Self-Cleaning CO₂ Reduction Systems: Unsteady Electrochemical Forcing Enables Stability

Abstract

The electrochemical conversion of CO 2 produces valuable chemicals and fuels. However, operating at high reaction rates produces locally alkaline conditions that convert reactant CO 2 into cell-damaging carbonate salts. These salts precipitate in the porous cathode structure, block CO 2 transport, reduce reaction efficiency, and render CO 2 electrolysis inherently unstable. We propose a self-cleaning CO 2 reduction strategy with short, periodic reductions in applied voltage, which avoids saturation and prevents carbonate salt formation. We demonstrate this approach in a membrane electrode assembly (MEA) with silver and copper catalysts, on carbon and polytetrafluoroethylene (PTFE)-based gas diffusion electrodes, respectively. When operated continuously, the C 2 selectivity of the copper−PTFE system started to decline rapidly after only ∼10 h. With the self-cleaning strategy, the same electrode operated for 157 h (236 h total duration), maintaining 80% C 2 product selectivity and 138 mA cm −2 of C 2 partial current density, at a cost of <1% additional energy input.

Valorizing carbon dioxide via electrochemical reduction on gas‐diffusion electrodes

“… 68 The corresponding full‐cell voltage was ~3 V, translating to an energy efficiency of ~42%. Note that this configuration might not be efficacious enough at higher current densities where higher carbonate formation rates would cause quick saturation and precipitation of the salt crystal, as recently suggested by Xu and co‐workers 17 . They developed a strategy: throttling the applied voltage back to 2.0 V periodically provides an interval to carbonate migration.…”

“…High current densities, on the one hand, create highly alkaline local environments that favor CO 2 electroreduction and suppress hydrogen evolution. On the other hand, they cause problems including carbonate buildup and severe instability, impeding the scale‐up of CO 2 electroreduction to demonstration scales 16–18 …”

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.…”

A Membrane Reactor with Microchannels for Carbon Dioxide Reduction in Extraterrestrial Space

“…KOH solution could provide a strong alkaline environment, which could inhibit hydrogen evolution reaction, strengthen the C-C coupling, and promote the Faraday efficiency (FE) of C2H4 [21]. However, the strong alkaline environment will lead to the reaction between CO2 and OH − to form CO3 2− , which could pass through the anion exchange membrane, resulting in cross-contamination, and dragging down the energy efficiency and raw material utilization rate [22,23]. Sargent pointed out that more than 50% of the energy used in the electroreduction of CO2 under alkaline conditions is used to recover the CO2 forming CO3 2− [24].…”