Abstract
Abstract At present it is indispensable to develop and implement new/state-of-the-art carbon nanomaterials as electrodes in electrochemical capacitors, since conventional activated carbon based supercapacitor cells cannot fulfil the growing demand of high energy and power densities of electronic devices of the present era, as a result of the rapid developments in this field. Functionalized carbon nanomaterials symbolize the type of materials with huge potential for their use in energy related applications in general and as an electrode active material for electrochemical capacitors in particular. Nitrogen doping of carbons has shown promising results in the field of energy storage in electrochemical capacitors, gaining attention of researchers to evaluate the performance of new heteroatoms functionalised materials such as sulphur, phosphorus and boron lately. Literature is widely available on nitrogen doped materials research for energy storage applications; however, there has been a limited number of review works on other functional materials beyond nitrogen. This review article thus aims to provide important insights and an up-to-date analysis of the most recent developments, the directions of future research, and the techniques used for the synthesis of these functional materials. A critical review of the electrochemical performance including specific capacitance and energy/power densities is made, when these single doped or co-doped active materials are used as electrodes in electrochemical capacitors.
Highlights
Energy landscape is expected to go through significant transformation attributed to the crisis instigated by the imbalance in world’s energy supply and demand
These nitrogen doped carbons produced through variety of synthesis techniques are widely used for electrical energy storage in supercapacitors since N-doping results in superior performance of the electrochemical capacitor cell where specific capacitance of nitrogen doped active material is the sum of both electric double layer capacitance (EDLC) due to the physical phenomenon occurring at the electrode/electrolyte interface and the pseudo capacitance (PC) due to the fast and fully revisable Faradic reaction coupled with electronic transfer owing to the electron donor properties of nitrogen [50] as represented by Equation 4 and 5
Even though nitrogen doped carbon materials have been investigated extensively for their application as electrodes in electrochemical capacitors, it is evident from this review that there is a class of functional materials which includes sulphur, phosphorus and boron beyond the nitrogen, possessing physio/chemical properties suitable for superior cell output
Summary
Energy landscape is expected to go through significant transformation attributed to the crisis instigated by the imbalance in world’s energy supply and demand. 5kWkg-1) [2], rapid charge discharge (millisecond), excellent cycle-ability ( > half a million cycles) [3] and high charge retention ( > 90% capacitive retention) [4]. Electrochemical capacitors (ECs) known as supercapacitors or ultra-capacitors (UCs) are high power electrical energy storage devices retaining inimitable properties such as exceptionally high power densities Depending on their charge storage mechanism, ECs can be classified into two categories; electric double layer capacitors (EDLCs) and pseudocapacitors (PCs). Figure 2:- Schematic diagram of A) an electric double layer capacitor [EDLC] B) a pseudocapacitor [PC] [6]
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