The insights into ionomer-catalyst interactions enabling high-efficiency CO2 electroreduction in pure water

With the development of renewable energy, electrochemical carbon dioxide reduction reaction (CO 2 RR) has become a potential solution for achieving carbon neutrality. However, until now, due to issues with salt precipitate and regeneration of the electrolyte, this technology faces challenges such as difficulty in maintaining long-term stable operation and excessive costs. The pure water CO 2 electrolyzers are believed to be the ultimate solution to eliminate the salt depreciation and electrolyte issues. This study develops an in-situ method tailored for CO 2 reduction in pure water. By employing distribution of relaxation times (DRT) analysis and in-situ electrochemical active surface area (ECSA) measurements, we carried out a comprehensive investigation into the mass transport and electrochemical active surface area of gas diffusion electrodes (GDE) under pure water conditions. The maximum 89% CO selectivity and high selectivity (>80%) in the range of 0–300 mA/cm 2 were achieved using commercial Ag nanoparticles by rational design of catalyst layer. We found that ionomers influence the CO 2 electrolyzers performance via affecting local pH, GDE-membrane interface, and CO 2 transport, while catalyst loading mainly influences the active area and CO 2 transport. This work provides benchmark and insights for future pure water CO 2 electrolyzers development.