Mass transfer and cell performance of a unitized regenerative fuel cell with nonuniform depth channel in oxygen-side flow field

In this study, the cell performance of nonuniform depth and conventional straight channel in a unitized regenerative fuel cell (URFC) is compared. Various shapes of oxygen-side channel cases are also proposed. Several parameters, such as the distribution of reactants and products and current density and powers in fuel cell (FC) and electrolytic cell (EC) modes, are investigated. A steady-state model of two-dimensional, two-phase, nonisothermal, and coupled electrochemical reaction is developed. Five oxygen-side channel shapes are also designed, in which the depth along the flow direction is narrowed. Result shows that narrowing the average channel depth can promote and guide the reactant transfer to the catalyst layer and avoid the blocking of the production. Thus, in comparison with the conventional channel, the cell performances of nonuniform depth and shallow straight channel cases are improved in both modes. In addition, with the decrease of average channel depth, the temperature uniformity gets better, which is also conductive to the improvement of cell performance. Furthermore, in FC mode at low voltage and EC mode, the cell net power basically increases with the decrease of the average channel depth ratio. And when the average channel depth is the same, the net power of straight channel is always lower than nonuniform depth case. This study introduces the round-trip energy efficiency as an evaluation indicator of URFC. This efficiency can be increased by improving the cell performance of both modes, especially at high current density.