Oxygen Vacancy Rich δ-MnO2 Nanosheets Encapsulating Single Cobalt Atoms-Anchored Carbon Nanotubes for Efficient Oxygen Evolution

Oxygen vacancy (OV_ac) and interface engineering are effective tactics for regulating the electronic structure of electrocatalysts and optimizing the absorption/desorption of reactants and intermediates on the catalyst surface to enhance the oxygen evolution reaction (OER). Herein, a self-supported electrocatalyst, comprising δ-MnO₂ nanosheets grown on Co single atoms (CoSAs) anchored on N-doped carbon nanotubes (NCNTs) embedded with Co nanoparticle on a carbon cloth (CC) (δ-MnO₂/Co_NP@Co_SAs-NCNTs/CC), was fabricated. Through in-situ growth of δ-MnO₂ nanosheets on Co_NP@Co_SAs-NCNTs/CC, the number of OV_ac is increased, as proved by X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and Positron annihilation lifetime spectrometer (PALS), due to the redox between MnO₂ and Co. Experimental results and theoretical calculations confirm that the formation of OV_ac rich δ-MnO₂ nanosheets and the construction of heterogeneous interface between δ-MnO₂ and Co_SAs-NCNTs endow the electrocatalyst with good conductivity, fast charge transfer, and multiple active sites, leading to rapid OER reaction kinetics. Therefore, the δ-MnO₂/Co_NP@Co_SAs-NCNTs/CC electrocatalyst demonstrates remarkable OER performance, requiring only 165 mV overpotential to reach a current density of 10 mA cm⁻² in an alkaline solution.