Ultrasonic doping and photo-reduction of graphene oxide films for flexible and high-performance electrothermal heaters
Graphical abstract
Introduction
Electrothermal heaters are resistive structures capable of self-heating by a joule effect wherein electrical energy is transduced to thermal energy [1]. Modern times have seen an ever-increasing demand for better performances in electrothermal heaters in terms of transduction efficiency, flexibility, weight, and power management [1]. Moreover, wearable applications such as hot clothing, thermotherapy packs, and other healthcare appliances make an extra demand for flexibility, stretchability, and energy savings in the next generation electrothermal heaters. The quest to satisfy all these performance features explains why flexible thin-film heaters (TFH) have gained substantial research grounds in recent years [1], [2], [3], [4], [5], [6], [7], [8].
Low heater resistance allows for high steady-state temperatures to be attained at relatively lower driving voltage. This renders the heater highly efficient in its function as an energy transducer [1]. Many research efforts have already been invested in the line of providing reliably innovative, flexible heating solutions. Some of these solutions include the preparation TFH from metal nanoparticles and nanowires [9], [10], [11], carbon nanotubes (CNT) [2], and graphene [12] on flexible or even stretchable substrates [13], [14]. Embedding metal nanostructures [8], [15], CNT [16], or reduced graphene oxide (rGO) [17] within conductive or non-conductive polymers matrices have also been proposed.
Along with poor adhesions to polymer substrates [6], metals nanostructures and CNT have proved capable of penetrating the human skin, which may yield toxic effects and are thus categorized as not suitable for wearable applications [18]. Moreover, at high temperatures, they also suffer contamination due to oxidation at the particle junctions. This increases their resistivity, thus deteriorating their performance [5]. As a result, there has been a shift in attention toward highly conductive noble metals such as gold and silver, wherein their nanoparticles have been embedded in transparent polymer matrices to form high performance transparent flexible heaters [9], [10]. However, the high cost of these precious metals makes them unattractive for wearable applications such as hot clothing, and thermotherapy packs wherein transparency is not needed.
Overall, the potentially low cost, lightweight, high electrical, and thermal conductivity of carbon-based materials such as graphene makes it a suitable candidate for joule heaters [5]. This makes graphene preparation routes that arrive at flexible heaters with high-performance features of paramount importance. Chemical exfoliation of graphite into GO, followed by reduction to rGO is one the most popular processing routes in research today because of its high yield and great potential for scalability [19]. Laser scribing has shown to be a chemical-free, rapid, low-temperature method to reduce GO deposited on flexible polymer substrates while affording the possibility for patterning for various applications [20], [21], [22], [23], [24], [25], [26] and the doping in the presence of precursor molecules [27], [28], [29], [30]. Photo-irradiation has also been used to induce graphene for polyimide films [3], [31] and from coal [32] via laser scribing. The heaters from laser-induced graphene (LIG) [3] showed excellent performance. However, they had slow heating rates and suffered degradation within extended periods of high applied power [3]. Zhang et al. [33] prepared flexible pattered heaters from Laser reduced graphene oxide (LrGO), which attained as a steady-state temperature of up to 247.3 °C at 18 V applied voltage. However, the heaters needed a longer response time of 20 s. Lin et al. [5] added silver nanoparticles to the GO films before laser reduction in attempts to build in conductive bridges between the graphene sheets in the c-direction. The heaters prepared from this nanocomposite attained a steady-state temperature of up to 229 °C after 5 s of applying 18 V. Even though the response time of these heaters were improved, their reliance upon high concentrations of costly precious metals make these films financially unattractive for large-scale wearable electronics. Also, more research efforts geared towards lowering the driving voltages of these flexible heaters are still necessary to render them compatible with portable electrochemical power sources.
Furthermore, doping graphene with elements such as boron, nitrogen, and sulfur has been proposed as a metal-free means of increasing charge carrier concentration [34], thus improving conductivity. Various methods have already been established for doping graphene, which can be separated into two categories. Firstly, the in-situ approaches, such as introducing the dopant atoms during graphene deposition by using CVD [28], [35], [36], [37]. The second approach includes post-treatment methods of GO, such as hydrothermal methods [38], thermal annealing in the presence of dopant molecules [39], wet chemical methods [40], with heteroatom precursors [34]. While the in-situ approaches suffered low yield and high cost, the post-treatment methods involve harsh processing conditions incompatible with the use of flexible substrates, and theses procedures are too complex to industrialize. Besides, these doping techniques result in excessive lattice defects in the 2D structures which inhibit the propagation of phonons in the lattice. While electrons still can jump over minor vacancy and substitutional defects, phonons do not.
Consequently, the mean free path for phonons is much shorter than that for electrons. High electron density in the π*state is just as relevant as a high degree of atomic ordering in electrothermal materials for adequate heat generation and the propagation of the generated heat, which occurs principally by the movement phonons in carbon-based materials [41]. For, joule effect is caused by the inelastic collisions between phonons and electrons in a material when a potential difference is applied [42]. This means that even though doping represents a low cost, metal-free, means to improve upon the electrical and electrochemical properties of graphene, more efforts are still required to improve upon the electrothermal behavior of doped graphene-based materials and to render them more compatible with flexible substrates.
In this work, present a novel low-temperature doping and reduction technique in which nitrogen dopants are driven into the graphene lattice in a wet chemical process with the aid ultrasonic cavitation energy and further processed by maskless, automated, rapid laser irradiation. Unlike other doping techniques, this method uniquely preserves order in the sp2 network of the graphene sheets while a high dopant concentration is attained. This not only allows for large amounts of heat to be generated by the heaters but also offers the doped films a larger capacity to propagate the generated heat. Consequently, a significant improvement in electrical and electrothermal behavior was observed in comparison with the undoped LrGO films. The low-temperatures applied in this approach contribute to its scalability and compatibility with flexible polymer substrates. This paper is structured as follows. In Section 2 of the article, the fabrication and characterization methods are described along with the performance measurement procedure. The evolution of chemical structure is presented in the first subsection of Section 3. A second subsection describes the electrical and transient electrothermal performance of the nitrogen-doped graphene-based heater while benchmarking it against other heaters presented in previous works. Thermal stability, robustness, and potential applications of the heaters are examined in a later subsection of Section 3, while Section 4 summarizes our key findings.
Section snippets
Materials
Extra-pure graphite powder with 5–20 µm grain size and 30% Ammonia solution [NH4OH] were purchased from Fisher Scientific, UK. Urea granules [CH4N2O] were obtained from Sigma Aldrich, Germany. All the other chemicals were reagent grade and used as received without any additional purification. Polyethylene Terephthalate (PET) substrates with 75 μm thickness were locally sourced.
Preparation of N-GO films
Graphite oxide was prepared according to the modified Hummer method [43], [44]. 10 g Graphite was oxidized with 60 g of
Structure and morphology
The XRD patterns of GO, LrGO, N-GO, and N-LrGO are shown in Fig. 2(a). The diffraction peak associated with the (0 0 2) plane of the graphene lattice, progresses from about 10.4° in GO and 10.26° in N-GO to 26.80° in LrGO and 24.46° in N-LGO. This signifies an increase in interlayer spacing (d(0 0 2)) from 0.848 nm in GO to 0.861 nm in N-GO, and the increase can be attributed to the incorporation of larger nitrogen functional groups [45] into the graphene lattice. Similarly, the corresponding
Conclusions
To sum up, we have successfully demonstrated a facile, scalable approach to the fabrication of high-performance flexible electrothermal heaters based on nitrogen-doped laser reduced graphene films for wearable heating applications. The N-LrGO film was prepared by the facile and scalable low-temperature technique involving the combination of ultrasonic wet chemical doping and solid-state photo-irradiation. This novel technique was shown to the reduced sheet resistance of the LrGO by 50%,
CRediT authorship contribution statement
Sandra A.N. Tembei: Methodology, Investigation, Data curation, Writing - original draft. Ahmed M.R. Fath El-Bab: Writing - review & editing, Resources. Amr Hessein: Writing - review & editing, Visualization, Supervision. Ahmed Abd El-Moneim: Conceptualization, Resources, Supervision, Project administration.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
We also want to acknowledge the Japan International Co-operation Agency (JICA) for their reliable sponsorship of our work. This research was conducted as part of the research project: graphene center of excellence for energy and electronic applications (ID ¼ 31306) that is supported by the science and technology development fund (STDF) in Egypt.
References (76)
- et al.
Flexible and robust laser-induced graphene heaters photothermally scribed on bare polyimide substrates
Carbon
(2019) - et al.
Highly elastic and transparent multiwalled carbon nanotube/polydimethylsiloxane bilayer films as electric heating materials
Mater. Des.
(2015) - et al.
Low-cost flexible supercapacitors based on laser reduced graphene oxide supported on polyethylene terephthalate substrate
J. Power Sources
(2016) - et al.
Three-dimensional micropatterning of graphene by femtosecond laser direct writing technology
Opt. Lett.
(2020) - et al.
Stimulated N-doping of reduced graphene oxide on GaN under excimer laser reduction process
Mater. Lett.
(2014) - et al.
Polyimide derived laser-induced graphene as adsorbent for cationic and anionic dyes
Carbon
(2017) - et al.
Upgrading coal to multifunctional graphene-based materials by direct laser scribing
Carbon
(2019) - et al.
High-quality nitrogen-doped graphene films synthesized from pyridine via two-step chemical vapor deposition
Carbon
(2020) - et al.
Forming mechanism of nitrogen doped graphene prepared by thermal solid-state reaction of graphite oxide and urea
Appl. Surf. Sci.
(2011) - et al.
Defect-engineered reduced graphene oxide sheets with high electric conductivity and controlled thermal conductivity for soft and flexible wearable thermoelectric generators
Nano Energy
(2018)
Hydrazine-reduction of graphite- and graphene oxide
Carbon
Raman spectroscopy in graphene
Phys. Rep.
Simple preparation of nanoporous few-layer nitrogen-doped graphene for use as an efficient electrocatalyst for oxygen reduction and oxygen evolution reactions
Carbon
Synthesis, characterization and prospective applications of nitrogen-doped graphene: a short review
J. Sci.: Adv. Mater. Devices
Transparent flexible heater based on hybrid of carbon nanotubes and silver nanowires
Carbon
Enhanced electrothermal efficiency of flexible graphene fabric Joule heaters with the aid of graphene oxide
Mater. Lett.
A flexible and stretchable polypyrrole/knitted cotton for electrothermal heater
Org. Electron.
Cost-effective and highly efficient surface heating elements using high thermal conductive carbon fibers
Compos. A Appl. Sci. Manuf.
Osteoarthritis: an overview of the disease and its treatment strategies
Semin. Arthritis Rheum.
Continuous low-level heat wrap therapy is effective for treating wrist pain11A commercial party with a direct financial interest in the results of the research supporting this article has conferred or will confer a financial benefit on the author or/or more of the authors.
Arch. Phys. Med. Rehabil.
A review of production methods of carbon nanotube and graphene thin films for electrothermal applications
Nanoscale
Carbon nanotube-based flexible electrothermal film heaters with a high heating rate
R. Soc. open sci.
Flexible and transparent electrothermal film heaters based on graphene materials
Small
High-performance graphene-based flexible heater for wearable applications
RSC Adv.
High-performance, transparent, and stretchable electrodes using graphene–metal nanowire hybrid structures
Nano Lett.
Highly stretchable graphene fibers with ultrafast electrothermal response for low-voltage wearable heaters
Adv. Electron. Mater.
Stretchable, transparent electrodes as wearable heaters using nanotrough networks of metallic glasses with superior mechanical properties and thermal stability
Nano Lett.
Highly flexible transparent film heaters based on random networks of silver nanowires
Nano Res.
Highly stretchable and transparent metal nanowire heater for wearable electronics applications
Adv. Mater.
Stretchable Ag electrodes with mechanically tunable optical transmittance on wavy-patterned PDMS substrates
Sci Rep
Nano-sized Ag inserted into ITO films prepared by continuous roll-to-roll sputtering for high-performance, flexible, transparent film heaters
RSC Adv.
Carbon black functionalized stretchable conductive fabrics for wearable heating applications
RSC Adv.
Silver nanowire coated threads for electrically conductive textiles
J. Mater. Chem. C
One-step fabrication of stretchable copper nanowire conductors by a fast photonic sintering technique and its application in wearable devices
ACS Appl. Mater. Interfaces
Stretchable heaters with composites of an intrinsically conductive polymer, reduced graphene oxide and an elastomer for wearable thermotherapy
J. Mater. Chem. C
Toxicity of nanomaterials
Chem. Soc. Rev.
Editors’ choice—critical review—a critical review of solid state gas sensors
J. Electrochem. Soc.
Graphene-based strain gauge on a flexible substrate
Sens. Mater.
Cited by (13)
Flexible and freestanding temperature sensors based on laser carbonization of carbon nanofibers
2024, Sensors and Actuators A: PhysicalAdvancements in organic pollutant remediation: The role of nitrogen-doped rGO-CeO<inf>2</inf> in photocatalytic efficiency enhancement
2024, Colloids and Surfaces A: Physicochemical and Engineering AspectsNon-enzymatic amperometric biosensor with anchored Ni nanoparticles for urinary glucose quantification
2023, Diamond and Related MaterialsWater-based chitosan/reduced graphene oxide ink for extrusion printing of a disposable amperometric glucose sensor
2022, FlatChemCitation Excerpt :Difficult synthesis of graphene using chemical vapor deposition under vacuum as well as long time chemical or mechanical exfoliation [23,24], was resulted to replacing graphene with reduced graphene oxide (rGO) in the recent studies. The reduction of graphene oxide (GO) can be carried out by applying high temperature, chemical reducing agents, ultrasonic and photo-treatment, or even UV irradiation to remove functional groups of GO, providing chemical, electrical, and mechanical properties close to graphene [25–27]. Among these various methods, chemical reduction was accepted as a facile and efficient method for fabrication of rGO with high level of reduction [28].
Graphene family, and their hybrid structures for electromagnetic interference shielding applications: Recent trends and prospects
2022, Journal of Alloys and CompoundsCitation Excerpt :Besides, when graphene is used in a 3D form (composite and aerogel), the presence of numerous interfaces results in the reflecting and scattering of EM waves [26–28]. If graphene is used in the oxide form (GO), numerous oxygen functional groups on its surfaces result in strong dipolar polarization and interfacial polarization, which further enhances its microwave attenuation ability [29–37]. Moreover, reducing GO (RGO) oxygen functional groups is interesting to prepare cost-effective graphene-based products.
Effects of multiwalled carbon nanotubes and reduced graphene oxide of different proportions on the electrothermal properties of cationic cellulose nanofibril-based composites
2022, Journal of Materials Research and TechnologyCitation Excerpt :It is a current challenge for electrothermal composites to obtain high power conversion efficiency while reducing the input voltage and achieving a feasible balance between production cost and performance. To address these challenges, research in recent years has focused on the utilization of carbon nanotubes and graphene as conductive units to prepare nanocarbon electrothermal composites [20,21]. Carbon nanotubes (CNTs) are mainly divided into single-walled carbon nanotubes (SWCNT) and multiwalled carbon nanotube (MWCNT), with an elastic modulus up to 1.34 TPa and strength up to 200 GPa.