Enhanced electrochemical performance by facile oxygen vacancies from lower valence-state doping for ramsdellite-MnO2

The urgent demands for sustainable and renewable energy resources facilitate the researches of energy storage devices, and the electrode materials are important for the performance of these devices. Transition metal oxides as the promising candidates are impeded by their limited electronic conductivity and low intrinsic activity. In this work, we propose a strategy of lower valence-state doping for ramsdellite-MnO2 to facilitate the formation of oxygen vacancies, which are effective to improve the conductivity and activity of ramsdellite-MnO2. Using DFT + U calculations, we find out that the formation energies of oxygen vacancies both in the bulk and on the surface of ramsdellite-MnO2 are decreased apparently after Zn doping. Notably, the surface oxygen vacancies could form spontaneously without any other impetus. In addition, the bulk Zn dopants will provide the enhanced electrons diffusion to the surface, and the positive surface oxygen vacancies will draw the electrons to the reaction sites. In the reaction sites, the oxygen vacancies and reduced Mn ions will improve the activity of the electrode reactions. This may be anticipated to improve the electrochemical performance of the similar binary metal oxides.