Highly Flexible Graphene-Film-Based Rectenna for Wireless Energy Harvesting

Herein,we report the design,fabrication,and performance of two wireless energy harvesting devices based on highly flexible graphene macroscopic films(FGMFs).We first demonstrate that benefiting from the high conductivity of up to 1×10^(6)S m^(-1)and good resistive stability of FGMFs even under extensive bending,the FGMFs-based rectifying circuit(GRC)exhibits good flexibility and RF-to-DC efficiency of 53%at 2.1 GHz.Moreover,we further expand the application of FGMFs to a flexible wideband monopole rectenna and a 2.45 GHz wearable rectenna for harvesting wireless energy.The wideband rectenna at various bending conditions produces a maximum conversion efficiency of 52%,46%,and 44%at the 5th Generation(5G)2.1 GHz,Industrial Long-Term Evolution(LTE)2.3 GHz,and Scientific Medical(ISM)2.45 GHz,respectively.A 2.45 GHz GRC is optimized and integrated with an AMC-backed wearable antenna.The proposed 2.45 GHz wearable rectenna shows a maximum conversion efficiency of 55.7%.All the results indicate that the highly flexible graphene-film-based rectennas have great potential as a wireless power supplier for smart Internet of Things(loT)applications.

Enhanced resonance frequency in Co2FeAl thin film with different thicknesses grown on flexible graphene substrate

The flexible materials exhibit more favorable properties than most rigid substrates in flexibility,weight saving,mechanical reliability,and excellent environmental toughness.Particularly,flexible graphene film with unique mechanical properties was extensively explored in high frequency devices.Herein,we report the characteristics of structure and magnetic properties at high frequency of Co2FeAl thin film with different thicknesses grown on flexible graphene substrate at room temperature.The exciting finding for the columnar structure of Co2FeAl thin film lays the foundation for excellent high frequency property of Co2FeAl/flexible graphene structure.In-plane magnetic anisotropy field varying with increasing thickness of Co2FeAl thin film can be obtained by measurement of ferromagnetic resonance,which can be ascribed to the enhancement of crystallinity and the increase of grain size.Meanwhile,the resonance frequency which can be achieved by the measurement of vector network analyzer with the microstrip method increases with increasing thickness of Co2FeAl thin film.Moreover,in our case with graphene film,the resonance magnetic field is quite stable though folded for twenty cycles,which demonstrates that good flexibility of graphene film and the stability of high frequency magnetic property of Co2FeAl thin film grown on flexible graphene substrate.These results are promising for the design of microwave devices and wireless communication equipment.

Design Engineering,Synthesis Protocols,and Energy Applications of MOF-Derived Electrocatalysts

The core reactions for fuel cells,rechargeable metal-air batteries,and hydrogen fuel production are the oxygen reduction reaction(ORR),oxygen evolution reaction(OER),and hydrogen evolution reaction(HER),which are heavily dependent on the efficiency of electrocatalysts.Enormous attempts have previously been devoted in non-noble electrocatalysts born out of metal-organic frameworks(MOFs)for ORR,OER,and HER applications,due to the following advantageous reasons:(i)The significant porosity eases the electrolyte diffusion;(ii)the supreme catalyst-electrolyte contact area enhances the diffusion efficiency;and(iii)the electronic conductivity can be extensively increased owing to the unique construction block subunits for MOFs-derived electrocatalysis.Herein,the recent progress of MOFs-derived electrocatalysts including synthesis protocols,design engineering,DFT calculations roles,and energy applications is discussed and reviewed.It can be concluded that the elevated ORR,OER,and HER performances are attributed to an advantageously well-designed high-porosity structure,significant surface area,and plentiful active centers.Furthermore,the perspectives of MOF-derived electrocatalysts for the ORR,OER,and HER are presented.

Ultra-small platinum nanoparticles segregated by nickle sites for efficient ORR and HER processes

In the electrochemical process,Pt nanoparticles(NPs)in Pt-based catalysts usually agglomerate due to Oswald ripening or lack of restraint,ultimately resulting in reduction of the active sites and catalytic efficiency.How to uniformly disperse and firmly fix Pt NPs on carbon matrix with suitable particle size for catalysis is still a big challenge.Herein,to prevent the agglomeration and shedding of Pt NPs,Ni species is introduced and are evenly dispersed in the surface of carbon matrix in the form of Ni-N-C active sites(Ni ZIF-NC).The Ni sites can be used to anchor Pt NPs,and then effectively limit the further growth and agglomeration of Pt NPs during the reaction process.Compared with commercial Pt/C catalyst,Pt@Ni ZIF-NC,with ultralow Pt loading(7 wt%)and ideal particle size(2.3 nm),not only increases the active center,but also promotes the catalysis kinetics,greatly improving the ORR and HER catalytic activity.Under acidic conditions,its half-wave potential(0.902 V)is superior to commercial Pt/C(0.861 V),and the mass activity(0.38 A per mg Pt)at 0.9 V is 4.7 times that of Pt/C(0.08 A per mg Pt).Besides,it also shows outstanding HER performance.At 20 and 30 mV,its mass activity is even 2 and 6 times that of Pt/C,respectively.Whether it is under ORR or HER conditions,it still shows excellent durability.These undoubtedly indicate the realization of dual-functional catalysts with low-Pt and high-efficiency properties.

Investigation of MXene nanosheets based radio-frequency electronics by skin depth effect

Various new conductive materials with exceptional properties are utilized for the preparation of electronic devices.Achieving ultra-high conductivity is crucial to attain excellent electrical performance.However,there is a lack of systematic research on the impact of conductor material thickness on device performance.Here,we investigate the effect of conductor thickness on power transmission and radiation in radio-frequency(RF)and microwave electronics based on MXene nanosheets material transmission lines and antennas.The MXene transmission line with thickness above the skin depth exhibits a good transmission coefficient of approximately-3 dB,and the realized gain of MXene antennas exceeds 2 dBi.Additionally,the signal transmission strength of MXene antenna with thickness above the skin depth is higher than 5-μm MXene antenna approximately 5.5 dB.Transmission lines and antennas made from MXene materials with thickness above the skin depth exhibit stable and reliable performance,which has significant implications for obtaining high-performance RF and microwave electronics based on new conductive materials.

Controlling electrodeposited Ni layers by different-sized graphene oxides enables conductive e-textiles for the highly sensitive electrochemical detection of glucose

With the increasing popularity of wearable electronic devices,there is an urgent demand to develop electronic textiles(e-textiles)for device fabrication.Nevertheless,the difficulty in reconciliation between conductivity and manufacturing costs hinders their large-scale practical applications.Herein,we reported a facile and economic method for preparing conductive e-textiles.Specifically,nonconductive polypropylene(PP)was wrapped by reduced graphene oxide(rGO),followed by the electrodeposition of Ni nanoparticles(NPs).Notably,modulating the sheet size of graphene oxide(GO)resulted in controllable deposition of Ni NPs with adjustable size,allowing for controlled manipulations over the structures,morphologies,and conductivity of the obtained e-textiles,which influenced their performance in electrochemical glucose detection subsequently.The optimal material,denoted as Ni/rGO+(0.2)/PP,exhibited an impressive conductivity of 7.94×10^(4)S·m^(−1).With regard to the excellent conductivity of the as-prepared e-textiles and the high electrocatalytic activity of Ni for glucose oxidation,the asprepared e-textiles were subjected to glucose detection.It was worth emphasizing that the Ni/rGO_(0.2)/PP-based electrode demonstrated promising performance for nonenzymatic/label-free glucose detection,with a detection limit of 0.36μM and a linear response range of 0.5μM to 1 mM.This study paves the way for further development and application prospects of conductive etextiles.

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.

High-performance thermal interface materials enabled by vertical alignment of lightweight and soft graphene foams

High-performance thermal interface materials (TIMs) are highly sought after for modern electronics. Two-dimensional (2D) materials as vertical aligned fillers can optimize the out-plane thermal conductivity (k ⊥), but their excessively high content or intrinsic rigidness deteriorate TIMs softness, leading to worsening for thermal contact resistance (R contact). In this study, 2D graphene materials are fabricated into lightweight and soft graphene foams (GFs) with high-orientation, acting as vertical filler frameworks to optimize the k ⊥ and R contact for vertical GF (VGF) TIMs. The VGF-TIM has a high k ⊥ of 47.9 W·m^(−1)·K^(−1) at a low graphene content of 15.5 wt.%. Due to the softness and low filler contents of GFs, the VGF-TIM exhibits a low compressive module (4.2 MPa), demonstrating excellent compressibility. The resulting TIM exhibit a low contact resistance of 24.4 K·mm2·W^(−1), demonstrating 185.1% higher cooling efficiency in practical heat dissipating scenario compared to commercial advanced TIMs. This work provides guidelines for the design of advanced TIMs and their applications in thermal management.

Flexible and transparent graphene/silver-nanowires composite ?lm for high electromagnetic interference shielding effectiveness

Herein, an efficient approach to prepare flexible, transparent, and lightweight films based on graphene nanosheets(GNS) and silver nanowires(AgNWs) for high electromagnetic interference(EMI) shielding effectiveness(SE) has been explained. High-conductive GNS were fabricated by liquid phase stripping and composited with AgNWs by a two-step spin-coating method. Owing to the high transparency, good conductivity, and homogeneous distribution of both GNS and AgNWs, the obtained GNS/AgNWs film exhibits superb EMI SE and light transmittance, yielding a significantly high EMI SE up to 26 dB in both Ku-band and K-band and light transmittance higher than 78.4%. Moreover, this GNS/AgNWs film shows good flexibility and excellent structural stability. The obtained flexible, light and transparent film could have a great potential for transparent EMI shielding and smart electronics.

High conductive graphene assembled films with porous micro-structure for freestanding and ultra-low power strain sensors

Graphene emerges as an ideal material for constructing high-performance strain sensors,due to its superior mechanical property and high conductivity.However,in the process of assembling graphene into macroscopic materials,its conductivity decreases significantly.Also,tedious fabrication process hinders the application of graphene-based strain sensors.In this work,we report a freestanding graphene assembled film(GAF)with high conductivity((2.32±0.08)×105 S m-1).For the sensitive materials of strain sensors,it is higher than most of reported carbon nanotube and graphene materials.These advantages enable the GAF to be an ultra-low power consumption strain sensor for detecting airflow and vocal vibrations.The resistance of the GAF remains unchanged with increasing temperature(20-100℃),exhibiting a good thermal stability.Also,the GAF can be used as a strain sensor directly without any flexible substrates,which greatly simplifies the fabrication process in comparison with most reported strain sensors.Additionally,the GAF used as a pressure sensor with only^4.7μW power is investigated.This work provides a new direction for the preparation of advanced sensors with ultra-low power consumption,and the development of flexible and energy-saving electronic devices.

Wideband and low sidelobe graphene antenna array for 5G applications

The upcoming fifth-generation(5G)mobile communication with low-latency,high-speed and high-data-capacity[1]can realize innovative services such as remote intelligent medical care,smart cities,Internet of Vehicles,and ultra-high-definition video[2,3].Compared with current mobile communications,5G services require a 5G network with 1000 times the capacity and 10–100 times the data transmission rate[4].5G communication can also realize large-scale connections between people and machines[5].It will be the era of Internet of Everything.The realization of the interconnection of all things is essentially the communication between the transmitting antenna and the receiving antenna.

Ultra-high conductive graphene assembled film for millimeter wave electromagnetic protection

轻质、高效、耐腐蚀、易于大规模制备的电磁防护材料正受到越来越多的关注.本文提出了一种二次高温退火工艺,大规模制备具有超高电导率的石墨烯组装膜,并应用于毫米波频段电磁防护.二次退火工艺提高了石墨烯组装膜的结晶度和层间规则性,使片层间接触电阻降低,电导率得到显著提升.石墨烯组装膜在超宽频带内都具备优异的电磁屏蔽性能,远高于目前所报道的相同厚度的各类碳基材料.另外,本文还研制了一种超低面密度且具有良好角度稳定性的毫米波石墨烯频率选择表面.石墨烯频段选择表面继承了石墨烯组装膜的特性,具有良好的柔韧性、高导热性和优异的机械稳定性.本研究采用标准方法证明了石墨烯组装膜用于毫米波电磁屏蔽和频率选择表面等电磁防护的新概念,从而开辟了一个新的研究方向.

Highly sensitive wearable sensor based on a flexible multi-layer graphene film antenna

The use of advanced carbon nanomaterials for flexible antenna sensors has attracted great attention due to their outstanding electromechanical properties. However, carbon nanomaterial based composites have yet to overcome drawbacks, such as low conductivity and toughness. In this work, a flexible multi-layer graphene film(FGF) with a high conductivity of 10~6 S/m for antenna based wearable sensors is investigated. A 1.63 GHz FGF antenna sensor exhibits significantly high strain sensitivity of 9.8 for compressive bending and 9.36 for tensile bending, which is super than the copper antenna sensor(5.39 for compressive bending and 4.05 for tensile bending). Moreover, the FGF antenna sensor shows very good mechanical flexibility, reversible deformability and structure stability, and thus is well suited for applications like wearable devices and wireless strain sensing.

Scalable fabrication of graphene-assembled multifunctional electrode with efficient electrochemical detection of dopamine and glucose

Conventional glassy carbon electrodes(GCE)cannot meet the requirements of future electrodes for wider use due to low conductivity,high cost,non-portability,lack of flexibility.Therefore,cost-effective and wearable electrode enabling rapid and versatile molecule detection is becoming important,especially with the ever-increasing demand for health monitoring and point-ofcare diagnosis.Graphene is considered as an ideal electrode due to its excellent physicochemical properties.Here,we prepare graphene film with ultra-high conductivity and customize the 3-electrode system via a facile and highly controllable laser engraving approach.Benefiting from the ultra-high conductivity(5.65×10^(5)S·m^(−1)),the 3-electrode system can be used as multifunctional electrode for direct detection of dopamine(DA)and enzyme-based detection of glucose without further metal deposition.The dynamic ranges from 1–200μM to 0.5–8.0 mM were observed for DA and glucose,respectively,with a limit of detection(LOD)of 0.6μM and 0.41 mM.Overall,the excellent target detection capability caused by the ultra-high conductivity and ease modification of graphene films,together with their superb mechanical properties and ease of mass-produced,provides clear potential not only for replacing GCE for various electrochemical studies but also for the development of portable and highperformance electrochemical wearable medical devices.

Accelerated reconstruction of ZIF-67 with significantly enhanced glucose detection sensitivity

Research on metal-organic framework(MOF)-based non-enzymatic glucose sensors usually ignores the impact of the surface reconstruction degree of MOF on the activity of catalyzing glucose oxidation.In this work,we choose zeolitic imidazolate framework-67(ZIF-67),which is commonly used in glucose sensing,as a representative to investigate the influence of reconstruction degree on its structure and glucose catalytic performance.By employing the electrochemical activation strategy,the activity of ZIF-67 in catalyzing glucose gradually increased with the prolongation of the activation time,reaching the optimum after 2 h activation.The detection sensitivity of the activated ZIF-67 was 19 times higher than that of the initial ZIF-67,and the limit of detection(LOD)was lowered from 7 to 0.4μM.Our findings demonstrate that the oxidation degree of ZIF-67 deepened rapidly with continuously activation and was basically reconstructed to CoOOH after 2 h activation,accompanied by a morphological change from cuboctahedral to flower-like.Simultaneously,theoretical investigation revealed that ZIF-67 is not suitable as a stable glucose sensor electrode since the adsorbed glucose molecules hasten the dissociation of ligands and the breaking of Co-N bond in ZIF-67.Therefore,our work has important implications for the rational design of next-generation MOF-based glucose sensors.

Hybrid ionic/electronic interphase enabling uniform nucleation and fast diffusion kinetics for stable lithium metal anode

Lithium(Li)dendrite issue,which is usually caused by inhomogeneous Li nucleation and fragile solid electrolyte interphase(SEI),impedes the further development of high-energy Li metal batteries.However,the integrated construction of a high-stable SEI layer that can regulate uniform nucleation and facilitate fast Li-ion diffusion kinetics for Li metal anode still falls short.Herein,we designed an artificial SEI with hybrid ionic/electronic interphase to regulate Li deposition by in-situ constructing metal Co clusters embedded in LiF matrix.The generated Co and LiF both enable fast Li-ion diffusion kinetics,meanwhile,the lithiophilic properties of Co clusters can serve as Li-ion nucleation sites,thereby contributing to uniform Li nucleation and non-dendritic growth.As a result,a dendrite-free Li deposition with a low overpotential(16.1 mV)is achieved,which enables an extended lifespan over 750 h under strict conditions.The full cells with high-mass-loading LiFePO_(4)(11.5 mg/cm^(2))as cathodes exhibit a remarkable rate capacity of 84.1 mAh/g at 5 C and an improved cycling performance with a capacity retention of 96.4%after undergoing 180 cycles.

ZIF-8/LiFePO4 derived Fe-N-P Co-doped carbon nanotube encapsulated Fe2P nanoparticles for efficient oxygen reduction and Zn-air batteries

Iron-based oxygen reduction reaction(ORR)catalysts have been the focus of research,and iron sources play an important role for the preparation of efficient ORR catalysts.Here,we successfully use LiFePO4 as ideal sources of Fe and P to construct the heteroatom doped Fe-based carbon materials.The obtained Fe-N-P co-doped coral-like carbon nanotube arrays encapsulated Fe2P catalyst(C-ZIF/LFP)shows very high half-wave potential of 0.88 V in alkaline electrolytes toward ORR,superior to Pt/C(0.85 V),and also presents a high half-wave potential of 0.74 V in acidic electrolytes,comparable to Pt/C(0.8 V).When further applied into a home-made Zn-air battery as cathode,a peak power density of 140 mW·cm^-2 is reached,exceeds commercial Pt/C(110 mW·cm^-2).Besides,it also presents exceptional durability and methanol resistance compared with Pt/C.Noticeably,the preparation method of such a high-performance catalyst is simple and easy to optimize,suitable for the large-scale production.What’s more,it opens up a more sustainable development scenario to reduce the hazardous wastes such as LiFePO4 by directly using them for preparing high-performance ORR catalysts.

A new strategy to access Co/N co-doped carbon nanotubes as oxygen reduction reaction catalysts

Carbon nanotubes(CNTs),as one-dimensional nanomaterials,show great potential in energy conversion and storage due to their efficient electrical conductivity and mass transfer.However,the security risks,time-consuming and high cost of the preparation process hinder its further application.Here,we develop that a negative pressure rather than a following gas environment can promote the generation of cobalt and nitrogen co-doped CNTs(Co/N-CNTs) by using cobalt zeolitic imidazolate framework(ZIF-67) as a precursor,in which the negative pressure plays a key role in adjusting the size of cobalt nanoparticles and stimulating the rearragement of carbon atoms for forming CNTs.Importantly,the obtained Co/N-CNTs,with high content of pyridinic nitrogen and abundant graphitized structure,exhibit superior catalytic activity for oxygen reduction reaction(ORR) with half-wave potential(E_(1/2)) of 0.85 V and durability in terms of the minimum current loss(2%) after the 30,000 s test.Our development provides a new pathway for large-scale and cost-effective preparation of metal-doped CNTs for various applications.

Size effect enabling additive-free MXene ink with ultrahigh conductivity for screen printing of wireless electronics

Facile preparation of additive-free inks with both high viscosity and high conductivity is critical for scalable screen printing of wireless electronics,yet very challenging.MXene materials exhibit excellent conductivity and hydrophilicity,showing great potential in the field of additive-free inks for screen printing.Here,we demonstrate the synthesis of additive-free two-dimensional(2D)titanium carbide MXene inks,and realize screen-printed MXene wireless electronics for the first time.The viscosity of MXene ink is solely regulated by tuning the size of MXene nanosheet without any additives,hence rendering the printed MXene film extremely high conductivity of 1.67×10^(5) S/m and fine printing resolution down to 0.05 mm on various flexible substrates.Moreover,radio frequency identification(RFID)tags fabricated using the additive-free MXene ink via screen printing exhibit stable antenna reading performance and superb flexibility.This article,thus offers a new route for the efficient,low-cost and pollution-free manufacture of printable electronics based on additive-free MXene inks.

Well-structured 3D channels within GO-based membranes enable ultrafast wastewater treatment

Graphene oxide(GO)-based membranes have been widely studied for realizing efficient wastewater treatment,due to their easily functionalizeable surfaces and tunable interlayer structures.However,the irregular structure of water channels within GO-based membrane has largely confined water permeance and prevented the simultaneously improvement of purification performance.Herein,we purposely construct the well-structured three-dimensional(3D)water channels featuring regular and negatively-charged properties in the GO/SiO_(2)composite membrane via in situ close-packing assembly of SiO_(2)nanoparticles onto GO nanosheets.Such regular 3D channels can improve the water permeance to a record-high value of 33,431.5±559.9 L·m^(−2)·h−1(LMH)bar−1,which is several-fold higher than those of current state-of-the-art GO-based membranes.We further demonstrate that benefiting from negative charges on both GO and SiO2,these negatively-charged 3D channels enable the charge selectivity well toward dye in wastewater where the rejection for positive-charged and negative-charged dye molecules is 99.6%vs.7.2%,respectively.The 3D channels can also accelerate oil/water(O/W)separation process,in which the O/W permeance and oil rejection can reach 19,589.2±1,189.7 LMH bar−1 and 98.2%,respectively.The present work unveils the positive role of well-structured 3D channels on synchronizing the remarkable improvement of both water permeance and purification performance for highly efficient wastewater treatment.