Observation of currentless redox reactions on surface of water jet immersed in low-pressure plasma

Abstract

We investigated oxidation–reduction reactions on the surface of water jet immersed in a low-pressure inductively coupled helium plasma. The electrical potential of the water jet was floating, and no electrical current was supplied from the plasma to the water jet. We observed the productions of molecular hydrogen and molecular oxygen. We also observed negligible consumption of water vapor in the gas phase, suggesting that the productions of hydrogen and oxygen were not owing to the conversion from water vapor. When we employed silver nitrate solution instead of pure water, we observed the decrease in the production rate of hydrogen, whereas the production rate of oxygen was the same in pure water and silver nitrate solution. In addition, we found the synthesis of silver particulates in the silver nitrate solution, indicating the competition between the reductions of H+ and Ag+. Thus, the experimental results reveal the simultaneous oxidation and reduction at the same plasma–liquid interface.