Erosion–Corrosion of Metal Electrodes in Liquid-Phase Spark Plasma With Phenol Solution Medium

Liquid-phase discharge plasma is a promising technology for environmental applications, but the erosion and corrosion of metal electrodes remain a critical challenge that limits its long-term efficiency and stability. This study investigates the erosion–corrosion behavior of seven metal electrodes (Fe, Al, Cu, W, Ti, Ni, and Mo) in a phenol solution under pulsed discharge plasma. The effects of discharge power, peak voltage, solution pH, and conductivity on electrode erosion–corrosion were investigated. Surface morphology and composition of the electrodes were analyzed using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). The results revealed that higher discharge power and peak voltage significantly increased erosion–corrosion, with Al exhibiting the highest material loss and Fe and Ti showing the least. Solution pH had minimal impact, while higher conductivity reduced erosion–corrosion due to suppressed plasma generation. Post-discharge analysis indicated the formation of distinct surface features, including smooth-edged pits on Fe, Al, and Mo electrodes and flat pits on Cu, W, and Ti electrodes. Metal oxides formed on the electrode surfaces, with Ti developing the thickest oxide layer. Residual metal ions (Fe<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup>, Fe<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup>, Al<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup>, Cu<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup>, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{WO}_{4}^{2-}$</tex-math> </inline-formula>, Ti<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup>, and Ni<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup>) and nanoparticles (80–300 nm) were detected in the solution, with Fe<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup>, Al<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup>, Cu<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup>, and Ni<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> forming hydroxide precipitates over time. This study provides critical insights into the erosion–corrosion mechanisms of metal electrodes under discharge plasma, offering a foundation for electrode material selection and optimization in plasma-based wastewater treatment systems.