Electrochemistry is the study of reactions taking place at the interface of a solid conductor and an electrolyte. Using sensor examples, we introduce some of the most important concepts in electrochemistry, i.e., the EDL, potentiometry, voltammetry, two-and three-electrode systems, Marcus theory of electron transfer, reaction rate-and diffusion ratecontrolled electrochemical reactions, and ultramicroelectrodes (UMEs). We also learn how different materials, such as metals, semiconductors, solid electrolytes, and mixed conductors, exposed to a solution offer the possibility for building different types of electrochemical sensors. Besides insights in electrochemical sensor construction, this section prepares the reader for an appreciation of the role of electrochemistry in the manufacture of microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS), i.e., in electrochemical machining as covered in
Volume II, Chapter 4 (electrochemical etching, a subtractive technique) and Volume II, Chapter 8 (electrochemical deposition, a forming technique). We conclude the electrochemistry section with more electrochemical sensor examples, including ion-sensitive field-effect transistors (ISFETs), potentiometric and amperometric immunosensors, and glucose sensors.