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The Fuel Cell is a highly efficient device that when integrated with hybrid technology yields even higher system-level efficiencies. This impressive efficiency is one of the key reasons fuel cell technology is one of the most promising future power sources. However, this benefit creates a significant challenge in cold climates. With so much of the energy converted directly to power, there is little waste heat compared to conventional internal combustion engine (ICE) technologies. This challenge is particularly apparent at system start up from ambient sub-freezing temperatures due to the fact that the fuel cell heats-up slower than internal combustion engines (ICEs). Clearly, the amount of heat generation can be increased if the total power produced by the system is increased proportionally, but this method can be challenging because the excess power must be consumed in some manner (such as by a cabin heater).

Toyota has been developing fuel cell hybrid vehicles (FCHV) since 1992 and is currently working to resolve issues that remain for commercialization. This research focused on one of the main issues for fuel cells (FC), namely water content of the electrolyte membrane, to develop a FC water content control system based on AC impedance measurement. Adopting this control system in the FCHV resolved the issue of reduced efficiency caused by FC membrane dry-out, and makes it possible to start up the FCHV in temperatures down to -30°C by performing appropriate water content control for freezing environments.