Graphene Nanowalls Research Articles

Improved solid-state lithium-ion battery on stainless steel substrate with graphene nanowalls by microwave plasma-enhanced chemical vapor deposition

Improved solid-state lithium-ion battery on stainless steel substrate with graphene nanowalls by microwave plasma-enhanced chemical vapor deposition

Investigating the mechanism of time dependent evolution of vertical graphene nanowalls

This work presents a time dependent multistage growth model for vertical graphene nanowalls (VGN). Factors mediating growth of VGN in both vertical and spatial direction at different stages were discussed. VGN films were deposited on Si (100) substrate using Radio Frequency Plasma-Enhanced Chemical Vapor Deposition technique by increasing the deposition time systematically for 15 min, 30 min, 60 min, 120 min, and 240 min, respectively. Scanning electron microscopy was carried out in both planar and cross section view to confirm the growth of VGN and quantification of its height. Atomic force microscopy was used to characterize the spatial growth of VGN. Raman scattering and in-plane GIXRD measurements were carried out to characterize the microstructure of VGN, which unveils that the strain relaxation and defects annihilation followed by increase in average crystallite size plays crucial role. Eventually, a schematic diagram was presented for time dependent evolution of VGN at different stages.

(Invited) Plasma Designing of Hybrid 2D Graphene: A Green Approach for Future Energy Materials

The global research interest in two-dimensional (2D) materials and their derivatives has increased significantly, driven by the requirements of application-oriented materials for different sectors, including energy storage. Among the various classes of material groups, 2D layered materials have emerged as a critical research area due to their high aspect ratio, open edge boundaries, high surface-to-volume ratios, and mechanical and electrical properties. Graphene is a widely researched 2D class material with an atomically thin structure, excellent electronic properties, very high intrinsic mobility and exceptional thermal and electrical conductivity1. Even though the research on the electronic properties of graphene is explored very well and in a matured state, the studies on non-electronic properties are still in the budding phase. One of the significant obstacles to extending the studies of graphene to different fields is the cost-effective and environmentally friendly large-scale synthesis and processing of high-quality graphene. Thus, a cutting-edge approach for probing graphene structures at the atomic scale is required to produce high-quality graphene for next-generation applications. As an alternative progressive technique, plasma-enabled methods have emerged as safe and green approaches to tailor different graphene structures at the nanoscale. During graphene production, plasma assembles the nanostructures from gaseous into a solid form or converts solid precursor to graphitic form 2,3. Besides, plasma techniques open up the possibility of tailoring the properties by crafting heteroatoms to the graphene lattice, which is beneficial for energy storage applications4. Therefore, this paper introduces the advantages of plasma-enabled techniques in designing graphene-based materials with different morphologies and orientations and tailoring them at the nanoscale using heteroatoms. Such plasma-assisted techniques ensure the high structural quality of graphene and controllability in the hybrid morphologies, making them frontrunner energy storage applications. Plasma also offers the production of graphene directly on any substrate surface, gives a new direction to designing binder-free electrodes for energy-related applications, and could be used as a competitive alternative approach to the widely known wet chemical procedures to design advanced graphene electrode materials for next-generation energy storage devices.Reference Geim, A. K. Graphene: Status and prospects. Science (1979) 324, 1530–1534 (2009).Dias, A. et al. N-Graphene-Metal-Oxide(Sulfide) hybrid Nanostructures: Single-step plasma-enabled approach for energy storage applications. Chemical Engineering Journal 430, 133153 (2022).Jagodar, A. et al. Growth of graphene nanowalls in low-temperature plasma: Experimental insight in initial growth and importance of wall conditioning. Appl Surf Sci 643, 158716 (2024).Santhosh, N.M. et al. N-Graphene Nanowalls via Plasma Nitrogen Incorporation and Substitution: The Experimental Evidence. Nanomicro Lett 12, 53 (2020).

Nitrogen modified graphene nanowalls for retrieval of trace level cerium from aqueous medium

Removal of cerium from environmental and aqueous streams is essential in waste water rejuvenation processes. Nitrogen modified graphene nano walls (N-GNWs) have shown ultra-high sorption efficiency of trivalent cerium from aqueous medium (Kd > 2 × 107) and a large sorption capacity of ∼ 2500 mg/g is achieved. N-GNWs were deposited on carbon paper substrate using PECVD technique. The three-dimensional nature of N-GNWs are revealed from high resolution FESEM images. Raman spectroscopic studies have shown that GNWs are defective and possess a few layer graphene like structure. Secondary Ion Mass Spectroscopic studies of the Ce sorbed N-GNWs and optical emission spectroscopy of the residual solution confirm the sorptive retrieval of cerium. Visual Minteq based ionization model is introduced to explain high (>90 %) sorption of Ce at pH≥7 and the mechanistic aspects of sorption for standard Cerium solution is discussed. The sorption involves attachment of cerium hydroxyl ions to the active cites on the sorbent surface.

A graphene flexible pressure sensor based on a fabric-like groove structure for high-resolution tactile imaging

Flexible pressure sensors hold significant promise for applications in fields such as prosthetics, electronic skin, robotics, and healthcare. Nevertheless, the challenge lies in preserving the linear sensitivity range of these sensors across a broad pressure range. In this study, we introduce a structure featuring Graphene Nano-walls (GNWs) arranged in a fabric-like groove pattern for flexible piezoresistive sensors. This design effectively accommodates material deformations, enabling the sensor to maintain exceptional sensitivity across a wide pressure range. The GNWs groove piezoresistive sensor exhibits ultra-high sensitivity (S = 2297.47 kPa−1) and outstanding linearity (R2 = 0.986) over an extensive pressure range (0.2 Pa − 425 kPa), while maintaining remarkable mechanical stability over 10,000 cycles. It boasts rapid response times of 9 ms and a recovery time of 7 ms. Owing to the fast response and high sensitivity of this sensor, we constructed a high-resolution tactile imaging system, with a surface height resolution of 20 μm and a elastic film thickness resolution of 0.1 mm. Noteworthy, we reconstructed the 3D texture of a leaf and reconstructed the shape of letters under soft elastomer. These applications underscore the potential of GNWs groove pressure sensors in various fields, including artificial intelligence, robotics, prosthetics, and so on.

High‐Resolution Carbon‐Based Tactile Sensor Array for Dynamic Pulse Imaging

AbstractWith the development of modern medicine, the importance of continuous and reliable pulse wave monitoring has increased significantly in physiological evaluation and disease diagnosis. Among them, the 3D reconstruction of the pulse wave is indispensable, and needs rely on ultra‐high resolution sensor arrays, that is, high spatial resolution, temporal resolution, and force resolution. Herein, a flexible high‐density 32 × 32 tactile sensor array based on pressure‐sensitive tunneling mechanism is develpoed. Conformal graphene nanowalls (GNWs) pattern arrays are deposited on micro‐pyramidal structural Si substrate via mask‐assisted plasma enhanced chemical vapor deposition (PECVD) method and are adopted as pressure‐sensitive electrode, exhibiting a spatial resolution of 64 dots/cm2, high sensitivity (222.36 kPa−1) and short response time (2 ms). More importantly, HfO2 tunneling layer can effectively suppress noise current, which made it sense weak pressure signals with 1/1000 force resolution and SNR of 36.32 dB. By leveraging its high‐resolution array, more holistic pulse signals are acquired and the 3D shape of the pulse wave are successfully replicated. This work shows high‐resolution sensors have significant promise for applications in remote intelligent diagnostics.

Efficient sequestration of plutonium from aqueous medium using nitrogen doped graphene nano walls

Nitrogen doped graphene nanowall(s) deposited on carbon paper is employed in sequestration of trace-level plutonium from aqueous solution using batch adsorption technique. Surface and structural characteristics of the sorbent are studied using SEM and Raman spectroscopy, respectively. Radiometric α-counting of the supernatant solution showed > 90% sorption at pH > 7. Visual Minteq modelling revealed that Pu(OH)4 species is responsible for high sorption. Freundlich model evolved as the best fit, implying multilayer deposition on a heterogeneous surface as the mechanism of sorption. The combination of 10 M HNO3 and EDTA resulted in 75% desorption. The results are promising for the sequestration of trace-level plutonium.

Vertical graphene nanowalls supported hybrid W2C/WOx composite material as an efficient non-noble metal electrocatalyst for hydrogen evolution

Research for the development of noble metal-free electrodes for hydrogen evolution has blossomed in recent years. Transition metal carbides compounds, such as W2C, have been considered as a promising alternative to replace Pt-family metals as electrocatalysts towards hydrogen evolution reaction (HER). Moreover, hybridization of TMCs with graphene nanostructures has emerged as a reliable strategy for the preparation of compounds with high surface to volume ratio and abundant active sites. The present study focuses in the preparation of tungsten carbide/oxide compounds deposited in a three-dimensional vertical graphene nanowalls (VGNW) substrate via chemical vapor deposition, magnetron sputtering and thermal annealing processes. Structural and chemical characterization reveals the partial carburization and oxidation of the W film sputtered on the VGNWs, due to C and O migration from VGNWs towards W during the high temperature annealing process. Electrochemical characterization shows the enhanced performance of the nanostructured hybrid W2C/WOx on VGNW compound towards HER, when compared with planar W2C/WOx films. The W2C/WOx nanoparticles on VGNWs require an overpotential of −252 mV for the generation of 10 mA cm−2. Chronoamperometry tests in high overpotentials reveal the compounds stability while sustaining high currents, in the order of hundreds of mA. Post-chronoamperometry test XPS characterization unveils the formation of a W hydroxide layer which favours hydrogen evolution in acidic electrolytes. We aspire that the presented insights can be valuable for those working on the preparation of hybrid electrodes for electrochemical processes.

Enhanced electromagnetic shielding with ultrathin VGNs-Metal hybrid structures

Designing and preparing lightweight electromagnetic shielding materials at the micron level is crucial for aerospace and military applications. Vertical graphene nanowalls (VGNs) offer high efficiency for electromagnetic shielding due to attributes such as high carrier mobility, porosity, and low density. This study presents the preparation of ultra-thin VGNs/metal stacked films via plasma-enhanced chemical vapor deposition (PECVD) for VGNs, and combined electron beam evaporation (EBE) with cyclic PECVD for metal layers. The PECVD technique ensures homogeneity and controllable thickness of the VGNs. The experimental results demonstrate that the interface between the VGNs and the metal layer exhibits good interfacial contact, resulting in high carrier mobility. Furthermore, incorporating a metal layer with a thickness ratio of 10 % significantly enhances conductivity by an order of magnitude. The hybrid structures exhibit remarkable electromagnetic shielding effectiveness per unit thickness (∼5300 dB mm−1) evaluated in the X-band range (8–12 GHz). Stacked films as thin as 0.01 mm achieve up to 53.4 dB of electromagnetic shielding. Finite element simulations indicate that the presence of opposing electric fields at the graphene-metal interface contributes to higher ohmic loss. The coupling effect at the interface significantly contributes to the material's excellent electromagnetic shielding effectiveness.

Processing and Functionalization of Vertical Graphene Nanowalls by Laser Irradiation.

The processing of vertical graphene nanowalls (VGNWs) via laser irradiation is proposed as a means to modulate their physicochemical properties. The effects of the number of applied pulses and fluence of each pulse are examined. Raman spectroscopy studies the effect of irradiation on the chemical structure of the VGNWs. Results show a decrease in density of defects and number of layers, which points toward a mechanism including evaporation of amorphous or loosely bonded C from defective points and recrystallization of graphene. Moreover, the effect of laser irradiation parameters on the morphology of Mo thin films deposited on VGNWs is investigated. The received thermal dosage results in the formation of particles. In this case, the number of pulses and pulse fluence are found to affect the size and distribution of these particles. The study provides a novel approach for the functionalization of VGNWs via laser irradiation, which can be extended to other graphene-based nanostructures.

Impact of shape of Inconel 600 substrate on deposition of carbon nanostructures by microwave plasma CVD

This study investigates the influence of shape of Inconel 600 substrate on the deposition process using Microwave Plasma Chemical Vapor Deposition (MPECVD) for carbon nanofibers (CNFs) and graphene nanowalls (GNWs) on Inconel 600 substrates. The unique shape of the substrate significantly directs the deposition, revealing a noteworthy shape influenced transition. Notably, a novel pathway emerges for the electric field-driven transformation of Carbon Nanofibers (CNFs) into GNWs—an observation unprecedented in MPECVD processes. Comprehensive characterization, incorporating FESEM, Raman spectroscopy, and fully electromagnetic 3D frequency domain simulations, illuminates the subtle yet impactful interplay between substrate morphology and nanomaterial formation, providing valuable scientific insights.

Enhancing Interfacial Capacitance by Boron Doping in Vertically Porous Carbon Toward High-Performance AC Filtering Electrochemical Capacitors.

Electrochemical capacitors (ECs) show great perspective in alternate current (AC)filtering once they simultaneously reach ultra-fast response and high capacitance density. Nevertheless, the structure-design criteria of the two key properties are often mutually incompatible in electrode construction. Herein, it is proposed that combining vertically oriented porous carbon with enhanced interfacial capacitance (Ci) can efficiently solve this issue. Theoretically, the density function theory calculation shows that the Ci of a carbon electrode can be enhanced by boron doping due to the corresponding compact induced charge layer. Experimentally, the vertical-oriented boron-doped graphene nanowalls (BGNWs) electrodes, whose Ci is enhanced from 4.20 to 10.16µFcm-2 upon boron doping, are prepared on a large scale (480 cm2) using a hot-filament chemical vapor deposition technique (HFCVD). Owing to the high Ci and vertically oriented porous structure, BGNWs-based EC has a high capacitance density of 996µFcm-2 with a phase angle of - 79.4° at 120Hz in aqueous electrolyte and a high energy density of 1953µFV2cm-2 in organic electrolyte. As a result, the EC is capable of smoothing 120Hz ripples for 60Hz AC filtering. These results provide enlightening insights on designing high-performance ECs for high-frequency applications.

Graphene nanowalls formation investigated by Electron Energy Loss Spectroscopy

The properties of layered materials are significantly dependent on their lattice orientations. Thus, the growth of graphene nanowalls (GNWs) on Cu through PECVD has been increasingly studied, yet the underlying mechanisms remain unclear. In this study, we examined the GNWs/Cu interface and investigated the evolution of their microstructure using advanced Scanning transmission electron microscopy and Electron Energy Loss Spectroscopy (STEM-EELS). GNWs interface and initial root layers of comprise graphitic carbon with horizontal basal graphene (BG) planes that conform well to the catalyst surface. In the vertical section, the walls show a mix of graphitic and turbostratic carbon, while the latter becomes more noticeable close to the top edges of the GMWs film. Importantly, we identified growth process began with catalysis at Cu interface forming BG, followed by defect induction and bending at ‘coalescence points’ of neighboring BG, which act as nucleation sites for vertical growth. We reported that although classical thermal CVD mechanism initially dominates, growth of graphene later deviates a few nanometers from the interface to form GNWs. Nascent walls are no longer subjected to the catalytic action of Cu, and their development is dominated by the stitching of charged carbon species originating in the plasma with basal plane edges.

Nanoengineered micro-supercapacitors based on graphene nanowalls for self-powered wireless sensing system

This work presents a comprehensive investigation of micro-supercapacitors (MSCs) based on graphene nanowalls (GNWs), covering core material synthesis, device fabrication, evaluation, and application demonstrations. Three-dimensional hierarchical GNWs structures are grown successfully by a microwave plasma-enhanced chemical vapor deposition (MPECVD), with detailed descriptions of the synthesis process and underlying mechanisms. The structural and morphological properties of the GNWs are thoroughly analyzed. Several types of MSCs are reported, ranging from thin-film to three-dimensional (3D) MSCs, as well as symmetric to asymmetric MSCs. Thin-film MSC is developed by a novel micromachining process for one-step fabricating GNWs-Ni core-shell composite microstructures. A solid-state MSC utilizing 3D hierarchical electrode is created by a fully micro electro mechanical system (MEMS)-compatible process. This involves depositing GNWs-RuOx hybrid nanostructures onto microstructure scaffolds formed using deep reactive ion etching (deep RIE). Additionally, another 3D MSC utilizes GNWs-PANI electrode material deposited on silicon nanowires generated through metal-assisted chemical etching (MACE) method. To enhance MSCs performance, asymmetric MSC is proposed and realized, incorporating GNWs-MnO2 acting as the positive electrode and carbon black serving as the negative electrode. Furthermore, the successfully combination of the fabricated MSCs with an energy harvesting system is demonstrated. The self-powered sensing system driven by solar energy, with the harvested energy stored in MSCs, is effectively showcased, opening up new possibilities for futuristic MSCs to accumulate and store harvested energy as usable electricity. This demonstration has significant potential in fields such as self-powered wireless IoT sensing systems, offering valuable contributions towards sustainable and autonomous energy solutions.

Cluster Mo2C deposited on graphene nanowalls by x-ray photoelectron spectroscopy

Molybdenum deposited on carbon graphene nanowalls was characterized by x-ray photoelectron spectroscopy with an Al Kα (1486.6 eV) excitation source. The sample was fixed to a stainless-steel sample holder with copper double-sided adhesive tape. Survey spectrum, C 1s, O 1s, Si 2p, and Mo 3d core levels spectra were acquired.

Enhancing in-plane uniformity of graphene nanowalls using a rotating platform for solid-state lithium-ion battery

Enhancing in-plane uniformity of graphene nanowalls using a rotating platform for solid-state lithium-ion battery

3D Printed Carbon Framework with the Graphene Aerogel for Microbial Fuel Cell Application

There is a high interest in living organism-compatible materials associated with electrically active interfaces. Bacteria/electrode interfaces implement smart, functional systems with responses, based on which it is possible to elaborate self-regulating energy generation systems. Carbon materials have a number of advantages, such as biocompatibility, low electrical resistance, and the possibility of increasing the electrode surface on an industrial scale. The most promising approach for the industrial production of electrodes is 3D printing. We propose a 3D-printed carbon electrode – a novel lightweight material for electrodes in bioelectrochemical systems for efficient bioelectricity utilization.The pyrolytic process for manufacturing carbon electrodes is promising for upscaling and industrial applications. However, there is a problem of volume loss when 3D-printed polymers are pyrolyzed in an inert environment. We propose a new strategy for the thermal treatment of 3D-printed polymers that allow for reduced volume loss under pyrolytic carbonization. In addition, to achieve a higher electrode surface area, the graphene aerogel could be impregnated into the 3D-printed scaffolds. Chemical modification of graphene surface can enhance biocompatibility. Specifically, the oxidation of graphene leads to forming a hydrophilic and biocompatible material. We tune graphene hydrophilic properties and electrical conductivity via control over the thermal reduction of the oxidized form of graphene–graphene oxide1.Such sponge morphology affords 3D-printed carbon scaffolds an excellent lightweight host scaffold for microorganisms, in which the graphene nanowalls are homogeneously occupied by S. oneidensis MR-1. We demonstrate a novel sustainable method to produce graphene-based lightweight 3D printed electrode materials for green energy production from biomass. The proposed technology creates the opportunity for novel, innovative, disruptive graphene applications that can lead to the establishment of new energy-related industries and facilitate many startups in the ecosystem. Acknowledgments This work was supported by the Ministry of Education (Singapore) through the Research Centre of Excellence program (grant EDUN C-33-18-279-V12, I-FIM). References Xuanye Leng, Ricardo J. Vazquez, Samantha R. McCuskey, Glenn Quek, Yude Su, Konstantin G. Nikolaev, Mariana C.F. Costa, Siyu Chen, Musen Chen, Kou Yang, Jinpei Zhao, Mo Lin, Zhaolong Chen, Guillermo C. Bazan, Kostya S. Novoselov, Daria V. Andreeva, Carbon, 205, 2023, 33-39.

Transfer-free preparation of flexible strain sensors using high quality VGNs

Recently, flexible mechanically stimulated sensors have attracted widespread attention in the field of wearable devices and soft robotics. Due to the high stretchability, vertical graphene nano-walls (VGNs) become a competitive candidate to be applied in the flexible strain sensors. Herein, by utilizing the inductively coupled plasma chemical vapor deposition (IC-PECVD) method, a transfer-free VGNs-based flexible strain sensors were successfully prepared on fluorphlogopite mica substrate at 600 ℃. The quality of as-grown VGNs were obviously improved by increasing the ratio of H2 to CH4. The directly prepared VGNs on interdigital electrode could improve the interfacial contact between VGNs and interdigital electrode. The results of bending tests show that flexible sensors which VGNs directly grown on the interdigital electrode have good performance. The combination of sleeves and the sensors reveal that the transfer-free flexible strain sensors could perform well in wearable devices.

Graphene nanowalls grown on copper mesh

Graphene nanowalls (GNWs) can be described as extended nanosheets of graphitic carbon where the basal planes are perpendicular to a substrate. Generally, existing techniques to grow films of GNWs are based on plasma-enhanced chemical vapor deposition (PECVD) and the use of diverse substrate materials (Cu, Ni, C, etc) shaped as foils or filaments. Usually, patterned films rely on substrates priorly modified by costly cleanroom procedures. Hence, we report here the characterization, transfer and application of wafer-scale patterned GNWs films that were grown on Cu meshes using low-power direct-current PECVD. Reaching wall heights of ∼300 nm, mats of vertically-aligned carbon nanosheets covered square centimeter wire meshes substrates, replicating well the thread dimensions and the tens of micrometer-wide openings of the meshes. Contrastingly, the same growth conditions applied to Cu foils resulted in limited carbon deposition, mostly confined to the substrate edges. Based on the wet transfer procedure turbostratic and graphitic carbon domains co-exist in the GNWs microstructure. Interestingly, these nanoscaled patterned films were quite hydrophobic, being able to reverse the wetting behavior of SiO2 surfaces. Finally, we show that the GNWs can also be used as the active material for C-on-Cu anodes of Li-ion battery systems.

Deposition and in-situ formation of nanostructured Mo2C nanoparticles on graphene nanowalls support for efficient electrocatalytic hydrogen evolution

To accelerate the transition to a green economy based on hydrogen, more efficient and cost-effective electrocatalysts should be adapted. Among them, transition metal carbides, particularly Mo2C, have gained significant attention within the scientific community due to their abundance and potential for high performance in the hydrogen evolution reaction (HER). This study introduces a bottom-up approach involving chemical vapor deposition, impregnation in solvent containing the Mo precursor and thermal annealing processes to carburize the Mo nanostructures anchored on vertical graphene nanowalls supports (GNWs). The role of GNWs is highlighted in the above processes. First, they provide abundant defective sites on their edges, which facilitate the binding of the metal compound molecules. Second, they provide C species during the annealing process which migrate and react with the transition metal to carburize it. Thus, they act as both C precursor and support system. Electrochemical characterization shows that the hybrids can be very efficient electrocatalysts towards hydrogen evolution reaction in acid electrolyte. When used as a cathode in a cell, it requires only − 141 mV to generate 10 mA/cm2 and shows excellent stability after hours of operation, making them highly promising for practical applications. This study paves the way for the design of hybrid nanostructures, utilizing nanocatalyst deposition on three-dimensional graphene supports. Such advancements hold great potential for driving the development of sustainable and efficient hydrogen production systems.