From NiCo-LDH to rare-earth-doped selenides: A pre-doping strategy for efficient hydrogen evolution

Rare-earth ion-doped selenides hold great promise for electrocatalysis owing to their abundant active sites, high stability, and excellent electron transport capability. However, the controllable incorporation of rare-earth ions into selenides remains challenging. Conventional one-pot routes, in which rare-earth ions are directly introduced during selenide synthesis, often suffer from uncontrollable morphology and structure, severely limiting their electrocatalytic performance. Herein, a facile rare-earth pre-doping strategy based on nickel cobalt layered double hydroxide (NiCo-LDH) was proposed, in which rare-earth ions were first incorporated into NiCo-LDH templates and subsequently converted into rare-earth-doped selenides of n-M-NiCoSe₂ (n = 0.2, 0.4, 0.6, 0.8; M = Ce, La, Sm) on nickel foam (NF) via high-temperature selenization. By tuning the type and dosage of the rare-earth dopants, the catalytic activity of the selenides toward the hydrogen evolution reaction (HER) was effectively regulated. Among all the doped samples, 0.6-Ce-NiCoSe₂/NF delivered the best HER performance, requiring an overpotential of only 123 ± 3.0 mV to reach the current density of 10 mA·cm^-2 with a Tafel slope of 44.6 mV·dec^-1. Theoretical calculations revealed that Ce doping induced charge redistribution in NiCoSe₂, which optimized the H^⁎ adsorption strength at the Ni, Co and Se sites, while the Ce sites also served as additional active sites with near-thermoneutral H^⁎ adsorption free energy, achieving the most balanced optimization among the three rare-earth-doped systems. Moreover, 0.6-Ce-NiCoSe₂/NF exhibited favorable oxygen evolution reaction activity. This work demonstrates that the rare-earth pre-doping strategy based on NiCo-LDH templates provides a feasible route to rare-earth-doped selenides, and the dopant type and dosage play a decisive role in regulating their electrocatalytic activities.