Electrocatalytic water splitting is a promising technique for producing sustainable hydrogen, but its effectiveness depends on the development of cost-effective and high-performance electrodes. In this work, phase-pure high entropy oxide (HEO) (Ni, Fe, Co, Cu, Mn)₃O₄ nanostructured coating electrodes were fabricated using a solution precursor plasma spray coating technique under optimized conditions with two different molar concentrations (1 M and 2 M) of solution precursors. This process enables precise deposition of a porous catalyst coating on stainless steel substrates, with an average thickness of 30 micrometers. The as-deposited coating shows a spinel structure, and its degree of crystallinity increases with higher molar concentrations of the solution precursors. The HEO coating electrodes demonstrate excellent activity in alkaline media for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), with low overpotentials of 129 mV and 220 mV, respectively, at a current density of 10 mA cm⁻². A two-electrode device was fabricated, and the results reveal that the required overall potential to achieve a current density of 10 mA cm⁻² is 1.47 V only. This work highlights the potential of solution precursor plasma spray coating as a versatile and scalable approach for producing phase-pure HEO-based water-splitting electrodes, paving the way for large-scale hydrogen generation in sustainable energy systems.

The plasma torch is the key component of the thermal plasma-assisted material processing system. Particularly, direct current (dc) nontransferred arc plasma torch is widely used in high-temperature material processing applications. The characteristics of the thermal plasma jet emanating from the plasma torch depend on many factors, including arc current, type of plasma forming gas, gas flow rates, gas injection configuration, torch geometry, and so on. This experimental study focuses on the comparison between the effects of CO ₂ and air on the arc voltage, electrothermal efficiency, and specific enthalpy of the plasma torch operated at the atmospheric pressure. For this purpose, a low-power dc plasma torch consisting of a rod-type thoriated tungsten cathode and the copper anode was customized. CO ₂ and air were used as the plasma forming gases along with a feeble amount of argon (15 lpm). The plasma torch was operated over a wide range of current (100–175 A) with fixed gas flow rates. The $I$ – $V$ characteristics and the electrothermal efficiency of the plasma torch were measured, and results were compared. The maximum electrothermal efficiency and specific enthalpy of the plasma torch when operated with CO ₂ were reported as 70% and 1900 KJ/Kg, respectively, which is higher than the same torch operated with air as the plasma forming gas. The electron number density and electron temperature of the air and CO ₂ plasma jet were measured by optical emission spectroscopy (OES). The calculated electron number density and electron temperature of the plasma jet with CO ₂ were $2.89\times 10\,\,^{\mathrm{ 16}}$ cm ⁻³ and 8598 K, respectively, which is higher than air plasma jet. It was found that CO ₂ has a stronger influence than air on the arc voltage fluctuation, electrothermal efficiency, and operating regime of the plasma torch.

This study explores the application of thermal plasma in submerged conditions for the efficient degradation of 4-nitrophenol (4-NP), a high-priority toxic pollutant. A customized 10 kW DC non-transferred arc thermal plasma torch was employed to generate the plasma using argon (Ar) and air as plasma-forming gases. The plasma jet was characterized through arc voltage fluctuations, optical emission spectroscopy, and submerged jet dynamics, offering detailed insights into the physical and chemical properties of the Ar/air plasma. The plasma treatment of an initial 50 mg l⁻¹ concentration of 4-NP in an aqueous medium resulted in 94% degradation and 58% mineralization within 30 min at the plasma input power of 6.2 kW. The removal process followed a pseudo-first-order kinetic model with a reaction rate constant of 0.0684 min^–1. The possible degradation intermediates and products were identified via Liquid chromatography-mass spectroscopy and Ion chromatography. The submerged thermal plasma technique demonstrated enhanced compound removal efficiency, making it a promising method for the treatment of toxic dissolved organic compounds in wastewater.

The organic adduct compounds of 2-nitrobenzoic acid crystals were grown as optically transparent crystals using the conventional slow evaporation solution technique. The crystals were powdered and irradiated with cold plasma. Cell parameter analysis confirmed the formation of a new crystalline material that resides in the triclinic P crystal system with space group P1. Fourier transform infrared spectra were recorded using the KBr pellet technique to determine the vibrational functional groups in the compound. Powder X-ray diffraction analysis was used to reveal the crystalline orientation of the powdered samples of the grown crystals. The obtained full width at half maximum for the (001) plane in the XRD spectrum indicates the excellent crystalline quality of the 2-nitrobenzoic acid crystals. The recorded UV–Vis absorption spectra reveal that the grown powdered crystal samples possess cut-off edges wavelengths at 428 and 428 nm and 353 and 354 nm for pure and plasma-treated samples, respectively. The optical energy bandgaps were found to be 2.0, 2.25, 4.06, and 4.02 eV for the pure and plasma-treated samples, respectively. The photoluminescence spectra show the blue emissions of the crystal. The FE-SEM images show the morphological modifications in which rounded platelets appear on the surfaces of the treated crystals.