Mesopore- and Macropore-Dominant Nitrogen-Doped Hierarchically Porous Carbons for High-Energy and Ultrafast Supercapacitors in Non-Aqueous Electrolytes

Sustainability, performance, and production perspectives of waste-derived functional carbon nanomaterials towards a sustainable environment: A review

The survival of humanity is severely threatened by the massive accumulation of waste in the ecosystem. One plausible solution for the management and upcycling of waste is conversing waste at the molecular level and deriving carbon-based nanomaterial. The field of carbon nanomaterials with distinctive properties, such as exceptionally large surface areas, good thermal and chemical stability, and improved propagation of charge carriers, remains a significant area of research. The study demonstrates recent developments in high-value carbon-based photocatalysts synthesis from various waste precursors, including zoonotic, phytogenic, polyolefinic, electronic, and biomedical, highlighting the progression as photocatalysts and adsorbents for wastewater treatment and water splitting applications. This review highpoints the benefits of using waste as a precursor to support sustainability and circular economy and the risks associated with their use. Finally, we support that a sustainable society will eventually be realized by exploring present obstacles and potential steps for creating superior carbon-based nanomaterials in the future.

Tuning pyridinic-N and graphitic-N doping with 4,4'-bipyridine in honeycomb-like porous carbon and distinct electrochemical roles in aqueous and ionic liquid gel electrolytes for symmetric supercapacitors

Doping engineering in nanostructured carbon materials is an effective approach to modify heteroatom species and surface electronic structures. Herein, an advanced electrode material based on a honeycomb-like porous carbon matrix with tunable N-doped configurations is prepared via 4,4'-bipyridine (4,4'-bpy)-assisted pyrolysis of SiO₂@ZIF-8 templates and subsequent etching treatment. Interestingly, the amounts of pyridinic-N and graphitic-N can be controlled by rationally varying the content of 4,4'-bpy which acts as the N source in the pyrolysis process. Both experimental results and density functional theory calculations have revealed that synergistically with 3D interconnected porous architecture, pyridinic-N and graphitic-N have different effects on the electrochemical performances in aqueous and ionic liquid gel electrolytes for symmetric supercapacitors. Highly exposed pyridinic-N endows the carbon electrode with a strengthened pseudocapacitance contribution manifested as a high specific capacitance of 436.1 F g^-1 and exceptional stability of almost 100% capacitance retention after 5000 cycles at 10 A g^-1 in the KOH/polyvinyl alcohol (PVA) electrolyte. By contrast, graphitic-N is propitious for reinforced electrical double-layer capacitance contribution, reflected by a maximum energy density of 125.4 Wh kg^-1 in the 1-ethyl-3-methylimidazolium tetrafluoroborate/poly(vinylidene fluoride-co-hexafluoropropylene) (EMIMBF₄/PVDF-HFP) electrolyte. This work offers an in-depth insight into the understanding of the energy storage mechanism of N-rich carbon electrodes in different electrolyte media.

Ultrathin Polypyrrole Layers Boosting MoO3 as Both Cathode and Anode Materials for a 2.0 V High-Voltage Aqueous Supercapacitor

An aqueous supercapacitor is an emerging energy storage unit on account of its low cost, fast energy delivery rate, and long service life. The energy density of an aqueous supercapacitor can be enlarged via extending the voltage window of electrode materials, while the aqueous electrolyte remains thermodynamically constant at 1.23 V. Herein, an aqueous supercapacitor with a 2.0 V high-voltage window is realized by core-shell MoO_3-x/polypyrrole (MP) nanocomposites as both cathode and anode materials. The ultrathin PPy layer on the MoO₃ core not only improves the conductivity and cycle stability of the nanocomposites but also acts as a reductant, leading to the formation of oxygen vacancies in the MoO₃ core. When used as a cathode material, the potential range of the as-obtained MP nanocomposite is up to 1.0 V. As an anode material, the stable potential range could reach -1.0 V. Due to the large potential range of the cathode and anode, the as-obtained 2.0 V aqueous supercapacitor shows a remarkably high delivery energy of 58.5 Wh kg^-1. The synthesis of MP nanocomposites is simple and the electrode performance is significantly enhanced; thus, it is a suitable candidate for high-energy-density aqueous supercapacitors.

Ultrafast Nonvolatile Ionic Liquids-Based Supercapacitors with Al Foam-Enhanced Carbon Electrode

The ultrafast frequency response supercapacitor is a promising candidate for alternating current line filtering. We report the fabrication of a special structured ionic liquid-based supercapacitor with an ultrafast response of only 1.5 ms. The three-dimensional aluminum (Al) foam in situ coated with carbon layer (∼500 nm) serves as the novel, highly efficient electrode-current collector. The high porosity (95%) of Al foam allows the rapid ion diffusion and the as-obtained Al/C interface with atomic-level mixing allows the fast electron transfer, two crucial factors for ultrafast response. Hence, it possesses an excellent specific mass capacitance of 68 mF g^-1 at 120 Hz, as well as an ultrahigh rate of up to 3000 V s ^-1. The supercapacitors exhibit frequency modulation performance in the range of 20 kHz to 16 MHz. They exhibit the similar even better alternating current filtering performance, as compared to the commercial aluminum electrolytic capacitors, detected at 10 Hz, 60 Hz, 100 Hz and 1 M Hz. These results suggest that, although ILs have high viscosity and low ion mobility, the IL-based supercapacitor has a great potential to be used as a device for alternating current line filtering, as well as providing nonvolatile and nonflammability safety.

3D hierarchical porous carbon matching ionic liquid with ultrahigh specific surface area and appropriate porous distribution for supercapacitors

Supercapacitors, as one of the most promising energy storage devices, have high power density but low energy density. An appropriate collocation of porous carbon electrodes and ionic liquid electrolytes can improve notably the performance of supercapacitors. Herein, we report a pre-assembly strategy to prepare three-dimensional (3D) hierarchical porous carbons (HPCs) as the electrode materials for supercapacitors. Three long-chain hydrophilic polymers polyacrylamide (PAM)/gelatin/F127 in water form 3D frameworks by pre-assembly and further form a hydrogel. Then the hydrogel is freeze-dried, carbonized, and etched to form 3D hierarchical porous carbons. The effects of pore volume, pore size, and ratio of mesopores to micropores on the performance of ionic liquid-based supercapacitors are investigated. The porous structure of the prepared HPCs can well match EMIMBF₄. Therefore, HPCs as electrode materials for supercapacitors exhibit an excellent specific capacity of 216.5 F g^-1 at 1 A g^-1, and the as-assembled symmetric supercapacitor delivers a superior energy density of 108.6 W h kg^-1 at a power density of 961.1 W kg^-1. Meanwhile, the symmetric supercapacitor maintains 84.4% of its initial capacitance after 10 000 cycles at 3 A g^-1. This work provides a guide for developing new porous carbon materials for supercapacitors with a high energy density.

Wood-Derived Carbon Materials and Light-Emitting Materials

Wood is a sustainable and renewable material that naturally has a hierarchical structure. Cellulose, hemicellulose, and lignin are the three main components of wood. The unique physical and chemical properties of wood and its derivatives endow them with great potential as resources to fabricate advanced materials for use in bioengineering, flexible electronics, and clean energy. Nevertheless, comprehensive information on wood-derived carbon and light-emitting materials is scarce, although much excellent progress has been made in this area. Here, the unique characteristics of wood-derived carbon and light-emitting materials are summarized, with regard to the fabrication principles, properties, applications, challenges, and future prospects of wood-derived carbon and light-emitting materials, with the aim of deepening the understanding and inspiring new ideas in the area of advanced wood-based materials.

Activated biochar derived from peanut shells as the electrode materials with excellent performance in Zinc-air battery and supercapacitance

The use of activated biochar-based electrode derived from waste biomass in energy technologies, such as metal-air batteries and supercapacitors, is an important strategy for realizing energy and environmental sustainability in the future. Herein, peanut shells (waste biomass) were employed to prepare activated biochar materials by pyrolysis in molten KCl and heat-treatment. The effective dispersion and corrosion effects of molten salt for the pyrolysis products during pyrolysis obviously increase defects and specific surface area of the activated biochar materials. The prepared activated biochar material (PS-800-1000) by pyrolysis in molten KCl at 800 °C and heat-treatment at 1000 °C exhibits excellent catalytic activity with half-wave potential of 0.84 V vs. RHE, comparable to commercial Pt/C for oxygen reduction reaction (ORR) in 0.1 M KOH and outstanding supercapacitance performance in 6 M KOH with high specific capacitance (355 F g^-1 at 0.5 A g^-1), which exceeds all reported biochar derived from peanut shells. The PS-800-1000-based zinc-air battery (ZAB) displays higher peak power density (141 mW cm^-2), specific capacity (767 mAh g_Zn^-1) and cycling stability than Pt/C-based ZAB. The activated biochar prepared by pyrolysis in molten KCl and heat-treatment method from peanut shells can be a promising candidate for replacing precious metals in energy conversion/storage devices.

High-performance electrochemical sensing platform based on sodium alginate-derived 3D hierarchically porous carbon for simultaneous determination of dihydroxybenzene isomers

Three-dimensional hierarchically porous carbon (denoted as SA-900) with a microporous, mesoporous and macroporous structure was facilely fabricated via direct carbonization of sodium alginate. SA-900 was fully characterized by N₂ adsorption-desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction and Raman spectroscopy to confirm its structure. SA-900 was coated onto a glassy carbon electrode surface to construct an ultrasensitive electrochemical sensing platform (SA-900/GCE). Electrochemical behaviors of hydroquinone (HQ), catechol (CC) and resorcinol (RC) on the SA-900/GCE surface were investigated, and it was found that SA-900 possesses excellent electrocatalytic activity towards them. Experimental conditions including carbonization temperature, pH value, SA-900 concentration, accumulation potential and accumulation time were optimized for quantitative assay. Under optimized conditions, linear ranges for simultaneous determination of HQ, CC and RC are 0.05-1.50 μM, 0.05-1.50 μM and 0.50-15.00 μM, respectively. Detection limits for HQ, CC and RC are calculated to be 0.0183 μM, 0.0303 μM and 0.3193 μM (S/N = 3). The SA-900/GCE based electrochemical sensing platform is applied for determining HQ, CC and RC in lake water samples with satisfactory results.

Dictyophora-derived N-doped porous carbon microspheres for high-performance supercapacitors

PCMS-T hierarchical porous structures were prepared from biomass dictyophora as electrodes for high-performance supercapacitors.

Sonochemical assisted fabrication of 3D hierarchical porous carbon for high-performance symmetric supercapacitor

A scalable fabrication of 3D hierarchical porous carbon structure (3D-HPC) has been achieved via a simple sonochemical route at different pyrolysis temperatures. It is worth noting that all the 3D-HPC samples possess oxygen-functional groups after activation by KOH and self-doped by nitrogen, which are beneficial to improving their surface wettability as well as increasing the electro-active surface area between the electrode and the surrounding electrolyte, consequently enhancing their electrochemical performance. Remarkably, the resulting carbon sample pyrolyzed at 850 °C (AC-850) possesses a maximum doping level of 2.75 at% and a high surface area of 1376.19 m² g^-1, which exhibits high electrochemical performance with high capacitance up to 269.19 F g^-1 at a current density of 2 A g^-1. Moreover remarkably, the AC-850-based symmetric supercapacitor delivers a high energy density of 21.4 Wh kg^-1 at a power density of 531.2 W kg^-1 with excellent rate performance and superior cycling stability (94.7% retention over 5000 cycles). The present approach is very suitable for large scale production of high-quality porous carbon materials at low cost, which can be used in different aspects, such as energy storage, gas storage, environmental remediation, and so on.

Atomistic Insights into the Layered Microstructure and Time-Dependent Stability of [BMIM][PF6] Confined within the Meso-Slit of Carbon

Clarifying the microstructures and time-dependent stability of ionic liquids (ILs) within the confinement of the meso-slit of carbon is the first step to understand the intrinsic synergy effect between ILs and a promising mesoporous carbon electrode. In this work, we adopted molecular dynamics to systematically investigate the behavior of [BMIM][PF₆] in the 2.8 nm-wide meso-slit of carbon. The confined ILs formed a pronounced layered spatial distribution and can be divided into three distinct regions, namely, com-, sub-, and cen-layer, according to valley coordinates in the number density profiles. In the com-layer region, the imidazolium rings of ILs possess two dominant orientations, namely, "parallel" and "tilted standing". The rotation ability of all the ions is highly restrained. In the sub-layer and cen-layer regions, a part of the [BMIM] imidazolium ring has a preferred "tilted standing" orientation. The [BMIM] cations are still in a rotational restrain state and show a preferred rotation motion along the x-y plane. The hydrogen bond between [BMIM] cations and [PF₆] anions play a crucial role in determining the confined multilayered spatial distribution and distinctive orientation properties of ILs.

Facile and Scalable Fabrication of Nitrogen-Doped Porous Carbon Nanosheets for Capacitive Energy Storage with Ultrahigh Energy Density

Porous carbon materials are the most commonly used electrode materials for supercapacitors because of their abundant structures, excellent conductivities, and chemical stability. However, the manufacture of carbon materials possessing sizable pores and remarkable wettability with the electrolyte remains challenging. Herein, we developed a facile and industrially scalable method for the production of nitrogen-doped porous carbon nanosheets (PNDC-4) with excellent pore size distribution, large specific surface area (>1200 m² g^-1), high conductivity (>700 S m^-1), and superb wettability either in aqueous or organic electrolyte. Particularly, PNDC-4 shows a high capacitance of 387 F g^-1 (1 A g^-1) in a three-electrode system with 3 M KOH and 80 F g^-1 (1 A g^-1) in a symmetric two-electrode system with EMIMBF₄. The device exhibits an ultrahigh energy density of 81 W h kg^-1 at a power density of 1.3 kW kg^-1 and can still maintain at 60.8 W h kg^-1 when the power density is increased to 266.6 kW kg^-1. Moreover, the devices show superb stability that 94% of its initial capacitance is still maintained after 100 000 cycles at 20 A g^-1.

Fabrication of nitrogen-rich three-dimensional porous carbon composites with nanosheets and hollow spheres for efficient supercapacitors

N-Rich 3D porous carbon composites with nanosheets and hollow spheres have been fabricated for efficient supercapacitors.

Confining Redox Electrolytes in Functionalized Porous Carbon with Improved Energy Density for Supercapacitors

It is a big challenge to improve the energy density of the carbon-based supercapacitors for wide applications. In this work, considering the properties of redox electrolytes, functionalized porous carbon has been synthesized with interconnected pores and oxygen functional groups, which is employed to well hold the redox electrolyte ions. As a result, the functionalized porous carbon shows a high capacitance of 454 F g^-1 at a current density of 1 A g^-1 and can maintain 88% of the initial capacitance after 10 000 charge-discharge cycles at 10 A g^-1. Especially, the as-prepared asymmetric supercapacitor obtains high energy density of 36.9 W h kg^-1 at the power density of 225 W kg^-1. This new design strategy by coordinating carbon materials with the redox electrolytes will guide the development of high-energy density supercapacitors.

Hierarchical Nanostructures of Nitrogen-Doped Porous Carbon Polyhedrons Confined in Carbon Nanosheets for High-Performance Supercapacitors

Interconnected close-packed nitrogen-doped porous carbon polyhedrons (NCPs) confined in two-dimensional carbon nanosheets (CNSs) have been prepared through a sustainable one-pot pyrolysis of a simple solid mixture of zeolitic imidazolate framework-8 (ZIF-8) crystals and with organic potassium as the precursors. The hierarchically organized framework of the NCP-CNS composites enables NCPs and CNSs to act as well-defined electrolyte reservoirs and mechanical buffers accommodating large volume expansions of NCPs, respectively. Among the unique composite nanostructures, the NCPs with vast micropores provide electric double-layer capacitances, while the CNSs bridge the individual NCPs to form a conductive pathway with a hierarchical porosity. As a result, the NCP-CNS composites with high electrical integrity and structural stability are used as electrode materials for high-performance supercapacitors, which exhibit excellent electrochemical capacitive characteristics in terms of an outstanding capacitance of 300 F g^-1 at 1 A g^-1, large energy density of 20.9 W h kg^-1, and great cycling performance of 100% retention after 6000 cycles. This work therefore presents a one-pot and efficient strategy to prepare an ordered arrangement of ZIF-8-derived porous carbons toward new electrode materials in promising energy storage systems.