Tailoring the oxygen evolution reaction activity of lanthanide-doped NiFe-LDHs through lanthanide contraction

Elemental doping is employed to tune the inherent activity and electronic structure of electrocatalysts for water electrolysis. Here, unique nanosheet arrays of NiFe-LDH doped with lanthanide metals (NiFeSm-LDH, NiFeCeLDH, and NiFeLa-LDH) were developed as high-performance electrocatalysts for oxygen evolution reaction (OER). Notably, NiFeSm-LDH exhibits the superior performance, with the lowest overpotentials of 203 mV (at 10 mA cm(-2)) for OER. Structural analysis, in-situ Raman spectra and DFT calculations reveal that the high activity of the catalysts can be attributed to synergistic functionalities. Firstly, compared to Ce in NiFeCe-LDH and La in NiFeLa-LDH, Sm element in NiFeSm-LDH can attract more electrons from the outermost 3d orbitals of Ni due to the effect of lanthanide contraction, resulting in the highest valence state and d-band center of Ni. Secondly, the formation of NiOOH phase on NiFeSm-LDH requires a lower overpotential ( 1.32 V) than those on NiFeCe-LDH (1.32 similar to 1.37 V) and NiFeLa-LDH (similar to 1.37 V) based on in-situ Raman spectra, which indicate that NiFeSm-LDH has faster kinetics to achieve the Ni(II)-Ni(III) transformation. Thirdly, First-principles simulations reveal that NiFeSm-LDH reduces the formation energy from OOH* to O-2 significantly, which eventually improves the catalytic activity. Furthermore, the NiFeSm-LDH||Pt/C couple exhibits a low voltage of 1.59 V at 100 mA cm(-2) for overall water splitting.