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Graphitic Carbon Nitride Heterostructures for Energy and Environmental Applications
Published in A. Pandikumar, K. Jothivenkatachalam, S. Moscow, Heterojunction Photocatalytic Materials, 2022
Kavil et al. [67] reported a novel flower-shaped semiconductor MoS2-GCN nanohybrid system for symmetric solid state capacitor device. MoS2 offers excellent ionic conductivity that stores charge on the individual atomic layers. The MoS2 nanoflowers with a size of 200 nm are uniformly distributed in the GCN matrix to form the heterostructure. The nanoflower morphology helps to enhance the surface area and facilitate the efficient wetting between electrode and electrolyte. The nanocomposite exhibited rectangular-shaped CV loops with a large capacitive area indicative of the typical charge storage characteristics. The nanocomposite electrode also shows lowered internal resistance with a specific capacitance of 45.5 F/g, which is attributed to the synergistic effect of the two types of charge storage mechanism (Faradaic and non-Faradaic) operating in the heterostructure. The MoS2 acts as a spacer in between the layers of GCN sheets, thereby facilitating effective charge transport between the electrode and the electrolyte surface. The specific capacitance decreases on increasing the current density due to the insufficient time spend by the electrolyte molecule to interact with the electrode surface. The composite sample exhibits excellent cyclic stability (∼98%) after 100 cycles.
Graphene-Inorganic Hybrids (I)
Published in Ling Bing Kong, Carbon Nanomaterials Based on Graphene Nanosheets, 2017
Ling Bing Kong, Freddy Boey, Yizhong Huang, Zhichuan Jason Xu, Kun Zhou, Sean Li, Wenxiu Que, Hui Huang, Tianshu Zhang
Figure 3.12 shows representative TEM images of the TiO2-GO hybrids [29]. The TiO2 nanoparticles were found to have both flower-like morphologies of 250–320 nm in length and seed-shaped structures, together with structures between the two extremes, as shown in Fig. 3.12 (a–c). Dark-field image revealed that each single seed was a single crystal, as demonstrated in Fig. 3.12 (d). HRTEM images indicated that each nanoflower/particle consisted of very small crystallites, with crystal sizes of 2–4 nm, which were crystallographically aligned with same orientation. The TiO2 nanoparticles possessed a porous microstructure, although no surfactant was used. Similar mesoporous crystallographically aligned anatase TiO2 structures from TiF4 hydrolysis were observed when using CNTs as template [39]. TGA/DTA experiments suggested that the GO was stabilized by the embedded TiO2 [40]. It has been reported that GO can contain up to 25% of water [37]. Accordingly, the sample with a 2.1 weight ratio of TiO2/GO was formed from an initial TiF4/GO weight ratio of 13.2.
Nanomaterials for Electrochemical Capacitor
Published in Hieng Kiat Jun, Nanomaterials in Energy Devices, 2017
Other than carbon–conducting polymer, nanocomposite of carbon material and metal oxide has appeared to be a promising electrode material as well. A nickel oxide (NiO)–CNT nanocomposite prepared by simple chemical precipitation method exhibits 160 F g−1 at 10 mA g−1 (Lee et al. 2005). It is around 31% higher than the specific capacitance achieved by bare NiO. The crystallite size of NiO nanoparticles coated on the CNT is smaller than bare NiO. The smaller particle size indicates a higher surface area that can offer more active sites for the occurrence of redox reaction. Intertwined CNT–vanadium oxide (V2O5) nanocomposite also possesses hierarchically porous structure that consists of small pores which can further increase the surface area effectively (Chen et al. 2011). An excellent cycle stability has been achieved by a composite of CNT arrays coated with manganese oxide nanoflower. It experiences only 3% of capacity loss after 20,000 cycles (Zhang et al. 2008a). The morphology study revealed that the nanoflower was evolved from nanosheets. Besides, the manganese oxide nanoflower was found to form favorably at the junction of CNT (Fig. 11). However, the growth mechanism is unclear. Thus, the main contributor for cycle stability is yet to be confirmed. Compared to the ternary composite that made up of carbon material and conducting polymer such as graphene–PANI–CNT and graphene–PPy–CNT, CNT–RGO–MnO2 can retain 70% of initial capacitance after 5000 cycles (Lu et al. 2016). The good stability could be attributed to the 3D structure formed by RGO and CNT with uniform distribution of MnO2 nanoparticles. At some extent, the dissolution of MnO2 which will greatly degrade the stability performance is restrained. RuO2–CNT–RGO ternary composite also has good cycle stability. The final specific capacitance is enhanced by 6% after 8100 cycles (Wang et al. 2014). This composite has a carbon hybrid backbone (CNT–RGO) coated on nickel foam, which assists in electrochemical stability of the substrate in electrolyte, bridges the RuO2 nanoparticles and substrate effectively, and provides a good conductive pathway (Fig. 12).
Spinel-based electrode materials for application in electrochemical supercapacitors – present status and future prospects
Published in Inorganic and Nano-Metal Chemistry, 2022
Vismaya Jose, Vinaya Jose, Clementz Edwardraj Freeda Christy, Arputharaj Samson Nesaraj
Compared to the other metal oxides, nickel ferrites with elevated hypothetical capacitance value have been linked as electrode material for energy capacity gadgets, that is, batteries and supercapacitors. Bashir et al., created graphene nano-sheets decorated with spherical copper substituted nickel ferrite nanoparticles for supercapacitors fabrication. The copper substituted and unsubstituted NiFe2O4 nanoparticles were arranged through wet chemical co-precipitation route. Reduced graphene oxide (rGO) was arranged by means of well-known Hummer’s strategy. After structural characterization of both ferrite (Ni1-xCuxFe2O4) nanoparticles and rGO, the ferrite particles were enhanced onto the graphene sheets to get Ni1-xCuxFe2O4@rGO nanocomposites. The cyclic stability experiments exhibit ∼65% capacitance maintenance after 1000 cycles. In any case, this maintenance was improved from 65% to 75% for the copper substituted nanoparticles (Ni0.9Cu0.1Fe2O4) and 65% to 85% for graphene-based composites. All this information recommend that these nanoparticles and their composites can be utilized for manufacture of supercapacitors.[83] Gita Singh and colleagues developed a 3 D nanoflower MnFe2O4@PANI composite as electrode fabric in supercapacitor. Manganese doped ferrites were synthesized by hydrothermal method taken after by in-situ chemical oxidative polymerization of aniline to make a nanoflower composite. The nanoscale MnFe2O4 were infused with polyaniline (PANI) which offers superior synergistic impacts by facilitating charge/ion transit route, which is improved by providing a broad electrochemical kinetic surface area. It shows high specific capacitance of 623 F/g at a current density of 1 A/g. A model of the created supercapacitor appeared amazing gadget execution with a high energy density of 179 Wh/kg and maximum power density of 982 W/kg with ∼95% maintenance of specific capacitance after 10,000 cycles.[84] CoMnFeO4 nanocomposites as a novel supercapacitor electrode material are arranged through hydrothermal and sol-gel ignition strategies. Their structures are explored and characterized by FT-IR, XRD, XPS, BET, SEM, EDX, and HR-TEM analysis. Moreover, magnetic properties of nanoparticles synthesized by two strategies are compared on a vibrant sample magnetometer (VSM) with most extreme saturation magnetization values found to be 28.83 emu g−1 and 23.17 emu g−1, individually. The hydrothermally synthesized sample appears high specific capacitance of 770 F g−1 in 3 M KOH whereas this value for the sample synthesized by sol-gel method is 150 F g−1. The higher specific capacitance can be asttributed to smaller particle size, more electroactive locales due to higher specific surface area, and quantum size impacts.[85]