Numerical modeling of a non-flooding hybrid polymer electrolyte fuel cell

Experimental results were recently reported regarding a novel “non-flooding” hybrid fuel cell consisting of proton exchange membrane (PEM) and anion exchange membrane (AEM) half-cells on opposite sides of a water-filled, porous intermediate layer. Product water formed in the porous layer, where it could permeate to the exterior of the cell, rather than at the electrodes. Although electrode flooding was mitigated, the reported power output was low. To investigate the potential for increased power output, a physicochemical charge transport model of the porous electrolyte layer is reported here. Traditional electrochemical modeling was generalized in a novel way to consider both ion transport and reaction in the aqueous phase and electronic conduction in the graphitic scaffold using a unified Poisson–Nernst–Planck framework. Though the model used no arbitrary or fitting parameters, the ionic resistance calculated for the porous layer agreed well with the highly non-Ohmic experimental values previously reported for the entire fuel cell. Interestingly, electronic charge carriers in the scaffold were found to obviate the need for counterion presence in this unique electrolyte structure. Still, the thickness- and temperature-dependent model results offer limited prospects for improving the power output.

► The electrochemistry of a porous layer in a hybrid fuel cell is numerically modeled. ► Traditional Poisson–Nernst–Planck behavior is generalized. ► The porous layer dominates the overall cell resistance. ► The porous layer must conduct electrons/holes to support high ionic conductivity. ► The porous layer's resistance is highly non-Ohmic and increases with temperature.