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Electrochemical processes have been extensively used for preparing thin films with their unique advantages in scalable production and ability to form films with precise control of thickness and its homogeneity [14]. Based on the principle of electrochemical processes, thin films made of metal, simple metal oxides, or polymerized organic film can be formed using anodization, cathodic electrolytic deposition, electrophoretic deposition, electro‐oxidative polymerization, and combinatory methods. All these mentioned methods are operating based on the manipulation of electrons induced by a simple power supply or potentiostat with various functionalities.

In principle, electrochemical method is a versatile technique because it involves only cost‐effective and basic apparatus setup as shown in Figure 3.1. A simple electrochemical setup consists of two electrodes (i.e. anode and cathode, with an optional separate reference electrode), a power supply or potentiostat, and a single or separated electrolyte medium. In a typical electrochemical process, driven by the applying voltage, electrons flow from anode to cathode through an external circuit. Oxidation–reduction (redox) reactions occur when electrons are withdrawn from anodic site (oxidation happens at anode) to reach the cathodic site to reduce substances (reduction happens at cathode). The potential can be manipulated with respect to the reference electrode in the case of a three‐electrode configuration (as shown in Figure 3.1) or simply across the anode and cathode in a two‐electrode configuration to control the extent or vigor of such redox reactions. As it is essential to have both reduction and oxidation to occur simultaneously to complete the electron‐flow circle, a redox reaction can also be called as two half‐reactions, i.e. one representing the oxidation process and the other reduction reaction, respectively. Basically, the foundation of electrochemical fabrication of thin films lies in the manipulation of such redox reactions at either anode or cathode of electrochemical setup. The techniques can be grouped into anodization (when the substrate of interest undergoes oxidation reaction), cathodic electrodeposition (when the substrate of interest undergoes reduction reaction), and electrophoretic deposition (attractions of oppositely charged particles onto the substrate) [15–17]. Recent developments also see the adoption of combinatory methods integrating electrochemical methods with other chemical or physical ways in preparing complex material thin film with binary, ternary, and multicomponent structures [18]. Sections below will introduce the working principle of anodization, cathodic electrodeposition (sometimes it is called electroplating), electrophoretic deposition, and some examples of combinatory methods. The resultant catalytic films with properties unique to the method will be discussed.

Figure 3.1 Schematic drawing of a general electrochemical setup with basic components used for electrochemical synthesis of nanostructured thin films. In this specific configuration, the cathode (on which the reduction reaction takes place) is the working electrode, with potential applied with respect to the reference electrode. The anode (on which the oxidation reaction takes place) in this case is the counter electrode. (See online version for color figure).