Introduction to Electrochemical Energy Storage

This chapter introduces two electrochemical energy storage technologies: Redox Flow Batteries (RFBs) and Electrolyzers (ELs) combined with Fuel Cells (FCs) in ELFC Energy Storage Systems (ESSs). These devices are quite different in their working principles, since RFBs are rechargeable batteries, namely real energy storage devices, whereas FCs and ELs are energy converters which must be coupled and provided with hydrogen storage capacity to form energy storage systems. However, both technologies have similar architectures because they use fluid reactants which must be flown from external tanks into the energy converter to produce the redox reactions. For this reason, they can be sized independently in power and energy, thus achieving a design flexibility unavailable in other electrochemical devices. In addition, their reactors present similar designs, consisting of stacks of several cells assembled one next to the other and provided with manifolds and channels to distribute fluids. Different types of RFBs, ELs and FCs exist, some at an advanced technological readiness level and others still at an early stage of research and developments. The major different types are presented in this chapter, outlining their differences and similarities, as well as their pros and cons, thus constituting an introduction to the following chapters forming the Section on the Electrochemical Storage of this Encyclopedia.