A multi-physics coupling model for proton ceramic electrolysis cell featuring precisely defined electric field boundary conditions at the electrode-electrolyte interface

Proton ceramic electrolysis cell (PCEC) can efficiently convert electrical energy into fuels like hydrogen by utilizing renewable energy at lower temperatures compared to solid oxide electrolysis cell (SOEC). Nonetheless, the advancement of PCEC is currently hindered by their low Faradaic efficiency (FE). The prevailing models for calculating FE are often based on defect flux or lack a clear elucidation. In contrast, we present a method for calculating FE based on the change in gas flow rate between the inlet and outlet. This is achieved by establishing accurate electric field boundary conditions, with particular emphasis on the leakage current at the electrode-electrolyte interface. The accuracy of the electric field boundary conditions is verified by comparing the calculated FE with experiments, showing a maximum relative error of less than 13.1 % at high current densities. The effects of various operating parameters on cell performance, especially on FE, are systematically studied. The results reveal that as the steam molar fraction rises from 0.1 to 0.9, FE experiences a substantial increase from 76.5 % to 95.3 %. It is also found that the FE has an optimal peak relative to the current density due to the influence of temperature, for instance, reaching 78.1 % at 600 degrees C and a current density of -0.8 A cm- 2. In conclusion, a multi-physics model incorporating detailed electric field boundary conditions is established to enable the direct calculation of FE. This advancement not only improves the model's accuracy but also offers valuable guidance for the design and operation of PCEC.