Gas Diffusion Electrode with Microporous Layers of Hydrophobicity Gradient Distribution for CO2 Electrolysis in a Zero-Gap Electrolyzer Operated with Pure Water

A zero-gap electrolyzer operated with pure water is much admired for electrochemical CO2 reduction (CO2RR), which could avoid the solid salt precipitation in the cathode. However, the current density of CO2RR in zero-gap electrolyzers is still much low, generally <100 mA cm–2. Herein, we present a wettability regulation strategy in the gas diffusion layer, in which the microporous layer with a hydrophobicity gradient (HG-MPL) is used to enhance the CO2 and electrolyte management. The HG-MPL provides an effective driving force for the removal of excess aqueous electrolytes, while the relatively hydrophilic sublayer of the MPL adjacent to the catalyst layer (CL) avoids overdrainage to maintain CL hydration. In addition, abundant hydrophobic pores, formed by interwoven particles between MPL sublayers, ensure gaseous CO2 transport. When tested in a zero-gap electrolyzer using pure water as an anolyte, the gas diffusion electrode with an HG-MPL obtains a current density of >200 mA cm–2 at 3.5 V with a Faradaic efficiency for CO of ∼89%, which effectively enhances the performance.