We report, for the first time, utilizing a rotating ring‐disc electrode (RRDE) assembly for detecting changes in the local pH during aqueous CO2reduction reaction (CO2RR). Using Au as a model catalyst where CO is the only product, we show that the CO oxidation peak shifts by −86±2 mV/pH during CO2RR, which can be used to directly quantify the change in the local pH near the catalyst surface during electrolysis. We then applied this methodology to investigate the role of cations in affecting the local pH during CO2RR and find that during CO2RR to CO on Au in an MHCO3buffer (where M is an alkali metal), the experimentally measured local basicity decreased in the order Li+> Na+> K+> Cs+, which agreed with an earlier theoretical prediction by Singh et al. Our results also reveal that the formation of CO is independent of the cation. In summary, RRDE is a versatile tool for detecting local pH change over a diverse range of CO2RR catalysts. Additionally, using the product itself (i.e. CO) as the local pH probe allows us to investigate CO2RR without the interference of additional probe molecules introduced to the system. Most importantly, considering that most CO2RR products have pH‐dependent oxidation, RRDE can be a powerful tool for determining the local pH and correlating the local pH to reaction selectivity.
We report, for the first time, utilizing a rotating ring‐disc electrode (RRDE) assembly for detecting changes in the local pH during aqueous CO2reduction reaction (CO2RR). Using Au as a model catalyst where CO is the only product, we show that the CO oxidation peak shifts by −86±2 mV/pH during CO2RR, which can be used to directly quantify the change in the local pH near the catalyst surface during electrolysis. We then applied this methodology to investigate the role of cations in affecting the local pH during CO2RR and find that during CO2RR to CO on Au in an MHCO3buffer (where M is an alkali metal), the experimentally measured local basicity decreased in the order Li+> Na+> K+> Cs+, which agreed with an earlier theoretical prediction by Singh et al. Our results also reveal that the formation of CO is independent of the cation. In summary, RRDE is a versatile tool for detecting local pH change over a diverse range of CO2RR catalysts. Additionally, using the product itself (i.e. CO) as the local pH probe allows us to investigate CO2RR without the interference of additional probe molecules introduced to the system. Most importantly, considering that most CO2RR products have pH‐dependent oxidation, RRDE can be a powerful tool for determining the local pH and correlating the local pH to reaction selectivity.
more » « less- NSF-PAR ID:
- 10127283
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie
- Volume:
- 132
- Issue:
- 4
- ISSN:
- 0044-8249
- Page Range / eLocation ID:
- p. 1691-1698
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Here, we demonstrate that small molecules such as H2, CO, HCOO−and their mixtures, generated from the electroreduction of CO2(CO2RR), can be detected and quantified on a rotating ring-disc electrode (RRDE). We describe a series of systematic calibration protocol to quantify CO2RR products on four model electrocatalysts (Pt, Au, Sn, [NiII(cyclam)]2+). In an RRDE assembly, products generated at the disc are convectively transported and detected at the ring detector before diffusing into the bulk solution, circumventing the need for product pre-concentration. As the electrochemical fingerprints of these small molecules and their mixtures on the Pt detector are unique, RRDE also excludes the need for separation. Thus, using the rotating ring detector significantly minimizes the time delay between product generation and detection compared to conventional techniques such as GC, LC and NMR. An RRDE allows faster screening of catalysts that can help accelerate catalyst discovery for CO2RR. It also enables time-dependent mechanistic studies of CO2RR catalysis.
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