Abstract
In recent years great effort has been taken to understand the effect of gas transport on the performance of electrochemical devices. This study aims to characterize the diffusion regimes and the possible inaccuracies of the mass transport calculation in Solid Oxide Fuel Cell (SOFC) anodes when a volume-averaged pore diameter is used. 3D pore size distribution is measured based on the extracted pore phase from an X-ray CT scan, which is further used for the calculation of a Knudsen number (Kn) map in the porous medium, followed by the voxel-based distribution of the effective diffusion coefficients for different fuel gases. Diffusion fluxes in a binary gas mixture using the lower boundary, upper boundary and average effective coefficients are compared, and the impact on overpotential is analyzed. The results show that pore diameters from tens to hundreds of nanometers result in a broad range of Knudsen number (1.1 ∼ 4.8 and 0.6 ∼ 3 for H2 and CH4 respectively), indicative of the transitional diffusion regime. The results highlight that for a porous material, such as an SOFC anode where Knudsen effects are non-negligible, using a volume-averaged pore size can overestimate the mass flux by ±200% compared to the actual value. The characteristic pore size should be chosen sensibly in order to improve the reliability of the mass transport and electrochemical performance evaluation.
Highlights
Concentration polarization is caused by the consumption of the fuel gas resulting in a reduction of concentration at the anode/electrolyte interface
Molecular diffusion refers to the relative motion and collisions between different gas species; Knudsen diffusion covers the effect of collisions between gas molecules and the walls of the porous medium, and viscous flow is associated with the bulk flow of the gas stream due to a pressure gradient
Mass transport in solid oxide fuel cell (SOFC) anodes is critical in determining the reaction rate and electrochemical performance
Summary
Concentration polarization is caused by the consumption of the fuel gas resulting in a reduction of concentration at the anode/electrolyte interface. This study aims to characterize the diffusion regimes in an SOFC anode for different fuel gases using the X-ray nano-CT technique, followed by the quantitative evaluation of the mass transport phenomenon in a binary gas mixture based on a broad distribution of the voxel-basis effective diffusion coefficients. These will provide with insights in the effect of mean pore diameter on the diffusive mass flux and overpotential calculation.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
