Metal Hydride Fuel Cells (MHFC)

Metal Hydride Fuel Cells are a subclass of alkaline fuel cells that work much like nickel metal hydride (NiMH) batteries. These fuel cells are currently in the research phase, with no commercial applications. Metal hydrides are also used for hydrogen storage purposes due to the fact that they absorb hydrogen.

Function and Reactions of MHFCs

MHFCs rely on hydrogen and oxygen to function. Oxygen is used to create/replenish the hydroxide ions of the electrolyte, which are converted into water and electrons in the presence of hydrogen.

Benefits of MHFCs

One of the interesting benefits of MHFCs is that hydrogen can be stored within the cell itself, absorbed in the metal hydride components. Like a sponge and water, metal hydrides are capable of absorbing and hold hydrogen, which is released slowly as the concentration of hydrogen in the surrounding environment drops. Absorption rates are approximately 2%, which allows these cells to run for a short period of time without an external hydrogen source. This allows for “hot swapping,” which means the fuel cell does not have to be shut down in order to exchange fuel tanks.

Metal hydride fuel cells also have the advantage of lower operating temperatures. They can function at temperatures as low as -20 C, which means there is no extended startup time. Combined with the “hot swapping” capabilities, MHFCs are able to overcome many of the latency dilemmas of other fuel cells.

Drawbacks of MHFCs

The two major drawbacks of MHFCs are their propensity for carbon monoxide poisoning and their relatively low efficiencies. These drawbacks have prevented MHFCs from being used outside of laboratory settings. They simply are not reliable enough for commercial application and their maintenance costs are far too high.