Hierarchical modeling of solid oxide cells and stacks producing syngas via H₂O/CO₂ Co-electrolysis for industrial applications

A hierarchical multi-physics continuum model is used to investigate syngas (H₂ + CO) production in a solid oxide button cell, single repeating unit and cell stack. A novel cluster algorithm and pseudo-homogenous approach enables a computationally efficient model scale-up from 1-D button cells to 3-D stacks with minimal loss of information across the scales. The model agrees well with polarization, temperature and outlet gas composition measurements made by Fu et al. on single Ni-GDC|YSZ|LSM-YSZ cells [ECS Transactions 35, 2949–2956 (2011)]. After, the model generates 3-D contour plots to map the performance of a single repeating unit of a F-design stack from Forschungszentrum Jülich [Fuel Cells 7, 204–210 (2007)] producing output H₂:CO ratios suitable for Fischer-Tropsch synthesis and hydroformylation. Over the range of conditions studied, the overall efficiency and syngas yield increases with residence time though beyond a threshold value, reactant starvation leads to a decrease in efficiency and a greater propensity for Ni coking. Increasing the operating temperature shifts peak efficiencies to lower voltages and the performance of the repeating unit is nearly identical for the two H₂:CO ratios studied. On scaling up to produce a commercial quantity of syngas, shorter stacks lead to lower capital costs and smaller electrolyzer areas while running at lower velocities has the opposite effect although it minimizes temperature gradients. Stack simulation over a wide range of operating regimes, including pure H₂O and CO₂ electrolysis, divulges the time constants of charge, mass and heat transport.