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The special characteristics of microplasma such as microscale geometry, atmospheric operation, self-organization property, and high radical density are suitable for the synthesis of nanoparticles. Trimanganese tetroxide (Mn 3 O 4) nanoparticles (NPs) were synthesized through plasma reduction mechanism by the use of sustainable, rapid, and microplasma array method at atmospheric conditions in a single step. 96.10% reaction yield of hausmannite Mn 3 O 4 NPs were gained by the reduction of potassium permanganate (KMnO 4) precursor solution in the presence of radicals in the microplasma discharge with a processing time of 30 minutes. The structure, oxidation state, morphology, composition, and specific surface area of synthesized particles were determined by XRD, FTIR, XPS, FE-SEM with EDX, HR-TEM, and BET characterization techniques. Spherical polydisperse particles with high surface area (304.01 m 2 g −1) and narrow distribution were obtained. The performance of synthesized Mn 3 O 4 NPs as an electrode material for supercapacitor application was analyzed by electrochemical workstation, which exhibited a high specific capacitance of 144.5 Fg −1 at a current density of 0.5 Ag −1 and the electrode material retained 43.54% of its initial capacitance after 1500 cycles. The asymmetric performance of Mn 3 O 4 NPs as one of the electrode materials exhibited high cyclic stability with 100% retention capacitance with an energy density of 3.33 Wh kg −1 at 0.1 Ag −1 and high power density of 422.5 W kg −1 at 0.5 Ag −1 , respectively. The present study gives new perspectives on a simple, efficient, eco-friendly, and powerful microplasma array method for the coalescence of Mn 3 O 4 NPs and the analysis of electrochemical behavior of corresponding NPs. K E Y W O R D S electrochemical performances, microplasma discharge, Mn 3 O 4 nanoparticles, supercapacitor 1 | INTRODUCTION The rapid growth of technology in all the aspects of our human and societal life has brought about many changes [Correction added on 10 February 2021, after first online publication: reference citations and Figure 13 have been corrected.]

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Plasma-assisted methanol reforming is an effective technology to produce hydrogen for various clean energy applications. In this study, hydrogen was produced from methanol reforming in a unique single stage microplasma reactor. Microplasma was produced between the capillary stainless steel tube electrodes by using high voltage direct current (DC) power supply. Blend of methanol and water was supplied to the microplasma reactor in a controlled flow rate using nitrogen as carrier gas. The effects of applied input power to the discharge and methanol feed rate on the performance of the plasma methanol decomposition were investigated. The experimental results showed that increasing the applied input power expressively increased the methanol conversion and hydrogen energy yield. In contrast, the increased feed rate significantly decreased the methanol conversion efficiency though it enriched the hydrogen energy yield. Under selective conditions, hydrogen energy yield of 24.14 g kW[Formula: see text] h[Formula: see text] was achieved with the conversion efficiency of 71% and 50% selectivity for H2, which is comparatively better than many of plasma-assisted methanol reforming processes. This investigation reveals that methanol reforming through a single stage microplasma reactor has the ability to produce hydrogen efficiently without coke formation at room-temperature and atmospheric pressure.