Performance in microfluidic electrochemical cell with gradient or double-layers porous electrode for CO2 diffusion

To obtain better electrical behavior, the linear or double-layers porous electrode is set in microfluidic electro-chemical cell for CO2 diffusion, which couples Tafel's law and Ohm's law with the flow equation and species transport equation for numerical calculations. This research analyzes the effects of linear or double-layer porosity, the thickness of double-layer porosity, and electrode structure in the electrode on current density, CO2 conversion, and Faraday efficiency under different working conditions. The higher current density and CO2 conversion occur in the case with smaller porosity in the electrode due to more reactive sites, and poor gas transport is observed simultaneously. Optimizing linear or double-layers porosity distribution results in higher current density, CO2 conversion, and Faraday efficiency. The Faraday efficiency can reach 91.54% in the case of stepwise increasing porosity from 0.3 to 0.9 in the electrode. Poor electrical behavior occurs as linear increasing porosity compared to stepwise porosity due to different porosity distributions, and the opposite is the case for decreasing linear porosity. Setting the double-layer porosity along the electrode thickness direction results in larger Faraday efficiency as a thickness ratio of 1:1 and larger current density and CO2 conversion as a thickness ratio of 4:1 in the case of porosity from 0.3 to 0.9. Better electrochemical behavior occurs with electrode thickness to length ratio of 10-20 and the CO2 gas channel to electrode thickness ratio of 1:1-4:1, and optimized electrode porosities tend to show higher Faraday efficiencies during electrode structural changes.