Porous carbon materials: Design, synthesis and applications in energy storage and conversion devices

Abstract

The dramatic environmental pollution and energy shortages have spurred internationally unprecedented interest in developing new energy technologies. Supercapacitors have emerged as a new class of green electrochemical devices for energy conversion and storage and are promising candidates for extensive applications. As a key component of supercapacitors, electrode materials are a crucial factor to the electrochemical performance based on its properties including surface area, pore structure, conductivity and surface functionalization. The well-designed synthesis strategies and conditions are usually fatal to tailor four mentioned properties. Due to the advantages of low cost, high specific surface area and conductivity, controllable microstructure, easy surface functionalization, remarkable chemical stability and outstanding electrolyte ion accessibility, porous carbon materials tailored through well-designed synthesis strategies and conditions, exhibit high energy density and power density as well as superb electrochemical cycling stability. In this review, we firstly provide a brief description of energy storage mechanisms for different types of electrode materials, followed by a comprehensive overview of recent advances in development of different carbon-based materials with activated carbon, carbon aerogels, carbon fiber, mesoporous carbon, carbon nanotube and graphene. Then we state the key parameters to evaluate the electrochemical properties, such as specific capacitance, energy density and power density, and also discuss the relationship between the influence parameters (e.g. surface area, pore structure, conductivity, and surface properties) and enhanced performances. Further, according to the research work of our group, we present a summary on the design, synthesis and applications in energy conversion and storage based on porous carbon materials, including carbons with different pore distributions (hierarchical porous carbon, porous carbon sphere, ultramicroporous carbon), functionalized porous carbon and porous carbon composite materials. In terms of carbons with different pore distributions, we list some characteristic synthetic methods (e.g. the self-template strategy for banana-peel-derived hierarchical porous carbon foams, the seeded synthetic strategy for phenolic-resin-derived porous carbon nanospheres and the solvothermal method for phloroglucinol-terephthaldehyde-derived ultramicroporous carbon nanoparticles), which can be concluded that micropores (especially ultramicropores) are electrochemically available for electrolyte ions because the solvation shell is squeezed through the pores less than the solvated ion size and such distortion reduces distance between the electrode surface and the ion center, while mesopores offer highly efficient pore channels for ion penetration and transport. In terms of functionalized porous carbon, we adopt the in situ synthesis approach to prepare nitrogen-doped carbons ( e.g. poly(1, 5-diaminonapthalene)-derived nitrogen-containing carbon microspheres and phenylenediamine-terephthalaldehyde-derived nitrogen-functionalized microporous carbon nanoparticles), which demonstrate that heteroatom doping, on the one hand, increases the surface wettability in the aqueous electrolyte to improve the mass transfer efficiency, and on the other hand, endows additional psedocapacitance for the electrode. In terms of porous carbon composite materials, we combine carbon-based materials with pseudocapacitive metal oxides (e.g. NiO and MnO2) for achieving high-performance supercapacitors, which is a wise choice to increase the energy density without sacrificing the high power capability. These strategies and methods provide new ideas to simple and highly efficient design of porous carbon materials and may be extendable to other systems such as metal or metal oxide materials. Additionally, the future trend of carbon based electrode materials for energy conversion and storage device is discussed. There are extensive applications outside the area of high-rate electrochemical energy storage, such as drug delivery, photonic crystals, adsorption and separation, and catalysis.