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Time-Resolved Local pH Measurements during CO(2) Reduction Using Scanning Electrochemical Microscopy: Buffering and Tip Effects

[Image: see text] The electrochemical reduction of CO(2) is widely studied as a sustainable alternative for the production of fuels and chemicals. The electrolyte’s bulk pH and composition play an important role in the reaction activity and selectivity and can affect the extent of the buildup of pH...

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Autores principales: Monteiro, Mariana C. O., Mirabal, Alex, Jacobse, Leon, Doblhoff-Dier, Katharina, Barton, Scott Calabrese, Koper, Marc T. M.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: American Chemical Society 2021
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8611793/
https://www.ncbi.nlm.nih.gov/pubmed/34849509
http://dx.doi.org/10.1021/jacsau.1c00289
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author Monteiro, Mariana C. O.
Mirabal, Alex
Jacobse, Leon
Doblhoff-Dier, Katharina
Barton, Scott Calabrese
Koper, Marc T. M.
author_facet Monteiro, Mariana C. O.
Mirabal, Alex
Jacobse, Leon
Doblhoff-Dier, Katharina
Barton, Scott Calabrese
Koper, Marc T. M.
author_sort Monteiro, Mariana C. O.
collection PubMed
description [Image: see text] The electrochemical reduction of CO(2) is widely studied as a sustainable alternative for the production of fuels and chemicals. The electrolyte’s bulk pH and composition play an important role in the reaction activity and selectivity and can affect the extent of the buildup of pH gradients between the electrode surface and the bulk of the electrolyte. Quantifying the local pH and how it is affected by the solution species is desirable to gain a better understanding of the CO(2) reduction reaction. Local pH measurements can be realized using Scanning Electrochemical Microscopy (SECM); however, finding a pH probe that is stable and selective under CO(2) reduction reaction conditions is challenging. Here, we have used our recently developed voltammetric pH sensor to perform pH measurements in the diffusion layer during CO(2) reduction using SECM, with high time resolution. Using a 4-hydroxylaminothiophenol (4-HATP)/4-nitrosothiophenol (4-NSTP) functionalized gold ultramicroelectrode, we compare the local pH developed above a gold substrate in an argon atmosphere, when only hydrogen evolution is taking place, to the pH developed in a CO(2) atmosphere. The pH is monitored at a fixed distance from the surface, and the sample potential is varied in time. In argon, we observe a gradual increase of pH, while a plateau region is present in CO(2) atmosphere due to the formation of HCO(3)(–) buffering the reaction interface. By analyzing the diffusion layer dynamics once the sample reaction is turned “off”, we gain insightful information on the time scale of the homogeneous reactions happening in solution and on the time required for the diffusion layer to fully recover to the initial bulk concentration of species. In order to account for the effect of the presence of the SECM tip on the measured pH, we performed finite element method simulations of the fluid and reaction dynamics. The results show the significant localized diffusion hindrance caused by the tip, so that in its absence, the pH values are more acidic than when the tip is present. Nonetheless, through the simulation, we can account for this effect and estimate the real local pH values across the diffusion layer.
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spelling pubmed-86117932021-11-29 Time-Resolved Local pH Measurements during CO(2) Reduction Using Scanning Electrochemical Microscopy: Buffering and Tip Effects Monteiro, Mariana C. O. Mirabal, Alex Jacobse, Leon Doblhoff-Dier, Katharina Barton, Scott Calabrese Koper, Marc T. M. JACS Au [Image: see text] The electrochemical reduction of CO(2) is widely studied as a sustainable alternative for the production of fuels and chemicals. The electrolyte’s bulk pH and composition play an important role in the reaction activity and selectivity and can affect the extent of the buildup of pH gradients between the electrode surface and the bulk of the electrolyte. Quantifying the local pH and how it is affected by the solution species is desirable to gain a better understanding of the CO(2) reduction reaction. Local pH measurements can be realized using Scanning Electrochemical Microscopy (SECM); however, finding a pH probe that is stable and selective under CO(2) reduction reaction conditions is challenging. Here, we have used our recently developed voltammetric pH sensor to perform pH measurements in the diffusion layer during CO(2) reduction using SECM, with high time resolution. Using a 4-hydroxylaminothiophenol (4-HATP)/4-nitrosothiophenol (4-NSTP) functionalized gold ultramicroelectrode, we compare the local pH developed above a gold substrate in an argon atmosphere, when only hydrogen evolution is taking place, to the pH developed in a CO(2) atmosphere. The pH is monitored at a fixed distance from the surface, and the sample potential is varied in time. In argon, we observe a gradual increase of pH, while a plateau region is present in CO(2) atmosphere due to the formation of HCO(3)(–) buffering the reaction interface. By analyzing the diffusion layer dynamics once the sample reaction is turned “off”, we gain insightful information on the time scale of the homogeneous reactions happening in solution and on the time required for the diffusion layer to fully recover to the initial bulk concentration of species. In order to account for the effect of the presence of the SECM tip on the measured pH, we performed finite element method simulations of the fluid and reaction dynamics. The results show the significant localized diffusion hindrance caused by the tip, so that in its absence, the pH values are more acidic than when the tip is present. Nonetheless, through the simulation, we can account for this effect and estimate the real local pH values across the diffusion layer. American Chemical Society 2021-10-13 /pmc/articles/PMC8611793/ /pubmed/34849509 http://dx.doi.org/10.1021/jacsau.1c00289 Text en © 2021 The Authors. Published by American Chemical Society https://creativecommons.org/licenses/by-nc-nd/4.0/Permits non-commercial access and re-use, provided that author attribution and integrity are maintained; but does not permit creation of adaptations or other derivative works (https://creativecommons.org/licenses/by-nc-nd/4.0/).
spellingShingle Monteiro, Mariana C. O.
Mirabal, Alex
Jacobse, Leon
Doblhoff-Dier, Katharina
Barton, Scott Calabrese
Koper, Marc T. M.
Time-Resolved Local pH Measurements during CO(2) Reduction Using Scanning Electrochemical Microscopy: Buffering and Tip Effects
title Time-Resolved Local pH Measurements during CO(2) Reduction Using Scanning Electrochemical Microscopy: Buffering and Tip Effects
title_full Time-Resolved Local pH Measurements during CO(2) Reduction Using Scanning Electrochemical Microscopy: Buffering and Tip Effects
title_fullStr Time-Resolved Local pH Measurements during CO(2) Reduction Using Scanning Electrochemical Microscopy: Buffering and Tip Effects
title_full_unstemmed Time-Resolved Local pH Measurements during CO(2) Reduction Using Scanning Electrochemical Microscopy: Buffering and Tip Effects
title_short Time-Resolved Local pH Measurements during CO(2) Reduction Using Scanning Electrochemical Microscopy: Buffering and Tip Effects
title_sort time-resolved local ph measurements during co(2) reduction using scanning electrochemical microscopy: buffering and tip effects
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8611793/
https://www.ncbi.nlm.nih.gov/pubmed/34849509
http://dx.doi.org/10.1021/jacsau.1c00289
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