Optimizing the Ink Formulation for Preparation of Cu-Based Gas Diffusion Electrodes Yielding Ethylene in Electroreduction of CO₂

Abstract

Cu-based gas diffusion electrodes (GDE) show excellent performance in the electrochemical reduction of CO 2 to ethylene. In the present work, we evaluate how the solvent of ink formulations containing Nafion-ionomer and unsupported Cu particles affects the polymerized Nafion-copper distribution in the as-prepared GDE and the obtained performance in the electrochemical reduction of CO 2 . Isopropanol (IPA), dimethyl sulfoxide (DMSO), ethylene glycol (EG), or N-methyl-2-pyrrolidone (NMP)) were used. Microscopic analyses of the Cu-GDEs demonstrate that NMP and DMSO lead to exposed islands of copper, with Nafion acting predominantly as an interparticle binder. Such geometry is confirmed by the relatively high electrochemical surface area (ECSA) and the low charge-transfer resistance (R ct ). IPA or EG induce the formation of Cu-catalyst particles embedded into and covered by (polymerized) Nafion films, in agreement with the relatively low ECSA, and high R ct , likely due to significant polymerization and agglomeration of Nafion in the ink formulation induced by the protic solvents prior to preparation of the catalyst layer. When evaluated in the electrochemical reduction of CO 2 at −1.1 V vs the reversible hydrogen electrode (RHE), the exposed particles prepared using NMP and DMSO lead to higher FE toward ethylene than EG or IPA-based GDEs (23.5% and 19.2% vs 10.2% and 13.4%, respectively). The lower ethylene FE for Nafion covered systems is tentatively attributed to the acidity and highly effective transport of protons by Nafion.

Evaluating the Effects of Membranes, Cell Designs, and Flow Configurations on the Performance of Cu-GDEs in Converting CO2 to CO

“…In order to confirm long-term stability of flow-through operation, we performed multiple chronoamperometry experiments using the same Cu-GDE electrode, without disassembling the electrochemical flow cell. − …”

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

“…15,22 Solvent selection in catalyst preparation is widely acknowledged as a critical parameter in fabricating catalyst layers for proton-exchange membrane (PEM) fuel cells. [23][24][25][26][27][28][29][30] However, gaps remain in understanding the role of the ionomer-solvent interactions on the final CL properties because of the ionomer's biphasic nature 28,31 and the potential effects from solvent evaporation rates, catalyst loadings, and ionomer loadings. The effects of the ionomer-solvent interactions in catalyst inks used to prepare cathodes for CO2 electrolysis are less understood than for fuel cell catalysts.…”

“…As the solvents in the ionomer dispersion influence the conformation of the ionomer in the film, we expect the choice of solvent will affect the wettability of both pure Aquivion® films and the catalyst layers prepared with the ionomer-solvent mixture, ultimately impacting CO2RR performance. 13,31,39,44 Figure 3 compares the contact angles of water droplets on Aquivion® film-coated Cu foils measured using a Sessile drop method. The data points for 0 g L -1 ionomer concentration in Figure 3 are control experiments with Cu foils washed in each solvent without any Aquivion®, and the blank (black colour) is a Cu foil that we did not wash in any solvent.…”

Contributions of Pulsed Operation Along with Proper Choice of the Substrate for Stabilizing the Catalyst Performance in Electrochemical Reduction of CO2 Toward Ethylene in Gas Diffusion Electrode Based Flow Cell Reactors

“…[18,20,21] When applying periodic anodic polarization to lead electrodes, the formation/stabilization of catalytically active PbCO 3 was observed during cathodic reduction of CO 2 to formate, also hinting at a necessary, oxidized state of the catalyst in this case. [22] Other studies show that the beneficial effect appears even if no anodic current flows and the surface structure of the electrode remains unchanged. [23,24] An explanation could be intermittent changes in concentrations of reactants and products close to the electrode surface.…”