Detachment of aluminium in NiCoAl-LDH modulates the active metal species to enhance oxygen evolution reaction activity

Abstract

Transition metal-based layered double hydroxide catalysts show highly catalytic activity of oxygen evolution reaction (OER), in which Co-based catalysts will undergo electro-induced chemical reconfiguration during the OER process to form a variety high valence Co species, such as Co⁴⁺. Co⁴⁺ has a high intrinsic activity of OER and can enhance the electrostatic attraction of negatively charged oxygenated species (such as OH^-) in the electrolyte. Meanwhile, the strong charge density of Co⁴⁺ can reduce the thickness of the double electric layer formed with OH^-, shorten the ion diffusion distance, accelerate the adsorption of OH^-, and regulate the OER kinetics to bring higher activity. However, the formation of Co⁴⁺ is a thermodynamic unfavorable process. In this study, the NiCoAl layered double hydroxide (LDH) was optimized by the embed and detach of aluminum, cause the change of morphology structure and chemical components, especially the following favorable generation of Co⁴⁺. Analyzed by quasi in situ X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) tests demonstrated that dissolution of aluminum induced the formation of Co⁴⁺, then significantly boosted OER activity which showed lower overpotential (η₁₀₀=303 mV), Tafel slope (34.3 mV dec^-1) and Rct (3.75 Ω), and simultaneously maintain excellent OER stability at a high current density. This work provides a reference for guiding the design of OER electrocatalysts and the study of the interface between active sites and electrolytes.