Mechanistic insights into electrocatalytically reduced OER performance in marigold-like trimetallic NiFe-based LDH: charge localisation and d-band orbital filling

Abstract

Here in this work, the electrocatalytic activity of trimetallic zinc–nickel–iron (ZNF) layered double hydroxide (LDH) and cobalt–nickel–iron LDH (CNF) has been mechanistically explained with reference to bimetallic nickel–iron LDH (NF). Intriguingly, the OER activity of ZNF and CNF was exacerbated compared to that of pristine NF in 1 M KOH. The underlying reason for such reduced activity has been explained based on the localization of charges and breakage in the charge transfer chain of Ni–O–Fe–O–Zn and Ni–O–Fe–O–Co moieties. EXAFS manifests change in the local coordination environment due to local distortion or vacancies in the case of ZNF and CNF, which affects the vibrational mode of the system. Further, the Raman profile exhibits a decrease in phonon lifetime and indicates the confinement of phonons. Encompassing all, it was found that the interaction of electrons with the confined phonons leads to the localization of charges, affecting the reaction pathway and kinetics, resulting in an overall reduced electrocatalytic activity in the trimetallic system. Furthermore, the hindrance in the charge transfer process for the aforementioned moieties has been explained in terms of filling of e_g and t_2g orbitals employing the concept of d band orbital splitting.