Unassisted cold start-up of polymer electrolyte membrane fuel cells: challenges and strategies

A polymer electrolyte membrane fuel cell is an alternative energy conversion device for electric vehicles, aquatic vessels, aircraft and space vehicles. However, at sub-zero temperatures, freezing of electrochemically generated water in the fuel cell stack significantly affects its performance. Water freezes at different locations of the cell components, blocks gas transport and impedes the reactant transport, which eventually shuts down the cell. Furthermore, sub-zero operation causes irreversible performance decay in the thermal cycles. This review presents an extensive discussion on cold start and different strategies applied in the last few years to overcome this challenge. Here, the effect of sub-zero temperature on cell performance is discussed in two broad categories: cold start and performance degradation. Many strategies have been applied to control water freezing and cell component degradation. Here, different technologies used in assisted and unassisted cold start-up modes have been discussed. Discussion is done on unassisted cold start and it is better than the assisted cold start in terms of energy efficiency and system cost. But more theoretical and experimental investigation is required to improve relevant techniques to have a technologically and commercially feasible device for the application in all environmental conditions.