Abstract: The performance of plasma-activated water (PAW) is strongly governed by the composition of reactive species in the liquid phase and their synergistic interactions, while the discharge polarity plays a decisive role in regulating energy injection modes and reaction pathways at the source level. In this work, a gas–liquid two-phase dielectric barrier discharge (DBD) system was employed to systematically compare the effects of positive and negative pulsed polarities on the electrical characteristics, chemical composition, and sterilization performance of PAW under identical applied voltages. The results show that the average power of negative-pulsed discharge is only approximately one-third of that of positive-pulsed discharge; nevertheless, the PAW produced under negative polarity exhibits superior sterilization capability and higher energy efficiency. At an applied voltage of 14 kV, the EEO value of negative-pulsed PAW reaches 17.2 kWh·m-3·log-1, which is markedly lower than that of positive-pulsed PAW (84.3 kWh·m-3·log-1). Fluorescence probe and quantitative analyses reveal that the difference in reactive oxygen species (ROS) generation between the two polarities is minimal, with the negative polarity showing only about 6.7% lower levels, whereas the concentration of reactive nitrogen species (RNS) under negative polarity is increased by approximately 12%. Further mechanistic analysis demonstrates that the enriched RNS significantly enhance the generation kinetics of ONOOH by promoting the coupled reaction between nitrite(NO- 2) and hydrogen peroxide(H2O2), thereby achieving stronger sterilization performance and higher energy efficiency under lower energy input. This disparity is attributed to the lower energy input of the negative pulse, which suppresses the water vaporization at the gas–liquid interface, consequently enhancing the probability of electron collisions with N2 and promoting the generation and liquid-phase dissolution of negative ions. This study provides new physicochemical insights and methodological strategies for directing liquid-phase reaction pathways via discharge polarity and constructing highly energy-efficient PAW systems.

Key words: Pulse polarity, Plasma-activated water, Reactive species, Dielectric barrier discharge, Bactericidal effect