Doped carbon xerogels as electrodes in solid-state asymmetric supercapacitors

Energy storage is one of the main current challenges to widespread the use of renewable energies, and improve hybrid electric vehicles and portable and smart devicessmart portable electronics. Among the different electrochemical energy storage devices, supercapacitors have attracted significant attention due to their high- power density, fast charge/discharge rate, and long cycle life. However, approaches to improve the energy density of supercapacitors are still required. One interesting strategy to address this issue is the assembly of asymmetric supercapacitors (ASC), which involve the use of two different electrode materials. ASC can enlarge the operating voltage window during the charge/discharge processes due to the non-identical potential changes in the two electrodes. In this scenario, studies have been carried out on different materials with pseudocapacitive and capacitive properties, being manganese oxide and carbon nanostructures an excellent combination of electrode materials for ASC. Manganese oxide has pseudocapacitive charge storage mechanismproperties, a large diffusion in nature, and is environmentally friendly and not costly. Its use as positive electrode significantly improves the capacitance and energy density of ASC. On the other hand, carbon nanostructures with high surface area are known to be excellent as negative electrodes. However, in addition to high surface area, it is also necessary to have a suitable pore size and high electrical conductivity. In this sense, carbon gels are presented as very promising materials as their porous and chemical properties can be easily modulated by modifying the synthesis process.