Preparation of hybrid paper electrode based on hexagonal boron nitride integrated graphene nanocomposite for free-standing flexible supercapacitors

Flexible energy storage devices have received great interest due to the increasing demand for wearable and flexible electronic devices with high-power energy sources. Herein, a novel hybrid flexible hexagonal boron nitride integrated graphene paper (BN/GrP) is fabricated from 2D hexagonal boron nitride (h-BN) nanosheets integrated with graphene sheets dispersion via a simple vacuum filtration method. FE-SEM indicated that layered graphene nanosheets tightly confined with h-BN nanosheets. Further, the Raman spectroscopy confirmed successful integration of BN with graphene. As-prepared BN/GrP free-standing flexible conductive paper showed high electrical conductivity of 5.36 × 10⁴ S m⁻¹ with the sheet resistance of 8.87 Ω sq⁻¹. However, after 1000 continuous bending cycles, the BN/GrP sheet resistance increased just about 8.7% which indicated good flexibility of the paper. Furthermore, as-prepared BN/GrP showed excellent specific capacitance of 321.95 F g⁻¹ at current density of 0.5 A g⁻¹. In addition, the power and energy densities were obtained as 3588.3 W kg⁻¹, and 44.7 W h kg⁻¹, respectively. The stability of the prepared flexible electrode was tested in galvanostatic charge/discharge cycles, where the results showed the 96.3% retention even after 6000 cycles. These results exhibited that the proposed BN/GrP may be useful to prepare flexible energy-storage systems.

As-prepared BN/GrP free-standing flexible conductive paper showed high electrical conductivity of 5.36 × 10⁴ S m⁻¹ with the sheet resistance of 8.87 Ω sq⁻¹. Furthermore, BN/GrP showed excellent specific capacitance of 321.95 F g⁻¹ at current density of 0.5 A g⁻¹. In addition, the power and energy densities were obtained as 3588.3 W kg⁻¹, and 44.7 W h kg⁻¹.     

Electrodeposited Pd/graphene/ZnO/nickel foam electrode for the hydrogen evolution reaction

Efficient electrocatalysts are crucial to water splitting for renewable energy generation. In this work, electrocatalytic hydrogen evolution from Pd nanoparticle-modified graphene nanosheets loaded on ZnO nanowires on nickel foam was studied in an alkaline electrolyte. The high electron mobility stems from the cylindrical ZnO nanowires and the rough surface on the graphene/ZnO nanowires increases the specific surface area and electrical conductivity. The catalytic activity arising from adsorption and desorption of intermediate hydrogen atoms by Pd nanoparticles improves the hydrogen evolution reaction efficiency. As a hydrogen evolution reaction (HER) catalyst, the Pd/graphene/ZnO/Ni foam (Pd/G/ZnO/NF) nanocomposite exhibits good stability and superior electrocatalytic activity. Linear sweep voltammetry (LSV) revealed an overpotential of −31 mV and Tafel slope of 46.5 mV dec⁻¹ in 1 M KOH. The economical, high-performance, and environmentally friendly materials have excellent prospects in hydrogen storage and hydrogen production.

Efficient electrocatalysts are crucial to water splitting for renewable energy generation.     

A 2D metal–organic framework/reduced graphene oxide heterostructure for supercapacitor application

Metal organic frameworks (MOFs) with two dimensional (2D) nanosheets have attracted special attention for supercapacitor application due to their exceptional large surface area and high surface-to-volume atom ratios. However, their electrochemical performance is greatly hindered by their poor electrical conductivity. Herein, we report a 2D nanosheet nickel cobalt based MOF (NiCo-MOF)/reduced graphene oxide heterostructure as an electrode material for supercapacitors. The NiCo-MOF 2D nanosheets are in situ grown on rGO surfaces by simple room temperature precipitation. In such hybrid structure the MOF ultrathin nanosheets provide large surface area with abundant channels for fast mass transport of ions while the rGO conductive and physical support provides rapid electron transport. Thus, using the synergistic advantage of rGO and NiCo-MOF nanosheets an excellent specific capacitance of 1553 F g⁻¹ at a current density of 1 A g⁻¹ is obtained. Additionally, the as synthesized hybrid material showed excellent cycling capacity of 83.6% after 5000 cycles of charge–discharge. Interestingly, the assembled asymmetric device showed an excellent energy density of 44 W h kg⁻¹ at a power density of 3168 W kg⁻¹. The electrochemical performance obtained in this report illustrates hybridization of MOF nanosheets with carbon materials is promising for next generation supercapacitors.

In this 2D NiCo-MOF/rGO hybrid, the MOF nanosheets provide abundant active sites while the conductive rGO provide rapid electron transport.     

CuO nanorods grown vertically on graphene nanosheets as a battery-type material for high-performance supercapacitor electrodes

This work reports the preparation and characterization of the CuO nanorods grown vertically on graphene nanosheets, denoted as CuO/rGO@NF. Graphene is deposited by electrostatic attraction showing the morphology of folded nanosheets, which improves the electrical conductivity of the electrode, while CuO is modified by filtered cathodic vacuum arc technology and subsequent electrochemical oxidation presenting the morphology of nanorods, which increases the contact area of active sites and shortens the ion and electronic diffusion path. The results show that the CuO/rGO@NF electrode deliver an ultrahigh specific capacity (2.51 C cm⁻² at 2 mA cm⁻²), remarkable rate performance (64.6%) and improved conductivity. A symmetrical supercapacitor is assembled by two identical electrodes, presenting the maximum energy density of 38.35 W h kg⁻¹ at a power density of 187.5 W kg⁻¹. Therefore, the CuO/rGO@NF electrode can be used as a prospective electrode for energy storage devices. In addition, the whole electrode preparation process is short in time, safe and environmentally friendly, which provides a new idea for the preparation of other electrode materials.

The CuO/rGO@NF electrode is prepared by a simple and time-saving method, which has ultrahigh area capacity and excellent rate performance.     

Electrochemical performance of graphene-coated activated mesocarbon microbeads as a supercapacitor electrode

Hybrid activated carbon/graphene materials are prospective candidates for use as high performance supercapacitor electrode materials, since they have the superior characteristics of high surface area, abundant micro/mesoporous structure due to the presence of activated carbon and good electrical conductivity as a result of the presence of graphene. In this work, the electrochemical performance of facile and low-cost graphene-coated activated mesocarbon microbeads (g-AM) is carefully studied. The results show that g-AM can only be formed at a very high temperature over a long activation time, resulting in the formation of a large pore size and low specific surface area, further resulting in poor electrochemical performance (110 F g⁻¹ at 0.1 A g⁻¹ in 6 M KOH solution). Ball milling for a short time is an effective way to improve the electrochemical performance (191 F g⁻¹ at 0.1 A g⁻¹ in 6 M KOH solution). Moreover, due to the strong resistance to aggregation and good electrical conductivity of graphene flowers, the g-AM had nearly 100% rate capability when increasing the current density from 5 to 50 A g⁻¹. The as-assembled two-electrode symmetric supercapacitor exhibits a high energy and power density (5.28 W h kg⁻¹ at 10 000 W kg⁻¹) in organic LiPF₆ electrolyte, due to its better electrical conductivity. It is expected that this type of hybrid structure holds great potential for scalable industrial manufacture as supercapacitor electrodes.

Activated carbon/graphene materials are prospective candidates as high performance supercapacitor electrodes, due to the presence of aggregation resisted graphene on the surface of activated carbon.     

Preparation of an electrospun tubular PU/GE nanofiber membrane for high flux oil/water separation

A simple, tubular structure polyurethane/graphene (PU/GE) nanofiber membrane for continuous oil/water separation was prepared using the following strategies: a polyester (PET) fiber braided tube was used for reinforcement, stearic acid (SA) was used to assist GE dispersion, and a PU solution containing GE was used to cover the outer layer of the PET fiber braided tube using the electrospinning method. Specifically, the PU/GE nanofiber membrane has a multi-branched structure. The tubular braid reinforced (TBR) PU/GE nanofiber membrane was characterized using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), confocal scanning microscopy (CSM) and capillary flow porometry. The contact angle results showed that the TBR PU/GE nanofiber membrane had good hydrophobic and lipophilic properties. The obtained membranes had good oil/water selectivity for oil–water separation (with a separation efficiency up to 99%). In addition, the optimized membrane can be effectively employed to separate a surfactant-stabilized water-in-oil emulsion with a separation efficiency up to 90% and a high permeate flux (137.5 L m⁻² h⁻¹). Our TBR PU/GE nanofiber membrane is therefore a desirable material for the highly efficient separation of water-in-oil emulsions, and shows broad application prospects in the field of oil/water separation.

A simple, tubular structure polyurethane/graphene (PU/GE) nanofiber membrane for continuous oil/water separation has been prepared.     

A self-assembled graphene/polyurethane sponge for excellent electromagnetic interference shielding performance

With the rapid development of personal computers and portable electronics, people have to get rid of a lot of unwanted electromagnetic pollution. The development of high performance electromagnetic interference (EMI) shielding materials is of critical importance to address ever-increasing military and civilian demand. Owing to its high electrical conductivity and flexible 3D structure, graphene sponge has great potential for excellent EMI shielding performance. However, its EMI shielding performance suffers from the material’s poor elasticity and durability. In this paper, we demonstrate the potential of a self-assembled graphene/polyurethane sponge composite, synthesized via a two-step hydrothermal method, for EMI shielding. This kind of material exhibits a high specific EMI shielding effectiveness of 969–1578 dB cm² g⁻¹ which is comparable or even superior to traditional graphene/polymer sponges. The excellent EMI shielding performance originates from the superconductivity of graphene and the highly porous structure of the graphene/polyurethane sponge. It is found that the polyurethane sponge works as a robust scaffold for graphene to shape its 3D structure. This work introduces a facile yet efficient two-step hydrothermal approach to prepare a graphene/polyurethane sponge with excellent EMI shielding performance and good durability.

Process diagram of PUG Sponge for electromagnetic interference shielding.     

Preparation of boron nitride nanosheets via polyethyleneimine assisted sand milling: towards thermal conductivity and insulation applications

Hexagonal boron nitride (h-BN) is often used as a filler in polymer composites due to its good thermal conductivity and insulation properties. However, the compatibility between h-BN and the matrix limits its application areas. To overcome this issue, a combination of mechanical liquid phase exfoliation and chemical interfacial modification was adopted in this work. Polyethyleneimine (PEI) was used as the exfoliation reagent to prepare PEI-functionalized h-BN nanosheets, denoted as PEI@BNNS. Thermoplastic polyurethane (TPU) composites with different contents of h-BN and PEI@BNNS which were recorded as h-BN/TPU and PEI@BNNS/TPU were successfully prepared through a hot-pressing process, respectively. The results show that PEI@BNNS/TPU composites have better in-plane thermal conductivity while maintaining insulation, and with the content of 5 wt% PEI@BNNS, the in-plane thermal conductivity of the PEI@BNNS/TPU composite is up to 0.61 W m⁻¹ K⁻¹, which is three times that of pure TPU (0.22 W m⁻¹ K⁻¹).

The PEI-grafted boron nitride nanosheets were successfully prepared via sand-milling process, which were doped into thermoplastic polyurethane matrix for better in-plane thermal conductivity while maintaining insulation properties.     

A composite with a gradient distribution of graphene and its anisotropic electromagnetic reflection

So far, it is still difficult to construct composites with a gradient distribution of graphene for decreasing the reflection and increasing the absorption of electromagnetic energy. Here, we introduce an electrochemical method to efficiently prepare a graphene/polyurethane composite with a gradient graphene distribution. And the composite shows obvious anisotropic reflection of electromagnetic waves, with low reflection loss (<−30 dB) and high absorption (>99.5%) in the whole X-band when electromagnetic waves are incident to the surface that has low graphene content. More importantly, the electrochemical method could be extended to the preparation of functional materials with similar structures based on the electrophoresis of charged nanoparticles.

An electrochemical method was introduced to prepare graphene/polyurethane foams with gradient graphene distribution, and this composite shows obvious anisotropic reflection of electromagnetic waves.

Microwave-absorbing materials can transform electromagnetic energy into heat through dielectric loss and/or magnetic loss, helping to eliminate electromagnetic radiation in the environment.^1–3 Therefore, electromagnetic absorbing composites containing magnetic fillers such as ferrite⁴ and carbonyl iron,⁵ or conducting fillers such as carbon fibers,⁶ conducting polymers,⁷ carbon nanotubes^8,9 and graphene,^10–12 have been created. Previous studies have shown that compared with graphite, carbon nanotubes and high-quality graphene, reduced graphene oxide (rGO) demonstrates better electromagnetic absorption characteristic of its residual defects and functional groups.^13–15The reflection of electromagnetic waves at the surface of a material is mainly caused by the mismatch in the impedance between the material and free space.^1,16 For maximal absorption but also low reflection, finely adjusting the electromagnetic constant of the material to satisfy the impedance matching is one solution.^1,17 Another important solution involves the preparation of multi-layered or gradient structures with gradually increasing concentrations of active fillers.^18–20 This kind of materials could reduce reflection at the input interface due to the low concentration of active fillers, and ensure absorption in the inner layers due to their higher filler content.^21–23 Current preparation methods of gradient structures mainly involve the multi-step assembly of composite slices with different active filler content^18,20 or time-consuming supercritical carbon dioxide technology.¹⁹ Compared with the multi-layered structure, a continuous variation of active filler content could more efficiently reduce the reflection to achieve continuously varied impedance. As far as we know, electromagnetic absorbing materials based on graphene composites with continuous variation of graphene content have not yet been reported.Here, we present an efficient electrochemical method to prepare reduced graphene oxide/polyurethane (rGO/PU) composite foams with continuous variation of graphene content. This method takes advantage of the negative correlation between the size of GO nanoparticles and their migration velocity in an electric field. Through optimizing the distribution by controlling the electrophoretic time, the gradient graphene composite shows obvious anisotropic reflection of electromagnetic waves. Furthermore, a low reflection (<−30 dB) and high absorption (>99.5%) in the whole X-band was attainted when the electromagnetic waves are incident to the surface with a low graphene content.The electrophoretic process for the preparation of the graphene oxide/polyurethane (GO/PU) composite foams is illustrated in Scheme 1, and the optical image of the equipment is shown in Fig. S1.^† The PU foam filled with graphene oxide solution was placed between two graphite electrodes and a direct voltage of 30 V was applied to the electrodes for a certain period of time. For the ionization of the carboxylic acid and phenolic hydroxyl groups on the GO sheets,²⁴ the negatively charged GO nanosheets migrated to the anode under the external electric field. According to colloid theory, the migration velocity v of GO can be determined by the applied electric field E and the electrophoretic mobility m based on the equation: v = Em; and m for GO nanosheets is given by the following formula:m = Cr^0.5n−11where C is a constant, n is a variable from 1 to 2, and r is the charged particle radius.²⁵ Therefore, the migration velocity is inversely proportional to the radius of the GO nanosheets. Because GO nanosheets from chemically oxidized graphite often exhibit a wide size distribution,²⁶ the smaller GO nanosheets quickly collected near the anode, and eventually formed a gradient distribution of GO in the PU foam. In succession, the PU foam was quickly immersed into dilute hydrochloric acid solution, and the GO nanosheets precipitated and deposited on the backbone of PU sponges due to the decrease of electrostatic repulsion between sheets.²⁴ After drying in an oven, the as-synthesized GO/PU composite foam was chemically reduced to rGO/PU composites. For convenience, the surface with a low rGO content was denoted as S_L, while the surface with a high rGO content was called S_H.Open in a separate windowScheme 1A schematic illustration of the preparation of a GO/PU composite with a gradient GO distribution using an electrophoretic process (left). The directions of the electric field (E) and migration velocity (v) of the GO nanosheets (right).As shown in Fig. 1a–c, after the deposition of GO, the color of the foam changed from white (for pure PU) to brown (for the GO/PU composite). After the reduction to rGO/PU composites by hydrazine in a hydrothermal environment, the color of rGO/PU turned to black, as shown in Fig. 1c. It is important to note that the color of the GO/PU composite continuously deepened along the direction from S_L to S_H, which indicates that the GO content in the composite gradually increased along this direction. The morphology and structure of the rGO/PU composite foam were investigated by scanning electron microscopy. As shown in Fig. 1d–f, the PU foam exhibits a highly porous and interconnected three-dimensional network structure with continuous macropores of several hundred micrometers. The morphology of rGO/PU is similar to that of PU foam but the skeleton of the network exhibits a peeled region marked by the white arrow in Fig. 1e, which is associated with the presence of graphene sheets. This indicates that the graphene sheets assembled around the PU backbones after the electrophoresis and reduction process.Open in a separate windowFig. 1Optical photographs of the (a) PU foam, (b) gradient GO/PU foam and (c) rGO/PU foam. SEM images of (d) PU foam and (e) rGO/PU foam. (f) A close-up view of the region marked by the white arrow in (e). (g) Raman spectra of the GO/PU composite before and after reduction.Raman spectra of the GO/PU composite sample before and after reduction of graphene oxide are shown in Fig. 1e. There are two strong major bands, the D-band at around 1352 cm⁻¹ and the G-band at around 1580 cm⁻¹, which originate from the disorder and the E_2g mode of the aromatic carbon rings,²⁷ respectively. The G-band was down-shifted from 1589 cm⁻¹ to 1575 cm⁻¹ after the reduction of graphene oxide, which was attributed to a certain degree of recovery of the aromatic rings.^28,29 Moreover, the intensity ratio of D-band to G-band increased notably after the reduction. This indicates that reduction increases the number of small domains of aromaticity responsible for the D-band, but not necessarily their overall size which is responsible for the G-band.³⁰In order to determine the GO relative content at different positions in the electrophoretically treated GO/PU composite, the GO/PU composite foam was uniformly sliced into six pieces along the direction parallel to S_L and S_H, and TGA was used to analyze the GO relative content in these pieces. As shown in Fig. 2a, the three stages of the degradation process of the pure PU sponge at 220–290 °C, 300–380 °C and 660–700 °C are referred to as T_1st, T_2nd and T_3rd, respectively.³¹ Compared with the PU sponge, there is an obvious weight loss in the range from 175 °C to 225 °C in the GO/PU composite, which could be due to the thermal decomposition of the oxygen-containing groups in graphene oxide.³² A close-up view of the weight loss in the temperature range from 165 °C to 235 °C is shown in the inset of Fig. 2a, and the arrow shows the order of the specimens. The weight loss in the temperature range of 175 °C to 225 °C gradually reduced along this order, which indicates that the GO content in these specimens gradually decreased. The relative content, defined as the ratio of GO content of the sample to that of S_L, could be concluded from the weight loss ratio. As shown in Fig. 2b, the farther away the sample was from S_L, the more GO it contained, further indicating that the content of rGO in the rGO/PU composite foam gradually increased from S_L to S_H, as shown in the inset in Fig. 2b.Open in a separate windowFig. 2(a) TGA curves of the PU foam and representative GO/PU composite. The inset shows the magnified thermal decomposition of GO/PU specimens. (b) The relative GO content at different positions in the GO/PU composite. The inset shows a schematic illustration of the rGO/PU composite with a gradient graphene distribution.According to the electromagnetic theory, when an electromagnetic wave travels through the interface of two materials with different impedance, reflection, absorption and transmission of the electromagnetic wave can be observed. The incident power is divided into reflected power, absorbed power and transmitted power. The corresponding power coefficients of absorptivity (A), reflectivity (R), and transmissivity (T) meet the equation of R = |S₁₁|², T = |S₂₁|², and A + R + T = 1, where the S₁₁ and S₂₁ are the forward reflection and transmission coefficients measured using the wave-guide method.^33,34 In the test of electromagnetic characteristics, the rGO/PU composites were placed into the middle of an aluminum waveguide fitted into the test fixture, as shown in Fig. S2.^† Fig. 3 shows the electromagnetic testing results of rGO/PU composites electrophoretically treated for different times. Increasing the time from 2 min to 4 min, the maximum reflection loss reduced from −23 dB to −30 dB. However, when the time was increased to 8 min, the maximum reflection loss enhanced to −27 dB. This indicates that the distribution of rGO in the composite significantly affects the reflection loss of electromagnetic waves. Meanwhile, the maximum transmission loss increased from −24 dB to −23 dB and −21 dB, as shown in Fig. 3b. These curves in Fig. 3c indicate that the composites treated for 4 min exhibit an absorption of higher than 99.5% over the whole frequency range, while the values for the other samples were less than 99.2% at certain frequencies. All these results indicate that the composite treated for 4 min not only exhibited significantly reduced reflection loss, but also demonstrated high absorption over the whole X-band. It is worth pointing out that the reflection loss of the rGO/PU composite is related to the incident direction of the electromagnetic waves. As shown in Fig. 3d, the reflection loss was higher than −20 dB over the whole X-band when S_H was irradiated with electromagnetic waves, but it significantly decreased to −30 dB over the whole X-band when the waves were incident to S_L. On the contrary, the curves of transmission loss almost coincide, showing that it is entirely unrelated to the incident direction.Open in a separate windowFig. 3The frequency dependence of (a) reflection loss, (b) transmission loss and (c) absorption of rGO/PU composites treated for different time periods as electromagnetic waves irradiated S_L. (d) A comparison between the reflection loss and transmission loss depending on the incident direction of the waves for the composite treated for 4 min.To gain a better understanding of the electromagnetic absorption of the gradient rGO/PU composites, we prepared several rGO/PU composites with uniform rGO content and studied their electromagnetic characteristics. For convenience, the rGO/PU composite prepared using GO solution with a concentration of n was denoted as rGO_n/PU. Fig. 4a and b show the variation in reflection loss and transmission loss of the uniform rGO/PU composites. By raising the rGO content, the reflection loss enhanced, and the maximum reflection loss increased to −15 dB for the rGO₄/PU composite, which could be attributed to the greater deterioration of the impedance matching between the rGO/PU composite and free space with increased rGO content. Due to the strong dissipation of electromagnetic waves on graphene, the transmission loss decreased to −32 dB with increasing content of rGO. These curves in Fig. 4c indicate that absorption increased with increasing content of rGO and reached 83% at 8 GHz for rGO₁/PU; when the rGO content was increased further, the absorption increased to about 99%. The real intensity of electromagnetic waves entering the interior of the composites is based on (1 − R), so the effective absorption (A_eff) could be described as: A_eff = (1 − R − T)/(1 − R), which can evaluate the real absorbing capacity of rGO/PU composites.³⁵ The A_eff values of the rGO/PU composites with different rGO content at the frequency of 10 GHz are shown in Fig. 4d. The A_eff value enhanced with increasing rGO content; however, the slope of the curve gradually decreased with increasing rGO content, which means that the absorption capacity per unit rGO mass decreased with increasing rGO content. This also clearly explains the phenomenon of gradient rGO/PU composites, in which the absorption firstly increases and then decreases with increasing the electrophoretic time.Open in a separate windowFig. 4The (a) reflection loss, (b) transmission loss, and (c) absorption curves of uniform rGO/PU composites with different rGO content values. (d) The effective absorption at a frequency of 10 GHz for the uniform rGO/PU composites versus the concentration of GO solution used for the preparation of the rGO/PU composites.     

Ultrathin flexible graphene films with high thermal conductivity and excellent EMI shielding performance using large-sized graphene oxide flakes

As the demand for wearable and foldable electronic devices increases rapidly, ultrathin and flexible thermal conducting films with exceptional electromagnetic interference (EMI) shielding effectiveness (SE) are greatly needed. Large-sized graphene oxide flakes and thermal treatment were employed to fabricate lightweight, flexible and highly conductive graphene films. Compared to graphene films made of smaller-sized flakes, the graphene film made of large-sized flakes possesses less defects and more conjugated domains, leading to higher electrical and higher thermal conductivities, as well as higher EMI SE. By compressing four-layer porous graphene films together, a 14 μm-thick graphene film (LG-4) was obtained, possessing EMI SE of 73.7 dB and the specific SE divided by thickness (SSE/t) of 25 680 dB cm² g⁻¹. The ultrahigh EMI shielding property of the LG-4 film originates from the excellent electrical conductivity (6740 S cm⁻¹), as well as multi-layer structure composed of graphene laminates and insulated air pores. Moreover, the LG-4 film shows excellent flexibility and high thermal conductivity (803.1 W m⁻¹ K⁻¹), indicating that the film is a promising candidate for lightweight, flexible thermal conducting film with exceptional EMI shielding performance.

As the demand for wearable and foldable electronic devices increases rapidly, ultrathin and flexible thermal conducting films with exceptional electromagnetic interference (EMI) shielding effectiveness (SE) are greatly needed.     

A N-doped graphene–cobalt nickel sulfide aerogel as a sulfur host for lithium–sulfur batteries

Herein, three-dimensional (3D) N-doped reduced graphene oxide (N-rGO) nanosheets were decorated with a uniform distribution of Co–Ni–S (CNS) nanoparticles to form the CNS/N-rGO composite as a sulfur host material for lithium–sulfur batteries. The CNS nanoparticles and N in CNS/N-rGO strongly interact with polysulfides, whereas graphene, as a conductive network, can improve its electrical conductivity. A CNS/N-rGO/sulfur composite cathode was prepared via the sulfur melting diffusion method. The electrochemical study showed that the CNS/N-rGO/sulfur cathode delivered an initial discharge capacity of 1430 mA h g⁻¹ at a current density of 0.1C. Moreover, it retained a specific capacity of 685 mA h g⁻¹ after 300 cycles at 0.5C with a coulombic efficiency of 98%, which was better than that of commercial rGO. This composite was used as a sulfur cathode for a lithium–sulfur battery, exhibiting excellent rate capability and remarkable performance in terms of long cycling stability.

Herein, three-dimensional (3D) N-doped reduced graphene oxide (N-rGO) nanosheets were decorated with a uniform distribution of Co–Ni–S (CNS) nanoparticles to form the CNS/N-rGO composite as a sulfur host material for lithium–sulfur batteries.     

Three-dimensional thiophene-diketopyrrolopyrrole-based molecules/graphene aerogel as high-performance anode material for lithium-ion batteries

Herein, 3,6-di(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (TDPP) and di-tert-butyl 2,2′-(1,4-dioxo-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-2,5(1H,4H)-diyl)diacetate (TDPPA) were synthesized, which were then loaded in graphene aerogels. The as-prepared thiophene-diketopyrrolopyrrole-based molecules/reduced graphene oxide composites for lithium-ion battery (LIB) anode composites consist of DPPs nanorods on a graphene network. In relation to the DPPs part, embedding DPPs nanorods into graphene aerogels can effectively reduce the dissolution of DPPs in the electrolyte. It can serve to prevent electrode rupture and improve electron transport and lithium-ion diffusion rate, by partially connecting DPPs nanorods through graphene. The composite not only has a high reversible capacity, but also shows excellent cycling stability and performance, due to the densely distributed graphene nanosheets forming a three-dimensional conductive network. The TDPP₆₀ electrode exhibits high reversible capacity and excellent performance, showing an initial discharge capacity of 835 mA h g⁻¹ at a current density of 100 mA g⁻¹. Even at a current density of 1000 mA g⁻¹, after 500 cycles, it still demonstrates a discharge capacity of 303 mA h g⁻¹ with a capacity retention of 80.7%.

Herein, TDPP and TDPPA were synthesized and then loaded on graphene by hydrothermal method to obtain TDPP/RGO and TDPPA/RGO aerogel, which were applied as anode for LiBs.     

Facile synthesis of an all-in-one graphene nanosheets@nickel electrode for high-power performance supercapacitor application

We report a facile and novel approach for the fabrication of all-in-one supercapacitor electrodes by in situ electrochemical exfoliation of flexible graphite paper (FGP) on a nickel collector. The binder-free three dimensional (3D) graphene nanosheets@Ni (GNSs@Ni) supercapacitor electrodes exhibit a high specific capacitance of 196.4 F g⁻¹ and 36.2 mF cm⁻², respectively, at a scan rate of 50 mV s⁻¹. Even at the high scan rate of 2500 mV s⁻¹ the specific capacitance of the capacitor still shows a retention of 85.6% (168 F g⁻¹, 31 mF cm⁻²). Meanwhile, the as-prepared electrode offers excellent cycling performance with 91.5% capacitance retention after 100 000 charging–discharging cycles even at the high current density of 11 A g⁻¹. Such high rate capability, specific capacitance and exceptional cycling ability of the GNSs@Ni electrode are attributed to the all-in-one architecture which provides unique properties including high electrical conductivity, large specific surface area and excellent electrochemical stability. We anticipate that these results will shed light on new strategies to synthesize high-performance hybrid nanoarchitectures electrodes using the prepared graphene nanosheets as the support, which offers great potential in energy storage devices and electrochemical catalysis applications.

GNSs@Ni electrode has a high current density, and the C_m and C_s are estimated to be 196.4 F g⁻¹ and 36.2 mF cm⁻².     

Effects of Cu2+/Zn2+ on the electrochemical performance of polyacrylamide hydrogels as advanced flexible electrode materials

Previously, solid-state electrode materials have been utilized for the fabrication of energy storage devices; however, their application is impeded by their brittle nature and ion mobility problems. To address issues faced in such a modern era where energy saving and utility is of prior importance, a novel approach has been applied for the preparation of electrode materials based on polyacrylamide hydrogels embedded with reduced graphene oxide and transition metals, namely, Cu²⁺ and Zn²⁺. The fabricated hydrogel exhibits high electrical properties and flexibility that make it a favorable candidate to be used in energy storage devices, where both elastic and electrical properties are desired. For the first time, a multi-cross-linked polyacrylamide hydrogel was constructed and compared in the presence of other electro-active materials such as reduced graphene oxide and transition metals. Polyacrylamide hydrogels embedded with reduced graphene oxide demonstrate excellent electrical properties such as specific capacitance, least impedance, low phase angle shift and AC conductivity of 22.92 F g⁻¹, 2115 Ω, 2.88° and 0.67 μδ m⁻¹ respectively as compared to Cu²⁺- and Zn²⁺-loaded hydrogels, which block all available active sites causing an increase in impedance with a parallel decrease in capacitance. The capacitance retention and coulombic efficiency calculated were 88.22% and 77.23% respectively, indicating high stability up to 150 cycles at 0.1 A g⁻¹. Storage moduli obtained were 10.52 kPa, which infers the more elastic nature of the hydrogel loaded with graphene oxide than that of other synthesized hydrogels.

A novel approach has been applied for the preparation of electrode materials based on polyacrylamide hydrogels embedded with reduced graphene oxide and transition metals, Cu²⁺ and Zn²⁺. The fabricated hydrogel exhibits high electrical properties and flexibility.     

Effects of poly(ethylene glycol)-grafted graphene on the electrical properties of poly(lactic acid) nanocomposites

Maleic anhydride was reacted with the armchair edges of graphene nanosheets (GN) via Diels–Alder reaction. Then, polyethylene glycol (PEG) was grafted onto the GN in the presence of anhydride groups through an esterification reaction. The PEG-grafted GN (PEG-g-GN) was characterised via FTIR analysis, thermogravimetric analysis, scanning electron microscopy, Raman spectroscopy and contact angle measurements, proving that PEG was successfully grafted onto the GN surface. The results indicated that PEG-g-GN possessed high electrical conductivity and was dispersed in polylactic acid (PLA). The composites were fabricated by using PEG-g-GN and GN as the conductive agent in the PLA matrix. Owing to the function of PEG molecular chains, PEG-g-GN can be uniformly dispersed in the PLA matrix and improve the tensile strength of composites to 59.46 MPa and conductivity to 9.69 × 10⁻⁴ S cm⁻¹ at a PEG-g-GN content of 1 wt%.

PEG-grafted GN has been synthesized and the effects of modification on the PLA composite conductivity, mechanical properties are investigated.     

Green and facile edge-oxidation of multi-layer graphene by sodium persulfate activated with ferrous ions

Effective edge oxidation of graphene with high structural integrity is highly desirable yet technically challenging for most practical applications. In this work, we have developed a green and facile strategy to obtain edge-oxidized graphene with good dispersion stability and high electrical conductivity by exploiting high edge reactivity of highly conductive multi-layer graphene and oxidizing radicals (SO₄⁻˙) generated from sodium persulfate (Na₂S₂O₈) with ferrous ion (Fe²⁺) activation. Owing to high structural integrity of pristine graphene and effective edge oxidation, the obtained edge-oxidized graphene exhibited excellent dispersion stability and satisfactory electrical conductivity (i.e. ≥240 S cm⁻¹). Moreover, the oxidation degree of pristine graphene can be well controlled by adjusting treatment time. The obtained edge-oxidized graphene is expected to find a variety of applications in many fields of anti-static films, energy storage materials, flexible sensors and high-performance nanocomposites.

A green and facile strategy is represented to obtain edge-oxidized graphene by exploiting sulfate radicals generated from Na₂S₂O₈ with Fe²⁺ activation.     

Tin disulphide/nitrogen-doped reduced graphene oxide/polyaniline ternary nanocomposites with ultra-high capacitance properties for high rate performance supercapacitor

In this work, tin disulfide/nitrogen-doped reduced graphene oxide/polyaniline ternary composites are synthesized via in situ polymerization of aniline monomers on the surface of tin disulfide/nitrogen-doped reduced graphene oxide nanosheets binary composites with different loading of the conducting polymers. The tin disulfide/nitrogen-doped reduced graphene oxide/polyaniline ternary composites electrode shows much higher specific capacitance, specific energy and specific power values than those of pure polyaniline and tin disulfide/nitrogen-doped reduced graphene oxide binary composites. The highest specific capacitance, specific energy and specific power values of 1021.67 F g⁻¹, 69.53 W h kg⁻¹ and 575.46 W kg⁻¹ are observed for 60% polyaniline deposited onto tin disulfide/nitrogen-doped reduced graphene oxide composites at a current density of 1 A g⁻¹. The above composites also show superior cyclic stability and 78% of the specific capacitance can be maintained after 5000 galvanostatic charge–discharge cycles. The good charge-storage properties of tin disulfide/nitrogen-doped reduced graphene oxide/polyaniline ternary composites is ascribed to the organic–inorganic synergistic effect. This study paves the way to consider tin disulfide/nitrogen-doped reduced graphene oxide/polyaniline ternary composites as excellent electrode materials for energy storage applications.

In this work, SnS₂/NRGO/PANI ternary composites are synthesized via in situ polymerization of aniline monomers on the surface of SnS₂/NRGO nanosheets binary composites with different loading of the conducting polymers.     

Preparation of cobalt sulfide@reduced graphene oxide nanocomposites with outstanding electrochemical behavior for lithium-ion batteries

Cobalt sulfide@reduced graphene oxide composites were prepared through a simple solvothermal method. The cobalt sulfide@reduced graphene oxide composites are composed of cobalt sulfide nanoparticles uniformly attached on both sides of reduced graphene oxide. Some favorable electrochemical performances in specific capacity, cycling performance, and rate capability are achieved using the porous nanocomposites as an anode for lithium-ion batteries. In a half-cell, it exhibits a high specific capacity of 1253.9 mA h g⁻¹ at 500 mA g⁻¹ after 100 cycles. A full cell consists of the cobalt sulfide@reduced graphene oxide nanocomposite anode and a commercial LiCoO₂ cathode, and is able to hold a high capacity of 574.7 mA h g⁻¹ at 200 mA g⁻¹ after 200 cycles. The reduced graphene oxide plays a key role in enhancing the electrical conductivity of the electrode materials; and it effectively prevents the cobalt sulfide nanoparticles from dropping off the electrode and buffers the volume variation during the discharge–charge process. The cobalt sulfide@reduced graphene oxide nanocomposites present great potential to be a promising anode material for lithium-ion batteries.

Cobalt sulfide@reduced graphene oxide nanocomposites obtained through a dipping and hydrothermal process, exhibit ascendant lithium-ion storage properties.     

Large-scale synthesis of ultrafine Fe3C nanoparticles embedded in mesoporous carbon nanosheets for high-rate lithium storage

Fe₃C modified by the incorporation of carbon materials offers excellent electrical conductivity and interfacial lithium storage, making it attractive as an anode material in lithium-ion batteries. In this work, we describe a time- and energy-saving approach for the large-scale preparation of Fe₃C nanoparticles embedded in mesoporous carbon nanosheets (Fe₃C-NPs@MCNSs) by solution combustion synthesis and subsequent carbothermal reduction. Fe₃C nanoparticles with a diameter of ∼5 nm were highly crystallized and compactly dispersed in mesoporous carbon nanosheets with a pore-size distribution of 3–5 nm. Fe₃C-NPs@MCNSs exhibited remarkable high-rate lithium storage performance with discharge specific capacities of 731, 647, 481, 402 and 363 mA h g⁻¹ at current densities of 0.1, 1, 2, 5 and 10 A g⁻¹, respectively, and when the current density reduced back to 0.1 A g⁻¹ after 45 cycles, the discharge specific capacity could perfectly recover to 737 mA h g⁻¹ without any loss. The unique structure could promote electron and Li-ion transfer, create highly accessible multi-channel reaction sites and buffer volume variation for enhanced cycling and good high-rate lithium storage performance.

Fe₃C modified by the incorporation of carbon materials offers excellent electrical conductivity and interfacial lithium storage, making it attractive as an anode material in lithium-ion batteries.     

In situ production of a two-dimensional molybdenum disulfide/graphene hybrid nanosheet anode for lithium-ion batteries

A solvent-free, low-cost, high-yield and scalable single-step ball milling process is developed to construct 2D MoS₂/graphene hybrid electrodes for lithium-ion batteries. Electron microscopy investigation reveals that the obtained hybrid electrodes consist of numerous nanosheets of MoS₂ and graphene which are randomly distributed. The MoS₂/graphene hybrid anodes exhibit excellent cycling stability with high reversible capacities (442 mA h g⁻¹ for MoS₂/graphene (40 h); 553 mA h g⁻¹ for MoS₂/graphene (20 h); 342 mA h g⁻¹ for MoS₂/graphene (10 h)) at a high current rate of 250 mA g⁻¹ after 100 cycles, whereas the pristine MoS₂ electrode shows huge capacity fading with a retention of 37 mA h g⁻¹ at 250 mA g⁻¹ current after 100 cycles. The incorporation of graphene into MoS₂ has an extraordinary effect on its electrochemical performance. This work emphasises the importance of the construction of the 2D MoS₂/graphene hybrid structure to prevent capacity fading issues with the MoS₂ anode in lithium-ion batteries.

A solvent-free, low-cost, high-yield and scalable single-step ball milling process is developed to construct 2D MoS₂/graphene hybrid electrodes for lithium-ion batteries.