Insights into carbon deposition process in microtubular SOEC for CO2 reduction via dimensionless Multiphysics modeling

• Large scale Multiphysics model is developed for a microtubular SOEC for CO 2 reduction. • The model is nondimensionalized using suitable reference parameters and scales. • Model is validated using experimental data and grid-independent solution is confirmed. • Comprehensive simulations and parametric studies are conducted. • Insights into carbon deposition process are obtained. CO 2 reduction with microtubular solid oxide electrolysis cells (SOECs) is a promising carbon–neutral technology to mitigate the challenge of greenhouse gas emissions. However, carbon deposition creates significant difficulty for the development of stable and durable SOEC technology. A fundamental understanding of the mechanisms is a critical step to address this issue. In this study, a comprehensive nondimensional multiphysics model is developed and employed to systematically investigate the effects of the Bu number, Damköhler number (Da 1 ), polarization voltage, as well as inlet fuel velocity and composition, on the distributions of various species in the electrodes. Results indicate that although both surface CO dissociation (CO(s) + Ni(s) ⇌ C(s) + O(s)) and the Boudouard reaction (2CO(s) ⇌ CO 2 (s) + C(s)) contribute to carbon deposition, the latter is the dominant pathway. The likelihood of carbon deposition increases in zones exhibiting elevated CO molar fractions combined with reduced CO 2 molar fractions, or where CO 2 consumption and CO formation rates are significant. Strategies to effectively mitigate carbon deposition include lowering the CO molar fraction in the inlet fuel, operating at elevated temperatures, increasing the inlet fuel velocity, reducing the outlet pressure, and improving the permeability of fuel electrode.