Improving round-trip energy efficiency of a unitized regenerative fuel cell by adopting staircase flow channel and counter flow configuration

Abstract

The flow field design is an effective measure to improve hydrothermal management within a fuel cell. This paper proposes a staircase flow channel used in the oxygen-side flow channel of a unitized regenerative fuel cell. Based on a two-dimensional two-phase non-isothermal model, the hydrothermal distribution variation induced by staircase channels with different step numbers is investigated in detail. Results show that oxygen transport is boosted and liquid water accumulation is reduced in the fuel cell mode with the use of staircase structures, thus local oxygen starvation under high current density is alleviated. In addition, the temperature uniformity of electrodes is effectively improved, and the fuel cell net power is enhanced by up to 14.24% at 0.2 V with a five-step flow channel. In electrolytic cell mode, however, the advantage of downward staircase structures is not prominent. Therefore, a counter-flow method is suggested during the mode switching stage, which can improve average current density by up to 10.83%. Besides, round-trip energy efficiency is introduced to evaluate the comprehensive performance. The staircase flow channel coupled with counter-flow method improves the efficiency of unitized regenerative fuel cell by up to 49.63% under high current density, compared with conventional flow channels with co-flow configuration.