Importance of Time‐Dependent Wetting Behavior of Gas‐Diffusion Electrodes for Reactivity Determination

Abstract

Tin foil and SnOx/C gas‐diffusions electrodes (GDEs) were investigated via electrochemical impedance spectroscopy (EIS) to extract the differential double‐layer capacitance (Cdl) as a measure of the wetted surface area. Time‐dependent Cdl values revealed an immediate stationary wetting for tin foil electrodes while a distinct increase of Cdl – which becomes stationary with time – was observed for GDEs. The time‐dependent wetting behavior of the GDEs was substantiated by physical post‐mortem characterization. Since the wetted surface area determines the number of reachable active sites the performance of GDEs should be normalized to the wetted surface area for evaluation of reactivity.

Visualisation and quantification of flooding phenomena in gas diffusion electrodes (GDEs) used for electrochemical CO2 reduction: A combined EDX/ICP–MS approach

“…Since flooding is widely believed to be triggered primarily by the massive formation of carbonate precipitates on-top, and within deeper layers of the GDE [7][8][9][10][11][12][13][14][15], the amount and distribution of carbonates -in case of CO 2 electrolysers operated with a KOH anolyte, these are typically potassium carbonates and bicarbonates-seem to be an important tracer of flooding within the threedimensional GDE structure.…”

Cracks as Efficient Tools to Mitigate Flooding in Gas Diffusion Electrodes Used for the Electrochemical Reduction of Carbon Dioxide

“…[68] Based on the results of consecutive electrolytic experiments performed with argon and CO 2 (Figure S14, Supporting Information), we support the view that flooding is not initiated by the carbonate precipitation, being in contradiction to the interpretation presented by Leonard et al [68] In fact, the intrusion of the electrolyte to micropores may be triggered by electrowetting at extreme cathodic potentials (Figure 3). [30][31][32][33][34][35][36][37][38][39][40] It is important to note that the ex situ SEM/EDX analysis of GDE cross sections, as performed in this work (Figures 4,5), can visualize areas to which the electrolyte has permeated during the electrolysis but cannot distinguish whether solid precipitates are formed during or after the electrolysis. [69] The MPL of 36BB contains cracks in low abundance (Figure 2; Figure S2, Supporting Information) and has high internal porosity (Table 1).…”

Pitfalls and Protocols: Evaluating Catalysts for CO2 Reduction in Electrolyzers Based on Gas Diffusion Electrodes

“…These opposing observations have been validated with oxygen reduction reaction, which provides information about the mass transport of gaseous reactants. , The reason behind the contradiction is still unclear, though we believe it could be attributed to the use of different GDE substrates: PTFE GDE vs carbon GDE. For example, for the benefits of Nafion to take effect, the ionomer–catalyst layer could require a direct contact with the gas–liquid interface, which may be a challenge in carbon GDEs . Recently, Bell and co-workers proposed a bilayer coating of cation- and anion-conducting ionomers on Cu to regulate the microenvironment, i.e., local concentration of OH – , H 2 O, and CO 2 , to favor the production of multicarbon molecules .…”

“…The crossover of gas products to the catholyte is also a concern for the accurate quantification of products as discussed previously. The extent of bubble formation can be further aggravated if the GDE is overly wetted or flooded, which pushes the gas–electrolyte interface further away from the catalyst layer (>10 μm). , Additionally, the crossover of gas reactant and products will be intensified if the pressure at the gas chamber is higher than that in the catholyte chamber. For example, Legrand et al reported that in their specified electrolyzer system, a pressure difference of more than 5 kPa would result in the undesired crossovers and thus formation of bubbles in the catholyte chambers .…”

“…For example, for the benefits of Nafion to take effect, the ionomer−catalyst layer could require a direct contact with the gas−liquid interface, which may be a challenge in carbon GDEs. 74 Recently, Bell and co-workers proposed a bilayer coating of cation-and anion-conducting ionomers on Cu to regulate the microenvironment, i.e., local concentration of OH − , H 2 O, and CO 2 , to favor the production of multicarbon molecules. 75 Nevertheless, the beneficial effect of this strategy in a GDE system has yet to be demonstrated.…”