Plasma activated water: a study of gas type, electrode material, and power supply selection and the impact on the final frontier

Abstract

An in-depth study of plasma activated water (PAW) generation was conducted to link changes in power supply, electrode material, input gas, and treatment time to the resulting reaction chemistry, all while maintaining a consistent electrode geometry. These changes in chemistry can help tailor PAW for different space applications. An AC, DC, and nanosecond pulsed power supply were each used to generate PAW with stainless steel, copper, tungsten, or platinum electrodes while utilizing air, nitrogen, carbon dioxide, helium, or argon as the feed gas. Tap or deionized (DI) water was treated for 1 to 15 minutes, and the generated PAW was tested for changes in pH, conductivity, and concentration of nitrates, nitrites, and ammonium. Calculations indicated that the production of reactive nitrogen species was the leading cause of the pH and conductivity changes. The DC generated air plasma, with a voltage between 2.5–3.14 kV and currents of 85–100 mA, was able to reduce the pH of DI water to 2.88 and generate 128 ppm of nitrates. The AC supply was less effective, producing a pH of 4.22 for DI water and 5 ppm of nitrates. The pulsed supply, operating at 20% of the input power of the DC supply, lowered the pH to 3.34 and generated 26 ppm of nitrates. When a simulated Martian gas mixture of 95% CO₂ and 5% N₂ was used as the feed gas, 24.8 ppm and 3.82 ppm of nitrates were generated with the DC and pulsed supplies, respectively.