Analytical evaluation of microplasma technologies for production of hydrogen fuel from water

A H2-based energy economy could alleviate fossil fuel environmental effects. Hydrogen is an ideal fuel because of its ultra-high energy density, availability in common sources like water, and lack of harmful combustion byproducts. However, H2 lacks global adoption as a fuel because virtually all H2 is synthesized from fossil fuels through expensive and energy-intensive industrial processes such as steam methane reforming. Alternatively, small amounts of hydrogen can be made on-demand through water electrolysis, but this process is more expensive, requires high electrolyte concentrations, and its non-specific reactions can produce harmful reaction byproducts. The numerous applications of on-demand H2 fuel encourage research to produce it at low cost and high efficiency despite technological limitations. Microplasma technologies utilize nonthermal and non-Maxwellian reaction conditions in nonconventional chemical reactions and could provide novel pathways to producing H2 fuel. The current work is the first demonstration of H2 production from H2O with microplasma technologies. Furthermore, it is one of the first demonstrations of H2 production from H2O with nonthermal plasma. The H2 yields and energy efficiencies are improved compared to previous nonthermal plasma studies. The relative efficiencies for the conversions of H2O to H2 were about 10%, 1%, and 7% for microplasma, uncatalyzed nonthermal plasma, and catalyzed nonthermal plasma, respectively. The energy efficiencies were about 0.3%, 0.0003%, and 2.1% for microplasma, uncatalyzed nonthermal plasma, and catalyzed nonthermal plasma, respectively. Lastly, this work characterizes microplasma plasmachemical and photochemical reactions, thereby demonstrating a lack of H2O2 and the dominance of O2 and O3. These chemical results indicate that microplasma chemical reactions follow similar pathways to other nonthermal plasmachemical reactions with water vapor and could provide H2 from H2O without the concurrent production of H2O2. The current work advances the potential of microplasmas for H2 production. Proof-of-concept experiments demonstrate the reliable and repeatable production of H2 from water vapor in microplasma channels. Hydrogen is produced in both the presence and absence of a carrier gas. Relevant physical parameters are characterized using optical and solid state characterization techniques. Electron density and gas rotational temperature are measured to be about 2∗1014 cm-3 and 363 K, respectively. These physical parameters are roughly constant over the total range of reduced electric field strengths. Chemical reactions are studied to propose preliminary chemical reaction mechanisms. It is hypothesized that O3 concurrently generated during H2 production limits overall H2 yields through alternative reaction pathways. Overall, the mechanistic insights provided by this work position future studies of H2 production in microplasmas to overcome observed limitations and continue to surpass the ability of nonthermal plasmas to produce H2 from H2O.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2018

Author dc:creator

• Wiersma, Zachary Scott Bender

Contributors dc:contributor

• Eden, James G.
• Sweedler, Jonathan V.
• McCall, Benjamin J.
• Ruzic, David N.

• plasma chemistry
• plasma physics
• hydrogen fuel
• water reactions

Statement dc:rights

• © 2018 Zachary Scott Bender Wiersma

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/100983

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/100983