Oxygen evolution reaction on NiFe-LDH/(Ni,Fe)OOH: theoretical insights into the effects of electronic structure and spin-state evolution

Abstract

NiFe-layered double hydroxides (NiFe-LDH) have emerged as promising oxygen evolution reaction (OER) catalysts in alkaline medium, but their commercial applications are limited due to the decrease in their activity as the electrolyte becomes less alkaline. Thus, a comprehensive understanding of the OER mechanism of NiFe-LDH in alkaline medium is desirable for the rational design of new catalysts with improved performances. Especially, their spin-related factors have rarely been systematically investigated during the OER (diamagnetic H₂O → paramagnetic O₂). Herein, we simulated the OER performance of NiFe-LDH and (Ni,Fe)OOH as NiFe-LDH underwent surface-reconstruction and formed (Ni,Fe)OOH under alkaline conditions. Results demonstrated an enhanced OER performance on (Ni,Fe)OOH, and the Fe active site of NiFe-LDH on losing 3H (namely, NiFe(OH)₂ – 3H) showed the lowest overpotential for OER because the d-orbital electron of the Fe atom shifted up to the Fermi level. Notably, the electronic interaction between Fe and OOH induced a change in the spin state of Fe, which further decreased the overpotential for the OER. Thus, the overpotential of the Fe site on NiFe(OH)₂ – 3H decreased from 0.55 eV to 0.46 eV. The density of states (DOS) analysis revealed that the spin flip of Fe promoted the formation of bonding states between Fe and OOH, endowing the catalyst with a better OER performance. Our findings can help pave the way for the development of high-performance OER catalysts at the spintronic level.