Effect of Rare-Earth Element Doping on NiFe-Layered Double Hydroxides for Water Oxidation at Ultrahigh Current Densities

Abstract

Electrochemical energy conversion processes such as water reduction to produce hydrogen and carbon dioxide reduction into valuable carbon products have attracted great attention as alternative green energy technologies to fossil fuels. Nevertheless, the conversion efficiency and long-term stability of these technologies remain very far from the requirements for industrial applications because of the sluggish kinetics of the oxygen evolution reaction (OER). In this study, La-doped NiFe-layered double hydroxides (LDHs) were synthesized on Ni foam via a facile hydrothermal method and applied as active and stable OER electrochemical catalysts. The La-doped NiFe-LDH having the optimal La doping level exhibits excellent OER catalytic activity with a low overpotential of 309 mV at a high current density of 500 mA cm–2, a low Tafel slope of 42 mV dec–1, and long-term stability in the OER process over 140 h at 100 mA cm–2. Remarkably, the full cell of NiFeLa LDH-2||NiMoOx achieves high current densities of 500 mA cm–2 at the voltage of 1.728 V with superior stability for overall water splitting during 600 h in 1 M KOH. The enhanced OER performance is ascribed not only to the high crystallinity of the nanosheet structure but also to the synergistic electronic interactions between Ni, Fe, and La, which result in a stronger metal–oxygen bond based on d-band theory, more exposed active sites with high-valence states, and increased oxygen vacancies.