On the Non-Faradaic Hydrogen Gas Evolution from Electrolytic Reactions at the Interface of a Cathodic Atmospheric-Pressure Microplasma and Liquid Water Surface

Abstract

The electrolysis of water is an important reaction in many aqueous electrochemical systems, including those where an atmospheric-pressure microplasma jet is formed at a liquid surface. Here, we quantitatively study the hydrogen gas evolved from this plasma electrolytic system. Unlike conventional water electrolysis with a metal cathode in contact with the solution, more hydrogen gas is produced than expected based on the quantity of electricity passed, and the apparent faradaic efficiency exceeds 100%. By varying the solution temperature and carrying out kinetic analysis, we show two parallel reaction mechanisms exist , specifically faradaic liquid-phase reactions involving solvated electron-mediated reduction of hydronium ions and non-faradaic gas-phase reactions involving electron impact dissociation of water vapor, that lead to the distinct behavior.