance of dual-phase nickel selenides on Ni foam for overall water splitting

NiSe2/Ni3Se4 dual-phase electrocatalysts are synthesized by calcining the Ni(OH)2 nanosheets on Ni foam and Se powder under an N2 atmosphere. The Ni’s charge-state, phase compositions, and electrocatalytic performances are dependent on the initial mass ratios of Ni to Se. The experimental results demonstrate that the electrocatalyst with a higher Ni charge-state and more Ni3Se4 phase facilitates oxygen evolution reaction (OER), whereas the one with a lower Ni charge-state and more NiSe2 phase boosts hydrogen evolution reaction (HER). Density functional theory calculations reveal that the interfacial electrons transfer from Ni3Se4 to NiSe2, which improves conductivity and optimizes adsorption/desorption energies. NiSe2/Ni3Se4/NF-4 containing more NiSe2 phase displays the best HER activity while NiSe2/Ni3Se4/NF-1 containing more Ni3Se4 phase shows the best HER activity. The electrolyzer, employing NiSe2/Ni3Se4/NF-4 and NiSe2/Ni3Se4/NF-1 as the cathode and anode, respectively, performs the full potential and demonstrates a low voltage of 1.56 V achieving 10 mA cm−2 with good durability. [Display omitted] •NiSe2/Ni3Se4 electrocatalysts are synthesized by calcining Ni(OH)2 nanosheets on Ni foam with Se powder.•Their electrocatalytic performances are related to the charge state of Ni element and phase compositions.•The higher Ni charge state and more Ni3Se4 phase facilitates OER, while more NiSe2 phase boosts HER.•The DFT calculations reveal that the interfacial electrons transfer from Ni3Se4 to NiSe2.•The fabricated electrolyzer shows a low voltage of 1.56 V at 10 mA cm−2 and good durability.