Oxygen-functionalized carbon nanofibers from kulim wood for high- performance supercapacitors via an integrated chemical–physical catalyst approach

Covalent functionalization of carbon nanotubes (CNTs) with oxygen-based or nitrogen-based functional groups is one of the most popular techniques to modify the surface energy and inherent properties of the CNTs.1 This functionalization generates interest for a broad range of applications including mechanically superior advanced composites,2 more sensitive gas sensors,3 enhanced energy storage materials4 or ultra-conductive fibers.5 As an alternative to the harsh chemicals used by traditional chemical functionalization, plasma-based surface treatments can be used with great efficacy and reduced reaction times, providing an array of application-specific benefits.Awareness of the environmental pollution caused by fossil fuels and the ever-increasing demand for energy has driven research focussed on zero-carbon renewable energy sources. Conscious of this, direct absorption solar thermal collectors are gaining prominence, both for domestic heating and steam generation. CNTs have been investigated as an additive to take advantage of the near blackbody absorption and high thermal conductivity to improve system efficiency. Critical to the success of the additive nanoparticles is the stability in the fluid, however, due to their high surface energy CNTs tend to agglomerate which can limit the efficacy of their integration into real-world products.In this work, macroscopic ribbon-like assemblies of carbon nanotubes are functionalized by plasma-induced non-equilibrium electrochemistry (PiNE) implemented through a simple direct current-based plasma-liquid system. This system utilizes the plasma-generated species in an electrolyte of 10 %vol ethanol in water, with or without a nitrogen precursor, for the oxygen and/or nitrogen functionalization of the carbon nanotube assembly. For this treatment, a ribbon-like piece of CNT was used as the anode and a helium plasma discharge triggered by applying 10 mA and 1 - 1.6 kV to act as the cathode. The plasma-generated species are then expected to migrate towards the CNTs and functionalize the sidewalls.The oxygen content is shown to be increased by between 70 % and 300 % when the treatment solution of 10 %vol ethanol is used in the ribbon electrode configuration. When ethylenediamine is added as a nitrogen precursor, the atomic concentration of nitrogen reaches 23 %, with amine groups, pyrrolic groups and graphitic nitrogen observed in the x-ray photoelectron spectra. This nitrogen content is unmatched in quantity when compared to either a simple soaking procedure or an electrolysis process with a platinum foil replacing the plasma as the counter-electrode. This demonstrates that the plasma either directly or indirectly, through plasma-generated species, facilitates and enhances the availability of nitrogen from the ethylenediamine precursor. The potential plasma-induced chemical pathways which lead to the functionalization of the CNTs are also investigated and discussed.In the application of a direct absorption solar collector system, it is found that the covalent functionalization provided by the plasma-liquid system enhances the stability of the CNT-ethylene glycol nanofluid, with the oxygen-functionalized samples producing the most stable nanofluids. This is explained through the lower value for contact angle measurements, suggesting greater hydrophobicity of the CNTs.References(1) Mallakpour, S.; Soltanian, S. Surface Functionalization of Carbon Nanotubes: Fabrication and Applications. RSC Adv. 2016, 6 (111), 109916–109935. https://doi.org/10.1039/c6ra24522f.(2) Williams, J.; Broughton, W.; Koukoulas, T.; Rahatekar, S. S. Plasma Treatment as a Method for Functionalising and Improving Dispersion of Carbon Nanotubes in Epoxy Resins. J. Mater. Sci. 2013, 48 (3), 1005–1013. https://doi.org/10.1007/s10853-012-6830-3.(3) Ham, S. W.; Hong, H. P.; Kim, J. H.; Min, S. J.; Min, N. K. Effect of Oxygen Plasma Treatment on Carbon Nanotube-Based Sensors. J. Nanosci. Nanotechnol. 2014, 14 (11), 8476–8481. https://doi.org/10.1166/jnn.2014.10007.(4) Hulicova-Jurcakova, D.; Seredych, M.; Lu, G. Q.; Bandosz, T. J. Combined Effect of Nitrogen- and Oxygen-Containing Functional Groups of Microporous Activated Carbon on Its Electrochemical Performance in Supercapacitors. Adv. Funct. Mater. 2009, 19 (3), 438–447. https://doi.org/10.1002/adfm.200801236.(5) Li, L.; Liu, E.; Shen, H.; Yang, Y.; Huang, Z.; Xiang, X.; Tian, Y. Charge Storage Performance of Doped Carbons Prepared from Polyaniline for Supercapacitors. J. Solid State Electrochem. 2011, 15 (1), 175–182. https://doi.org/10.1007/s10008-010-1087-8. Figure 1

Awareness of the environmental pollution caused by fossil fuels and the ever-increasing demand for energy has driven research focussed on zero-carbon renewable energy sources. Conscious of this, direct absorption solar thermal collectors are gaining prominence, both for domestic heating and steam generation. Carbon nanotubes (CNTs) have been investigated as an additive to take advantage of the near blackbody absorption and high thermal conductivity to improve system efficiency. Critical to the success of the additive nanoparticles is the stability in the fluid, however, due to their high surface energy CNTs tend to agglomerate which can limit the efficacy of their integration into real-world products. Covalent functionalization of the CNT sidewalls with oxygen-based or nitrogen-based functional groups is one of the most popular techniques to modify the surface energy of the CNTs.1 As an alternative to the harsh chemicals used by traditional chemical functionalisation, plasma-based surface treatments can be used with great efficacy and reduced reaction times.In this work, macroscopic ribbon-like assemblies of carbon nanotubes are functionalized using a simple direct current-based plasma-liquid system. This system utilizes the plasma-generated species in a fluid of 10 %vol ethanol in water, with or without a nitrogen precursor, for the oxygen and/or nitrogen functionalisation of the carbon nanotube assembly. For this treatment, a ribbon-like piece of CNT was used as the anode and a helium plasma discharge triggered by applying 10 mA and 1 - 1.6 kV to act as the cathode. The plasma-generated species are then expected to migrate towards the CNTs and functionalisation the sidewalls.The oxygen content is shown to be increased by between 50 % and 200 % when the treatment solution of 10 %vol ethanol is used in the ribbon electrode configuration. When ethylenediamine is added as a nitrogen precursor, the atomic concentration of nitrogen reaches 23 % in the ribbon electrode configuration, with amine groups, pyrrolic groups and graphitic nitrogen observed in the x-ray photoelectron spectra. This nitrogen content is unmatched in quantity when compared to either a simple soaking procedure or an electrolysis process with a platinum foil replacing the plasma as the counter-electrode. This demonstrates that the plasma either directly or indirectly, by means of plasma-generated species, facilitates and enhances the availability of nitrogen from the ethylenediamine precursor. The potential plasma-induced chemical pathways which lead to the functionalization of the CNTs are also investigated and discussed.In the application of a DASC system, it is found that the covalent functionalisation provided by the plasma-liquid system enhances the stability of the CNT-EG nanofluid, with the oxygen-functionalized samples producing the most stable nanofluids. This functionalization method generates interest for a broader range of applications including mechanically superior advanced composites,2 more sensitive gas sensors,3 enhanced energy storage materials4 or ultra-conductive fibres.5 References (1) Mallakpour, S.; Soltanian, S. Surface Functionalization of Carbon Nanotubes: Fabrication and Applications. RSC Adv. 2016, 6 (111), 109916–109935.(2) Williams, J.; Broughton, W.; Koukoulas, T.; Rahatekar, S. S. Plasma Treatment as a Method for Functionalising and Improving Dispersion of Carbon Nanotubes in Epoxy Resins. J. Mater. Sci. 2013, 48 (3), 1005–1013.(3) Ham, S. W.; Hong, H. P.; Kim, J. H.; Min, S. J.; Min, N. K. Effect of Oxygen Plasma Treatment on Carbon Nanotube-Based Sensors. J. Nanosci. Nanotechnol. 2014, 14 (11), 8476–8481.(4) Hulicova-Jurcakova, D.; Seredych, M.; Lu, G. Q.; Bandosz, T. J. Combined Effect of Nitrogen- and Oxygen-Containing Functional Groups of Microporous Activated Carbon on Its Electrochemical Performance in Supercapacitors. Adv. Funct. Mater. 2009, 19 (3), 438–447.(5) Li, L.; Liu, E.; Shen, H.; Yang, Y.; Huang, Z.; Xiang, X.; Tian, Y. Charge Storage Performance of Doped Carbons Prepared from Polyaniline for Supercapacitors. J. Solid State Electrochem. 2011, 15 (1), 175–182. Figure 1

Systematic investigation of reduced graphene oxide foams for high-performance supercapacitors

In the past decades, fossil energy depletion, environmental pollution, and greenhouse gas emissions have resulted in serious health threats and ecological imbalances, which prompt researchers to explore green and sustainable supercapacitor energy storage and conversion systems. Biomass is a promising renewable energy source to use for biomass porous carbon for supercapacitor devices because it is renewable and has abundant reserves, a low price, and low pollution carbon energy. To date, although some reports have screened different biomass precursors, carbonization methods, and activation strategies and mechanisms, a comprehensive evaluation and critical review of the correlation among biomass porous carbon properties, including pore structure and surface chemistry, and electrochemical energy storage performances of supercapacitors are absent from a multidisciplinary assessment perspective. Therefore, in this review, we summarize recent advances in the biomass porous carbon synthesis process focusing on different carbonization and activation strategies, point out the scope of applicability and advantages/disadvantages of these methods in supercapacitor applications, and reveal the reaction mechanisms and limitations for commercial production. Then, the relationships among biomass porous carbon properties, including hierarchical porous structure, surface chemistry, specific surface area, and electrochemical performances of supercapacitors are reviewed in detail, which enables researchers to prepare and design advanced materials in a more rational way and facilitates them to explore more cutting-edge energy storage materials. Finally, two effective techniques including heteroatom doping and composite material construction are reviewed to address the general problem of low supercapacitor energy density. This review demonstrates the great potential of biomass porous carbon with superior properties, provides advanced tailoring and design viewpoints for the application fields of high-performance supercapacitors, and is expected to inspire new exploration and boost the practical commercial applications of biomass-derived hierarchical porous carbon material in more energy storage and conversion fields.

Nanocomposites of honeycomb double-layered MnO2 nanosheets /cobalt doped hollow carbon nanofibers for application in supercapacitor and primary zinc-air battery

Aluminum (Al) current collector is one of the most important components of supercapacitors, and its performance has vital effects on the electrochemical performance and cyclic stability of supercapacitors. In the present work, a scalable and low-cost, yet highly efficient, picosecond laser processing method of Al current collectors was developed to improve the overall performance of supercapacitors. The laser treatment resulted in hierarchical micro-nanostructures on the surface of the commercial Al foil and reduced the surface oxygen content of the foil. The electrochemical performance of the Al foil with the micro-nanosurface structures was examined in the symmetrical activated carbon-based coin supercapacitors with an organic electrolyte. The results suggest that the laser-treated Al foil (laser-Al) increased the capacitance density of supercapacitors up to 110.1 F g-1 and promoted the rate capability due to its low contact resistance with the carbonaceous electrode and high electrical conductivity derived from its larger specific surface areas and deoxidized surface. In addition, the capacitor with the laser-Al current collector exhibited high cyclic stability with 91.5% capacitance retention after 10 000 cycles, 21.3% higher than that with pristine-Al current collector due to its stronger bonding with the carbonaceous electrode that prevented any delamination during aging. Our work has provided a new strategy for improving the electrochemical performance of supercapacitors.

Nanoporous activated biocarbons derived from biomass offer a sustainable alternative to traditional carbon materials in various applications. Even though multiple methods are available to prepare these carbon materials with different biomasses and activating agents, there are still many challenges such as optimizing pore structure, surface functionalization control, and maintaining high electrical conductivity which are critical to achieve high performance in energy storage applications. These challenges can be overcome by choosing the appropriate biomass with different chemical structure and composition. Herein, we use food waste garlic to synthesize nanoporous biocarbon through the activation process using potassium hydroxide (KOH) as an activating agent. The resulting biocarbon exhibited a high specific surface area of 3449.2 m 2 g −1 and a pore volume of 1.67 cm 3 g −1 , together with sulfur and oxygen functionalities. Pyrolysis was employed to fine-tune the pore structure, achieving a balance of microporosity and mesoporosity, which are beneficial for energy storage and carbon capture applications. The nanostructured materials delivered exceptional CO 2 adsorption capacity at low (5.25 mmol/g at 1 bar) and high pressure (30.6 and 24.9 mmol/g at 0 and 25 °C at 30 bar), making it a promising sorbent for both post-combustion and pre-combustion CO 2 capture. The breakthrough studies combined with the dynamic adsorption models like the Yoon-Nelson and Thomas models demonstrated superior CO 2 capture and rate constant for practical applications. Furthermore, the biocarbon revealed excellent electrochemical performance as a supercapacitor electrode with a specific capacitance of 262 F/g at 0.5 A g −1 and stability over 10,000 cycles with excellent retention and coulombic efficiency. The presence of oxygen and sulfur functionalities enhanced hydrophilicity and wettability, contributing to the superior electrochemical performance. The study highlights the potential of functionalized nanoporous biocarbon with a tunable porous structure derived from waste biomass as a sustainable and efficient material for CO 2 capture and energy storage applications.

Bimetallic transition metal sulfides (TMSs) exhibit considerable potential for energy storage. However, to keep improving the performance of electrochemical systems, effective synthetic techniques for advantageous electrode architecture still need to be developed. The present study involved the synthesis of a NiCo2S4/NiS2/Co9S8 nanocomposite (NCS/NS/CS) employing polyethyleneimine by the solvothermal technique, resulting in the creation of an NiCo-precursor. After that, we annealed the NiCo-precursor with S powder for two hours at 300 °C in an argon atmosphere. The enhanced morphology and NCS/NS/CS electrode conductivity allow for fast ion transport, giving them an excellent electrochemical energy storage feature. At 0.5 A/g, the NCS/NS/CS nanocomposite displays a capacitance of 326 F/g. Additionally, utilizing an NCS/NS/CS electrode for each of the positive and negative electrodes, an NCS/NS/CS//NCS/NS/CS symmetric device was created, providing an exceptional 18.9 Wh k/g of specific energy at a specific power of 529 W k/g at 1 A/g. According to these, the NCS/NS/CS nanocomposite is an excellent choice for an electrode material with remarkable performance in supercapacitors.

Structural energy storage materials refer to a broad category of multifunctional materials which can simultaneously provide load bearing and energy storage to achieve weight reduction in weight‐sensitive applications. Reliable and satisfactory performance in each function, load bearing or energy storage, requires peculiar material design with potential trade‐offs between them. Here, the trade‐offs between functionalities in an emerging class of nanomaterials, carbon nanofibers (CNFs), are unraveled. The CNFs are fabricated by emulsion and coaxial electrospinning and activated by KOH at different activation conditions. The effect of activation on supercapacitor performance is analyzed using two electrode test cells with aqueous electrolyte. Porous CNFs show promising energy storage capacity (191.3 F g−1 and excellent cyclic stability) and load‐bearing capability (σf > 0.55 ± 0.15 GPa and E > 27.4 ± 2.6 GPa). While activation enhances surface area and capacitance, it introduces flaws in the material, such as nanopores, reducing mechanical properties. It is found that moderate activation can lead to dramatic improvement in capacitance (by >300%), at a rather moderate loss in strength (<17%). The gain in specific surface area and capacitance in CNFs is many times those observed in bulk carbon structures, such as carbon fibers, indicating that activation is mainly effective near the free surfaces and for low‐dimensional materials.

New Strategies for Novel MOF-Derived Carbon Materials Based on Nanoarchitectures

Manganese dioxide coupled with hollow carbon nanofiber toward high-performance electrochemical supercapacitive electrode materials

Exploring the porous organic frameworks with carbonaceous materials for superior electrochemical performance of hybrid supercapacitors

The energy storage capability of the aqueous supercapacitors is mainly attributed to the relatively low operating voltage of the device, as the thermodynamic decomposition voltage of water is 1.23 V. Therefore, the extension of the working voltage of the aqueous capacitor beyond the electrolyte decomposition limit is an important subject for the development of environmentally friendly energy storage devices. In this study, a commercial activated carbon (AC) and synthesized phosphorus-doped reduced graphene oxide (P-rGO) were used to gain insight into the influence of both textural properties and the surface chemistry on the electrochemical performance of high-voltage aqueous supercapacitors. Materials on the opposite end of the spectrum (highly porous, undoped AC and heteroatom-rich phosphorus-doped reduced graphene oxide with low porosity) were compared in a symmetric cell, operating in a wide voltage window of 2.0 V in 2 M NaClO4 electrolyte. Additionally, AC-based cell was tested in 1 M Na2SO4 solution to assess the differences in its performance in different sodium-based electrolytes. The obtained results demonstrate that both a porous structure and high contribution of heteroatoms, which improve the hydrophilicity of the electrode, are required to achieve high specific energy density values. However, with increasing current and higher power densities, a developed porous structure is required to maintain good energy storage characteristics. Achieving high operating voltage in the aqueous symmetric full-carbon supercapacitors is a promising energy storage solution. The assembled devices show a good specific energy density of up to 13 Wh kg−1 at a power density of 30 W kg−1.Graphical abstract

With the rapid development of new energy technologies, hybrid supercapacitors have received widespread attention owing to their advantages of high power density, fast charging/discharging rate and long cycle life. In this case, the selection and design of electrode materials are the key to improving the energy storage performance of supercapacitors. Herein, zeolitic imidazolate framework-67 (ZIF-67) is presented as a good candidate material for the fabrication of supercapacitor electrodes because of its controllable pore size, constant cavity size and large specific area. Moreover, pristine ZIF-67 and ZIF-67-derived porous carbon have shown exemplary performances in supercapacitors. However, they belong to the class of electric double layer capacitor materials and have a lower magnitude of energy storage compared with pseudocapacitor materials. Therefore, to improve the energy density of hybrid supercapacitors, other ZIF-67 derivatives need to be explored, especially chalcogenides. This review mainly reports the application of ZIF-67-derived transition metal chalcogenides (TMCs, C including Oxide, Sulfide, Selenide, Telluride) in supercapacitors. Moreover, the strategies for the preparation of ZIF-67-derived TMCs and their electrochemical performance in supercapacitors are further discussed. Finally, the remaining challenges and future perspectives are highlighted.

Electrospun One Dimensional (1D) Pseudocapacitive nanorods embedded carbon nanofiber as positrode and graphene wrapped carbon nanofiber as negatrode for enhanced electrochemical energy storage.