Effects of charge rearrangement on interfacial contact resistance of TiO2/graphite from first-principles calculations

Abstract

Titanium bipolar plates have been widely employed in fuel cells, due to the high resistance achieved by the oxide film (TiO2). However, that also results in high interfacial contact resistance between the titanium and the gas diffusion layer of graphite, reducing the cells’ efficiency significantly. To improve the conductivity properties, the effects of thirty-five metallic dopants on the contact resistance and electrical conductivity were studied based on the first-principles merged with the Schottky-Mott theory and Boltzmann transport equation. The results show that the contact resistance depends on the charge distribution induced by graphite. The contact resistance depends on the conductivity when the charge depletion and accumulation layer are distributed in the space-charge region. If the charge rearrangement occurs in the heterojunction as a whole, the contact resistance is determined by the electronic injection. In addition, the single conduction path between titanium, oxygen and graphite atoms disappears in the TiO2 doped with Zn, Cd, etc., because those dopants have stronger electron affinity in the heterojunction. While a stronger built-in electric field is formed that can further enhance the electronic conductivity.