Effect of oxygen vacancies on the electronic structure and electrochemical performance of MnMoO4: computational simulation and experimental verification

Abstract

Porous nanopetals of MnMoO₄ with oxygen vacancies were prepared by hydrothermal synthesis and a hydrogenation reduction method. MnMoO₄–OV porous nanopetals have a higher specific surface area together with a more diverse pore size distribution than MnMoO₄ nanopetals. The density functional theory calculation results reveal that MnMoO₄–OV has a lower energy band gap (0.642 eV) than MnMoO₄ (1.095 eV). The electronic density of states plots reveal that MnMoO₄–OV displays more electron state distribution at the Fermi energy level than MnMoO₄. The MnMoO₄–OV porous nanopetals achieve a higher specific capacitance (1920 g⁻¹) than MnMoO₄ (921 F g⁻¹) at 1 A g⁻¹. They also achieve a superior capacitance retention rate (85.5%) to that of MnMoO₄ (69.1%) with the current density increasing from 1 to 10 A g⁻¹. The introduction of oxygen vacancies can increase the carrier density, accelerate the electron transfer, enhance the electrical conductivity, and accordingly strengthen the redox reactivity of MnMoO₄–OV. An asymmetric supercapacitor was also constructed by using MnMoO₄–OV as the positive electrode and activated carbon as the negative electrode. It achieves a high energy density of 59.8 W h kg⁻¹ at a power density of 750 W kg⁻¹, together with a good cycle life. Both experimental measurements and theoretical calculations were conducted to prove the promotive role of oxygen vacancies in achieving the supercapacitive performance of MnMoO₄–OV.