Charge-Transfer Percolation Modeling of Randomly Distributed Vanadium Oxides Films on Electrically Conductive Plates for Fuel Cell Applications

Abstract

A heterogeneous charge transfer percolation model has been developed to simulate electrical resistance variation of vanadium oxides films on electrically conductive plates for fuel cell application particularly under subzero temperature operating condition. To materialize a disordered system of vanadium oxides, the model incorporated two types of vanadium oxides, vanadium pentoxide and vanadium dioxide by the implementation of the fractional distribution of granular grains. In the first section, the sample was generated by the random distribution in square lattice sites under given fraction of vanadium oxides consist of vanadium pentoxide and vanadium dioxide that work as temperature sensitive resistive materials and the void that implies the electrical resistance infinitely high. The following section, internal current distribution and electrical potential field were calculated based on the charge conservation and Ohm`s law as governing equations by implementing the finite difference approximation at each node. Computational result indicates that the vanadium oxides system exhibits typical negative temperature coefficients as the fraction of vanadium pentoxide increases while the onset of metal-semiconductor transition of vanadium oxides is suppressed by the dilute distribution of vanadium dioxide. Accordingly, the model is applicable to conventional fuel cell transport model for the analysis of subzero temperature operations by implementing joule heating effects in more generalized case that accounts for spatial distribution of heterogeneous resistive material.