Electrolyte migration through electrochemical membranes: Potential source of error in batch electrochemical cells

Electrochemical membranes (ECMs) and porous electrodes have gained much attention in a broad range of applications including water and wastewater treatment, energy production and storage, and carbon dioxide capture. Lab scale batch experiments (electrochemical stirred cells) are the baseline for developing ECMs and porous electrodes. We observed electrochemical dissolution of metal fasteners (alligator clips), used to hold porous conductive and non-conductive membranes in batch electrochemical cells, despite being kept outside the electrolyte. The electrolyte migrated through the porous membranes by the action of capillary forces, forming a closed electrochemical circuit with the metal fasteners. This unexpected leaching can lead to misleading results for electrochemical experiments on porous electrodes and ECMs. In this study, we compared (1) porous membranes versus non-porous electrodes, (2) hydrophilic versus hydrophobic membranes, and (3) conductive versus non-conductive membranes in their ability to cause capillary wetting-induced corrosion of metal fasteners. We proposed a simple solution for the problem: separating the metal fasteners from the porous membrane electrode with a non-porous conductive graphite foil, which keeps the electrochemical circuit open. We have validated this solution and propose it as a standard method for experiments using porous electrodes and electrically conductive membranes.