A 3D model for the free-breathing direct methanol fuel cell: Methanol crossover aspects and validations with current distribution measurements

A three-dimensional model has been developed for the free-breathing direct methanol fuel cell (DMFC) assuming steady-state isothermal and single-phase conditions. Especially the MeOH crossover phenomenon is investigated and the model validations are done using previous cathodic current distribution measurements. A free convection of air is modelled in the cathode channels and diffusion and convection of liquid (anode) and gaseous species (cathode) in the porous transport layers. The MeOH flow in the membrane is described with diffusion and protonic drag. The parameter ψ in the model describes the MeOH oxidation rate at the cathode and it is fitted according to the measured current distributions. The model describes the behaviour of the free-breathing DMFC, when different operating parameters such as cell temperature, MeOH concentration and flow rate are varied in a wide range. The model also predicts the existence of the experimentally observed electrolytic domains, i.e. local regions of negative current densities. Altogether, the developed model is in reasonable agreement with both the measured current distributions and polarization curves. The spatial information gained of mass transfer phenomena inside the DMFC is valuable for the optimization of the DMFC operating parameters.