Assessing the impacts of using porosity gradients in solid oxide electrolysis cell: A 3D numerical study

Present day studies on solid oxide electrolysis (SOE) focus on performance improvement of SOE cells, of which, functionally graded materials (FGM) have been evolving. In this study, a 3D numerical model of a solid oxide electrolysis has been first validated against an experimental dataset and two different case studies for porosity gradient: linear and non-linear (inverse hyperbolic tan) profiles have been studied. Microstructure Analysis Toolbox (MATBOX) was used to obtain properties such as pore diameter, tortuosity and particle diameter for the graded structures which were then used in COMSOL. The results from the analysis show that the graded structures improve the cell performance, especially at higher current densities by reducing the overall operating voltage. The improved diffusion inside the electrodes lowered concentration as well as activation overpotential by increasing the electrode utilization for graded cases. At 950C and 3.6 A / c m 2 , the overall voltage was found to reduce from 1.45 V at homogeneous case to 1.41 and 1.43 V for linear and non-linear cases. The major reduction in kinetic overpotential was observed at the cathode–electrolyte interface where lower local current density was observed for the graded cases. Moreover, the effective diffusion coefficient was found to be directly proportional to pore-diameter of electrodes since Knudsen diffusion is a function of pore-diameter. The graded structures were found to perform better under the ribs enhancing diffusion in the cathode. Finally, the steam utilization was also found to be better for graded cases with values as 27.4%, 31.35% and 31.96% for homogeneous, linear and non-linear cases respectively.