Electrolyte Design Using "Porous Water" for High-purity Carbon Monoxide Electrosynthesis from Dilute Carbon Dioxide.

Electrosynthesis of high-purity carbon monoxide (CO) from captured carbon dioxide (CO2) remains energy-intensive due to the unavoidable CO2 regeneration and post-purification stages. Here, we propose a direct high-purity CO electrosynthesis strategy employing an innovative electrolyte, termed porous electrolyte (PE), based on "porous water". Zeolite nanocrystals within PE provide permanent pores in the liquid phase, enabling physical CO2 adsorption through an intraparticle diffusion model, as demonstrated by molecular dynamics simulations and in situ spectral analysis. Captured CO2 spontaneously desorbs under applied reductive potential, driven by the interfacial CO2 concentration gradient, and is subsequently reduced electrochemically. The high CO2 concentration in PE enhances mass transfer, and surface ion exchange between Si-OH groups and K+ ions on the zeolite surface generates a stronger interfacial electric field, promoting electron transfer steps. This optimized kinetics for mass and electron transfer confers heightened intrinsic activity toward CO2 electroreduction. The PE-based electrolysis system demonstrated superior CO Faradaic efficiency and partial current density compared to the conventional CO2-fed system. A circular system using PE and a Ni-N/C cathode realized continuous production of high-purity CO (97.0 wt %) from dilute CO2 (15 %) and maintained >90.0 wt % under 150 mA cm-2, with significantly reduced energy consumption and costs.