Probing time-resolved plasma-driven solution electrochemistry in a falling liquid film plasma reactor: Identification of HO$$^−_2$$ as a plasma-derived reducing agent
Journal Article
·
· Journal of Chemical Physics
- Univ. of Minnesota, Minneapolis, MN (United States)
- Northwestern Univ., Evanston, IL (United States)
Many applications involving plasma–liquid interactions depend on the reactive processes occurring at the plasma–liquid interface. In this article, we report on a falling liquid film plasma reactor allowing for in situ optical absorption measurements of the time-dependence of the ferricyanide/ferrocyanide redox reactivity, complemented with ex situ measurement of the decomposition of formate. We found excellent agreement between the measured decomposition percentages and the diffusion-limited decomposition of formate by interfacial plasma-enabled reactions, except at high pH in thin liquid films, indicating the involvement of previously unexplored plasma-induced liquid phase chemistry enabled by long-lived reactive species. We also determined that high pH facilitates a reduction-favoring environment in ferricyanide/ferrocyanide redox solutions. In situ conversion measurements of a 1:1 ferricyanide/ferrocyanide redox mixture exceed the measured ex situ conversion and show that conversion of a 1:1 ferricyanide/ferrocyanide mixture is strongly dependent on film thickness. We identified three dominant processes: reduction faster than ms time scales for film thicknesses >100 µm, •OH-driven oxidation on time scales of <10 ms, and reduction on 15 ms time scales for film thickness <100 µm. We attribute the slow reduction and larger formate decomposition at high pH to HO$$^−_2$$ formed from plasma-produced H2O2 enabled by the high pH at the plasma–liquid interface as confirmed experimentally and by computed reaction rates of HO$$^−_2$$ with ferricyanide. Overall, this work demonstrates the utility of liquid film reactors in enabling the discovery of new plasma-interfacial chemistry and the utility of atmospheric plasmas for electrodeless electrochemistry.
- Research Organization:
- Univ. of Michigan, Ann Arbor, MI (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC); USDOE Office of Science (SC), Fusion Energy Sciences (FES)
- Grant/Contract Number:
- SC0020232
- Other Award/Contract Number:
- W911NF-20-1-0105
- OSTI ID:
- 3024918
- Alternate ID(s):
- OSTI ID: 2578482
- Journal Information:
- Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 9 Vol. 160; ISSN 1089-7690; ISSN 0021-9606
- Publisher:
- American Institute of Physics (AIP)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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