Defect-engineered MnO2 nanoparticles by low-energy ion beam irradiation for enhanced electrochemical energy storage applications

With the increasing demand of energy storage devices various material prospects have been explored to enhance the performance, which include increasing surface area, creating surface defects, and enhancing the conductivity of the active electrode materials. In that context, we demonstrate enhancement of charge storage performance of MnO2 nanoparticles by low energy (5 keV) ion beam irradiation. The ion beam leads to alteration of morphology of the nanoparticles and introduces large-number of surface defects, which are also predicted by TRI3DYN simulation. The measurements show that overall electrical conductivity of the modified nanoparticles increases and there is a gain in specific surface area after ion irradiation. The charge storage properties of pristine and irradiated MnO2 nanoparticles were characterized in a standard three-electrode electrochemical cell. The cyclic voltammetry measurements were carried out for both the pristine and irradiated samples at different scan rates, and constant current charge-discharge curves were obtained at different normalized currents. It is observed that the sample, which was irradiated with an ion fluence of 3 x 10(16) cm(-2), yields enhanced charge storage properties with an almost 60% increase in the specific capacitance value than that of pristine sample. The stability test for both pristine and irradiated samples showed barely any loss of specific capacitance over 2000 cycles. The experimental data are qualitatively corroborated by density functional theory-based simulations for both the pristine and the ion beam modified MnO2 nanoparticles. It turns out that defected MnO2 shows metallic behaviour and thereby increases the conductivity, reduction of diffusion energy barrier and increase of charge transfer occur, which lead to the enhancement of the charge storage performance.