Raghunathan Rengasamy

The limited availability of conventional energy carriers has increased the demand for renewable energy sources to cater to the ever increasing energy demand. The present chapter focusses on phosphoric acid fuel cells (PAFCs) detailing their working principles and application potential. The different materials used in PAFCs, including electrolyte, catalysts and bipolar plates and their importance in the ultimate performance are summarized. The degradation behavior due to acid leaching which affect several components of the cell is outlined. Researchers’ contributions towards early identification of degradation of catalyst and catalyst support in particular due to the presence of excess quantity of phosphoric acid, is also described. The importance of having anticorrosive coatings on bipolar plates is outlined in view of achieving life enhancement of the cell operation. Significant work has been carried out in PAFC modeling (1D–3D, steady state and dynamic models) and these are reviewed. The important design considerations during scale-up such as gasket selection and its arrangement, planarity of electrodes, fabrication method of membrane electrode assemblies (MEAs), thermal stress management etc. are described in detail. The chapter outlines various applications explored from power ratings of 20–500kW and also future requirements to be addressed in material as well as engineering issues.

An overview of the phosphoric acid fuel cell (PAFC) technology is provided in this chapter. The various components that are part of PAFC stack and the working principles behind the PAFC are described in detail. The various fuels that can be used are discussed. Efficiency and performance considerations are important for any energy conversion technology. Achievable power densities and system efficiencies when using PAFC technology are outlined. The lifetime of fuel cell stacks is a critical factor in fuel cell commercialization. While PAFC stacks have demonstrated large lifetimes (greater than 40,000h), there are still several challenges that need to be addressed before such reliability becomes routinely achievable. Various performance loss mechanisms are described in detail. The state-of-the-art in modeling of PAFC systems is explored, in brief. The advantages and disadvantages of PAFCs when compared with other fuel cell technology are described at appropriate locations. The chapter concludes with a discussion on the future prospects for the PAFC technology.

Interfacial contact resistance in fuel cells is one of the primary challenges that needs to be overcome in the commercialization of fuel cells. This paper summarizes the governing parameters of the resistance such as surface morphology, contact pressure at the interface, electrical conductivities and corrosion resistance of gas diffusion layer and bipolar plate. Also, researchers’ contributions in modifying the cell components and clamping techniques are discussed in detail. Gas diffusion layer is found to be a crucial factor to control the contact resistance and hence its modification techniques are discussed. Moreover, surface of bipolar plate is prone to oxidation in acidic environment of the fuel cell. Different materials, anticorrosive coatings as well as surface modification techniques for the bipolar plate are therefore discussed in detail. Effect of clamping pressure on distribution of contact pressure is highlighted and various clamping techniques suggested by researchers are summarized. Effect of gasket selection on contact pressure distribution is considerable and therefore included in the paper. The review would be helpful for researchers in understanding the importance, reasons of existence and factors influencing the contact resistance at the interface of gas diffusion layer and bipolar plate.