**Abstract**

The demand for engineering and advancement of supercapacitor electrodes are increasing globally. To address the production and storage capacity of the supercapacitor electrodes, the development of new kind of composite materials are highly needful. To design materials with high surface area, excellent conductivity, porosity, and mechanical stability are the main critical points that need to be addressed. Various strategies have been utilized to fabricate excellent composite materials for supercapacitor electrodes. The effect of many composite materials was found to enhance the cyclability and storage capacities of the supercapacitor electrodes. In a class of materials, graphene-based nanocomposites and their derivatives were found to be the most excellent and suitable candidates to design and fabricate supercapacitor electrodes. The alliance of several active materials when analyzed with graphene and its derivatives was found to improve further the performance and stability of supercapacitor electrodes.

**Keywords:** graphene, nanocomposites, supercapacitor, electrodes, metal oxides

### **1. Introduction**

Supercapacitor is an attractive electrochemical device that fulfills the requirement of all advanced electronic and electrical devices [1]. Supercapacitors have gained a lot of attention and have been employed in various fields, including various electronic devices, power supplies, and electric vehicles due to their high-power densities, rapid charge/discharge rates, and exceptional cycling stability [2–5]. Supercapacitors are divided into two categories depending on their charge storage capacity: 1) electrical double-layer capacitors (EDLCs) made of various carbon-based materials, while 2) pseudocapacitors made of transition metal oxides and other conductive polymers as active materials [6–9]. Ions are arranged on the interface of the electrode and electrolytes in EDLC charge storage. In this mechanism, ions adsorb and desorb quickly at the electrolyte-electrode contact, resulting in high power density. Furthermore, no chemical reactions are involved in this charge storage process; simply the transport and adjustment of ions occur during the process [10]. The energy storage of pseudocapacitors, on the other hand, is caused by the fast redox reactions or faradaic mechanisms

of the electrochemically active materials in the electrode [11]. When EDLCs and pseudocapacitors are merged into a single device, a new subcategory known as hybrid capacitors is constructed [12]. The most important components of supercapacitors are the electrode materials that are used in cathodes and anodes [13]. The essential component of a supercapacitor is the electrode material, which directly influences the electrochemical performance [14]. As a result, the development and application of innovative electrode materials are critical for improving supercapacitor performance.

Graphene-based composite electrodes are regarded as one of the most effective electrode materials because of their impressive chemical, mechanical, and physical properties, such as excellent electrical conductivity, electrochemically active surface area, thermal conductivity, good mechanical strength, and optical transmittance [15–20]. Graphene can be combined with different metals to make its composites for supercapacitor electrodes. In this chapter, we mainly focus on different graphenebased composite electrode materials for supercapacitor applications.
