Preventing Salt Formation in Zero-Gap CO₂ Electrolyzers by Quantifying Cation Accumulation

The electrochemical CO₂ reduction reaction (CO₂RR) in a membrane electrode assembly (MEA) efficiently turns CO₂ into a feedstock. However, unfavorable steady-state concentrations of ions in the cathode compartment result in salt formation if unaddressed, which restricts the access of CO₂ and causes cell failure. Here, we systematically show the relationship between salt accumulation and four system parameters including cation species, anolyte concentration, membrane thickness, and operating temperature. To compare each metric, we quantified the cation accumulation rate at predefined operating times. Notably, we show that operating at temperatures above 50 °C with properly humidified CO₂ stream fully avoids salt formation. We further show that combining separate operating conditions is also highly effective, showing operation for >144 h with no measurable salt deposition at 200 mA/cm². Collectively, our work systematically demonstrates that salt formation is a prevalent yet surmountable CO₂RR challenge that can be overcome by elevated cell temperatures or switching to more soluble alkali cations.