Discharge-mode modulation and reactive species formation in corona reactors with floating electrodes and water-film boundaries

Abstract

Low-temperature plasma technology provides a promising approach for air purification and microbial control; however, achieving a balance among reactive species generation, ozone formation, and treatment efficiency remains a major challenge in plasma-based environmental applications. In this study, the modulation of discharge characteristics and reactive species formation was investigated in corona reactors by introducing a floating electrode between the high-voltage wire electrode and a water-film boundary. Three reactor configurations, including wire–water-film (w–wf), wire–copper plate, and wire–wire–water-film (w–w–wf) reactors, were systematically compared under positive and negative DC polarities. Electrical measurements and ICCD imaging revealed that the floating electrode significantly modified the discharge behavior, inducing a transition from relatively stable corona discharge to a multi-channel pulsed discharge under positive polarity. This discharge-mode transition was accompanied by enhanced hydroxyl-radical-related fluorescence intensity, with the positive-polarity w–w-wf reactor exhibiting an OH-related fluorescence signal approximately 76% higher than that of the corresponding w–wf reactor. Meanwhile, the introduction of the water-film boundary increased the local humidity in the discharge region and altered the competitive pathways between ozone formation and hydroxyl-related reactions. The positive-polarity w–w–wf reactor achieved enhanced inactivation of S. aureus (4.12-log reduction) compared with the corresponding w–wf configuration (3.58-log reduction), while maintaining a relatively low ozone concentration (1.5 ppm) compared with copper-plate-based configurations. However, the negative-polarity w–wf reactor exhibited the highest bacterial inactivation efficiency, and the positive-polarity w–wf reactor produced the lowest ozone concentration among all tested configurations. These results indicate that floating-electrode and water-film boundary engineering can be used to regulate discharge modes and reactive species distributions in atmospheric-pressure corona systems. Rather than delivering universally superior performance, the floating electrode serves as an additional parameter for tailoring plasma characteristics by controlling the balance among discharge behavior, reactive species generation, ozone formation, and microbial inactivation.