Elucidating the effects of solvent-ionomer interactions on copper catalyst layers for CO2 electrolysis to multicarbon products

We report the influence of ionomer and catalyst dispersion solvent interaction on the structure and ionomer film wettability in copper (Cu) catalyst layers (CLs) in a gas diffusion electrode (GDE). Our results show that acetone and methanol dispersion solvents interact differently with the perfluorinated sulfonic acid (PFSA) ionomer Aquivion, which is composed of hydrophobic backbones and hydrophilic ionic heads. Acetone solvates more with the hydrophobic backbones in the PFSA compared to methanol. Consequently, the ionomer film fabricated from casting Aquivion and acetone mixture on a flat surface is more continuous and hydrophobic than its methanol counterpart. Such ionomer-solvent interaction also leads to a more uniform and flooding-tolerant GDE when producing the copper catalyst layer with acetone (acetone-CL) compared to methanol (methanol-CL). As a result, acetone-CL yields higher selectivity to C2+ products at high current density, up to 29 % greater than methanol-CL at 500 mA cm-2. Ethylene is the primary product for both CLs, reaching 47.5 4.0 % and 43.9 5.5 % at 300 mA cm-2 for acetone-CL and methanol-CL, respectively. The improvement in C2+ product selectivity for the acetone-CL is attributed to the CLs high resistance against flooding at current densities above 300 mA cm-2. Our findings offer a new strategy to advance CO2 electrolysis by manipulating solvent-ionomer interactions.