A plasma gas bubble‐in‐liquid method for high production of selectable reactive species using a nanosecond pulse generator has been developed. The gas of choice is fed through a hollow needle in a point‐to‐plate bubble discharge, enabling improved selection of reactive species. The increased interface reactions, between the gas‐plasma and water through bubbles, give higher productivity. H2O2 was the predominant species produced using Ar plasma, while predominantly NnormalO3− and NO2 were generated using air plasma, in good agreement with the observed emission spectra. This method has nearly 100% selectivity for H2O2, with seven times higher production, and 92% selectivity for NnormalO3−, with nearly twice the production, compared with a plasma above the water.

Front Cover: The selected gas is injected through a hollow needle at a gap to a second, mesh electrode. Both electrodes are placed within the liquid. A plasma is generated inside the bubbles. The increased interface reactions between the gas‐plasma and water gives fast mass transport enabling higher production of reactive species. Argon plasma generates hydrogen peroxide (H2O2) with nearly 100% selectivity, while using air leads to high concentrations of NO3− and NO2. Further details can be found in the article by Xiujuan J. Dai et al. http://doi.wiley.com/10.1002/ppap.201500156.

Front Cover: The reactive plasma species nitrate (NO3‐) and hydrogen peroxide (H2O2) were produced in high selectivity in water using air and argon, respectively, in a needle and plate electrode assembly. The plasma treated water was used as an efficient and environmentally friendly electrolyte for anodizing titanium metal. The NO3‐ from air plasma is the key factor in the formation of TiO2 nanotubes and the H2O2 from the argon plasma assists the oxidation process. Further details can be found in the article by A. T. Ambujakshan et al. on page http://doi.wiley.com/10.1002/ppap.201600219.

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Underwater discharges inside helium (He) gas bubbles were generated using a 30-needles-to-plate electrode system with the gas flowing through the needles. The set-up allows continuous treatment of flowing water. The plasma electron temperature and density determined from spectral line intensities and profiles of the Hα and Hβ hydrogen lines were found to be 1.1 ± 0.6 eV and ∼5 × 1016 cm−3, respectively. These parameters are comparable with those of plasmas generated by other underwater gas bubble discharges for the production of OH radicals. The two main long-lived species, hydrogen peroxide (H2O2) and nitrate ions (NO3−), produced in plasma treated water were measured. It was found that without a continuous water flow, the energy yield of H2O2 was comparable with other underwater discharges, while with a continuous flow, the production of H2O2 appeared to be somewhat reduced by nitrites from dissolved air.