Hydrogen is a resource that provides energy and forms water only after reacting with oxygen. Because there are no emissions such as greenhouse gases when hydrogen is converted to produce energy, it is considered one of the most important energy resources for addressing the problems of global warming and air pollution. Additionally, hydrogen can be useful for constructing “smart grid” infrastructure because electrical energy from other renewable energy sources can be stored in the form of chemical energy by electrolyzing water, creating hydrogen.
Among the many hydrogen generation systems, solid oxide electrolysis cells (SOECs) have attracted considerable attention as advanced water electrolysis systems because of their high energy conversion efficiency and low use of electrical energy. To find the relationship between operating conditions and the performance of SOECs, research has been conducted both experimentally, using actual SOEC cells, and numerically, using computational fluid dynamics (CFD). In this investigation, we developed a 3-D simulation model to analyze the relationship between the operating conditions and the overall behavior of SOECs due to different contributions to the over-potential.
All SOECs involve the transfer of mass, momentum, species, and energy, and these properties are correlated. Furthermore, all of these properties have a direct influence on the concentration of the gases in the electrodes, the pressure, the temperature and the current density. Therefore, the conservation equations for mass, momentum, species, and energy should be included in the simulation model to calculate all terms in the transfer of mass, heat and fluid. In this simulation model, the transient term was neglected because the steady state was assumed.
All governing equations were calculated using Star-CD (CD Adapco, U.S). The source terms in the governing equations were calculated with in-house code, i.e., user defined functions (UDF), written in FORTRAN 77, and these were linked to the Star-CD solver to calculate the transfer processes. Simulations were performed with various cathode inlet gas compositions, anode inlet gas compositions, cathode thickness, and electrode porosity to identify the main parameters related to performance.