An Insight into Water and Temperature Management in Unitised Regenerative Fuel Cell (URFC) during Mode Change

Although water-related issues are no stranger to conventional fuel cells, unitised regenerative fuel cells (URFC) sustain amplified effects from this condition due to their transition states. Fuel cell (FC) mode start-ups post water electrolyser (WE) operations suffer significantly due to flooding. Past studies validated the significance of water and heat distribution towards the dynamic response of URFC. Due to complications involved in the numerical study of mode change conditions, this paper suggests the basic procedures required for numerical analysis of the WE to FC mode conversion in a URFC where the final result of each mode is taken as the initial result for the next one. Water removal through gas purging is currently one of the best methods to reduce transient time and increase FC start-up efficiency. However, crucial purging conditions such as operating current density, temperature and purging period play an important role in the successful transition. Lower operating current density, ranging below 0.02A/cm2 is reported to have a smoother transition compared to current density above 0.12A/cm2. Gas purge relative humidity is only effective up to 4% at the anode and poses no effect during a severe flooding condition. Furthermore, the temperature has the lowest response towards the cell heat source, increasing the transient period. The cell experiences high WE mode efficiency at 80˚C, but it suffers significant catalytic loss. The insight will provide a more profound comprehension of water management during WE mode and a suitable administrative method to achieve smooth FC start-ups.