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A graphene-base hot electron transistor integrated with a 2D material heterojunction is demonstrated as a frequency modulator. Our device can operate as a doubler or tripler with AC signals from 100 kHz to 10 MHz in single tunneling transistor.

Na3V2(PO4)3 (NVP) is a member of the sodium superionic conductor (NASICON) family and has been extensively studied as a cathode material for sodium-ion batteries (SIBs) for more than three decades due to its stable voltage platform, high capacity, and stable cycle life. However, the presence of toxic and expensive V elements restricts the utilization of NVP-based SIBs. To overcome this, energy researchers have employed a cation swapping approach, which resulted in new NASICON-type manganese-substituted sodium vanadium phosphate (MSVP) cathodes for SIBs. Na4MnV(PO4)3 (NMVP) is among the new generation of high-energy, risk-free NASICON-type MSVP cathodes, and its use for SIBs was documented in 2016. There has been strong acceptance of MSVP-based cathodes among materials researchers due to their cost and economic advantages. In a short period, considerable work has been done to increase the commercial potential of MSVP-based cathodes for SIBs. This review summarizes the pioneering developments made with MSVP-based cathodes, with a special focus on their structural and electrochemical evolution. This review can serve as a reference for future energy researchers fabricating highly efficient and safer NASICON cathodes not only for SIBs but also for other energy storage applications.

Single-atom catalysts (SACs) with metal–nitrogen (M–N) moiety are effective in boosting the redox kinetics of lithium–sulfur (Li–S) batteries. However, the precise preparation of SACs with controll...

Background The yield rate for the synthesis of large-area and high-quality graphene, based on the chemical vapor deposition (CVD) method, is limited by the reactor size of a tubular furnace. Additionally, the reported methods to achieve a high-throughput process are still challenging. Currently, the rolled-up or vertically stacked configuration setup is applied to increase the loading growth. However, the reported methods limit the kinetic reaction of CVD growth and lead to the degradation of the uniformity and crystallinity of as-grown graphene. Methods Here, we propose a novel method to produce a high-yield and uniform monolayer graphene film by helical stacking of Cu with highly porous carbon cloth as an efficient interdiffusion mediator. Additionally, computational fluid dynamics (CFD) is applied to simulate the dynamic distribution within the mediator. Significant Findings This method allows the rapid synthesis of graphene films of up to 900 cm2 for each batch of growth in a 1-inch furnace. Graphene with optimized conditions exhibits a high crystallinity (ID/IG: 0.16) and electrical conductivity (760 Ω/sq). The comprehensive study on recipe optimization together with the multiphysical simulation suggests that the proposed carbon cloth is an ideal spacing mediator for CVD graphene with a high Cu-loading density. This enhancement is attributed to the homogeneous interdiffusion of reactive gas/species in both the transverse and radial directions, resulting in homogeneous nucleation and equivalent kinetic growth. The capacity could reach 15.56 m2/hour in an 8-inch system. The CFD simulation indicates that the porous mediator can improve gas distribution and balance the pressure between the Cu foils to enhance high-yield graphene synthesis. This method provides an efficient strategy for the synthesis of high-throughput and large-area CVD graphene films, which is beneficial for cost-effective and versatile graphene-based applications.

The use of Si and nitrogen-doped graphene to fabricate composite anodes in lithium-ion batteries (LIBs) is attracting intense attention. However, the reported strategies are limited to achieving a cost-effective, scalable, and facile approach. In particular, many reports on Si/N-graphene (N-Gra) anodes cannot achieve a high first discharge capacity while retaining a high Coulombic efficiency (CE). Herein, we report a Si@N-Gra composite with core–shelled microballs of Si NPs and electrochemically exfoliated graphene by NH₃ as a nitrogen source. We use H₂ and NH₃ to control the O and N content and to optimize the anode performance. It is found that N-Gra in the Si@N-Gra composite anode highly improves the electric conductivity and ion mobility. As a result, the microballs structure (Si@N-ECGB) exhibit the highest initial discharge capacity of up to 2604.5 mAh/g with an 85.2% CE. This excellent performance is attributed to efficient lithiation/delithiation that maintains the stability of the Si@N-ECGB. A full cell of Si@N-ECGB||NMC 811 (Ni/Mn/Co = 8:1:1) is demonstrated, from which a high initial capacity (170 mAh/g) and ∼84% retention after 100 cycles are achieved. This work provides a potential strategy for achieving high capacity and stability in LIBs.

Even though “metal-free” carbonaceous electrocatalysts like heteroatom(s)-doped graphene exhibit several advantages, such as cost-effectiveness and high stability toward hydrogen evolution reaction...

Graphene shows unique properties such as high mechanical strength and high thermal and chemical stability, making it promising for versatile applications. However, the lack of either interlayer or interface covalent bonds causes this type of 2D materials assembled via van der Waals forces to suffer from weak adhesion with the underlying substrates, thus hindering their application. In this study, a novel method based on a hydrothermal reaction was proposed to synthesize fluorinated graphene (FG) through a facile, scalable, and highly safe process, where a mixture of poly(perfluorosulfonic acid) (C7HF13O5S·C2F4, PFSA) and graphene oxide (GO) as the precursor was employed. The FG sheets prepared by the electrophoretic deposition (EPD) method exhibit superior conformity layered structure on a metal foil. Due to the in situ formation of ionic-covalently bonded F-Cu-F and Cu-F-C between fluorine on the FG sheets and dissolved Cu ions from the copper foil, the deposited film shows ultrastrong adhesion that can sustain up to 3 MPa of shear force. Furthermore, by changing the parameters in the EPD process, such as the EPD duration and applied voltage, the thickness and hydrophobicity of the film can be well controlled from 0.20 μm to 2.51 μm with a contact angle from 93.03˚ to 122.44˚. This study provides a new strategy to prepare a robust film for the assembly of 2D materials, not limited to graphene, with ultrastrong adhesion on substrates, which could solve the long-reported issue of weak adhesion and low durability of graphene-/2D-based functional composites and coatings.

Most two-dimensional (2D) semiconductors suffer from intrinsic instability under ambient conditions, especially 2D black phosphorus (BP). Although much effort has been made to study the passivation of 2D materials against corrosion by oxygen and water molecules, facile and effective passivation with long-term stability is still challenging; in particular, selective passivation, which is critical for integration into nanoelectronics, is still lacking. Here, we develop a novel passivation route for BP using a fluorinated self-assembled thin film of PFSA (perfluorosulfonic acid, PFSA), where the surface modifier with high hydrophobicity on BP presents extremely stable characteristics over five months under ambient conditions. Moreover, we report for the first time in situ cleaning and selective fluorination of only BP flakes on a SiO2/Si substrate by a spin-coating process followed by ultrasonication, which was attributed to the formation of P-F covalent bonds on the BP surface. Selectively fluorinated BP shows not only enhanced stability in air but also electrical properties of the BP field-effect transistor (FET), with the on-current of the BP FET increasing and presenting enhanced carrier mobility (125 cm2 V-1 s-1) and on/off ratio (104). This significant finding sheds light on fabricating vertical 2D heterostructures to realize high performance and reliability with versatile 2D materials. This work demonstrates an emerging passivation approach for long-term stability together with superior electrical properties, which paves the way for integrating 2D semiconductors into critical channel materials in FETs that are favorable for next-generation digital logic circuits.

Functional nanostructures with abundant exposed active sites and facile charge transport through conductive scaffolds to active sites are pivotal for developing an advanced and efficient electrocatalyst for water splitting. In the present study, by coating ∼3 nm MoSx on nitrogen-doped graphene (NG) pre-engrafted on a flexible carbon cloth (MNG) as a model system, an extremely low Tafel slope of 39.6 mV dec-1 with cyclic stability up to 5000 cycles is obtained. The specific fraction of N on the NG framework is also analyzed by X-ray photoelectron spectroscopy and X-ray absorption near edge spectroscopy with synchrotron radiation light sources, and it is found that the MoSx particles are selectively positioned on the specific graphitic N sites, forming the unique Mo-N-C bonding state. This Mo-N-C bonding is founded to facilitate highly effective charge transfer directly to the active sulfur sites on the edges of MoSx, leading to a highly improved hydrogen evolution reaction (HER) with excellent stability (95% retention @ 5000 cycles). The functional anchoring of MoSx by such bonding prevents particle aggregation, which plays a significant role in maintaining the stability and activity of the catalyst. Furthermore, it has been revealed that MNG samples with adequately high amounts of both pyridinic and graphitic N result in the best HER performance. This work helps in understanding the mechanisms and bonding interactions within various catalysts and the scaffold electrode.

In this work, we have fabricated high-performance thin-film electrodes for electrochemical capacitors (ECs) via thermal decomposition syntheses of RuO2–Ta2O5 coating layers on Ti substrates. The influences of decomposition temperature as well as the Ru/Ta molar ratio on material and electrochemical properties of the EC electrodes are systematically investigated. The thermal decomposition of 300 °C preserves a large fraction of hydrous RuO2·xH2O within the hybrid oxide and consequently improves the electrode capacitance. The amorphous Ta2O5 incorporation can manipulate the RuO2 crystallinity and thus its specific capacitance. An optimal Ru/Ta molar ratio of 7:3 is determined for the RuO2–Ta2O5 electrode, which can deliver an energy density of 4.8 Wh kg−1 at a power density of 8,720 W kg−1 (or 8.3 Wh L−1 at 15,000 W L−1). In addition, an excellent durability of 97.6% capacitance retention after 3,000 charge-discharge cycles is found for this electrode. The proposed RuO2–Ta2O5 thin-film electrode has paved the way for next-generation ECs with superior capacitances, energy/power densities, and cyclability.

Aqueous rechargeable lithium ion batteries (ARLIBs) have attracted wide attention in the energy storage field due to their nontoxicity and high safety. Nevertheless, they face many challenges relating to capacity and stability due to the restricted selection of anode materials that can act within the narrow stable potential window of water. Herein, we developed a highly reversible Zn//LiTi2(PO4)3@C dual-ion hybrid battery, where the LiTi2(PO4)3@C material was synthesized via a facile sol–gel method and used as the cathode. A Zn sheet was chosen as the anode, and a solution consisting of 0.5 M ZnSO4 and 0.25 M Li2SO4 was the electrolyte. This aqueous rechargeable dual-ion hybrid battery exhibited stable cycling performance and excellent rate performance. After 500 cycles at a high current density of 12C (1C = 138 mA g−1), the reversible discharge capacity was 49 mA h g−1, not much less than the initial capacity. In a rate test, the discharge capacity rebounded to a value of 60 mA h g−1 when the current density was returned from 18C back to 12C after 10 cycles. This battery system may provide great insight into designing dual-ion hybrid battery systems with high rate performances.

Aqueous rechargeable batteries have been a hot research topic due to their high conductivity, low cost, and operational safety. Bismuth is deemed as a kind of promising anode material owing to its suitable negative working window and highly reversible redox reaction in aqueous chloride ion battery; however, it exhibits poor stability and volume expansion when oxidized to BiOCl during electrochemical process. Herein, we present a novel synthesized method of bismuth metal nanoparticles through the thermal reduction of Bi-MOF under hydrogen atmosphere. The Bi-particles with ~ 100 nm size are uniformly coated with a layer of carbon film. The aqueous chloride ion battery system consists of the synthesized bismuth as the anode, AgCl as the cathode, and 1 M NaCl (pH = 2) as the electrolyte. After 200 cycles, the specific capacity is 87.9 mAh g−1 at the current density of 400 mA g−1. After 1000 cycles, a durable specific capacity of 51.8 mAh g−1 was achieved under the current density of 1200 mA g−1 and the coulombic efficiency is above 99%. The electrochemical mechanism was further investigated by X-ray diffraction. The current work will be significant for the chloride ion energy storage and battery desalination.

Development of n-/p-type semiconducting graphenes is a critical route to implement in graphene-based nanoelectronics and optronics. Compared to the p-type graphene, the n-type graphene is more difficult to be prepared. Recently, phosphorous doping was reported to achieve air-stable and high mobility of n-typed graphene. The phosphorous-doped graphene (P-Gra) by ion implantation is considered as an ideal method for tailoring graphene due to its IC compatible process; however, for a conventional ion implanter, the acceleration energy is in the order of kiloelectron volts (keV), thus severely destroys the sp2 bonding of graphene owing to its high energy of accelerated ions. The introduced defects, therefore, degrade the electrical performance of graphene. Here, for the first time, we report a low-damage n-typed chemical vapor deposition (CVD) graphene by an industrial-compatible ion implanter with an energy of 20 keV where the designed protection layer (thin Au film) covered on as-grown CVD graphene is employed to efficiently reduce defect formation. The additional post-annealing is found to heal the crystal defects of graphene. Moreover, this method allows transferring ultraclean and residue-free P-Gra onto versatile target substrates directly. The doping configuration, crystallinity, and electrical properties on P-Gra were comprehensively studied. The results indicate that the low-damaged P-Gra with a controllable doping concentration of up to 4.22 at % was achieved, which is the highest concentration ever recorded. The doped graphenes with tunable work functions (4.85-4.15 eV) and stable n-type doping while keeping high-carrier mobility are realized. This work contributes to the proof-of-concept for tailoring graphene or 2D materials through doping with an exceptional low defect density by the low energy ion implantation, suggesting a great potential for unconventional doping technologies for next-generation 2D-based nanoelectronics.

Nanoporous holey-graphene (HG) shows potential versatility in several technological fields, especially in biomedical, water filtration, and energy storage applications. Particularly, for ultrahigh electrochemical energy storage applications, HG has shown promise in addressing the issue of low gravimetric and volumetric energy densities by boosting of the ion-transport efficiency in a high-mass-loaded graphene electrode. However, there are no studies showing complete control over the entire pore architecture and density of HG and their effect on high-rate energy storage. Here, we report a unique and cost-effective method for obtaining well-controlled HG, where a copper nanocatalyst assists the predefined porosity tailoring of the HG and leads to an extraordinary high pore density that exceeds 1 × 10

Two-dimensional (2D) materials are promising anodes for Na-ion batteries owing to their unique architectures and tunable physiochemical properties. However, their high surface area requires sophist...

Graphene doped with heteroatoms is known to create a unique electronic structure with comparatively much higher active sites by the synergistic coupling effect. However, in the earlier attempts, th...

Renewable energy-related technologies have become more important due to the increasing energy consumption. Herein, we put forward a novel organic flow desalination battery (ORFDB) using redox-active organic molecule electrolyte materials dissolved in the aqueous sodium chloride feed. Riboflavin-5’-phosphate sodium salt dihydrate (FMN-Na) is used as the anolyte, and the catholyte is 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO). Sodium and chloride ions in salt feed were moved respectively to anolyte and catholyte by electrochemical reaction of electrolytes during the charge process, and return to the feed during the discharge process. This ORFDB system possesses the stable stability up to fifty cycles and the excellent rate performance. This ORFDB exhibits the cost-effective renewable energy storage and the possibility of salt removal based on the electrochemistry of organic molecules.

Atomically thin graphene is a transparent, highly electrically and thermally conductive, light-weight, and the strongest material. To date, graphene has found applications in many aspects including transport, medicine, electronics, energy, defense, and desalination. We demonstrate another disruptive application of graphene in the field of laser-ion acceleration, in which the unique features of graphene play indispensable role. Laser driven ion sources have been widely investigated for pure science, plasma diagnostics, medical and engineering applications. Recent developments of laser technologies allow us to access radiation regime of laser ion acceleration with relatively thin targets. However, the thinner target is the less durable and can be easily broken by the pedestal or prepulse through impact and heating prior to the main laser arrival. One of the solutions to avoid this is plasma mirror, which is a surface plasma created by the foot of the laser pulse on an optically transparent material working as an effective mirror only for the main laser peak. So far diamond like carbon (DLC) is used to explore the ion acceleration in extremely thin target regime (< 10 nm) with plasma mirrors, and it is necessary to use plasma mirrors even in moderately thin target regime (10-100 nm) to realize energetic ion generation. However, firstly DLC is not 2D material, and therefore, it is very expensive to make it thin and flat. Moreover, graphene is stronger than diamond at extremely thin regime, and much more reasonable for mass-production. Furthermore, installing and operating plasma mirrors at high repetition rate is also costly. Here we show another direct solution using graphene as the thinnest and strongest target ever made. We develop a facile transfer method to fabricate large-area suspended graphene (LSG) as target for laser ion acceleration with precision down to a single atomic layer. Direct irradiation of the LSG targets with an ultra intense laser generates energetic carbons and protons evidently showing the durability of graphene without plasma mirror. This extends the new frontier of science on graphene under extreme electromagnetic field, such as energy frontier and nuclear fusion.

Functional nanostructures with abundant exposed active sites and facile charge transport through conductive scaffolds to active sites are pivotal for developing an advanced and efficient electrocatalyst for water splitting. In the present study, by coating ∼3 nm MoS

In this study, various nitrogen-containing functional groups, namely, pyridine (N-6), pyrrole (N-5), oxidized N (N-O), and quaternary N (N-Q), are created on activated carbon (AC) surface via melamine, ammonia, and nitric oxide doping methods. N-5 and N-6 groups markedly alter the specific surface area and pore size of AC. N-O is found to affect electrolyte wettability, and the N-Q content is closely associated with AC electronic conductivity. The nitrogen-containing groups do not contribute to pseudocapacitance in propylene carbonate and acetonitrile electrolytes. However, the nitric-oxide-treated carbon (AC-NO) exhibits the best high-rate charge-discharge performance among the investigated materials. The N-Q-enriched and N-5/N-6-depleted AC-NO most effectively suppresses the leakage current and gas evolution of supercapacitors. Online gas chromatography is used to analyze the gaseous species produced from AC electrodes. With an appropriate surface functionality on carbon, the cell voltage can be increased to ∼3 V, increasing the energy and power densities. The aging behavior of the carbon electrodes with and without nitrogen modification after being floated at 2.5 V and 70 °C for 3 days is investigated. An effective strategy for enhancing supercapacitor performance and reliability is proposed.

An aqueous chloride ion battery (CIB) is an emerging technology for electrochemical energy storage as well as battery desalination systems. However, the instability and decomposition of electrode materials in an aqueous medium is a major issue in CIBs. Herein, in one step, we synthesized fine antimony nanoparticles with a size of ∼20 nm on reduced graphene oxide (Sb@rGO) sheets using a hydrothermal route with facile and cost-effective processes. It is proposed as a new anode material and coupled with the AgCl cathode in an aqueous CIB. The specific capacity is maintained constantly at 51.6 mA h g-1 at a current density of 400 mA g-1 even after 200 cycles. In addition, characterization methods such as electrochemical analysis, X-ray diffraction, etc. were used to confirm the reaction mechanism. The chloride ion capture material developed in this research work will be significant for CIBs as an energy storage technology or battery desalination system.

Efficiently storing electricity generated from renewable resources and desalinating brackish water are both critical for realizing a sustainable society. Previously reported desalination batteries need to work in alternate desalination/salination modes and also require external energy inputs during desalination. Here, we demonstrate a novel zinc-air battery-based desalination device (ZABD), which can desalinate brackish water and supply energy simultaneously. The ZABD consists of a zinc anode with a flowing ZnCl

Microsupercapacitors (MSCs) are alternative power sources that have the potential to fulfill the increasing demand for wearable and on-chip electronics as they are small and lightweight, and show extremely high charge–discharge rates and power densities, and have high flexibility. However, the critical challenge of recent MSCs is the limitation of low energy density and complicated fabrication processes that are high cost and time-consuming. Here, we reported an all-screen-printable method for fabricating all-solid (including electrolytes) and flexible MSCs by rationally designed composite electrodes with electrochemically exfoliated graphene (ECG) and long single-walled carbon nanotubes (CNTs). This method demonstrated to be a facile and scalable route to fabricate and assemble MSCs in a cost-effective manner and with high throughput. As a result, the resulting MSC devices exhibit an areal capacitance of 7.7 mF cm−2 and volumetric capacitance of 77.3 F cm−3, with an excellent cyclic stability of >99% after 15 000 cycles; this can be attributed to the creation of a high diffusion path and the promotion of ion transport capability. The cell exhibits energy and power densities of 10.7 mW h cm−3 and 3.17 W cm−3, respectively. Moreover, there was negligible degradation in capacitance when subjected to bending deformation with radius reduced to 0.5 mm, indicating excellent mechanical flexibility and operation stability. Further, the output voltage and current can be rationally designed by multiple connections of MSC devices in series and parallel to fulfill the demands of various applications. This study provides a scalable and cost-effective method to produce solid-state MSCs with high energy density, which paves the way for their applications in potential wearable devices.

Encapsulating silicon (Si) nanoparticles with graphene nanosheets in a microspherical structure is proposed to increase electrical conductivity and solve stability issues when using Si as an anode material in lithium-ion batteries (LIBs). Currently the main strategies to produce high-quality Si-graphene (Si@Gra) electrodes are (1) chemical vapor deposition (CVD) of graphene grown in situ on Si by hydrocarbon precursors and (2) encapsulating Si with a graphene oxide followed by postannealing. However, both methods require a high-temperature and are costly and time-consuming procedures, which hinders their mass scalability and practical utilization. Herein, we report a Si@Gra composite with a ball-like structure that is assembled by a facile spray drying process without a postannealing treatment. The graphene sheets are synthesized by an electrochemical exfoliation method from natural graphite. The resulting Si@Gra composite exhibits a unique core-shell structure, from which the ball-like morphology and the number of graphene layers in the Si@Gra composites are found to affect both the electric conductivity and ionic conductivity. The Si@Gra composites are found to increase the capacity of the anode and provide excellent cycling stability, which is attributed to the high electrical conductivity and mechanical flexibility of the layered graphene; additionally, a void space in the core-shelled ball structure inside the Si@Gra compensates for the Si volume expansion. As a result, the Si@few-layer graphene ball anode exhibits a high initial discharge capacity of 2882.3 mA h g-1 and a high initial coulombic efficiency of 86.9% at 0.2 A g-1. The combination of few-layer graphene sheets and the spray drying process can effectively be applied for large-scale production of core-shell structured Si@Gra composites as promising anode materials for use in high-performance LIBs.

The NaF dual-ion battery was demonstrated as potential battery where fluoride and sodium ions were extracted from NaF electrolyte respectively during discharging; while the charging process causes the release of ions to the electrolyte. However, previous studies reveal that electrode configuration with large-sized particles will significantly reduce the energy density and stability. Herein, we proposed a novel hybrid electrode assembly of bismuth nanoparticles/carbon nanotubes (nano-Bi@CNTs), which could achieve the excellent electrochemical stability. The new NaF dual-ion battery, consisting of nano-Bi@CNTs-Na0.44MnO2 (NMO), demonstrates a high specific capacity of 109.5 mAh/g after 80 cycles with 100 mA/g current density. Moreover, the electrochemical mechanism of fluoride ion in this system was comprehensively investigated. The current research is significant for the novel anion energy storage system.

The anion battery system is a new research area in the energy storage field. Herein, a novel aqueous rechargeable dual-ion battery based on fluorine ion and sodium ion electrochemistry is proposed, consisting of bismuth fluoride as the anode, sodium manganese oxides (NMO) as the cathode and aqueous NaF solution as the electrolyte. The bismuth fluoride electrode can electrochemically release/capture fluoride ion in aqueous electrolyte and sodium ion can be de-intercalated/intercalated at the NMO cathode during charge/discharge process. The electrochemical behavior was confirmed by cyclic voltammetry, charge–discharge curves as well as X-ray powder diffraction. The reversible and stable discharge capacity is obtained with a coulombic efficiency of 98.44%. After 40 cycles, the specific capacity can be still maintained at 47.28 mAh g−1 at the current density of 100 mA g−1. The current battery system possesses excellent rate performance. It can operate at 3200 mA g−1 (10.6C) with 82.8% specific capacity as that at 100 mA g−1. This is the first demonstration that the aqueous dual-ion battery can work based on fluoride ion and sodium ion electrochemistry and it will be significant for future energy storage and ion removal.

In this study, graphene was grown on nickel foam by chemical vapor deposition method. The morphology and crystallization of graphene films were characterized by scanning electron microscopy and Raman spectroscopy. Graphene-coated nickel foams have been used as flow distributor in a single PEM fuel cell, and the current density of the cell reached 1000 mA/cm2 at 0.6 V. Tafel analysis indicates that graphene-coated samples showed greatly lower corrosion current density (nine times) than the uncoated ones. The contact angle was 35% larger than uncoated sample. These results clearly show that graphene-coated metal foams significantly enhances electrical conductivity and hydrophobicity.

Molybdenum sulfide (MoS x ) has recently emerged as a promising catalyst for the hydrogen evolution reaction (HER) in water splitting that may replace the noble metal, such as platinum, as a cost-effective and high catalytic materials. It has been reported that two-dimensional structured MoS x exhibit significant amount of exposed S-edge, which can be an active electrocatalytic catalyst for hydrogen production. However, the current reports mainly focusing on the planar electrode, where the catalyst utilization and the number of active sites are limited due to the lower exposed specific surface area (SSA) of supporting electrodes. In this work, we utilize the freeze-drying method to produce a porous three-dimensional (3D) structure assembled by graphene flakes. The as-prepared 3D graphene scaffold shows high surface area, high porosity while low density, which makes it as an ideal conductive electrode for supporting of MoS x catalysts. Moreover, it was found out that the crystallinity of MoS x , controlled by thermolysis temperature of thiosalts precursor ((NH 4 ) 2 MoS 4 ), shows significantly influence the performance of HER. The optimized annealing temperature for the designed hybrid electrodes (MoS x /3D-graphene) was found to create a lot of active sites, which facilitate the electrocatalytic performance for water splitting (overpotential of 163 mV @10 mA/cm 2 and a Tafel slope of 41 mV/dec). The study provides a potential material, which could pave the way for future applications of hydrogen energy.

Surface modifications through conductive carbon based coatings, such as graphene (G) and graphene oxide (GO) are studied to enhance the pool boiling heat transfer performance. In this study, four different mechanisms for G/GO coatings in the nanoscale and microscale were evaluated. We report the results of specifically designed experiments and discuss the effects of (i) thermal conductivity of graphene films, (ii) wettability, (iii) contact angle hysteresis, and (iv) morphological effects. For the nanoscale coatings, an atmospheric pressure chemical vapor deposition (APCVD) process was used to exercise control over the number of layers. For these samples, it was seen that the thermal conductivity and wettability through increased wickability were not contributing factors, but the large contact angle hysteresis (∼50°) was seen as a possible mechanism. The microscale coatings were developed through a dip-coating technique. Morphological features were generated by varying the dip-coating duration between 2 and 20 min. Pool boiling tests were conducted with distilled water at atmospheric pressure which resulted in a maximum CHF of 192 W/cm 2 corresponding to the sample with ridge microstructures. In addition to the contact angle hysteresis in these samples, the roughness was seen to be responsible for the CHF enhancement with longer dip-coating durations (in excess of 5 min) which was further verified by using a roughness based CHF model. In the case of shorter duration coatings, the unique ridge microstructures enhanced the microlayer evaporation. Bubble growth rates in the initial inertia controlled region were obtained to provide further details on the heat transfer mechanism. In summary, contact angle hysteresis, roughness, and evaporation from ridge partitioned microlayer were identified as the three mechanisms associated with nanoscale and microscale G/GO coated surfaces.

An eco-efficient synthetic route for the preparation of high-performance carbonate anodes for Li+ and Na+ batteries is developed. With supercritical CO2 (scCO2 ) as the precursor, which has gas-like diffusivity, extremely low viscosity, and near-zero surface tension, CoCO3 particles are uniformly formed and tightly connected on graphene nanosheets (GNSs). This synthesis can be conducted at 50 °C, which is considerably lower than the temperature required for conventional preparation methods, minimizing energy consumption. The obtained CoCO3 particles (ca. 20 nm in diameter), which have a unique interpenetrating porous structure, can increase the number of electroactive sites, promote electrolyte accessibility, shorten ion diffusion length, and readily accommodate the strain generated upon charging/discharging. With a reversible capacity of 1105 mAh g-1 , the proposed CoCO3 /GNS anode shows an excellent rate capability, as it can deliver 745 mAh g-1 in 7.5 min. More than 98 % of the initial capacity is retained after 200 cycles. These properties are clearly superior to those of previously reported CoCO3 -based electrodes for Li+ storage, indicating the merit of our scCO2 -based synthesis, which is facile, green, and can be easily scaled up for mass production.

Graphene has been applied to thermal technology including boiling and condensation heat transfer, from which the pool boiling enhancement relies on adjusting the surface morphology and wettability that is favorable to catalyze the vaporization on the fluid/graphene interface. However, previous works using graphene or reduced graphene oxide (RGO) flake coatings, where the morphology of graphene coating is nonuniform and most of the underlying structured cavities are sealed by graphene flakes. For a long time, this hampered the unraveling of the mechanism behind the enhanced boiling performance by graphene coatings. Moreover, the previous work relied on using water-based pool boiling, which limits the scope of its practical applications since the versatile nonpolar refrigerant has been widely used in boiling heat transfer. The pool boiling was carried out on a plain copper surface to study the effect of fluorinated graphene (F-graphene) coating using nonpolar refrigerant R-141b as the working fluid along with bubble dynamic visualization. It was found that the increase of contact angle leads to more active cavities and enhances heat transfer performance up to twice as much, by applying the F-graphene coating. Moreover, the mechanism of graphene-enhanced heat transfer performance was unraveled and mainly attributed to the hydrophobic surface and effective cavity structure. This research provides a practical and reliable route for enhancing the heat transfer through F-graphene-coatings, which paves the way for potential application in graphene-based thermal technologies.

In this study, we demonstrated the integration of black phosphorus (BP) nanoflakes in a resistive random access memory (RRAM) with a facile and complementary metal-oxide-semiconductor-compatible process. The solution-processed BP nanoflakes embedded in polystyrene (PS) as an active layer were sandwiched between aluminum electrodes (Al/BP:PS/Al). The device shows a figure of merit with typical bipolar behavior and forming-free characteristics as well as excellent memory performances such as nonvolatile, low operation voltage (1.75 V) and high ON/OFF ratio (>102) as well as the long retention time (>1500 s). The improved device performances were attributed to the formation of effective trap sites from the hybrid structure of the active layer (BP:PS), especially the BP nanoflakes and the partly oxidized species (P x O y ). Moreover, the extrinsic aluminum oxide layer was observed after the device operation. The mechanism of switching behavior was further unveiled through the carrier transport models, which confirms the conductive mechanisms of space-charge-limited current and Ohmic conductance at high resistance state (HRS) and low resistance state, respectively. Additionally, in the high electric field at HRS, the transfer curve was well fitted with the Poole-Frenkel emission model, which could be attributed to the formation of the aluminum oxide layer. Accordingly, both the trapping/de-trapping of carriers and the formation/rupture of conductive filaments were introduced as transport mechanisms in our devices. Although the partial P x O y species on BP were inevitable during the liquid phase exfoliation process, which was regarded as the disadvantages for various applications, it turns to a key point for improving performances in memory devices. The proposed approach to integrating BP nanoflakes in the active layer of the RRAM device could pave the way for next-generation memory devices.