Tailoring the performance of mechanically robust highly conducting Silver/3D graphene aerogels with superior electromagnetic shielding effectiveness
Introduction
Graphene a single-layer two-dimensional (2D) densely packed lattice made of sp2–hybridized carbon atoms with unique properties have been realized as a promising candidate for potential applications such as transparent electrodes in nanoelectronics [1], sensors [2], energy storage [3], electrocatalysis [4], and electromagnetic interference (EMI) shielding [5]. Past studies have be done on the 2D graphene-based hybrid nanostructures and have been chosen as alternatives and potential candidates to replace conventional electrodes (such as ITO) for various electronic devices due to its high electrical conductivities. Also, these 2D graphene sheets were intercalated with various metal oxides and metallic nanoparticles realizing nanocomposite structures to improve the performance in sensors [6], energy storage [7], catalysis [8], and electromagnetic interference (EMI) shielding applications [9]. Moreover, the presence of surface defects in graphene leads to sheet-to-sheet restacking causing a high degree of aggregation resulting decrease in the surface area and alters the performance in many applications such as energy storage/conversion and shielding applications. Thus, an effective suitable approach is a pre-requisite to prevent aggregation. The concept of 3D graphene is one selective approach to overcome the above difficulties by random orientation and partial stacking of graphene sheets in 3D networks forming microporous structures.
Recently, 3D graphene structures (eg. Aerogels) has captivated great attention because of its higher surface area, electrical conductivity, and transport efficiency over the graphene and thus increases the energy storage and shielding performance due to the induced electronic interactions and availing the charges to move freely in the microporous geometry. Zang et al. reported a simple and green method utilizing the hydrothermal method to develop 3D-graphene porous at bulk scale with high specific surface area 3523 (m2/g) and conductivity 303 (S/m) for supercapacitors [10]. A precursor-assisted chemical vapor deposition technique was employed to develop 3D graphene networks grown on various substrates (such as Al2O3, Si, GaN, or Quartz) and transferred easily on flexible devices. The 3D graphene networks achieved a conductivity of 52 S/cm, high surface area (1025 m2/g), and a porosity 3.4 cm3/g [11]. Likewise, numerous techniques have been reported to develop 3D-graphene porous structures. Further, to improve the properties and the performance of the 3D graphene structures various composites have been reported to enhance the charge storage capacity via an increase in surface area and porous nature for various energy storage [12,13], sensors [14], water splitting [15], and EMI shielding applications [16]. Moreover, the methods utilized were quite expensive and environmentally hazardous. In our previous work, we reported an environmentally friendly and low-cost ice template freeze casting route to the extensive development of 3D-graphene/noble metal nanocomposites for catalytic, supercapacitor, and antibacterial materials [13]. We observed the addition of silver (Ag) nanostructures in graphene structure significantly improved the electrochemical performance with more electrode/electrolyte accessibility as well as capacitive properties.
In the present work, we report the synthesis of Ag/GAs with various concentrations of Ag nanoparticles through the freeze-casting process. The influence of Ag content alone on the electrical and shielding performance of GAs and its interaction with EM waves was studied extensively. Frequency-dependent conductivity study was carried out to know the effect of Ag nanoparticles on the charge transport phenomenon of Ag/GAs. An increase in the Ag concentration significantly enhanced the charge carrier and showed a predominant increase in conductivity to about 0.032 S/cm. Thereafter, the effect of Ag nanofiller in the Ag/GAs was put forward for EMI studies to know the shielding performance of nanocomposites where enhanced conductivity is a desirable criterion. Also, incorporation of Ag into the Ag/GAs acts as a conductive additive to improve the charge transportation in flexible electronics and EMI shielding application.
Section snippets
Materials used
Graphite powder (45 μm, 99.99%) and AgNO3 were purchased from Sigma-Aldrich. The rest of the chemicals used in this study were purchased from Merck Specialties Private Limited and were of analytical grade. Deionized water was used for all aqueous solutions preparation throughout the experiments.
Procedure used to synthesize Ag/GAs with different loading of Ag
Ag/GAs with different loading of Ag (10, 20, and 40%) were prepared using a method similar to our previous work [13]. In a typical procedure for the preparation of Ag/GAs with different loading of Ag,
Results and discussion
Powder X-ray diffraction (XRD) was used to characterize the crystal structure of GO, bare GA, and Ag/GA-40. XRD pattern of GO in Fig. 2 (A) (i) shows diffraction peaks at 10.8 and 43°, which assigned to the reflection from (002) and (100) planes, respectively [17]. A broad diffraction peak at 25° in the XRD pattern of GA in Fig. 2 (A) (ii) corresponding to (002) plane, which is due to the short-range order of stacked graphene sheets [18]. But, there is nearly disappearance of (002) plane in the
Conclusion
A low-cost freeze-casting process was adopted for the large-scale synthesis of Ag/GAs integrated with Ag nanoparticles of various concentrations. These multifunctional Ag/GAs showed enhanced conductivity ⁓0.032 S/cm with excellent mechanical stability under compressive loading and EMI shielding effectiveness ⁓32 dB. Incorporation of Ag nanofiller enhances the charge transport and reduces the skin depth by improving the shielding performance and contributing to the multiple reflections and
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.
Acknowledgements
Authors thank the support of Defence Institute of Advanced Technology (DIAT) and Siksha ‘O' Anusandhan (Deemed to be University) for facilitating infrastructure and characterizations to carry out the research work. Author R. Aepuru gratefully acknowledge FONDECYT Postdoctoral project: 3180172, CONICYT, Santiago-Chile.
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