Mn single atoms coordinated with N and O and embedded in activated carbon for supercapacitor and oxygen evolution reaction applications

Abstract

With the aim of increasing the potential applications of activated carbon (AC) in supercapacitors and zinc-air batteries, the present work prepared AC composites doped with Mn, N and O using various methods. These materials exhibited superior capacitive and oxygen evolution reaction (OER) electrocatalytic activity. Analytical characterizations and density functional theory calculations demonstrated that the specimen subjected to calcination and heating under N2 and NH3 (AC-Mn-3) had a higher specific surface area, an optimized distribution of pyridinic and pyrrolic N and single Mn atom active sites. These factors improved the supercapacitor performance and OER catalytic activity of this material. The hierarchical pore structure of the AC matrix also facilitated electrolyte transport while simultaneously reducing internal resistance and protecting the electrode structure during cycling. An AC-Mn-3 electrode provided a high specific capacitance of 516.20 F/g at 1 A/g while a symmetric supercapacitor based on this electrode delivered an exceptional energy density of 71.69 Wh/kg at a power density of 500 W/kg. When applied to the OER, the AC-Mn-3 achieved a low overpotential of 270.21 mV at 10 mA/cm2 in 1 M KOH. Theoretical calculations suggested that single Mn atoms coordinated with N and O effectively bound oxygenated intermediates to lower the adsorption energy barrier associated with the OER rate-determining step going from OH* to O*. These results provide new insights concerning the mechanism by which improved supercapacitor performance and OER catalytic activity can be realized and demonstrate an effective strategy for AC modification.