Investigation of Electrolyte-Dependent Carbonate Formation on Gas Diffusion Electrodes for CO₂ Electrolysis

Abstract

The electrochemical reduction of CO 2 (ECO 2 R) is a promising method for reducing CO 2 emissions and producing carbonneutral fuels if long-term durability of electrodes can be achieved by identifying and addressing electrode degradation mechanisms. This work investigates the degradation of gas diffusion electrodes (GDEs) in a flowing, alkaline CO 2 electrolyzer via the formation of carbonate deposits on the GDE surface. These carbonate deposits were found to impede electrode performance after only 6 h of operation at current densities ranging from −50 to −200 mA cm −2 . The rate of carbonate deposit formation on the GDE surface was determined to increase with increasing electrolyte molarity and became more prevalent in K + -containing as opposed to Cs + -containing electrolytes. Electrolyte composition and concentration also had significant effects on the morphology, distribution, and surface coverage of the carbonate deposits. For example, carbonates formed in K + -containing electrolytes formed concentrated deposit regions of varying morphology on the GDE surface, while those formed in Cs + -containing electrolytes appeared as small crystals, well dispersed across the electrode surface. Both deposits occluding the catalyst layer surface and those found within the microporous layer and carbon fiber substrate of the electrode were found to diminish performance in ECO 2 R, leading to rapid loss of CO production after ∼50% of the catalyst layer surface was occluded. Additionally, carbonate deposits reduced GDE hydrophobicity, leading to increased flooding and internal deposits within the GDE substrate. Electrolyte engineering-based solutions are suggested for improved GDE durability in future work.

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.…”

Local Chemical Environment Governs Anode Processes in CO2 Electrolyzers

“…High electrolyte concentration, however, leads to the formation of alkali metal carbonates/bicarbonates in the gas diffusion electrode (GDE) cathode, leading to the clogging of the gas channels and the concurrent selectivity decrease for CO2RR (with the simultaneous increase of the hydrogen evolution reaction (HER) rate). 33 − 36 Ni foam has also been applied in non-zero-gap flow cells with a bipolar membrane or paired with a molecular catalyst for CO2RR. 26 , 27 , 31 Additionally, NiO nanoparticles were employed to oxidize 5-(hydroxymethyl)furfural to 2,5-furandicarboxylic acid, paired with CO2RR.…”

Probing the local activity of CO2 reduction on gold gas diffusion electrodes: effect of the catalyst loading and CO2 pressure

“…As EDX characterization was performed after CO 2 electrolysis in KHCO 3 , K is found throughout the whole imaged area. As recently shown by Cofell et al 33 , this is due to KHCO 3 deposition due to concentration gradients and increased local alkalinity developed during electrolysis.…”