Various CO₂-to-CO Electrolyzer Cell and Operation Mode Designs to avoid CO₂-Crossover from Cathode to Anode

Abstract

The electrochemical CO2 reduction reaction (CO2RR) towards CO allows to turn CO2 and renewable energy into feedstock for the chemical industry. Previously shown electrolyzers are capable of continuous operation for more than 1000 h at high faradaic efficiencies and industrially relevant current densities. However, the crossover of educt CO2 into the anode gas has not been investigated in current cell designs: Carbonates (HCO3− and CO32−) are formed at the cathode during CO2RR and are subsequently neutralized at the anode. Thus, CO2 mixes into the anodically evolved O2, which is undesired from commercial perspectives. In this work this chemical transport was suppressed by using a carbonate-free electrolyte. However, a second transport mechanism via physically dissolved gases became apparent. A transport model based on chemical and physical absorption of CO2 and O2 will be proposed and two solutions were experimentally investigated: the use of an anode GDL (A-GDL) and degassing the anolyte with a membrane contactor (MC). Both solutions further reduce the CO2 crossover to the anode below 0.1 CO2 for each cathodically formed CO while still operating at industrially relevant current densities of 200 mA/cm2.

Investigation and Optimisation of Operating Conditions for Low-Temperature CO2Reduction to CO in a Forward-Bias Bipolar-Membrane Electrolyser

“…Mathematical modelling combined with additional experimental work will be required to increase understanding on how to better control and optimise humidity levels within the BPM electrolyser and improve overall CO 2 RR performance. A mathematical model investigating transport effects in gapcells was recently published by Reinisch et al 83 Relative humidity of cathode gas feed.-Following the conceptual considerations of the H 2 O influence on cell performance, it becomes apparent that the relative humidity of the cathode feed gas is one of the key operating parameters and its influence was thus investigated first. For this purpose, a sensitivity study was performed at 0, 50 and 100%RH, respectively, and the obtained results are summarised in Fig.…”

Industrial Application Aspects of the Electrochemical Reduction of CO2 to CO in Aqueous Electrolyte

“…(1), (7) and (9) induced transport of overall 18 % of the supplied CO 2 at the anode might not be tolerable from an economical and perception point of view. There are several concepts reducing the CO 2 transport to the anode [19], which will be implemented during further scaling.…”

Role of ion-selective membranes in the carbon balance for CO2 electroreduction via gas diffusion electrode reactor designs

“…This nding indicates that many of the current techno-economic analyses for high-rate electroreduction of CO 2 must be reconsidered if signicant CO 2 crossover occurs. 29,30 One approach to reduce the CO 2 crossover would be to use a two-step cascade process, which consists of an initial CO 2 reduction to CO and a subsequent CO conversion into highly valuable multi-carbon products that have no carbon source crossover. 31,32 However, even in this two-step procedure with 100% CO faradaic efficiency for the rst step, 50% of all consumed CO 2 could still be emitted out of the anolyte using an AEM.…”