Achieving long-term stability in low-temperature anion exchange membrane zero-gap carbon dioxide (CO2) electrolysers is challenging, with few reports of cells operating for >1,000 hours at industry-relevant current densities (>200 mA cm−2). Most cells fail on much shorter timescales owing to salt precipitation and/or flooding, both of which restrict CO2 transport to the catalyst layer. In principle, both failure mechanisms can be mitigated by optimizing the water and ion balance within the system but the interconnected nature of ion and water transport is rarely addressed. In this Perspective, we examine the ion and water transport processes that currently limit long-term operation of these cells and outline the implications for future salt- and water-management strategies in anolyte-fed and water-fed anion exchange membrane CO2 electrolysers. We highlight that zero-gap CO2 electrolysers are inherently prone to water and ion imbalances and require simultaneous balancing to prolong system lifetimes towards industry requirements. ... Read more

CO2 electrolysis is an emerging technology for the sustainable production of fuels and chemicals. Its transition from laboratory-scale research to real-world application is strongly driven by both regulatory and strategic means, aimed at achieving net-zero greenhouse gas emissions. To meet this goal, accelerated progress in CO2 electrolysis research and technological development is essential to ensure economic viability. This requires clear performance targets, reference materials, and standardized testing protocols that serve as a basis for reliable performance comparison within the CO2 electrolysis community. To address this need, a Round Robin experiment was conducted involving well-established R&D entities in the field of CO2 electrolysis. The objective was to identify and mitigate the main sources of experimental variability, thereby enhancing reproducibility. We found that especially the modes of temperature measurements and cell/anolyte heating alongside pressure fluctuations and overpressures during product analysis are considerable differences among labs, while adjustments to the initial electrochemical protocol helped in minimizing voltage spikes in changing operation. As a result of multiple measurement campaigns and in-depth discussions among participants, a recommendation for a standardized testing protocol and test setup requirements for CO2 electrolyzers are provided. ... Read more

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. ... Read more

Electrochemical CO2 reduction offers a promising method of converting renewable electrical energy into valuable hydrocarbon compounds vital to hard-to-abate sectors. Significant progress has been made on the lab scale, but scale-up demonstrations remain limited. Because of the low energy efficiency of CO2 reduction, we suspect that significant thermal gradients may develop in industrially relevant dimensions. We describe here a model prediction for non-isothermal behavior beyond the typical 1D models to illustrate the severity of heating at larger scales. We develop a 2D model for two membrane electrode assembly (MEA) CO2 electrolyzers; a liquid anolyte fed MEA (exchange MEA) and a fully gas fed configuration (full MEA). Our results indicate that full MEA configurations exhibit very poor electrochemical performance at moderately larger scales due to non-isothermal effects. Heating results in severe membrane dehydration, which induces large Ohmic losses in the membrane, resulting in a sharp decline in the current density along the flow direction. In contrast, the anolyte employed in the exchange MEA configuration is effective in preventing large thermal gradients. Membrane dehydration is not a problem for the exchange MEA configuration, leading to a nearly constant current density over the entire length of the modeled domain, and indicating that exchange MEA configurations are well suited for scale-up. Our results additionally indicate that a balance between faster kinetics, higher ionic conductivity, smaller pH gradients and lower CO2 solubility causes an optimum operating temperature between 60 and 70 °C. ... Read more