Graphenated carbon nanotube

SEM series of graphenated CNTs with varying foliate density

Graphenated carbon nanotubes (G-CNTs) are a relatively new hybrid that combines graphitic foliates grown along the sidewalls of multiwalled or bamboo style carbon nanotubes (CNTs). Yu et al.[1] reported on "chemically bonded graphene leaves" growing along the sidewalls of CNTs. Stoner et al.[2] described these structures as "graphenated CNTs" and reported in their use for enhanced supercapacitor performance. Hsu et al. further reported on similar structures formed on carbon fiber paper, also for use in supercapacitor applications.[3] Pham et al. [4][5] also reported a similar structure, namely "graphene-carbon nanotube hybrids", grown directly onto carbon fiber paper to form an integrated, binder free, high surface area conductive catalyst support for Proton Exchange Membrane Fuel Cells electrode applications with enhanced performance and durability. The foliate density can vary as a function of deposition conditions (e.g. temperature and time) with their structure ranging from few layers of graphene (< 10) to thicker, more graphite-like.[6]

The fundamental advantage of an integrated graphene-CNT structure is the high surface area three-dimensional framework of the CNTs coupled with the high edge density of graphene. Graphene edges provide significantly higher charge density and reactivity than the basal plane, but they are difficult to arrange in a three-dimensional, high volume-density geometry. CNTs are readily aligned in a high density geometry (i.e., a vertically aligned forest)[7] but lack high charge density surfaces—the sidewalls of the CNTs are similar to the basal plane of graphene and exhibit low charge density except where edge defects exist. Depositing a high density of graphene foliates along the length of aligned CNTs can significantly increase the total charge capacity per unit of nominal area as compared to other carbon nanostructures.[8]

G-CNTs address several limitations of graphene and SWCNTs. While graphene has high edge density, it suffers from restacking in bulk forms due to π–π interactions between layers, which reduces accessibility of edge sites and limits surface area for reactions like charge transfer. SWCNTs, though excellent for mechanical strength and 1D electron mobility, have limited edge density as most of their carbon atoms are in the basal plane of the tube, with edge sites only at the tube ends. In contrast, G-CNTs integrate the high surface area of CNTs with additional graphene foliates on the sidewalls, significantly increasing the edge density and providing more active sites for charge transfer. Additionally, G-CNTs avoid the bundling issues seen in SWCNTs and the restacking issues seen in graphene, maintaining a stable 3D structure where the graphene foliates prevent agglomeration and keep the edges exposed for reactions like charge storage and catalysis. This enhanced edge density, coupled with their stable, non-bundling structure, ensures greater reactivity, better ion accessibility, and improved durability in high-performance applications. G-CNTs offer a highly efficient and durable solution, combining the high surface area of CNTs with the excellent edge reactivity of graphene.

In a study by Lawal et al. [9], G-CNTs were added to titanium dioxide (TiO2) to improve the performance of bifacial dye-sensitized solar cells (DSSCs). G-CNTs was incorporated at concentrations of 0.0025 wt%, 0.0050 wt%, and 0.0100 wt%. The aim was to boost charge transfer efficiency and light absorption. The best results came from using 0.005 wt% G-CNTs, which increased the power conversion efficiency (PCE) by 20%, from 3.76% to 4.53%. Adding a second layer of the optimized TiO2/g-CNT composite further raised the PCE to 5.90%, a 56.8% improvement over TiO2 and 27.7% over the TiO2/g-CNT variant. g-CNTs enhanced light absorption, especially on the back side of the DSSC, where light is weaker. This lowered series resistance (from 12.80 Ω/13.38 Ω) and charge transfer resistance (from 7.5 Ω to 5.5 Ω), indicating improved charge transfer and less recombination. The G-CNTs also helped maintain the composite's stability, confirmed by imaging and analysis, and its graphitic structure improved charge transfer efficiency.

Ismail et al. [10] investigated a continuous synthesis of bulk cotton-like (aerogel) structure of graphenated carbon nanotubes (G-CNTs) via floating catalyst chemical vapor deposition (FCCVD) method. They analysed how changes in the injection rate of the carbon source influenced G-CNTs formation. Their research revealed that an injection rate of 5 ml/h led to optimal synthesis, resulting in improved electrical conductivity and superior gas-sensing capabilities compared to traditional carbon nanotubes (CNTs). Abdullah et al [11] introduced grapeseed oil as a precursor for G-CNTs hybrids, synthesizing mesoporous three-dimensional (3D) G-CNT aerogels with unique morphological features, such as highly disordered multi-wall carbon nanotube (MWCNT) bundles rounded by graphene foliate structures. Yusuf et al [12] conducted a comparative study of G-CNTs as counter electrodes in dye-sensitized solar cells (DSSCs), demonstrating their superior electrical conductivity and catalytic activity compared to standard carbon nanotubes and even conventional platinum layers. Yusuf et al's investigation [13] also highlighted the excellent conductivity of G-CNT sheets, attributing it to their hybrid structure, which presents them as promising candidates to replace conventional platinum as counter electrodes in DSSCs.

In addition to their promise in fuel cells and DSSCs, G-CNTs have shown considerable potential in flexible supercapacitor applications. Flexible SCs, typically fabricated using carbon-based materials, are vital for powering next-generation lightweight, wearable electronics. However, improvements in their energy density, power density, and cycling durability remain key challenges. A study describes the use of G-CNT cotton substrates integrated with vertically aligned MoS₂ and WS₂ nanosheets, synthesized through time-modulated radio frequency (RF) magnetron sputtering.[14] The high volume-to-surface ratio of these transition metal dichalcogenide (TMD) vertical structures, when combined with the conductive, high-surface G-CNT substrate, resulted in significantly enhanced SC performance. Galvanostatic charge–discharge (GCD) measurements recorded an aerial capacitance of 131.2 mF cm⁻² for WS₂ electrodes and 97.60 mF cm⁻² for MoS₂ electrodes. Flexibility tests using angle-dependent cyclic voltammetry (CV) confirmed mechanical robustness, and stability studies over 10,000 cycles demonstrated capacitance retention exceeding 96%. These findings underscore the feasibility of integrating G-CNTs with vertically aligned TMD nanostructures to fabricate next-generation flexible SCs with enhanced capacitance, stability, and flexibility.

Together, these studies illustrate the growing significance of G-CNT hybrids in diverse energy applications—from gas sensing and DSSCs to flexible supercapacitors—where their unique hybrid morphology enables performance enhancements that surpass those of conventional carbon nanomaterials.

## References

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2. ^ Stoner, Brian R.; Akshay S. Raut; Billyde Brown; Charles B. Parker; Jeffrey T. Glass (2011). "Graphenated carbon nanotubes for enhanced electrochemical double layer capacitor performance" (PDF). Appl. Phys. Lett. 18. 99 (18): 183104. Bibcode:2011ApPhL..99r3104S. doi:10.1063/1.3657514. hdl:10161/10603.
3. ^ Hsu, Hsin-Cheng; Wang, Chen-Hao; Nataraj, S.K.; Huang, Hsin-Chih; Du, He-Yun; Chang, Sun-Tang; Chen, Li-Chyong; Chen, Kuei-Hsien (2012). "Stand-up structure of graphene-like carbon nanowalls on CNT directly grown on polyacrylonitrile-based carbon fiber paper as supercapacitor" (PDF). Diamond and Related Materials. 25: 176–9\. Bibcode:2012DRM....25..176H. doi:10.1016/j.diamond.2012.02.020.
4. ^ Pham, Kien-Cuong; Chua, Daniel H.C.; McPhail, David S.; Wee, Andrew T.S. (2014). "The Direct Growth of Graphene-Carbon Nanotube Hybrids as Catalyst Support for High-Performance PEM Fuel Cells". ECS Electrochemistry Letters. 3 (6): F37 – F40. doi:10.1149/2.009406eel.
5. ^ Pham, Kien-Cuong; McPhail, David S.; Mattevi, Cecilia; Wee, Andrew T.S.; Chua, Daniel H. C. (2016). "Graphene-Carbon Nanotube Hybrids as Robust Catalyst Supports in Proton Exchange Membrane Fuel Cells". Journal of the Electrochemical Society. 163 (3): F255 – F263. doi:10.1149/2.0891603jes. hdl:10044/1/37534. S2CID 100673665.
6. ^ Parker, Charles B.; Akshay S. Raut; Billyde Brown; Brian R. Stoner; Jeffrey T. Glass (2012). "Three-dimensional arrays of graphenated carbon nanotubes". J. Mater. Res. 7. 27 (7): 1046–53\. Bibcode:2012JMatR..27.1046P. doi:10.1557/jmr.2012.43.
7. ^ Cui, Hong-tao; O. Zhou; B. R. Stoner (2000). "Deposition of aligned bamboo-like carbon nanotubes via microwave plasma enhanced chemical vapor deposition". J. Appl. Phys. 88 (10): 6072–4\. Bibcode:2000JAP....88.6072C. doi:10.1063/1.1320024.
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9. ^ Lawal, Ismail; Shafie, Suhaidi; Pandey, Shyam S.; Jafaar, Haslina; Mustafa, Mohd Amrallah; Ismail, Ismayadi; Kamarudin, Mazliana Ahmad; Mohd Noor, Ikhwan Syafiq; Liu, Xinzhi; AlSultan, Hussein A.; Babani, Suleiman; Abdulhamid, Ibrahim Bako; Norddin, Nurbahirah (2025-03-01). "Maximizing solar energy harvesting: Enhancing the efficiency of bifacial dye-sensitized solar cells with Graphenated carbon nanotubes composites in multi-layered stacked photoanode". Optical Materials. 160: 116721. doi:10.1016/j.optmat.2025.116721. ISSN 0925-3467.
10. ^ Ismail, Ismayadi; Mamat, Md Shuhazlly; Adnan, Noor Lyana; Yunusa, Zainab; Hasan, Intan Helina (2019-10-14). "Novel 3-Dimensional Cotton-Like Graphenated-Carbon Nanotubes Synthesized via Floating Catalyst Chemical Vapour Deposition Method for Potential Gas-Sensing Applications". Journal of Nanomaterials. 2019: e5717180. doi:10.1155/2019/5717180. ISSN 1687-4110.
11. ^ Abdullah, Hayder Baqer; Irmawati, Ramli; Ismail, Ismayadi; Zaidi, Muhammad Azizan; Abdullah, Ahmad Aimanuddin Amzar (2021-11-11). "Synthesis and morphological study of graphenated carbon nanotube aerogel from grapeseed oil". Journal of Nanoparticle Research. 23 (11): 244. Bibcode:2021JNR....23..244A. doi:10.1007/s11051-021-05363-6. ISSN 1572-896X.
12. ^ Yusuf, 11) Yusnita (2021). "A Comparative Study of Graphenated-Carbon Nanotubes Cotton and Carbon Nanotubes As Catalysts For Counter Electrode In Dye-Sensitized Solar Cells". Malaysian Journal of Microscopy. 17 (2): 162–174.`{{cite journal}}`: CS1 maint: numeric names: authors list (link)
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14. ^ Perişanoğlu, Ufuk; Perişanoğlu, Esra Kavaz; Kudaş, Züleyha; Ekinci, Duygu; Ismail, Ismayadi; Gür, Emre (2025-03-13). "Advanced flexible supercapacitors: vertical 2D MoS2 and WS2 nanowalls on graphenated carbon nanotube cotton". Nanoscale. 17 (11): 6704–6717\. doi:10.1039/D5NR00329F. ISSN 2040-3372.