Modelling of solid oxide steam electrolyser: Impact of the operating conditions on hydrogen production

A 2D multi-physic in-house-model has been developed to analyse the performances of Solid Oxide Electrolysis Cell (SOEC) stack. This model encompasses a combined electrochemical and thermal description of the electrolyser. An analytical solution for multi-species diffusion across the porous cathode has been implemented in the model. This numerical tool is useful to provide all the important parameters of the stack operation: distribution of temperature, heat fluxes, local current densities, gas concentrations and overpotentials.Simulations show that thermal equilibrium of the stack is strongly dependant on radiative heat losses, whereas convective heat transfers are limited. In the exothermic operation mode, the cell warming depends on the radiation efficiency.A parametric study has been carried out to analyse SOEC irreversible losses. It is found that the anode activation overpotential is significant, whereas the polarisation due to the cathode activation remains much more limited. Anode concentration overpotentials are found to be insignificant whatever the operating condition. Cathode concentration overpotentials are found to be moderate in the case of Electrolyte Supported Cell (ESC), while they can increase drastically with current density in the case of Cathode Supported Cell (CSC). Addition of diluent gases into the H2, H2O mixture is found to increase the concentration overpotentials.