Enhancing the water oxidation electrocatalysis of correlated perovskite nickelates by disordering NiO6 octahedra

Abstract

While distorting the octahedral structure is generally recognized to regulate the electronic structure and functionalities of correlated perovskite oxides such as rare-earth nickelates (ReNiO₃), the potential influence of the alignment of these distorted octahedrons has not yet been studied. Herein, we demonstrate the improvement in the water oxidation (OER) electrocatalysis of rare-earth co-occupied Sm_xNd_1−xNiO₃, wherein the potential orbital reconfiguration owing to the disordering of NiO₆ octahedra alignments was previously overlooked. The orbital reconfigurations of Ni-3d and O-2p for Sm_xNd_1−xNiO₃ owing to disordered NiO₆ octahedral alignment is depicted by combining near-edge X-ray absorption fine structure analysis and density functional theory (DFT) calculations. The resultant centralized p–d hybridization largely enhances OER electrocatalytic activity; in particular, the current density of Sm_0.5Nd_0.5NiO₃ is enhanced by ten times compared to the well investigated nickelate catalyst NdNiO₃. The exploration of the OER mechanism using DFT calculation reveals the participation of the lattice oxygen (O_L) in the OER, as is further confirmed through a probe reaction in TMAOH electrolyte. By quantifying the diffusion coefficient of O_L, the highest OER electrocatalytic activity of Sm_0.5Nd_0.5NiO₃ is demonstrated to be associated with a ∼300% enhancement in the diffusion coefficient of O_L as compared to NdNiO₃. The enhancement of OER electrocatalysis via rare-earth co-occupation is further demonstrated to be intrinsic by measuring the electrochemical surface area and reproducing such enhancement in rare-earth co-occupied bulk samples. We highlight the additional freedom in optimizing the electrocatalysis reactivity of ReNiO₃ associated with the alignment in their NiO₆ octahedra, in addition to the already known perspectives, such as iso-valent or aliovalent doping, defect controlling, and strain engineering.