Numerical Simulation of Solid Oxide Fuel Cells Comparing Different Electrochemical Kinetics

Solid oxide fuel cells (SOFCs) produce electricity with high electrical efficiency and fuel flexibility without pollution, for example, CO₂, NO_x, SO_x, and particles. Still, numerous issues hindered the large‐scale commercialization of fuel cell at a large scale, such as fuel storage, mechanical failure, catalytic degradation, electrode poisoning from fuel and air, for example, lifetime in relation to cost. Computational fluid dynamics (CFD) couples various physical fields, which is vital to reduce the redundant workload required for SOFC development. Modeling of SOFCs includes the coupling of charge transfer, electrochemical reactions, fluid flow, energy transport, and species transport. The Butler‐Volmer equation is frequently used to describe the coupling of electrochemical reactions with current density. The most frequently used is the activation‐ and diffusion‐controlled Butler‐Volmer equation. Three different electrode reaction models are examined in the study, which is named case 1, case 2, and case 3, respectively. Case 1 is activation controlled while cases 2 and 3 are diffusion‐controlled which take the concentration of redox species into account. It is shown that case 1 gives the highest reaction rate, followed by case 2 and case 3. Case 3 gives the lowest reaction rate and thus has a much lower current density and temperature. The change of activation overpotential does not follow the change of current density and temperature at the interface of the anode and electrolyte and interface of cathode and electrolyte, which demonstrates the non‐linearity of the model. This study provides a reference to build electrochemical models of SOFCs and gives a deep understanding of the involved electrochemistry.