Electrolysis of water vapor at high temperature and pressure is a very studied process with the aim to use pure hydrogen as combustible and the remanent heat of nuclear station for an electrolytic process which would be more performing and economical than the classical electrolysis.
This complex modeling implies the coupling of different equations:
- Heat conservation in reactors (conduction, convection, Joule effect, thermo-chemistry) ;
- Reaction kinetics at the level of triple points (generalized equation of Butler Volmer);
- Transport equations of Brinkman, transport of species in the fluid : Dusty Gas Model;
- Transport of charged species in conductors: Ohm law;
- Reality of gases through compressibility coefficients.
The resulted model, developed using Comsol Multiphysics, enable to establish how some given operating conditions may have a significant influence of the electrolyzer performance. Indeed, we have assessed the importance of oxygen retro-diffusion and thus the polarization of concentration if the vapor flow at the cathode level is too low (Peclet number lower than 1), the reaction rate profile inside the anodic cermet in function of some parameters like the relative metal/perovskite conductivity and temperature profiles in function of the feed gas velocity.
Temperature profile inside the membrane electrolyser in function of the velocity of the feed gas. (adapted from M. Dumortier, J. Sanchez, M. Keddam, O. Lacroix. Int. J. Hydrogen Energ., 2013, 38, 2610-2623.)