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.