Paper PS+EM-MoM11
Reactions at the Interface of Plasmas and Aqueous Electrodes: Identifying the Role of Electrons

Monday, October 29, 2012, 11:40 am, Room 24

Plasmas formed at the surface of or inside liquids have been of historical interest for the potential to mediate electrochemical reactions with gaseous species.¹ Recently, there has been technological interest in plasma/liquid systems for a wide range of applications including nanomaterials synthesis, water treatment, and medicine. However, the nature of reactions at the plasma/liquid interface remains poorly understood. Specifically, since plasmas are a source of electrons, ions, UV light, and radicals, it has been difficult to isolate and identify the role of the various species on reactions that occur in the liquid phase.

Here, we present evidence of electrolytic reactions at the plasma/liquid interface. Experiments were carried out with a non-thermal, atmospheric-pressure, direct-current microplasma jet formed at the surface of an aqueous electrolyte. The plasma was operated as the cathode with a Pt foil immersed in solution as the anode. To isolate the role of electrons, we selected model electrolytic reactions such as the conversion of ferricyanide [Fe(CN)₆^3-] to ferrocyanide [Fe(CN)₆^4-] which can be easily monitored by UV-vis absorbance spectroscopy.² Cyclic voltammetry was performed to verify that ferricyanide was not dissociated. Alternatively, using acidic solutions, hydrogen gas was detected by mass spectrometry, indicating that protons (H⁺) are electrochemically reduced by the plasma.³ Overall, these results reveal the significant role electrons can play in plasma/liquid systems.

1. J. Gubkin, Ann. Phys. Chem. N. F. 32, 114 (1887).

2. M. Witzke et al., J. Am. Chem. Soc. 133, 17582 (2011).

3. M. Witzke et al., submitted.