Ta-doping triggered electronic structural engineering and strain effect in NiFe LDH for enhanced water oxidation

Structural manipulation of electrocatalyst via doping strategy has always held great interests for developing advanced and stable non-noble metal electrocatalyst for oxygen evolution reaction (OER). Herein, a high-valence state tantalum (Ta) was incorporated into the pristine NiFe layered double hydroxide (LDH) by hydrothermal method. Interestingly, as revealed by structural characterizations, Ta doping causes the lattice expansion of LDH and electronic structure modification through electron transfer from Fe to Ta. DFT calculations further verified that the modulated electronic structure among Ni, Fe and Ta and the modified eg orbital of Ta induced by charge transfer are beneficial for the adsorption of OH species on Ta site in Ta-doped NiFe LDH and increasing the intrinsic metallic property of NiFe LDH. Consequently, the Ta site has lower overpotential compared with other sites on NiFe LDH including the pristine oxygen vacancies, which can improve the electrocatalytic activity for OER. Furthermore, the optimized Ta-NiFe LDH (0.5:6:1.5) exhibited a superior OER activity in contrast to bimetallic LDH, with a low overpotential of 260 mV to drive the current density of 50 mA·cm−2 and a small Tafel slope of 58.95 mV·dec-1. This work provides the theoretical basis for the enhancement of electrochemical OER activity by doping LDH with high-valence state foreign metal.