Chapter 2 - Principles of operation

Abstract

This chapter provides an overview of the operating principles, with brief discussions on (1) thermodynamic aspects of cell operation, (2) key features of the fuel cell, (3) types of fuel and oxidant, and (4) other elements of a fuel cell power system. A solid oxide fuel cell (SOFC) is a ceramic device that converts the chemical energy of a fuel gas and an oxidant gas directly to electrical energy without combustion as an intermediate step. The operating principles of a SOFC and other types of fuel cells are similar to those of a battery—that is, electrochemical combination of reactants to generate electricity. Currently, the most common fuel and oxidant for use in SOFCs are hydrogen and oxygen (electrochemically active). Thus, for SOFCs having an oxygen-ion-conducting electrolyte, the reactions in the fuel cell involve the oxidation and reduction of oxygen at the electrodes. Similarly, for SOFCs having a proton-conducting electrolyte, the reactions involve the oxidation and reduction of hydrogen. However, direct conversion of fuel energy to electricity is the key characteristic of fuel cell operation. In a conventional thermal power system, the chemical energy of the fuel is transformed first to thermal energy, then to mechanical energy, and finally to electrical energy. Other energy systems such as magnetohydrodynamic (MHD) generators and thermionic converters involve the conversion of chemical energy to thermal energy and then to electricity.