Modeling of Shunt Current in Liquid Electrolyte Fuel Cells

Abstract

A general electrolyte model for calculation of the liquid electrolyte transport in fuel cells is presented. A 2-D formulation is used to describe the transport in an alkaline fuel cell. Numerical results were obtained by using commercial CFD software, in conjunction with the user defined functions that calculate the source terms of the transport equations. An order of magnitude analysis is conducted of the energy transport in the separator and electrode regions. The numerical calculation also examines the local primary current at the anode and cathode electrodes. The calculated current flux showed a higher value near the separator entrance and it decreased along the stream-wise direction. The non-uniformity of the local primary current is caused mainly by the species transport resistance between the electrodes instead of the temperature difference. The effects of four different electrolytes were also studied. The results suggested that the cell voltage differences were due to the competing effects of electrolyte conductance and species diffusion. Numerical calculation also captured the presence of shunt current. A net shunt current as high as 0.1 A/cm2 is calculated at the separator inlet and exit. Provisions to reduce shunt currents seem to be warranted for AFC operated at a condition similar to that examined in this paper.