High-entropy-induced CoO6 octahedral distortion for boosted oxygen evolution reaction at high temperature

Abstract

Modulation of the distortion of BO₆ octahedra plays a pivotal role in determining the physicochemical properties and electrocatalytic performance of the perovskite oxides (ABO_3−δ). By tailoring the degree of octahedral tilting and bond angle, the electronic structure, oxygen vacancy, and ionic transport pathways within the perovskite lattice could be finely tuned. Herein, we propose an efficient strategy to tune the BO₆ (CoO₆) octahedral distortion through A-site high-entropy engineering in the Nd_0.2Pr_0.2La_0.2Ba_0.2Sr_0.2CoO_3−δ anode, with the average Co–O–Co angle decreasing from 175° to 149°. Ex situ and in situ characterization studies combined with density functional theory calculations reveal that the high-entropy-induced CoO₆ octahedral distortion shifts the O 2p band center of the perovskite anode towards the Fermi level, thereby activating the lattice oxygen and accelerating the transport of oxygen ions. Electrochemically, the CoO₆-distorted Nd_0.2Pr_0.2La_0.2Ba_0.2Sr_0.2CoO_3−δ anode delivers enhanced high-temperature oxygen evolution reaction (OER) performance in solid oxide electrolysis cells (SOECs), achieving a high current density of 3.96 A cm⁻² at 800 °C and 1.5 V along with excellent stability over 600 hours, which is superior to that of most reported anode materials. This work discloses the impact of CoO₆ octahedral distortion on high-temperature OER performance at the atomic scale and proposes an effective strategy for designing efficient and durable anodes of SOECs.