Charge transfer-driven modulation of hydrogen evolution activity in NiCo LDHs via main group and 4d metal doping

Layered double hydroxides (LDHs) are promising electrocatalysts for the oxygen evolution reaction (OER); however, their catalytic activity toward the hydrogen evolution reaction (HER) remains limited. Developing bifunctional catalysts that are active for both OER and HER is highly desirable for efficient overall water splitting, as it can simplify device design and reduce material costs. In this work, we explore elemental doping as a strategy to enhance the HER performance of LDHs using first-principles density functional theory calculations. Specifically, we systematically investigate the effects of doping 4d transition metals and main-group elements into NiCo LDHs. Among the dopants considered, Bi and Sb are identified as particularly effective in improving HER activity. A linear correlation is observed between the charge transfer of adsorbed hydrogen (Δq) and the hydrogen adsorption free energy (ΔG_H*), suggesting that Δq can serve as a useful indicator of HER activity. Δq also correlates with the bond length between hydrogen and its adsorption site, indicating that charge transfer influences the local geometric structure. The p-band center (ε_P) of the dopant further shows a strong relationship with ΔG_H*, serving as an electronic indicator for adsorption strength. Projected density of states analysis suggests that hybridization between the p orbitals of Bi/Sb and the H s orbital plays a key role in determining the adsorption strength. These findings provide insight into the electronic origin of HER activity enhancement upon doping and highlight the potential of NiCo LDHs as efficient catalysts for water splitting.