Single Pass CO₂ Conversion Exceeding 85% in the Electrosynthesis of Multicarbon Products via Local CO₂ Regeneration

Abstract

The carbon dioxide reduction reaction (CO 2 RR) presents the opportunity to consume CO 2 and produce desirable products. However, the alkaline conditions required for productive CO 2 RR result in the bulk of input CO 2 being lost to bicarbonate and carbonate. This loss imposes a 25% limit on the conversion of CO 2 to multicarbon (C 2+ ) products for systems that use anions as the charge carrierand overcoming this limit is a challenge of singular importance to the field. Here, we find that cation exchange membranes (CEMs) do not provide the required locally alkaline conditions, and bipolar membranes (BPMs) are unstable, delaminating at the membrane−membrane interface. We develop a permeable CO 2 regeneration layer (PCRL) that provides an alkaline environment at the CO 2 RR catalyst surface and enables local CO 2 regeneration. With the PCRL strategy, CO 2 crossover is limited to 15% of the amount of CO 2 converted into products, in all cases. Low crossover and low flow rate combine to enable a single pass CO 2 conversion of 85% (at 100 mA/cm 2 ), with a C 2+ faradaic efficiency and full cell voltage comparable to the anion-conducting membrane electrode assembly.

Electroreduction of CO2/CO to C2 Products: Process Modeling, Downstream Separation, System Integration, and Economic Analysis

“…In the first electrolyzer, we assume Faraday efficiencies of 95% for CO and 5% for hydrogen at a current density of 300 mA/cm 2 and a cell voltage of 2.5 V. Furthermore, we assume a CO 2 conversion of 50%. 95 The small amount of hydrogen is neglected in the process design (i.e., no downstream processing is designed for the separation of hydrogen from CO and unconverted CO 2 ). The CO 2 /CO mixture from the first electrolyzer can in principle directly be fed to the second electrolyzer, but initial experimental results show that the presence of large amounts of CO 2 in the mixture has a detrimental effect on the product distribution.…”

Cation-Driven Increases of CO2 Utilization in a Bipolar Membrane Electrode Assembly for CO2 Electrolysis

“…For instance, recent work from O’Brien et al demonstrated a CO 2 single pass conversion of 85% using pure water and an IrO 2 catalyst on the anode side with a CEM for proton shuttling. 18 …”

“… 24 − 28 Combining these observations with previous BPMEA demonstrations that have traditionally suffered from poor CO 2 reduction selectivities, we hypothesized that the low selectivity in a BPMEA system could be overcome by increasing cation concentrations at the cathode. 17 , 18 , 27 Thus, if the low parasitic CO 2 loss of BPM’s can be achieved simultaneously with improved CO 2 reduction performance, high CO 2 utilization efficiencies would be possible as a result.…”

“…Other solutions could be coating the catalyst layer with an ionomer that has suitable cation groups in favor of ECO2R. 18 Using catalysts that have better kinetics for ECO2R than Ag could also favor ECO2R over HER. 37 Further developments may also allow for a reduction in cell voltages.…”

Sequential vs integrated CO2 capture and electrochemical conversion: An energy comparison

“…2a. Such strategies use acidic environments and bipolar membranes to introduce protons to regenerate carbonate 35,36 or optimize local reaction environments or operating conditions 37,38 . For simplicity of this model, however, our analysis assumes a gas-fed CO2 conversion of 50% with additional steps for product separation and carbonate regeneration processes.…”