High pressure H-type electrochemical cell enabling gas collection: application to CO₂ electrolysis

A high pressure H-type electrochemical cell was developed to enable collection and quantitative analysis of gaseous and liquid electrolysis products. Owing to the use of transparent chambers, the volume of evolved gas can be estimated. The cell includes septum-sealed sampling ports on cathodic and anodic chambers, allowing direct gas and liquid sampling using syringes after depressurizing to ambient pressure. This setup enables quantitative evaluation of overall product distribution under pressure, providing a comprehensive view of pressure-dependent reaction selectivity. As a demonstration, CO2 electrolysis was performed under hydrostatic pressures of up to 50 MPa, during which key CO2 reduction products (CO, CH4, and C2H4) and H2 from the hydrogen evolution reaction were detected. These results demonstrate that the cell can operate reliably at pressures up to 50 MPa while providing quantitative access to evolved products, indicating its suitability for mechanistic studies of electrochemical reactions involving both gaseous and dissolved products.