Three-dimensional modeling and analysis of polymer electrolyte membrane SO2-depolarized electrolyzer

SO2-depolarized electrolyzers (SDEs) offer a promising alternative to direct water electrolyzers for hydrogen production because of their lower theoretical voltage (0.158 V vs. 1.23 V). However, their underlying working mechanism is still not well understood. In this study, a detailed 3D liquid-fed SDE model with multiphysics was developed for the first time. The model demonstrated excellent consistency when validated against in-house experimental data. Furthermore, the effect of current density, temperature, and electrolyte concentration on the cell performance was investigated. At 100 mA cm- 2, the SO2 concentration in the anode catalyst layer was between 2.926 and 3.532 kmol m- 3. Conversely, at 500 mA cm- 2, the lowest SO2 concentration in the under- land region was 0.559 kmol m- 3, and the concentration difference was 2.448 kmol m-3. The kinetic over- potential at the cathode was only 62.6 mV, which is much lower than that at the anode (508.0 mV) under the same condition. Moreover, the limited diffusivity of the dissolved reactant and ionic product severely affected cell performance, highlighting the significance of mass transfer in SDEs. The SO2-oxidation reaction predominantly occurred in the under-channel region. Furthermore, the produced H2SO4 accumulated on the surface of the diffusion layer and was transported away by convection in the flow direction, rather than diffusing throughout the channel. As the temperature increases, the anodic equilibrium potential increases, while the kinetic overpotential decreases.