Strategies for the mitigation of salt precipitation in zero-gap CO₂ electrolyzers producing CO

Abstract

Salt precipitation in the cathode gas diffusion electrodes of zero-gap CO2 electrolyzers producing CO is a major challenge to the stability and durability of this technology. In this review, we...

Bipolar Membrane with Porous Anion Exchange Layer for Efficient and Long‐Term Stable Electrochemical Reduction of CO2 to CO

“…To mitigate the need for the OH − recovery in AEM-based electrolyzers, they can be directly operated with neutral electrolytes at the cost of increased cell voltages. [14] However, this significantly reduces the energy demand to ≈905 kJ mol −1 CO as it removes the need for the OH − recovery (2.8 V cell voltage at 100 mA cm −2 as measured with 0.1 m KHCO 3 anolyte under the same operating conditions as in the BPM measurements, see Figure S13, Supporting Information). Hansen et al published comparable cell performance at 100 mA cm −2 with a KHCO 3 -based anolyte and 40 °C.…”

“…K + or Cs + , from the anolyte migrate to the cathode side, they may form low soluble (bi)carbonate salts, that can block the CO 2 from reaching the catalysts active sites. [9,12,13] This typically leads to rapid performance decrease in cells that use electrolytes with salt concentration above 0.1 m. [14] If alkaline electrolytes are used on the anode side, the hydroxide ions are consumed by the oxygen evolution reaction. When (bi)carbonate ions from the cathode side arrive at the anode, the pH of the electrolyte is neutralized over time.…”

Gas-Induced Structural Damages in Forward-Bias Bipolar Membrane CO2 Electrolysis Studied by Fast X-ray Tomography

“…We employ time-resolved operando XTM to study degradation in BPM-CO2ELY. Flooding and salt precipitation known in AEM-CO2ELY ,− are not observed. However, different degradation processes related to the formation of gaseous CO 2 are identified.…”

“…Practical application of CO2ELY at a large scale currently lacks the required current density and stability to be economically feasible . Gas-fed CO 2 -electrolyzers in a zero-gap architecture with an anion exchange membrane (AEM) are considered to be the most promising architecture . However, AEM CO2ELY has two major issues: CO 2 crossover and salt precipitation.…”

“…Alkali metal cations from the anode reach the cathode by electro-osmotic diffusion due to gradients in electric potential and concentration. Empirical data suggest the need of an alkaline electrolyte for good performance and stability, e.g., KOH or KHCO 3 , at the anode . Recent studies could furthermore show that sufficient direct supply of alkali cations at the cathode improves performance and stability. − Effectively, cations not only have an apparent positive effect on the CO 2 reduction reaction but also lead to salt precipitation and fast performance degradation, calling for a delicate balance , or regularly regenerating the cathode .…”