The oxygen path mechanism from Ni-OOOO-Fe species in oxygen evolution reaction on NiFe layered double hydroxides

Abstract

The oxygen evolution reaction (OER) with large overpotential is the bottleneck of the whole water electrolysis process. NiFe layered double hydroxide (NiFe-LDH) represent one of the potential catalysts for OER in alkaline media. For the LDH, it was well established that both adsorption evolution mechanism and lattice oxygen mechanism could appear at a single site, but Ni-OOOO-Fe species would provide a different OO path mechanism at dual-O sites due to the complexity and diversity of LDH surface. Here, using first-principles study, tetra-oxygen path mechanism (t-OPM) was proposed to investigate the OER performance of NiFe-LDH by considering surface 2O were as active sites (Oac) and other O as environment O (Oev) with different exposed degrees (0–6). It was found that the optimal performance of the NiFe-LDH surface could be achieved when 2 ∼ 4 Oev were exposed under the explored mechanism in different paths (path 1 and path 2) with overpotential η = 0.07 ∼ 0.35 V, and path 1 was slightly better than path 2. At the same time, the solvation effect (SE) was used to study the effect on the OER performance, the results showed that SE had a little influence on the case of 2 ∼ 4 Oev exposed while had a large effect on the other cases. The detailed analysis of the electronic structure showed a smaller difference Δε between the energy Fe-3d band center and Oac-2p, which imply the stronger the interaction between them. Thus, the t-OPM was feasible in OER on NiFe-LDH. It was anticipated that our work could provide a fresh perspective on the understanding of the excellent OER performance of LDH in alkaline environment, which was complementary to the traditional mechanism to some extent.