How membrane characteristics influence the performance of CO₂ and CO electrolysis

Abstract

Due to the ability to produce sustainably carbon-based chemicals and fuels, CO2 electrolysis and the closely related CO electrolysis are advancing rapidly from fundamental studies toward industrial applications. Many near...

Unintended cation crossover influences CO2 reduction activity in Cu-based zero-gap electrolysers

“…While the principles governing membrane permselectivity are generally established, 34,36,38,39 it appears that many (or most) demonstrations of CO 2 ER using AEMs with liquid electrolytes are operating under conditions where co-ion exclusion is not expected to be signi cant -i.e., when using electrolytes of high ionic strength in comparison to the density of xed charges in the membrane. One must not simply assume perfect ion selectivity occurs when using ion-exchange membranes, and that careful consideration of the membrane's in uence on the cathode reaction environment is critically important among the multitude of factors affecting CO 2 ER selectivity.…”

“…One must not simply assume perfect ion selectivity occurs when using ion-exchange membranes, and that careful consideration of the membrane's in uence on the cathode reaction environment is critically important among the multitude of factors affecting CO 2 ER selectivity. 34 Some reports indeed mention that overcoming Donnan exclusion can lead to co-ion crossover, 11,30 but without providing detail of what this means in practice, or how it might guide electrolyte choices. Based on our results and general calculations of Donnan exclusion, 38,39 signi cant exclusion occurs only when using electrolytes which are substantially more dilute (≤ 0.05 M) than those typically employed by researchers in this eld.…”

“…Further innovations in reactor design towards addressing this carbonate problem are necessary. 28,58−60 In general, careful studies should be devoted to understanding the role of the membrane in CO 2 ER, 34 and to investigating the in uence of its physical properties (thickness and polymer backbone) on the ability of cation crossover. Additionally, operando mapping the cation movements and speciation as function of membrane type, time, and applied bias using operando tomography/radiography will be valuable for further development of AEM-based electrolysers.…”

Enriching Surface‐Accessible CO2 in the Zero‐Gap Anion‐Exchange‐Membrane‐Based CO2 Electrolyzer

“…Among these species, anions (HCOO À , CO 3 2À and HCO 3 À ) will crossover the AEM under an electric field towards the positively charged anode and can potentially be further reacted. [12] HCOO À can be oxidized to CO 2 at the anode due to it being thermodynamically favored to oxidize before the oxygen evolution reaction (by > 1.3 V @ pH = 8). [1a] With Experimental conditions [a] Total CO 2 supply 1 I: 100 % P CO2 , 20 mL min À 1 cm À 2 , � 14 × 10 À 6 mol s À 1 2 II: 100 % P CO2 , 10 mL min À 1 cm À 2 III: 50 % P CO2 , 20 mL min À 1 cm À 2 � 7 × 10 À 6 mol s À 1 3 IV: 100 % P CO2 , 5 mL min À 1 cm À 2…”

“…The total CO 2 consumption can be divided into CO 2 reduction (with the generation of CO and HCOO − ) and CO 2 neutralization (forming CO 3 2− and HCO 3 − ). Among these species, anions (HCOO − , CO 3 2− and HCO 3 − ) will crossover the AEM under an electric field towards the positively charged anode and can potentially be further reacted [12] . HCOO − can be oxidized to CO 2 at the anode due to it being thermodynamically favored to oxidize before the oxygen evolution reaction (by >1.3 V @ pH=8) [1a] .…”