Gas Diffusion Electrode Design for CO2 Electroreduction Beyond 1 a cm-2

Abstract

Electrochemical CO2 conversion to fuels and chemicals addresses the CO2 emission and renewable energy storage problems simultaneously. Existing infrastructure can be leveraged to take advantage of these fuels, and recycling CO2 results in a low- or zero-carbon fuel cycle. Converting CO2 into chemical feedstock enables the sequestration of CO2 into valuable products such as polymers.Electrochemical CO2 conversion can be performed in aqueous- or gas-phase systems. Aqueous electrolysis, wherein the gaseous reactants are dissolved in the electrolyte, can achieve high selectivity. However, due to the low solubility of the gas reactants in the aqueous electrolyte and the long diffusion distance, current densities remain below few tens of mA/cm2—far from the >500 mA/cm2 regime needed to make ECC economically viable.Gas-phase electrolysis of CO2 could overcome the diffusion limitation of the aqueous system, thereby enabling a much higher current density. In a gas-phase ECC system, a catalyst to reduce CO2 is deposited onto a porous hydrophobic substrate (gas diffusion layer) to form a gas diffusion electrode. The CO2 reaches the catalyst through the gas diffusion layer, reducing the required diffusion length and improving the mass transport. Current densities in the hundreds of mA/cm2 have been achieved using a gas-phase electrolysis system. However, other liquid-phase electrochemical technologies such as water electrolysis achieve multi Amperes/cm2. Also, critical challenges related to stability at high current densities remain.Here, we present the gas diffusion electrode design that drives CO2 electroreduction to ethylene and ethanol at a current density > 100 mA/cm2 for > 100 hours. We then design the catalyst layer to achieve CO2 gas-phase electrolysis at current densities in the > 1 A/cm2 regime, and with the generation of multicarbon products. We report C2+ partial currents exceeding 1.3 A/cm2 at cathodic energy efficiencies above 40% – a sixfold increase relative to the best previously-reported comparable catalysts. These result in a full-cell energy efficiency towards C2 products of 20% above 1 A/cm2 operating currents.