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Applications of Rotating Ring-Disc Electrode in CO2 Electrochemical Reduction in Aqueous Media

Zhang, Fen
http://orcid.org/0000-0001-6053-5427
http://rave.ohiolink.edu/etdc/view?acc_num=osu1577812269219211

Abstract Details

2020, Doctor of Philosophy, Ohio State University, Chemistry.
Electrochemical reduction of CO2 (CO2RR) is a promising route to convert CO2 to value-added chemicals such as carbon monoxide, formic acid, methanol, and others. Efficient conversion of CO2 using renewable sources of electricity can potentially mitigate the rising CO2 concentration in the atmosphere in addition to alleviating our dependence on fossil fuels to generate chemicals. Most of the CO2RR studies to date focus on designing novel catalysts to improve the reaction activity and selectivity for real-world applications. However, being able to quickly and accurately evaluate the performance of newly-designed catalysts and to rapidly screen catalyst candidates remain an essential part of the catalyst discovery process. Traditional product analysis routine includes sample pre-concentration (e.g. using long electrolysis time), sample preparation, instrument detection (e.g. GC or NMR) and/or instrument availability. This time-consuming routine heavily impedes the efficient evaluation and screening of newly-designed CO2RR catalysts. It also limits our ability to investigate the catalyst degradation mechanism within a short time frame like minutes. In this work, a rotating ring-disc electrode (RRDE)-based method was proposed and demonstrated to be able to shorten the total product analysis time from several hours (even days) to less than 1 minute. Small CO2RR product molecules such as H2, CO, HCOOH and their mixtures were proved to be quantified successfully on an RRDE assembly based on their electrochemical fingerprints. During CO2RR, OH- is always generated concurrently with reduction products. The accumulation of OH- near the catalyst surface during CO2RR remains a critical issue since the local pH can easily be over 3 pH units higher than the bulk during electrolysis and thus directly affects the CO2RR activity and selectivity. To systematically investigate the role of local pH on CO2RR selectivity and consequently the reaction pathway, in this work, an RRDE-based method was proposed for the local pH detection during CO2RR where the electroactive CO2RR product molecule itself served as the local pH probe. Using Au as a model catalyst where CO was the only product, the CO oxidation peak measured by the ring electrode in an RRDE assembly was proved to shift by -86 +/- 2 mV per unit local pH change during CO2RR, which provided a measurable quantitative descriptor for local pH change near the catalyst surface during electrolysis. The local basicity measured by the proposed RRDE-based method decreased in the order Li+ > Na+ > K+ > Cs+, which experimentally proved the effect of electrolyte cation on the local pH change during CO2RR. There is an urgent need to build a standardized test protocol for CO2RR to reasonably compare results from different research groups, since the activity and selectivity of CO2RR are directly affected by local pH and the local pH is easily affected by experimental parameters like the geometric configuration of the electrochemical cell, solution flow rate, gas bubbling rate, porosity of gas bubbler and others. In this work, the rotating electrode technique (either RDE or RRDE) was proposed to be coupled with an on-line gas chromatograph through a self-designed H-type electrochemical cell. Rotating created a well-defined hydrodynamic condition, where the local pH during CO2RR only depended on the rotation rate and the electrolysis current irrespective of all other experimental parameters. In summary, in this dissertation, the applications of rotating ring-disc electrode in CO2RR in the aqueous media were proposed and systematically evaluated. Rotating ring-disc electrode was proved to be a powerful electrochemical tool that enabled fast product detection and quantification, local pH measurement as well as the study of controlled mass transport over a diverse range of CO2RR catalysts.
Anne Co (Advisor)
142 p.
Analytical Chemistry; Chemistry
CO2 electrochemical reduction; rotating ring-disc electrode

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Citations

  • Zhang, F. (2020). Applications of Rotating Ring-Disc Electrode in CO2 Electrochemical Reduction in Aqueous Media [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1577812269219211

    APA Style (7th edition)

  • Zhang, Fen. Applications of Rotating Ring-Disc Electrode in CO2 Electrochemical Reduction in Aqueous Media. 2020. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1577812269219211.

    MLA Style (8th edition)

  • Zhang, Fen. "Applications of Rotating Ring-Disc Electrode in CO2 Electrochemical Reduction in Aqueous Media." Doctoral dissertation, Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1577812269219211

    Chicago Manual of Style (17th edition)

osu1577812269219211
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This open access ETD is published by The Ohio State University and OhioLINK.