Metastable intermediate phase engineering of NiSe electrocatalyst for enhanced hydrogen evolution reaction

Phase engineering of transition metal chalcogenides is a promising strategy for optimizing catalytic performance. In this work, we investigate the phase-dependent catalytic properties of NiSe. Using density functional theory (DFT) and Variable-cell nudged elastic band technique, we reveal a metastable intermediate phase (MIS-2′) within the confinement the of interface on the transition path from hexagonal (H–NiSe) to rhombohedral (R–NiSe) structures. Gibbs free energy calculations show that the MIS-2′ phase has superior hydrogen adsorption (ΔG H ∗ = −0.02 eV) compared to H–NiSe and R–NiSe. NiSe catalysts with different phases were synthesized by hydrothermal methods, and electrochemical tests in 1 M KOH show that the sample containing both MIS-2′ and R–NiSe prepared at 150 °C, delivers the best HER performance (η 10  = 105.08 mV, Tafel slope = 121.12 mV dec −1 ). This improvement is attributed to the synergistic effects of the two phases, especially the involvement of MIS. These findings highlight the potential of phase engineering to enhance catalytic activity and offer a new pathway for optimizing transition-metal chalcogenides based electrocatalysts for sustainable energy applications.