Bixbyite-type Ln₂O₃ as promoters of metallic Ni for alkaline electrocatalytic hydrogen evolution

The active-site density, intrinsic activity, and durability of Ni-based catalysts are critical to their application in industrial alkaline water electrolysis. This work develops a kind of promoters, the bixbyite-type lanthanide metal sesquioxides (Ln₂O₃), which can be implanted into metallic Ni by selective high-temperature reduction to achieve highly efficient Ni/Ln₂O₃ hybrid electrocatalysts toward hydrogen evolution reaction. The screened Ni/Yb₂O₃ catalyst shows the low overpotential (20.0 mV at 10 mA cm^-2), low Tafel slope (44.6 mV dec^-1), and excellent long-term durability (360 h at 500 mA cm^-2), significantly outperforming the metallic Ni and benchmark Pt/C catalysts. The remarkable hydrogen evolution activity and stability of Ni/Yb₂O₃ are attributed to that the Yb₂O₃ promoter with high oxophilicity and thermodynamic stability can greatly enlarge the active-site density, reduce the energy barrier of water dissociation, optimize the free energy of hydrogen adsorption, and avoid the oxidation corrosion of Ni.