Chapter 19 - MOFs-carbon nanocomposites for supercapacitors

Abstract

With the ever-increasing consumption of nonrenewable resources (e.g., coal, oil, natural gas), the associated environmental pollution is getting serious and the global energy demand increased dramatically. Thus, developing efficient, environmentally-friendly, and sustainable technologies for energy storage and conversion are urgently desired. Considerable efforts have been devoted to explore varieties of renewable energy sources, such as solar, wind, hydroelectricity, and biomass, as well as advanced energy storage technologies including water electrolysis, batteries (Li-ion batteries, Li–S batteries, Li–O2 batteries, and sodium-ion batteries), and supercapacitors. Among the currently available energy storage and conversion systems, supercapacitors have received tremendous attention due to the high power density, fast charge/discharge kinetics, and long cycle life. The energy charge storage mechanisms for supercapacitors can be divided into three categories: (1) electrical double-layer capacitors are mainly based on carbon materials, which store electrical energy at the electrode–electrolyte interface by means of electrostatic forces; (2) pseudocapacitors are usually based on metal oxides, metal nitrides/carbides, and conductive polymers, which store charge through the fast and reversible surface redox reaction; and (3) hybrid supercapacitors are composed of a battery-type and a capacitive material as positive and negative electrode, which possess both high energy and power density in one electrochemical cell. The electrochemical performance of supercapacitors is greatly affected by the electrode, which is closely related to the surface area, porosity, size, as well as the crystallinity of the electroactive species. Therefore, rational design and carefully selected efficient electrode materials are the key strategy to achieve high-performance supercapacitors.