Product Crossflow through a Porous Gas Diffusion Layer in a CO2 Electrochemical Cell with Pressure Drop Calculations

CO2 electroreduction flow cells with three compartments (CO2, catholyte, and anolyte) are promising as scalable and viable systems for industrial applications. CO2 and catholyte are separated by a porous gas diffusion layer (GDL), allowing enhanced CO2 diffusion to the catalyst. While CO2 diffusion is an expected phenomenon in the electroreduction cell, a pressure difference between both sides of the GDL can lead to unfavorable CO2-to-catholyte or catholyte-to-CO2 crossflows. These two crossflows are detrimental to the electrochemical performance by decreasing the diffusion mass transfer while damaging the cell. The particular geometry and feed conditions of a cell stack can induce pressure variations along the fluid path, leading to these undesirable crossflows. Using a commercial GDL with no microporous layer for the present numerical study, we found that the amplitude of the pressure difference between both sides must be lower than 5 kPa to prevent these unfavorable crossflows. The effects of CO2 and catholyte mass flow rates, channel size in the CO2 distribution side, and surface area of the cell are evaluated in a single-cell system and in a 50-cell stack, made possible by our mathematical resolution of the Z-manifold systems in a straight parallel channel configuration. Small cells (10 cm2) have a wider range of favorable conditions for enabling crossflows compared to larger cells (0.5 m2). CO2 and catholyte mass flow rates of, respectively, 1.5 × 10–4 and 6.6 × 10–2 kg/s for the 0.5 m2 cell were found to prevent any unfavorable crossflows by limiting the pressure difference within the desirable range.