Microenvironment Regulation Strategies Facilitating High-Efficiency CO₂ Electrolysis in a Zero-Gap Bipolar Membrane Electrolyzer

In alkaline and neutral zero-gap CO 2 electrolyzers, the carbon utilization efficiency of the electrocatalytic CO 2 reduction to CO is less than 50% because of inherently homogeneous reactions. Utilization of the bipolar membrane (BPM) electrolyzer can effectively suppress (bi)carbonate formation and parasitic CO 2 losses; however, an excessive concentration of H + in the catalyst layer (CL) significantly hinders the activity and selectivity for CO 2 reduction. Here, we report a microenvironment regulation strategy that controls the CL thickness and ionomer content to regulate local CO 2 transport and the local pH within the CL. We report 80% faradaic efficiency of CO at a current density of 400 mA/cm 2 without the use of a buffering layer, exceeding that of state-of-the-art catalysts with a buffering layer. A carbon utilization efficiency of 63.6% at 400 mA/cm 2 is also obtained. This study demonstrates the significance of regulating the microenvironment of the CL in a BPM system.