Ozone-enhanced electrodeless bubble discharge for plasma-activated water: An energy efficient, high selectivity route to liquid phase nitrogen fixation

An integrated plasma-activated water (PAW) generation system based on electrodeless underwater bubble discharge was used to achieve high liquid-phase reactive nitrogen species (RNS) selectivity and low energy cost for nitrogen fixation. The electrodeless configuration eliminates electrode erosion, enabling stable long-term operation. 0.1% O 3 was introduced into the air feed gas, providing additional oxidizing pathways toward highly soluble, high-valence NO x species, particularly N 2 O 5 . Direct bubble discharge in water enables reactive oxygen and nitrogen species (RONS) generation, oxidation, transport, and absorption to occur in a coupled manner within the bubbles, which helps reduce N 2 O 5 transport losses. Experimental results demonstrated that nearly all RONS were transferred into the liquid phase, achieving at least 99.4% liquid-phase capture, with RNS comprising 99.1% of liquid products. The corresponding RNS production rate and energy cost were 6.36 mmol/h and 9.9 MJ/mol, respectively. Compared with ozone-enhanced multi-stage PAW nitrogen fixation processes reported previously, the system reduces process complexity while maintaining high efficiency and competitive energy performance, providing a route for distributed agricultural nitrogen fixation. • Bubble discharge enables coupled NO x generation, oxidation, transport and absorption. • Ozone oxidizes NO x toward soluble N 2 O 5 to achieve 99.1% liquid RNS selectivity. • Integrated process design reduces N 2 O 5 transport loss, leading to lower energy cost. • Electrodeless system avoids electrode erosion for distributed agriculture.