A decarbonized society is essential to maintain and further improve the standard of living for humankind. However, the chemical industry still requires carbon-based fuels as a resource, hindering decarbonization [1]. One carbon-neutral technology to produce base chemicals is electrochemical carbon dioxide electrolysis (CO₂E), powered by renewable electricity. CO₂E targets multiple base chemicals, ranging from carbon monoxide (CO) and ethylene (C₂H₄) [2].

CO₂E is well established at lab-scale, normally utilizing gas-fed membrane electrode assembly (MEA) cells. However, lab-scale MEA CO₂ electrolysers are suffering from limited runtimes far below industry requirements of >10.000 h [3]. De facto, most CO₂ MEA cells lose their carbon product selectivity within a couple of hours of operation under industry-relevant conditions.

Extensive flooding and salt formation are the main bottlenecks for the operation runtime in the current state of the art, often occurring at the same time or briefly after each other [4]. Both limit the access of CO₂ at the cathodic catalyst layer and impede the cell's selectivity [5]. While salt mitigation strategies are more understood [6,7], a deeper understanding of flooding and the underlying water management within the MEA cell and especially at the cathodic reaction environment, where the CO₂ reduction takes place, is still absent. Hence, in this work, we present model-aided experimental work, investigating the dominant water transport mechanism and its effect on product selectivity to extend the system's lifetime.

To do so, experiments in an AEM-based MEA cell using sputtered Ag as the cathode-side catalyst partnered with an oxygen-evolving IrO₂ catalyst at the anode are executed to reduce CO₂ to CO. We perform a model-guided sensitivity analysis for industry-relevant conditions under current density up to 500 mA cm^-2 in a temperature corridor from 25°C to 65°C, using CsHCO₃ as anolyte varying from 0.01 M to 0.5 M to understand the impact of the different water transport mechanisms. Our data, combined with the model predictions, indicate that diffusive water drag driven by ion gradients across the membrane is the dominating mechanism for water transport to the cathode. Based on the above operation conditions regarding membrane thickness, anolyte concentration, current density and temperature, are determined to flatten ion profiles and mitigate flooding. That way, stable selectivity under current density of up to 500 mA cm^-2  for the investigated timeframe of 24h is achieved. Using the above findings, we hope to contribute to the mitigation of water management-related and underlying ion management-related bottlenecks for CO₂E on the pathway to industrial application.