Abstract
AbstractElectrochemical capacitors (best known as supercapacitors) are high‐performance energy storage devices featuring higher capacity than conventional capacitors and higher power densities than batteries, and are among the key enabling technologies of the clean energy future. This review focuses on performance enhancement of carbon‐based supercapacitors by doping other elements (heteroatoms) into the nanostructured carbon electrodes. The nanocarbon materials currently exist in all dimensionalities (from 0D quantum dots to 3D bulk materials) and show good stability and other properties in diverse electrode architectures. However, relatively low energy density and high manufacturing cost impede widespread commercial applications of nanocarbon‐based supercapacitors. Heteroatom doping into the carbon matrix is one of the most promising and versatile ways to enhance the device performance, yet the mechanisms of the doping effects still remain poorly understood. Here the effects of heteroatom doping by boron, nitrogen, sulfur, phosphorus, fluorine, chlorine, silicon, and functionalizing with oxygen on the elemental composition, structure, property, and performance relationships of nanocarbon electrodes are critically examined. The limitations of doping approaches are further discussed and guidelines for reporting the performance of heteroatom doped nanocarbon electrode‐based electrochemical capacitors are proposed. The current challenges and promising future directions for clean energy applications are discussed as well.
Highlights
This review focuses on performance enhancement of carbon-based supercapacitors by doping other elements
It can be seen that the areal capacitance of B-doped Reduced graphene oxide (rGO) microsupercapacitors starts to decrease after a certain level of B-precursor loading during the growth process.[113]
Noting the enhanced gravimetric capacitance of 315.2 F g−1 at 0.42 A g−1 in 6 m KOH (3E), it is important to summarize that P-doping in graphene structures leads to i) distortion of graphene wrinkles due to longer P C bond than C C bond which results in the higher surface area, increased inter-layer spacing of graphene oxide (GO) (≈3.63 Å compared to pristine GO of 3.55 Å), ii) improved electrical conductivity, and iii) induced topological defects.[176]
Summary
While research in the area of doped nanocarbon based supercapacitors has been very intense in the last few decades, only a limited number of reviews with specific focal points are available.[43,44,45,46] There are several aspects that require more exhaustive coverage and in-depth discussion, especially of the underlying mechanisms One such area is the structure–property–performance relation versus the suitable electrolytes. This review aims to fill the gap in standardization of evaluation of performance of supercapacitors utilizing nanocarbon-based electrodes by providing the guiding principles which we believe should be followed to consistently report research on supercapacitor performance based on heteroatom-doped electrodes This effort may potentially lead to standardization of nanocarbon doping well beyond the existing energy storage applications. We hope that the present review will serve as a one-stop reference on heteroatom doping of carbon nanomaterials for next-generation clean energy applications and will be of interest to the broad advanced energy materials research community
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