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.

In this study, we evaluate the effect of cell configuration parameters on electrochemical reduction of CO2 using Cu gas-diffusion electrodes (Cu-GDEs), including the use of proton- or anion-exchange membranes, the CO2 flow configuration, and the Nafion content used in the ink formulation to prepare the Cu-GDEs. Using a cell configuration (i) containing a Sustainion membrane, (ii) allowing a liquid flow of catholyte and anolyte, and (iii) providing convective supply of CO2 in a flow-through mode, outstanding faradaic efficiencies toward carbon monoxide (FECO = ∼85%, at −0.88 V vs RHE, and 50 mA·cm–2) were obtained. We attribute this performance to an efficient desorption and transport of CO to the exit of the reactor, in agreement with the remarkably low FE toward ethylene at the applied electrochemical potentials. Most importantly, in this configuration and optimizing the Nafion content in the ink formulation to 10 wt %, cell performance could be maintained for at least 10 h of continuous operation at the high FECO of ∼85%.