Microwave-tuned Mn-doped ZnO for all-in-one supercapacitors: Correlating defect chemistry with electrochemical behavior

Zinc oxide-based (ZnO) electrode materials have emerged as contenders for heightened cost efficiency, fast charge-discharge prowess, outstanding performance metrics, and remarkable cycle stability in supercapacitor technologies. Among the myriad synthesis techniques, the microwave-assisted approach distinguishes itself with an array of advantages, being time-efficient, eco-friendly, and adept at providing accurate control over the complex ZnO morphology. Introducing ions like into the ZnO lattice further propels the electrochemical performance of supercapacitors into superior territories. Hence, this investigation meticulously prepared a series of undoped and Mn-doped ZnO materials utilizing a microwave-assisted synthesis method across four different microwave powers ranging from 160 to 800 W. Cutting-edge morpho-structural characterization techniques, including X-ray diffraction, scanning electron microscopy, electron paramagnetic resonance, photoluminescence, and Raman spectroscopy, were employed to delve into the structure and defect centers of the ZnO-based samples. It has been conclusively demonstrated that the concentration of is pivotal, offering additional charge carriers without compromising the crystallinity of ZnO while also enhancing diffusion correlated with Faradaic redox reactions-thereby escalating the supercapacitor's properties. A doping concentration of 2% Mn-ions balances charge carriers with structural integrity. This sample achieved a specific capacitance of 340 F/g, a power density of 59.7 kW/kg, and an energy density of 47.1 Wh/kg. Across the board, all samples demonstrate impressive stability, retaining over 70% capacity after 5000 charge-discharge cycles. Notably, ZnO with 2% Mn synthesized at 160 W excels with over 90% capacitance retention. This distinct behavior is attributed to the transformative influence of Mn ion doping on ZnO's structural and morphological attributes.