Monolithic Graphene Research Articles

Lithium Functionalization in a Three-Dimensional Graphene Monolith for Enhanced Adsorption–Desorption Hydrogen Storage

Lithium Functionalization in a Three-Dimensional Graphene Monolith for Enhanced Adsorption–Desorption Hydrogen Storage

Enhancing CO2 capture through innovating monolithic graphene oxide frameworks

The advancement and engineering of novel crystalline materials is facilitated through the utilization of innovative porous crystalline structures, established via KOH-treated monolithic graphene oxide frameworks. These materials exhibit remarkable and versatile characteristics for both functional exploration and applications within the realm of CO2 capture. In this comprehensive study, we have synthesized monolithic reduced graphene oxide-based adsorbents through a meticulous self-assembly process involving different mass ratios of GO/malic acid (MaA) (1:0.250, 1:0.500, and 1:1 by weight). Building upon this foundation, we further modified MGO 0.250 through KOH-treatment by chloroacetic acid method, leading to the creation of MGO 0.250_KOH, which was subjected to CO2 capture assessments. The comprehensive investigation encompassed an array of parameters including morphology, specific surface area, crystal defects, functional group identification, and CO2 capture efficiency. Employing a combination of FT-IR, XRD, Raman, BET, SEM, HR-TEM, and XPS techniques, the study revealed profound insights. Particularly notable was the observation that the MGO 0.250_KOH adsorbent exhibited an exceptional CO2 capture performance, leading to a significant enhancement of the CO2 capture capacity from 1.69 mmol g−1 to 2.35 mmol g−1 at standard conditions of 25 °C and 1 bar pressure. This performance enhancement was concomitant with an augmentation in surface area, elevating from 287.93 to 419.75 m2 g−1 (a nearly 1.5-fold increase compared to MGO 1.000 with a surface area of 287.93 m2 g−1). The monolithic adsorbent demonstrated a commendable production yield of 82.92%, along with an impressive regenerability of 98.80% at 100 °C. Additionally, adsorbent's proficiency in CO2 adsorption, rendering it a promising candidate for post-combustion CO2 capture applications. These findings collectively underscore the capacity adsorbents to significantly amplify CO2 capture capabilities. The viability of employing this strategy as an uncomplicated pre-treatment technique in various industrial sectors is a plausible prospect, given the study's outcomes.

UV activated monolithic graphene Oxide-Based adsorbents for dynamic CO2 Capture: Kinetic, isotherm and thermodynamic studies

In this research article, the synthesis of monolithic graphene oxide-based adsorbent was prepared by the self-assembly process of graphene oxide followed by oxalic acid reduction with various mass ratios and activated by UV treatments. The optimized adsorbent reveals an excellent dynamic CO2 capture capacity of 1.65 mmol g−1 at 25 °C, owing to its elevated BET surface area of 577.3 m2/g. Considering the desorption step with a constant volume flow rate, it becomes evident that the pressure drop results in excessive consumption of desorbing gas (N2) approximately 50 % for the regeneration process. Several studied were investigated; the regenerability of 98.8 %, an excellent CO2/N2 selectivity, fast kinetics, the pseudo-second-order kinetic model and Freundlich isotherm model were best fitted. Thermodynamic studies reveal the heterogeneity of adsorption site, the adsorption process endothermic nature, as indicated by ΔH° value of + 13.1154139 KJ mol−1, underscoring the distinctive characteristic property of chemisorption.

A topological nodal surface carbon honeycomb for sodium-ion battery anode

Motivated by the successful synthesis of three-dimensional (3D) graphene monoliths, we propose a 3D carbon honeycomb structure, tC40, composed of graphene-nanoribbons linked with 5-5-8 defects based on first-principles calculations. This structure is not only dynamically, thermally, and mechanically stable, but also possesses interesting electronic properties, including the multiple topological nodal surfaces on the high-symmetry plane k3=0 with double and quadruple degeneracies of bands in the reciprocal space, and the nontrivial surface states connecting different topological nodal surfaces parallel to the z-axis. By using the k·p model, we further show that, unlike previously reported nodal surfaces, the energy dispersion of the quadruply degenerated nodal surface is proportional to the k32, while the Hamiltonian of the doubly degenerated nodal surface is formed by the essential degeneracy of the valence and conduction bands. In addition, we explore the application of this nodal surface carbon as an anode material for sodium-ion batteries (SIBs), and find that tC40 exhibits good performance with a high reversible capacity of 186 mAh·g−1, a low sodium ion migration barrier of 0.1 eV, and a small charging/discharging volume change of 0.79 %. This work expands the family of topological carbon materials and their applications in SIBs.

A new 3D porous metallic carbon allotrope composed of 5–7 nanoribbons as an anode material for sodium-ion batteries

Motivated by the successful synthesis of three-dimensional (3D) graphene monoliths, tremendous effort has been devoted to the design of 3D porous metallic carbon allotropes with rich topology by assembling various nanoribbons for the anode materials of metal-ion batteries in recent years. Going beyond the allotropes reported so far we propose a new 3D carbon monolith, Hex-C57, by using 5–7 nanoribbons observed in the experiment as the building block. Hex-C57 is found to be dynamically, thermally, and mechanically stable, and electronically metallic. An analysis based on the tight-binding model reveals that the metallicity originates from the pz-orbitals of the sp2-hybridized carbon atoms, forming the conducting channels along the axial direction. With the advantages of intrinsic metallicity, mechanical ductility, and ordered pores, Hex-C57 is a highly promising anode material for sodium-ion batteries (SIBs). Calculations of the electrochemical properties show that Hex-C57 possesses a high reversible gravimetric capacity (334.69 mAhg−1) and volumetric capacity (314.61 mAhcm−3), a small volume change (1.45%), very low diffusion barriers (0.046–0.070 eV), and a low average open-circuit voltage (0.18 V). This work not only expands the 3D porous carbon family with different nanoribbons as the building blocks, but also demonstrates the functionality of unconventional 5–7 carbon rings-assembled materials.

Simultaneous solar-driven seawater desalination and continuous oil recovery

Oil spills and freshwater scarcity remain two worldwide challenging issues. Emerging efforts have been made either to recover oil from oil/water mixture or to extract freshwater from abundant seawater. However, almost all current devices focus on oil recovery or seawater desalination separately, which is lack of energy efficiency. Herein, we propose a design of mechanically robust, bi-functional graphene devices (BGDs), containing vertical graphene sheets decorated on inverted U-shaped graphene monoliths, to achieve simultaneous solar-driven vapor generation and continuous oil recovery from oil-contaminated seawater. Benefiting from the unique wettability design of the BGDs, water evaporates on the hydrophilic surfaces, and meanwhile oil can be spontaneously recovered through the hydrophobic/oleophilic interior channels due to siphon action. Moreover, the strong photothermal effect of vertical graphene can boost both the seawater desalination and oil recovery performance. As a result, a vapor generation rate of 2.04 kg m−2 h−1 and an oil recovery rate of 105.8 L m−2 h−1 are concurrently achieved under 1-sun irradiation. The design of bi-functional devices provides a new means to maximize the utilization of solar power and reduce the costs for multi-functional practical environmental engineering applications.

Density and porosity optimization of graphene monoliths with high mass‐loading for high‐volumetric‐capacitance electrodes

AbstractImproving the volumetric capacitance of graphene materials for supercapacitors without sacrificing their rate capability, especially at high mass‐loading, is a challenge because of the sluggish electrochemical kinetics of compact graphene electrodes. Here, a compact graphene monolith (dense graphene ribbons [DGRs]‐0.6) was fabricated by using graphene oxide ribbons as building blocks and deliberately harmonizing the graphene primitive unit structure and interlayer spacing. The DGRs‐0.6 contained abundant oxygen‐containing functional groups and a highly interconnected pore structure, resulting in a large ion‐accessible surface area, a high packing density, and fast electron/ion transport pathways. The DGRs‐0.6 electrode exhibited a volumetric capacitance of 316 F cm–3, a rate capability of 220 F cm–3 at 100 A g–1, and ultralong cycling stability. For a mass loading of 11 mg cm−2, the DGRs‐0.6 delivered volumetric capacitances of 150 F cm−3 at 1 A g−1 and 109 F cm−3 at 50 A g−1. The good rate capability and volumetric capacitance of DGRs‐0.6 under high mass loading demonstrate its potential as a supercapacitor electrode for practical applications.

Zinc-guided 3D graphene bulk materials for high-performance binder-free anodes of potassium-ion batteries

Potassium ion batteries are promisingly proposed for the large cale energy storage. However, potassium with large ion radius causes severe volumetric expansion of anodes during charging, which deteriorates the rate and the cycling performances of batteries. Herein, a honeycomb-like graphene monolith with rich micropores is prepared. The monolith is further applied as the binder-free anode for potassium ion batteries. It shows the remarkable rate performance with a capacity of 180 mAh g−1 at a current density of 10 A g−1, and it can stably run for 4000 cycles at 1 A g−1. Kinetic studies and theoretical analyses reveal that the large graphitic interlayer spacing, the nitrogen doping, and the 3D network structure can significantly promote the diffusion rate, the absorption of potassium ions, as well as the transports of electrons and ions. The graphene-based potassium ion batteries can thus boost the development of renewable energies.

Fabrication and Characterization of Micrometer Scale Graphene Structures for Large-Scale Ultra-Thin Electronics

Graphene offers many useful properties that can revolutionize modern electronic devices. Specifically, it provides high charge carrier mobility in a mechanically robust, atomically thin form factor. Many of these properties are observed in graphene which is prepared from exfoliated graphite and processed with electron beam lithography. These processes are both time intensive and cost- prohibitive for the large-scale production necessary for use in consumer electronics. This work details the processing and characterization of commercially available graphene from chemical vapor deposition (CVD) on SiO2/Si and on hBN-layered SiO2/Si wafers using conventional photolithography on the 4″ wafer standard. The findings indicate that the CVD graphene films are resilient after processing even for lengths up to 1 mm. Electrical characterization via resistance measurements and the Hall Effect at room temperature clearly indicates the influence of the substrate material on the graphene’s electrical properties. At these length scales, graphene on SiO2 resembles that of a lightly doped semiconductor in terms of its carrier density (7.8 × 1015 cm−2), yet its carrier mobility (2.6 cm2/Vs) resembles that of a metal. Graphene on hBN/SiO2 has a carrier density of 8.2 × 1012 cm−2 and carrier mobility of 2.68 × 103 cm2/Vs—comparable to existing high-mobility semiconducting materials. CVD graphene and conventional photolithography does provide a cost-effective means for producing large form-factor graphene devices for low to moderate mobility applications and eventually for large-scale monolithic graphene electronics.

Nitrogen-Doped Graphene Monolith Catalysts for Oxidative Dehydrogenation of Propane.

It’s of paramount importance to develop renewable nanocarbon materials to replace conventional precious metal catalysts in alkane dehydrogenation reactions. Graphene-based materials with high surface area have great potential for light alkane dehydrogenation. However, the powder-like state of the graphene-based materials seriously limits their potential industrial applications. In the present work, a new synthetic route is designed to fabricate nitrogen-doped graphene-based monolith catalysts for oxidative dehydrogenation of propane. The synthetic strategy combines the hydrothermal-aerogel and the post thermo-treatment procedures with urea and graphene as precursors. The structural characterization and kinetic analysis show that the monolithic catalyst well maintains the structural advantages of graphene with relatively high surface area and excellent thermal stability. The homogeneous distributed nitrogen species can effectively improve the yield of propylene (5.3% vs. 1.9%) and lower the activation energy (62.6 kJ mol−1 vs. 80.1 kJ mol−1) in oxidative dehydrogenation of propane reaction comparing with un-doped graphene monolith. An optimized doping amount at 1:1 weight content of the graphene to urea precursors could exhibit the best catalytic performance. The present work paves the way for developing novel and efficient nitrogen-doped graphene monolithic catalysts for oxidative dehydrogenation reactions of propane.

Spontaneous power generation from broad-humidity atmospheres through heterostructured F/O-bonded graphene monoliths

Spontaneous energy-harvesting from the environment without external stimuli is a challenging task for clean and renewable power. However, existing carbon-based energy generators require the sequential gradient structure and can only produce a low and desultory power relying on the atmospheric moisture. Here we develop a direct dry-compression molding strategy to rapidly manufacture the heterostructured F/O-bonded graphene monolith (H-OGF) with two integrated parts of fluorinated oxidized graphene (FOG) and oxidized graphene (OG) for the first time. Fabricated H-OGF device spontaneously generates a voltage of ~1.25 V (the largest voltage reported for spontaneous carbon-based energy-harvesting devices) and it also achieves a continuous power output for external resistance over 40,000 s with good stability and recyclability. The initial energy input is originated from the transformation of moisture from the gaseous state in atmosphere to the agminated state in H-OGF. This promotes the H+ dissociation and the spontaneous formation of self-maintained and huge H+ concentration difference between FOG and OG layers, which works as the driving force for the continuous power production. Moreover, the introduced fluorine with the maximal electronegativity (3.98) accelerates the carboxyl’s ionization and further magnifies H+ concentration difference. Connecting several H-OGF devices proportionally amplifies voltage up to 10 V for powering electronics and obtains a wearable power supply. Our findings make H-OGF devices promising candidates for low-budget and self-sustaining energy systems as rigorous requirement of location or environmental conditions is loosened.

Glycol-Thermal Continuous Flow Synthesis of Graphene Gel

Hydrothermal treatment of graphene oxide (GO) aqueous dispersion has been extensively applied to create graphene (a.k.a., chemically modified graphene, or reduced GO) hydrogels, which were dried to yield high-density graphene monoliths and powders with promising potential for electrochemical energy storage applications. Here, we demonstrated a glycol-thermal route that allows the preparation of a graphene gel at around 150 °C, which is below the boiling point of ethylene glycol (EG) and thus eliminates the need for a sealed pressurized reaction vessel. As a result, flow synthesis can be achieved by flowing a GO dispersion in EG through a Teflon tube immersed in a preheated oil bath for continuous production of a graphene gel, which, upon drying, shrinks to yield a densified graphene solid.

Cobalt-Doping of Molybdenum Disulfide for Enhanced Catalytic Polysulfide Conversion in Lithium-Sulfur Batteries.

Metal sulfides, such as MoS2, are widely investigated in lithium-sulfur (Li-S) batteries to suppress the shuttling of lithium polysulfides (LiPSs) due to their chemical adsorption ability and catalytic activity. However, their relatively low conductivity and activity limit the LiPS conversion kinetics. Herein, the Co-doped MoS2 is proposed to accelerate the catalytic conversion of LiPS as the Co doping can promote the transition from semiconducting 2H phase to metallic 1T phase and introduce the sulfur vacancies in MoS2. A one-step hydrothermal process is used to prepare such a Co-doped MoS2 with more 1T phase and rich sulfur vacancies, which enhances the electron transfer and catalytic activity, thus effectively improving the LiPS adsorption and conversion kinetics. The cathode using the three-dimensional graphene monolith loaded with Co-doped MoS2 catalyst as the sulfur host shows a high rate capability and long cycling stability. A high capacity of 941 mAh g-1 at 2 C and a low capacity fading of 0.029% per cycle at 1 C over 1000 cycles are achieved, suggesting the effectively suppressed LiPS shuttling and improved sulfur utilization. Good cyclic stability is also maintained under a high sulfur loading indicating the doping is an effective way to optimize the metal sulfide catalysts in Li-S batteries.

Highly compressible graphene aerogel with high thermal conductivity along both in-plane and through-plane directions

Graphene-based thermal interface materials (TIMs), such as horizontal graphene papers and vertical graphene monoliths, commonly possess high thermal conductivity (TC) only along either in-plane or through-plane direction due to their high anisotropy structure. Three-dimensional (3D) graphene monoliths with interconnected network can extend the excellent thermal transport performances of two-dimensional graphene to macro monoliths along multi-directions. However, the high porosity of 3D graphene monoliths usually leads to low TC. Here, highly compressible graphene aerogels (HCGAs) with closely packed cell walls and regularly cellular structure were prepared. The HCGAs can be highly compressed (95% compressive strain) to reduce the porosity while maintaining the continuously thermal transport paths. Significantly increased TC along both in-plane and through-plane directions can be obtained by directly mechanical compression of the aerogels. HCGAs with initial density of 11.5 mg cm−3 at 95% compressive strain possess in-plane TC of 167.2 W m−1K−1 and through-plane TC of 46.8 W m−1K−1, which outperforms other carbon-based TIMs reported previously.

3D isotropic hole-in-platelet graphene hydrogels with high surface area and fast mass transfer ability as efficient adsorbents

Abstract Integrating the advantages in adsorption and solving the problems of agglomeration and reclamation of 2D graphene, 3D graphene have been regarded as the idea adsorbents for next generation. Nerveless, the mediocre adsorption capacity and comparatively long adsorption time are the key bottlenecks hindering the practical implementations of graphene monolith. Here, we displayed the rational design of 3D graphene hydrogels with isotropic microstructure and in-platelet holes (3D NGH). The isotropic microstructure induced by reducing the size of graphene oxide (GO) lamellae effectively reduced the overlap ratio of graphene and rendered NGH an desired specific surface area (SSA) of 437.07 m2 g−1. Benefiting from that, NGH exhibited an ultrahigh maximal adsorption capacity of 1120.28 mg g−1, where methylene blue (MB) was chosen as the verifiable pollutant. Meanwhile, the in-platelet holes of NGH obtained by simply HNO3 etching significantly improved the mass transfer ability and adsorption rate of SGH (about a fivefold increase from 2.235 × 10−5 to 12.670 × 10−5 g mg−1 min−1). This facile and scalable preparation tackled the two critical issues of 3D graphene adsorbents simultaneously and laid a valuable groundwork for future development in constructing graphene-based composite materials for environmental or energy applications.

Rational design of high-performance thermal interface materials based on gold-nanocap-modified vertically aligned graphene architecture

The rapid increase of the packaging integration and power density of devices in electronics leads to urgent demands for high-performance thermal interface materials (TIMs) to efficiently solve the accompanying thermal management problem. Although various highly thermally conductive materials (such as graphene, carbon nanotube, and boron nitride nanosheet) combined with diversified structure design have been proposed to address this issue, it remains challenging to achieve a satisfactory TIM with both high through-plane thermal conductivity (κ⊥) and low contact thermal resistance (Rcontact) for meeting the practical application requirements. This study solves this problem by constructing a loosely packed and vertically aligned graphene monolith (VAGM), which was prepared by simply rolling up hybrid double-layer strips composed of porous polymer foam adhered onto the graphene paper, exhibiting an ultrahigh κ⊥ of 276 W m-1 K-1. Moreover, a cap modification strategy by transferring the nanometer-thick gold (Au) foils onto both sides of VAGM was carried out to further optimize the contact state with roughness surface from heater/heat sink, finally giving a low Rcontact of 0.41 K cm2 W-1 (double sides). As a result, our proposed graphene-based TIM exhibits an enhancement in cooling efficiency of ≈1.15 times compared to that of the state-of-the-art TIM (≈30 W m-1 K-1) in the TIM performance test, manifesting its superior ability to meet the ever-increasing heat dissipation requirement.

A graphene-based hydrogel monolith with tailored surface chemistry for PFAS passive sampling.

Aquatic contamination by per- and polyfluorinated alkyl substances (PFAS) has attracted global attention due to their environmental and health concerns. Current health advisories and surface water regulatory limits require PFAS detection in the parts per trillion (ppt) range. One way to achieve those low detection limits is to use a reliable passive sampling-based monitoring tool for PFAS, as exists for numerous nonpolar persistent organic pollutants. Here we introduce a new graphene-based hydrogel monolith and describe its synthesis, chemical functionalization, property characterization, and testing as a PFAS equilibrium passive sampler. The graphene monoliths were self-assembled by hydrothermal treatment from graphene oxide (GO) aqueous dispersions to produce free standing cylinders of ~563 mm3 volume consisting of ~4 wt-% thin-walled porous graphene and ~96 wt-% water. The uptake of 23 PFAS was measured on the as-produced monoliths, and equilibrium partition coefficients (KSW), were derived for longer chain (C≥8) perfluoroalkyl acids (PFAA) and neutral precursors such as sulfonamides (log KSW range 1.9 - 3.6). To increase the KSW for shorter chain PFAA, the monoliths were chemically modified by a new diazonium-based grafting reaction that introduces positive surface charge without damage to the graphenic backbone. Introduction of benzylamine moieties through the diazonium intermediate switches zeta potential at pH 7 from -45mV (as-produced graphene) to + 5mV. This modification increased the sorption of short and middle chain PFAA by ten-fold (e.g. log KSW for PFBA increased from 1.3 to 2.2), thereby improving the functionality of the passive sampler device for a wider range of PFAS. Field deployments demonstrated that the graphene monoliths were capable of detecting key PFAS in the Delaware River.

Fabrication of 3D monolithic graphene foam/polycaprolactone porous nanocomposites for bioapplications

Aiming at the production of light, porous, conductive, biosafe composites, in this paper we are presenting a novel fabrication method for monolithic, three-dimensional (3D) graphene foam (GF)/porous polymer composites. The synthesis adopts a novel process architecture by using Ni foam templates in an inductive heating chemical vapor deposition growth process, and by removing Ni chemically while retaining graphene integrity by the reversible application of cyclododecane (CD); finally, nondestructive coating procedures with polycaprolactone (PCL) solutions have been developed. The composites can be optimized to enhance electrical conduction, flexibility and mechanical properties, while mixing PCL and CD allows to coat the GF with a novel mesoporous polymer coating. By tuning the GF properties, the typical electrical resistance of the 3D forms can be reduced to a few 10 s of Ohms, values that are maintained after the PCL coatings. The current study achieved a GF fraction ranging between 1 and 7.3 wt%, with even the lower graphene content composites showing acceptable electrical and mechanical properties. The properties of these conductive 3D-GF/PCL composites are in line with the requirements for applications in the field of nerve tissue engineering.Graphical abstract

Fabrication of Graphene‐Based Self‐Assembly Monoliths through Reversible Fluorination and Defluorination Strategy

AbstractThe low bending stiffness and inferior self‐lubricating ability of graphene bring about flexible nanosheet and poor mobility, greatly restricting its well‐organized self‐assembly in direct solid‐phase molding. Herein, abundant fluorine atoms are introduced onto graphene nanosheet to obtain fluorinated graphene (FG). A direct dry‐compression molding achieves to rapidly fabricate highly compact FG monolith under room temperature. Tracing origins, the enhanced bending stiffness guarantees relatively flat FG nanosheet and excellent self‐lubricating ability actuates flat FG nanosheets to automatically slip, thereby accomplishing well‐organized and compact layer‐by‐layer stacking with interlock structure. Whereafter, highly compact graphene monolith is finally obtained by high‐temperature annealing, because interlock structure in FG monolith restricts graphene′s deformations during defluorination. Obtained graphene monolith owns a high conductivity of 5.5 × 104 S m−1 and compression strength of 77 MPa, while graphene without above process only forms fluffy foam with a low conductivity of 6.8 S m−1. Interestingly, transitional FG monolith presents a higher compression strength of 102 MPa, ultralow dielectric constant of 1.72 and prolongable chemical reactivity for preparing “Janus” monolith. Designing reversible fluorination and defluorination strategy offers an unexplored avenue to effectively manufacture high‐quality graphene‐based monoliths.

Acoustoelectric Amplifier With 1.2-dB Insertion Gain Monolithic Graphene Construction and Continuous Wave Operation.

While there have been many years of research on the acoustoelectric effect, there has not been a successful approach or demonstration to provide a manufacturable, continuous wave (CW) acoustoelectric amplifier (AEA) with insertion gain. This letter will present the results of a 169.5-MHz surface acoustic wave (SAW) delay line on 128YX lithium niobate with an embedded monolithic coupled AEA (CAEA) demonstrating a terminal gain of 1.2 dB. The impedance-matched delay line without the CAEA has an insertion loss of 4.6 dB, and with the operational CAEA, the measured gain is 1.2 dB, yielding a net insertion gain of 5.8 dB. The CAEA uses approximately 137 mW dc power at the current peak operational gain. This letter will present experimental results of device performance and discuss the new embodiment for achieving the net insertion gain.