Scalable Membrane-Free Electrolyzers for Electrochemical CO₂ Conversion

Bicarbonate electrolysis offers an attractive approach to conducting electrochemical carbon dioxide (CO 2 ) conversion within the same working fluid used in commonly considered carbon capture processes. However, conventional membrane-based electrolyzers face significant challenges related to scale-up, durability, and CO 2 utilization. Here, we present a scalable packed bed membraneless electrolyzer (PBME) design for which liquid bicarbonate electrolyte flows sequentially through alternating porous flow-through anodes and cathodes. Within this design, hydrogen oxidation at porous anodes is used to produce protons that trigger in situ CO 2 release immediately upstream of porous cathodes, where electrochemical CO 2 reduction generates the desired product and returns the solution pH back towards its inlet value. By using the sequential flow-cell arrangement, the PBME offers the ability to mitigate large concentration overpotentials and non-uniform current distributions that naturally arise during scale-up of conventional membrane-based electrolyzers that rely on lateral flow of catholyte parallel to the surface of the electrodes. This study uses in situ colorimetric imaging to highlight the ability of PBME to rebalance pH across adjacent electrodes. In addition, results obtained with a multi-cell PBME demonstrate the scalability of this concept and reveal the ability to increase CO 2 utilization from 12.9% for a single-cell PBME up to 20.5% for a four-cell PBME operated under baseline conditions. With operating the PBME at elevated pressure, the performance can be further improved by increasing the concentration of CO 2 in the dissolved phase, which results in higher CO partial current density.