Electrode surface modification of graphene-MnO₂ supercapacitors using molecular dynamics simulations

In this study, molecular dynamics (MD) simulations have been performed to explore the variation of ion density and electric potential due to electrode surface modification. Two different surface morphologies, having planer and slit pore with different conditions of surface charge, have been studied for graphene-MnO₂ surface using LAMMPS. For different pore widths, the concentration of ions in the double layer is observed to be very low when the surface of the graphene-MnO₂ electrode is charged. With a view to identify the optimal pore size for the simulation domain considered, three different widths for the nano-slit type pores and the corresponding ion-ion interactions are examined. Though this effect is negligible for pores with 9.23 and 3.55 Å widths, a considerable increase in the ionic concentration within the 7.10 Å pores is observed when the electrode is kept neutral. The edge region of these nano-slit pores leads to effective energy storage by promoting ion separation and a significantly higher charge accumulation is found to occur on the edges compared to the basal planes. For the simulation domain of the present study, partition coefficient is maximum for a pore size of 7.10 Å, indicating that the ions' penetration and movement into nano-slit pores are most favorable for this optimum pore size for MnO₂-graphene electrodes with aqueous NaCl electrolyte. Graphical Abstract The importance of understanding the commercial feasibility of supercapacitor material has made qualitatively predicting the optimized electrode structure one of the main targets of energy related researches. While great progress has been made in recent years, a coherent theoretical picture of the optimized electrode structure remains elusive. This article discusses the most favorable design of supercapacitor electrode for ion-electrode interaction.