Formic Acid as a Hydrogen Carrier for Fuel Cells Toward a Sustainable Energy System

Formic acid is considered as one of the promising organic liquid hydrogen carriers for the next generation; it can offer a viable method for safe hydrogen transport. In this chapter, we introduce the potential of formic acid in terms of thermodynamics and mechanism as described in earlier work in this area, as well as homogeneous catalysts providing a viable method for the production of molecular hydrogen as a sustainable fuel source through dehydrogenation. In addition, pentamethylcyclopentadienyl irid- ium (CpIr) catalysts are also focused upon for this reaction and shown as a strategy to improve catalyst activity by introducing hydroxyl groups to increase turnover num- bers. One of the major advantages of using formic acid as a hydrogen source is the regeneration of formic acid through the interaction with carbon dioxide, thus maintaining a continuous cycle, and offers a possibility for high energy output appli- cations. The developed catalyst, CpIr has potential to produce hydrogen gas with very high pressure, 120 MPa, without facing the problem of decomposition. The gen- erated gas pressure is sufficient for feeding a fuel cell vehicle, which requires 75 MPa, according to the present standard of a hydrogen gas station. Furthermore, even though the generated gas consists of hydrogen and carbon dioxide with the ratio of 1:1, hydrogen can be separated easily and purified from the generated gas under supercritical conditions, by simply cooling to change the gas–liquid state of the sys- tem while maintaining the pressure. Finally, we introduce some applications of this gas generation system in fuel cells, and also for the production of electric power. It is worth mentioning that commercialization of the developed process for hydrogen generation via transformation of formic acid may be achievable in the near future.