Metal-Free Carbon-Based Supercapacitors—A Comprehensive Review

Abstract

Herein, metal-free heteroatom doped carbon-based materials are being reviewed for supercapacitor and energy applications. Most of these low-cost materials considered are also derived from renewable resources. Various forms of carbon that have been employed for supercapacitor applications are described in detail, and advantages as well as disadvantages of each form are presented. Different methodologies that are being used to develop these materials are also discussed. To increase the specific capacitance, carbon-based materials are often doped with different elements. The role of doping elements on the performance of supercapacitors has been critically reviewed. It has been demonstrated that a higher content of doping elements significantly improves the supercapacitor behavior of carbon compounds. In order to attain a high percentage of elemental doping, precursors with variable ratios as well as simple modifications in the syntheses scheme have been employed. Significance of carbon-based materials doped with one and more than one heteroatom have also been presented. In addition to doping elements, other factors which play a key role in enhancing the specific capacitance values such as surface area, morphology, pore size electrolyte, and presence of functional groups on the surface of carbon-based supercapacitor materials have also been summarized.

Recent Advancements in the Synthesis and Application of Carbon-Based Catalysts in the ORR

“…Presently, carbon materials have become of great interest to many researchers and have been used in different applications, one of which is as electrocatalysts for the ORR [22,23]. Carbon is naturally abundant and can be obtained from different sources including biomass, naturally occurring materials, and chemically synthesized starting materials.…”

“…Many renewable carbon sources have also been known to contain various heteroatoms, such as nitrogen (N), phosphorus (P), and sulfur (S), which can play a vital role in electrocatalytic activity of their resultant activated carbons. Additionally, their syntheses can be performed economically and with no harsh chemicals [16,22,24]. Current research works have focused on developing next generation fuel cells by producing ORR catalysts from naturally abundant materials and waste which are less expensive compared to metal-based catalysts [16,25,26].…”

A Review of Electrospun Carbon Nanofiber-Based Negative Electrode Materials for Supercapacitors

“…Compared to carbon-based materials, metal-based negative electrode materials have been reported to show superior capacitance values. The major concerns of metal-based materials are the phase changes that occur due to the redox activity during long-term use and their low conductivity, notably limiting their uses [33][34][35]. Thus far, only carbon materials have been used in commercial electrical supercapacitor devices due to their excellent stability under various conditions, such as pH and temperature.…”

A Review of Electrospun Carbon Nanofiber-Based Negative Electrode Materials for Supercapacitors

“…Compared to carbon-based materials, metal-based negative electrode materials have been reported to show superior capacitance values. The major concerns of metal-based materials are the phase changes that occur due to the redox activity during long-term use and their low conductivity, notably limiting their uses [32][33][34]. Thus far, only carbon materials have been used in commercial electrical supercapacitor devices due to their excellent stability under various conditions, such as pH and temperature.…”