Elucidation of Critical Catalyst Layer Phenomena toward High Production Rates for the Electrochemical Conversion of CO to Ethylene

Abstract

This work utilizes EIS to elucidate the impact of catalyst−ionomer interactions and cathode hydroxide ion transport resistance (R CL , OH − ) on cell voltage and product selectivity for the electrochemical conversion of CO to ethylene. When using the same Cu catalyst and a Nafion ionomer, varying ink dispersion and electrode deposition methods results in a change of 2 orders of magnitude for R CL , OH − and ca. a 25% change in electrode porosity. Decreasing R CL , OH − results in improved ethylene Faradaic efficiency (FE), up to ∼57%, decrease in hydrogen FE, by ∼36%, and reduction in cell voltage by up to 1 V at 700 mA/cm 2 . Through the optimization of electrode fabrication conditions, we achieve a maximum of 48% ethylene with >90% FE for nonhydrogen products in a 25 cm 2 membrane electrode assembly at 700 mA/cm 2 and <3 V. Additionally, the implications of optimizing R CL , OH − is translated to other material requirements, such as anode porosity. We find that the best performing electrodes use ink dispersion and deposition techniques that project well into roll-to-roll processes, demonstrating the scalability of the optimized process.

Understanding Limitations in Electrochemical Conversion to CO at Low CO2 Concentrations

“…The chemistry of the ionomer can affect the hydrophobicity of the catalyst layer, ion conductivity, and reactant gas permeability . The conformation of the ionomer can also be influenced by the catalyst ink , and deposition method, netting changes in competitive adsorption processes and local gas transport. Significantly thick ionomer films can result in underutilized catalyst sites, where reactant gases are forced around areas with low permeability.…”

“…Electrochemical impedance spectroscopy (EIS) was used to elucidate the maximum available electrochemical surface area as a function of RH. Catalyst utilization describes the fraction of catalyst that is available to the electrochemical reaction (for discussion, see refs and ).These experiments were performed as previously described (Figure S12). Briefly, we will measure the EIS in a region where no or little charge transfer is occurring.…”

Recent Developments on CO2 Hydrogenation Performance over Structured Zeolites: A Review on Properties, Synthesis, and Characterization

“…As it happens in electrochemical systems where both ionic transport and electrical interactions are crucial for the reaction outcomes, in zeolite catalysts, these characteristics can affect the diffusion of reactants and When discussing electrical and plasma interactions in such catalytic systems, it is useful to look at the wider meaning of ionic conductivity and its impact on catalytic processes. The work of Henckel et al [78] is a relevant example of this, as they used Electrochemical Impedance Spectroscopy (EIS) to investigate the interaction between the catalyst and ionomer, with a particular interest in the transport of hydroxide ions in the electrochemical CO to ethylene conversion. The results confirmed that fine-tuning ionic conductivity can substantially promote the Faradaic efficiency of ethylene and the cell voltage.…”

Recent Developments on CO2 Hydrogenation Performance over Structured Zeolites: A Review on Properties, Synthesis, and Characterization

“…al. [37] utilized Electrochemical Impedance Spectroscopy (EIS) for investigating the interplay between the catalyst and ionomer, as well as the resistance to the transport of hydroxide ions at the cathode, in the process of converting CO to ethylene electrochemically. Their work showed that the selection of the optimal synthesis conditions and factors such as the ionic conductivity brought improved ethylene Faradaic efficiency and cell voltage.…”