Electrochemical capacitors, also called supercapacitors, store energy using either ion adsorption (electrochemical double layer capacitors) or fast surface redox reactions (pseudo-capacitors). They can complement or replace batteries in electrical energy storage and harvesting applications, when high power delivery or uptake is needed. A notable improvement in performance has been achieved through recent advances in understanding charge storage mechanisms and the development of advanced nanostructured materials. The discovery that ion desolvation occurs in pores smaller than the solvated ions has led to higher capacitance for electrochemical double layer capacitors using carbon electrodes with subnanometre pores, and opened the door to designing high-energy density devices using a variety of electrolytes. Combination of pseudo-capacitive nanomaterials, including oxides, nitrides and polymers, with the latest generation of nanostructured lithium electrodes has brought the energy density of electrochemical capacitors closer to that of batteries. The use of carbon nanotubes has further advanced micro-electrochemical capacitors, enabling flexible and adaptable devices to be made. Mathematical modelling and simulation will be the key to success in designing tomorrow's high-energy and high-power devices.

https://hal.archives-ouvertes.fr/hal-02417326/document

Materials for electrochemical capacitors

[Liu, Chang; Li, Feng; Ma, Lai-Peng; Cheng, Hui-Ming] Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China.;Cheng, HM (reprint author), Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, 72 Wenhua Rd, Shenyang 110016, Peoples R China;cheng@imr.ac.cn

Advanced Materials for Energy Storage

Conducting-polymer-based supercapacitor devices and electrodes

Recent progress in syntheses of porous carbons with designed pore architecture has rejuvenated the field of carbon chemistry and promises to provide new advanced materials. In order to reap the full benefit of designer carbons, it is necessary to develop chemistries for functionalizing the porous carbon surfaces. This Review examines methods of functionalizing porous carbon through direct incorporation of heteroatoms in the carbon synthesis, surface oxidation and activation, halogenation, sulfonation, grafting, attachment of nanoparticles and surface coating with polymers. Methods of characterizing the functionalized carbon materials and applications that benefit from functionalized nanoporous carbons with designed architecture are also highlighted.

Functionalization of Porous Carbon Materials with Designed Pore Architecture

The design and fabrication of three-dimensional multifunctional architectures from the appropriate nanoscale building blocks, including the strategic use of void space and deliberate disorder as design components, permits a re-examination of devices that produce or store energy as discussed in this critical review. The appropriate electronic, ionic, and electrochemical requirements for such devices may now be assembled into nanoarchitectures on the bench-top through the synthesis of low density, ultraporous nanoarchitectures that meld high surface area for heterogeneous reactions with a continuous, porous network for rapid molecular flux. Such nanoarchitectures amplify the nature of electrified interfaces and challenge the standard ways in which electrochemically active materials are both understood and used for energy storage. An architectural viewpoint provides a powerful metaphor to guide chemists and materials scientists in the design of energy-storing nanoarchitectures that depart from the hegemony of periodicity and order with the promise—and demonstration—of even higher performance (265 references).

Multifunctional 3D nanoarchitectures for energy storage and conversion.

Polyaniline was electrochemically synthesized on carbon polyacrylonitrile aerogel electrodes for use as active material in supercapacitor devices. Electrochemical characterization was performed by cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and charge–discharge experiments in aqueous medium. Two types of electrochemical phenomenon were observed; the first is based on electrostatic energy storage in the double layer at the interface solution/carbon polyacrylonitrile (PAN) aerogel, the other is associated with the redox processes in polyaniline, for which the faradaic charge depends on the potential range. The performance of the supercapacitor was tested for capacity, energy and power density and self-discharge. Specific capacitance as high as 230 F g−1 was reached. A symmetrical supercapacitor showed good cyclability (over 3000 cycles) during repeated charge–discharge cycles. The results are very promising and demonstrate the viability of a symmetric supercapacitor based on carbon PAN aerogel covered by an electronically conducting polymer.

H. Talbi

Papers

Electropolymerization of aniline on carbonized polyacrylonitrile aerogel electrodes: applications for supercapacitors