9 - Regenerative fuel cells

Abstract

This chapter provides an overview of Regenerative Fuel Cells (RFCs). A RFC is a single device or system capable of functioning either as an electrolyzer or a fuel cell. RFCs come in two basic types: Discrete Regenerative Fuel Cells ((DRFCs) and Unitized Regenerative Fuel Cells (URFCs). In a DRFC, the device used to perform the electrolysis is separate to that used as a fuel cell but these two devices are both integrated into a single system. A URFC is likewise a single device that can work in either Electrolyzer mode (E-mode) or Fuel Cell mode (FC-mode). The vast majority of URFCs built to date have employed a Proton Exchange Membrane (PEM) as a solid electrolyte. Falling between the URFC and DRFC concepts is a regenerative fuel cell in which a fuel cell stack is joined directly to an electrolyzer stack; therefore, the two stacks are in line and form a single unit although separate cells are still used in E- and FC-modes. This arrangement allows efficient exchange of gases, water and sometimes also heat between the two stacks. Some have called this design a URFC too, but it does not have the defining URFC characteristic of having just one cell or stack of cells working reversibly to provide the E and FC-mode functions. On account of PEM URFCs being the subject of more widespread study and use, the chapter focuses on these URFCs.