Development of high-performance zero-gap carbon dioxide electrolysis cells using a hydrophilic porous membrane

A hydrophilic porous membrane is adopted as the diaphragm in zero-gap CO₂ electrolysis cells in order to improve their efficiency and durability. The hydrophilic porous membrane is sparse and nonpolar, which are features opposite to those seen in the anion-exchange membranes commonly used as the diaphragm in CO₂ electrolysis cells. These characteristics result in high ion permeability, which contributes to decreased power consumption. A cell with an active area of 16 cm² achieves high Faradaic efficiency of 90% at a current density of 1000 mA/cm² and a lower cell voltage compared with anion-exchange membranes. Optimization of the operating temperature achieves maximal energy efficiency of around 50% at 200 mA/cm² under neutral electrolyte conditions. Excellent chemical stability of the porous membrane is demonstrated through experiments in a simulated practical environment and under long-term operation with application of a variable power source and introduction of impurity gases. The cells using the membrane was operated for an unprecedented 1000 h in a 400 mA/cm² durability test. Furthermore, a CO₂ electrolysis cell scaled up to a 10 × 100 cm² cell stack is demonstrated as a step toward the development of an industrial-scale CO₂ electrolysis cell. These results suggest that the hydrophilic porous membrane is a promising diaphragm option for the practical application of CO₂ electrolyzers.