Direct observation of the local microenvironment in inhomogeneous CO2 reduction gas diffusion electrodes via versatile pOH imaging. Issue 4 (20th March 2023)

• Record Type: Journal Article
• Authors: Böhme, Annette; Bui, Justin C.; Fenwick, Aidan Q.; Bhide, Rohit; Feltenberger, Cassidy N.; Welch, Alexandra J.; King, Alex J.; Bell, Alexis T.; Weber, Adam Z.; Ardo, Shane; Atwater, Harry A.
• Is Part Of: Energy & environmental science. Volume 16:Issue 4(2023)
• Page Start: 1783
• Page End: 1795
• Publication Date: 2023-03-20
• Subjects: Energy conversion -- Periodicals; Fuel switching -- Periodicals; Environmental sciences -- Periodicals; Environmental chemistry -- Periodicals; 333.79
• DOI: 10.1039/d2ee02607d
• Languages: English
• ISSNs: 1754-5692

Abstract

Abstract : We demonstrate pOH imaging with confocal microscopy to probe the microenvironment of an operating CO2 reduction gas diffusion electrode. We find that the micrometer-scale morphology plays an important role in defining the CO2 reduction performance. Abstract : We report how the micrometer-scale morphology of a carbon dioxide reduction (CO2 R) gas diffusion electrode (GDE) affects the mass transport properties and with it, the local CO2 R performance. We developed a technique to probe the microenvironment in a CO2 R GDE via local pOH imaging with time- and three-dimensional spatial, micrometer-scale resolution. The local activity of hydroxide anions (OH − ), represented by the pOH value, around a GDE in contact with an aqueous electrolyte is a crucial parameter that governs the catalytic activity and CO2 R selectivity. Here, we use fluorescence confocal laser scanning microscopy (CLSM) to create maps of the local pOH around a copper GDE by combining two ratiometric fluorescent dyes, one of which is demonstrated as a pOH sensor for the first time in this work. We observe that the local pOH decreases when current is applied due to the creation of OH − as a byproduct of CO2 R. Interestingly, the pOH is lower inside microtrenches compared to the electrode surface and decreases further as trenches become more narrow due to enhanced trapping of OH − . We support our experimental results with multiphysics simulations that correlate exceptionally well with measurements. These simulations additionally suggest that the decreased pOH inside microcavities in the surface of a CO2 R GDE leads to locally enhanced selectivity towards multicarbon (C2+ ) products. This study suggests that narrow microstructures on the length scale of 5 μm in a GDE surface serve as local CO2 R hotspots, and thus highlights the importance of a GDE's micromorphology on the CO2 R performance.