| AVS 58th Annual International Symposium and Exhibition | |
| Plasma Science and Technology Division | Monday Sessions |
| Session PS+BI-MoA |
| Session: | Multiphase (Liquid, Solid, Gas) and Biological Related Plasmas |
| Presenter: | Megan Witzke, Case Western Reserve University |
| Authors: | M. Witzke, Case Western Reserve University C. Richmonds, Case Western Reserve University B. Bartling, Case Western Reserve University S.W. Lee, Case Western Reserve University J. Wainright, Case Western Reserve University C.-C. Liu, Case Western Reserve University R.M. Sankaran, Case Western Reserve University |
| Correspondent: | Click to Email |
Electrochemical reactions are normally studied at the interface of a solid metal electrode and an aqueous ionic electrolyte. A smaller number of experiments exist, dating back to more than 100 years ago1, of plasmas formed at the surface or inside of liquids to initiate electrochemical reactions at the interface of a plasma electrode and a liquid electrolyte. Despite this long history, reactions at the plasma-liquid interface remain poorly understood. Plasmas that are formed at low pressures require liquids with extremely low vapor pressure, limiting previous studies to ionic liquids (i.e. molten salts)2. In addition, plasmas are characterized by a complex environment (e.g. ions, electrons, UV, etc.) which has made it difficult to differentiate charge-transfer reactions from other non-faradaic reactions such as radical generation and chemical dissociation.
We have recently developed a novel microplasma source that allows a non-thermal, atmospheric-pressure plasma to be stably formed at the surface of aqueous ionic electrolytes3-5, facilitating fundamental study of charge-transfer reactions at the plasma-liquid interface. Electron transfer reactions between the plasma and the liquid are studied by using the well-known ferricyanide-ferrocyanide redox couple. The electrochemical reduction of ferricyanide is monitored by UV-vis absorbance spectroscopy and cyclic voltammetry. We find that ferricyanide is indeed reduced by the plasma, confirming that charge transfer reactions can occur at the plasma-liquid interface. The rate of ferricyanide reduction is found to depend on the discharge current, which controls the electron flux delivered to the surface of the solution. By comparing the (discharge) current to the amount of ferricyanide reduced, we obtain a reduction efficiency of ~1%. To address the relatively low efficiency, we have measured the potential at the plasma-liquid interface to determine whether the potential is high enough for water electrolysis and measured hydrogen generation by mass spectrometry. In this talk, we will present our overall methodology and discuss these results in detail.
1. J. Gubkin, Ann. Phys. 32, 114 (1887).
2. S. Z. El Abedin, M. Polleth, S. A. Meiss, J. Janek, and F. Endres, Green Chemistry 9, 549 (2007).
3. C. M. Richmonds and R. M. Sankaran, Appl. Phys. Lett. 93, 131501 (2008).
4. W-H. Chiang, C. Richmonds, and R. M. Sankaran, Plasma Sources Sci. Technol. 19, 034011 (2010).
5. F-C. Chang, C. Richmonds, and R. M. Sankaran, J. Vac. Sci. Technol. A 28, L5 (2010).