Plasma-activated water for improved intercalation and pseudocapacitance of MnO2 supercapacitor electrodes

Portable energy storage devices and carbon-neutral manufacturing are experiencing an ever-increasing demand and research interest. Plasma-assisted synthesis of materials has shown early success in addressing these demands due to the low carbon emissions and good versatility offered by such techniques. Herein, non-thermal atmospheric pressure plasma is used to assist the synthesis of MnO2 as supercapacitor electrode materials as a fast, energy-efficient approach. MnO2 is electrochemically synthesized on carbon fiber cloth and modified using plasma and plasma-activated water (PAW). This work develops the first use of PAW (pH 3.2) for the synthesis of MnO2 supercapacitor materials that exhibit high specific capacitance. A peak capacitance of 93.4 Fg-1 was achieved with good cycle stability of 96.1% after 1000 cycles with a mixture of only 1 ml PAW and 50 ml KMnO4 electrolyte. The results revealed that PAW is an effective delivery system for nitrogen functional groups and promotes significant hydration of interlayer spaces within the electrode materials. It is demonstrated that the addition of PAW causes charge storage mechanisms to become more surface redox dominated and can improve both the specific capacitance and cycle stability of the electrodes.