Facile magnetoresistance adjustment of graphene foam for magnetic sensor applications through microstructure tailoring

Graphene foam is becoming a material of choice for magnetoelectronic devices due to its large,linear and unsaturated room temperature magnetoresistance.However,the magnetoresistance of graphene foam is not as large as that of monolayer graphene.Herein,we describe how magnetoresistance^100%was detected at room temperature under a magnetic field of 5 T that is comparable to the magnetoresistance in monolayer graphene;the highest magnetoresistance of^158%was detected at 5 K under a magnetic field of 5 T.Unlike monolayer graphene,graphene foam is far more comfortable with producing in gram scale and utilizing in magnetoelectronic devices.

Dynamic surface wettability of three-dimensional graphene foam

In this work, three-dimensional graphene foams （GFs） are synthesized and characterized by scanning electron micro- scope （SEM） and Raman spectroscopy. The SEM images indicate that after the growth of graphene, the graphene covers the surface of nickel （Ni） foam uniformly. Raman spectra show that the percentages of monolayer, bilayer, trilayer, and multilayer graphenes are - 58%, - 32%, - 8%, and ,.o 2%, respectively. The contact angle （CA） （-- 12°） of water droplet （3 p-L） on GF is found to be larger than that on Ni foam （,- 107°）, indicating that graphenes have changed the surface wettability of the Ni foam. Meanwhile, the dynamic characteristics of CA of water droplet on GF are different from those on Ni foam. The mechanisms for different behaviors are discussed, which are attributed to volatilization and seepage of water droplets.

Scalable graphene foam with ultrahigh conductivity for stabilizing Pt towards efficient hydrogen evolution

For the carbon-based catalyst to be active and stable,especially in harsh electrochemical environments,the key is to decrease the concentration of defects and raise the degree of graphitization of the carbon support.Herein,we develop a highly graphitized graphene foam with multiplicated structure to fabricate self-supporting Pt-based catalysts for efficient and stable hydrogen evolution reaction(HER)performance.Graphene foam(GO-2850)is obtained through an ultra-high temperature treatment at 2850℃,with perfect graphene structure and extremely low defect,ensuring high electrical conductivity and corrosion resistance.Additionally,its multiplicated structure provides an inherently favorable environment for the dispersion of Pt nanoparticles(Pt NPs)and offers abundant channels for electrolyte infiltration during the catalytic process.As a result,the as-prepared Pt/GO-2850 is far active and stable than the Pt NPs supported on commercial carbon paper(Pt/CP)counterpart toward catalyzing HER,exhibiting an outstanding activity and long-term durability(300 h@10 mA·cm^(−2))in acidic/alkaline/seawater electrolytes.This can be attributed to the stronger interaction between the lower-defect GO-2850 substrate and Pt,as evidenced by characterization and theoretical calculations.This work extends further insight into the design self-supporting catalysts of high activity and stability with promising prominent application toward green energy devices.

Hierarchical graphene foam-based phase change materials with enhanced thermal conductivity and shape stability for efficient solar-to-thermal energy conversion and storage

Recently, graphene foam （GF） with a three-dimensional （3D） interconnected network produced by template-directed chemical vapor deposition （CVD） has been used to prepare composite phase-change materials （PCMs） with enhanced thermal conductivity. However, the pore size of GF is as large as hundreds of micrometers, resulting in a remarkable thermal resistance for heat transfer from the PCM inside the large pores to the GF strut walls. In this study, a novel 3D hierarchical GF （HGF） is obtained by filling the pores of GF with hollow graphene networks. The HGF is then used to prepare a paraffin wax （PW）-based composite PCM. The thermal conductivity of the PW/HGF composite PCM is 87% and 744% higher than that of the PW/GF composite PCM and pure PW, respectively. The PW/HGF composite PCM also exhibits better shape stability than the PW/GF composite PCM, negligible change in the phase-change temperature, a high thermal energy storage density that is 95% of pure PW, good thermal reliability, and chemical stability with cycling for 100 times. More importantly, PW/HGF composite PCM allows light-driven thermal energy storage with a high light-to- thermal energy conversion and storage efficiency, indicating its great potential for applications in solar-energy utilization and storage.

Study of the effect of chemical composition on the surface wettability of three-dimensional graphene foams

The chemical composition obviously affects the surface wettability of a three-dimensional(3D)graphene material apart from its surface energy and microstructure.In the hydrothermal preparation,the heteroatom doping changes the chemical composition and wettability of the 3D graphene material.To realize the controllable surface wettability of graphene materials,aminobenzene sulfonic acid(ABSA)was selected as a typical doping agent for the preparation of nitrogen and sulfur co-doped 3D graphene foam(SNGF)using a hydrothermal method.Different from using o-ABSA or p-ABSA as the dopant,SNGF with tunable surface wettability is obtained only when m-ABSA is used.This result indicates that the substituent position of-SO3H group in the benzene ring of ABSA is rather important for the tunable wettability.This work provides some theo retical foundations for dopant selection and some new insights in manipulating the properties of 3D graphene foams by adjusting the configuration of dopants.

Heat dissipation in graphene foams

Graphene foam(GF)—a three-dimensional network of hollow graphene branches—is a highly attractive material for diverse applications.However,to date,the heat dissipation characteristics of GFs have not been characterized.To fill this gap,we synthesized GF devices,subjected them to high temperatures,and investigated their thermal behavior by using infrared microthermography.We find that while the convective area of GF devices is comparable to that of bulk materials(such as metals),the coefficient of convection of these devices is several orders of magnitude higher than that of metals.In addition,the GF devices showed a reproducible thermal behavior,which we attribute to negligible temperature-induced morphological changes(as confirmed by Raman analysis).Taken together,our findings suggest GF as a promising candidate material for advanced cooling applications where efficient heat dissipation is needed,e.g.,in electrical circuits.

Graphene foam resonators:Fabrication and characterization

Three-dimensional graphene foams(GFs)benefit from a large surface area and unique physical properties.We present here the first-ever miniaturized GF-based resonators.We developed a simple yet reliable fabrication process,in which GFs are synthesized and assembled on a cavity to form suspended GF devices.We electrostatically excited these devices and analyzed their resonance and ring-down responses.We observed significant energy dissipation,as the quality factor of the devices was in the order of several tens.Additionally,we investigated the influence of temperature on the operation of the devices and found that high temperatures mechanically soften the resonators but also considerably enhance energy dissipation.Finally,our devices demonstrated a mode-coupling of a resonance mode and a mode having twice its frequency.Thus,this work paves the way toward the development of novel GF resonators that could be integrated into future devices,such as GF-based nano-electromechanical sensors,electrical circuits,and oscillators.

Graphene and boron nitride foams for smart functional applications

Graphene and boron nitride(BN)foams,as two types of three-dimensional(3D)nanomaterials consisting of two-dimensional(2D)nanosheets,can inherit a series of excellent properties of the 2D individuals.The internal 3D network can prevent aggregation or restacking between isolated graphene or BN nanosheets,and provide a highway for phonon/electron transports.Moreover,the interconnected porous structure creates a continual channel for the mass exchange of exotic species.The light-element graphene and BN foams can thus possess the characteristics of low density,high porosity,high surface area,and excellent mechanical,thermal,and electrical properties.Benefiting from these advantages,they show a wide range of applications.The usual synthesis methods and the recent functional applications of graphene and BN foams are reviewed herein,including their applications as supporting materials,elastic materials,acoustic shielding materials,thermal interface materials,electromagnetic shielding materials,adsorption materials,electrocatalysis and thermal catalyses materials,electrochemical energy storage,and thermal energy storage materials.Current challenges and outlooks are additionally discussed.

Fabrication of porous lithium titanate self-supporting anode for high performance lithium-ion capacitor

Lithium titanate has unique "zero-strain" characteristics, which makes it promising for rapid energy storage lithium-ion capacitors. However, extremely low electronic conductivity and lithium ion diffusion coefficient severely limit its performance at high rate. Herein, we have constructed in situ clusters of porous lithium titanate nanoparticles on self-supporting carbon nanotube film by combining iron oxide hard template method and F127 soft template method. Due to the nano-structured particle size and the penetrating lithium ion transmission channel, a greatly improved lithium ion diffusion coefficient has been achieved, which brings significantly better electrochemical performance than dense lithium titanate. By assembling with a durable graphene foam cathode, a lithium-ion capacitor with an energy density of up to 101.8 Wh kg-1 was realized(at a power density of 436.1 W kg-1). And its capacitance retention reaches 84.8% after 5000 cycles. With such an alluring result, our work presents a novel lithium-ion capacitor system with practical application prospects.

Au nanoparticles decorated graphene/nickel foam nanocomposite for sensitive detection of hydrogen peroxide

The Au nanoparticles decorated graphene（AuNPs@Gr）/nickel foam（Gr/NiF） nanocomposite（AuNPs@Gr/NiF） was prepared by chemical vapor deposition followed by electrophoretic deposition of AuNPs on Gr/NiF. The morphology, microstructure and sensing performance of the as-prepared AuNPs@Gr/NiF nanocomposite were characterized and measured, respectively by scanning electron microscope, transmission electron microscope, ultraviolet visible spectroscopy and chemical workstation. The asprepared AuNPs@Gr/NiF nanocomposite was used as the electrode to construct a chemical sensor for the detection of hydrogen peroxide（H2O2）. The results showed that the AuNPs distributed homogenously and stably on the surface of Gr/NiF. The chemical sensor exhibits a sensitive and selective performance to the detection of H2O2.

Facile synthesis of lightweight 3D hierarchical Ni Co_(2)O_(4) nanoflowers/reduced graphene oxide composite foams with excellent electromagnetic wave absorption performance

Considering the high filling ratios,high densities,and narrow absorbing bandwidths of the current electromagnetic wave(EMW) absorbers,in this work,we successfully synthesized a 3 D hierarchical NiCo_(2) O_(4) nanoflowers/reduced graphene oxide(NiCo_(2) O_(4)/RGO) composite foam by a simple method under gentle condition.The NiCo_(2) O_(4) nanoflowers and unique 3 D foam structure are beneficial to the refraction and scattering of EMW,which endows the prepared 3 D foam with highly efficient EMW absorption performance.When the ratio between NiCo_(2) O_(4) and RGO in the foam is 1:1,5% mass fraction of NiCo_(2) O_(4/)RGO foam in paraffin wax can reach a minimum reflection loss(RL_(min)) value of-52.2 dB with a thin thickness merely 2.6 mm.Simultaneously,the effective absorption bandwidth(EAB,RL exceeding-10 dB) is7.04 GHz that covers the whole Ku band(10.96-18 GHz).Moreover,the effects of the thickness of the absorber and the loading ratios of the foam in paraffin wax matrix on the EMW absorption properties are also carefully investigated.The results indicate that the optimum EMW absorption performance of NiCo_(2) O_(4/)RGO can be tuned in different bands.The EMW absorption mechanism is ascribed to the proper impedance matching and larger dielectric and magnetic loss produced by the synergy of NiCo_(2) O_(4) and RGO.Therefore,the NiCo_(2) O_(4/)RGO hybrid foam is ideal candidate to be used as high-efficient EMW absorbers with low filling ratio,light weight,and broad frequency bandwidths.

Robust self-supported anode by integrating Sb2S3 nanoparticles with S,N-codoped graphene to enhance K-storage performance

Developing high-performance anode materials for potassium-ion batteries is significantly urgent. We here demonstrate Sb_2S_3 nanoparticles(~20 nm) homogeneously dispersed in porous S,N-codoped graphene framework(Sb_2S_3-SNG) as a self-supported anode material for potassium-ion batteries. The rational structure design of integrating Sb_2S_3 nanoparticles with S,N-codoped graphene contributes to high reactivity, strong affinity, good electric conductivity, and robust stability of the composite, enabling superior K-storage performance. Moreover, the self-supported architecture significantly decreases the inactive weight of the battery, resulting in a high energy density of a Sb_2S_3-SNG/KVPO_4 F-C full cell to ~166.3 W h kg^(-1).

Highly sensitive piezoresistive pressure sensors based on laser-induced graphene with molybdenum disulfide nanoparticles

Wearable pressure sensors have drawn significant attention because of their extensive applications in motion detection, tactile sensing, and health monitoring. However, the complex manufacturing process and high cost of active materials make low-cost,large-scale production elusive. In this work, we report a flexible piezoresistive pressure sensor assembled with two 3D laserinduced graphene(LIG) foam electrodes on a polyimide thin film from a simple laser scribing process in the ambient environment. The design of the air gap between the two foam electrodes allows the sensor to showcase a low limit of detection of 0.274 Pa, which provides favorable sensing performance in motion detection and wrist pulse monitoring. The addition of spherical MoS2 nanoparticles between the two foam electrodes further enhances the sensitivity to 88 k Pa-1 and increases the sensing range to significantly outperform the previous literature reports. The demonstrated LIG pressure sensors also exhibit fast response/recovery rates and excellent durability/repeatability.

Recent progress on three-dimensional nanoarchitecture anode materials for lithium/sodium storage

High-performance batteries with high density and low cost are needed for the development of largescale energy storage fields such as electric vehicles and renewable energy systems.The anode with threedimensional(3D)nanoarchitecture is one of the most attractive candidates for high-performance lithiumion batteries(LIBs)and sodium-ion batteries(SIBs)due to its efficient electron/ion transport and high active material mass loading.Although some important breakthroughs have been made in 3D nanoarchitecture anode materials,more improvements are still needed for high cycling stability and high energy density.Herein,the latest research progress of 3D nanoarchitecture anode materials for LIBs and SIBs is reviewed,including nanoporous metal,nanoporous graphene,and their derived foams.Specifically,the storage properties of Li/Na ions,the kinetics of ion/electron transport,and specific chemical interactions are discussed based on the structure design.In addition,the research strategies and structural characteristics of 3D nanoarchitecture anode materials are summarized,providing a reference for the further development of LIBs and SIBs.Meanwhile,the future research directions of LIBs and SIBs have also prospected.