A Single‐Step Hydrothermal Route to 3D Hierarchical Cu2O/CuO/rGO Nanosheets as High‐Performance Anode of Lithium‐Ion Batteries

As anodes of Li‐ion batteries, copper oxides (CuO) have a high theoretical specific capacity (674 mA h g^?1) but own poor cyclic stability owing to the large volume expansion and low conductivity in charges/discharges. Incorporating reduced graphene oxide (rGO) into CuO anodes with conventional methods fails to build robust interaction between rGO and CuO to efficiently improve the overall anode performance. Here, Cu₂O/CuO/reduced graphene oxides (Cu₂O/CuO/rGO) with a 3D hierarchical nanostructure are synthesized with a facile, single‐step hydrothermal method. The Cu₂O/CuO/rGO anode exhibits remarkable cyclic and high‐rate performances, and particularly the anode with 25 wt% rGO owns the best performance among all samples, delivering a record capacity of 550 mA h g^?1 at 0.5 C after 100 cycles. The pronounced performances are attributed to the highly efficient charge transfer in CuO nanosheets encapsulated in rGO network and the mitigated volume expansion of the anode owing to its robust 3D hierarchical nanostructure.     

Ultrahigh Capacity Due to Multi‐Electron Conversion Reaction in Reduced Graphene Oxide‐Wrapped MoO2 Porous Nanobelts

Multivalent transition metal oxides (MO_x) containing redox centers which can theoretically accept more than one electron have been suggested as promising anode materials for high‐performance lithium ion batteries (LIBs). The Li‐storage mechanism of these oxides is suggested to involve an unusual conversion reaction leading to the formation of metallic nanograins and Li₂O; however, a full‐scale conversion reaction is seldom observed in molybdenum dioxide (MoO₂) at room temperature due to slow kinetics. Herein, a full‐scale multi‐electron conversion reaction, leading to a high reversible capacity (974 mA h g^?1 charging capacity at 60 mA g^?1) in LIBs, is realized in a hybrid consisting of reduced graphene oxide (rGO) sheet‐wrapped MoO₂ porous nanobelts (rGO/MoO₂ NBs). The rGO wrapping layers stabilize the nanophase transition in MoO₂ and alleviate volume swing effects during lithiation/delithiation processes. This enables the hybrid to exhibit great cycle stability (tested to around 1900 cycles) and ultrafast rate capability (tested up to 50 A g^?1).     

石墨烯/银纳米颗粒复合材料的制备及其对双氧水的电化学检测

以氧化石墨烯(GO)和硝酸银为原材料,聚乙烯吡咯烷酮(PVP)为还原剂和稳定剂,通过水热法制备出还原氧化石墨烯/银纳米颗粒(rGO/AgNPs)复合材料。采用透射电子显微镜(TEM)、X射线衍射(XRD)及紫外-可见分光光度计(UV-Vis)对rGO/AgNPs复合材料的形貌、组成和结构进行表征。同时,将rGO/AgNPs复合材料修饰到玻碳电极表面制备出过氧化氢(H_2O_2)电化学传感器,通过循环伏安法(CV)和计时安培响应法(i-t)对传感器进行电化学性能测试。实验结果表明:制备的rGO/AgNPs传感器具有较好的电化学性能,其对H_2O_2检测的灵敏度为340.6μA·(mmol/L)~(-1)·cm~(-2),响应时间为3s,最低检测极限为7.5μmol/L(S/N=3),线性检测范围为20~4950μmol/L(线性相关系数为R=0.9973)。     

Enhancing the Sequential Conversion‐Alloying Reaction of Mixed Sn–S Hybrid Anode for Efficient Sodium Storage by a Carbon Healed Graphene Oxide

To date, the possible depletion of lithium resources has become relevant, giving rise to the interest in Na‐ion batteries (NIBs) as promising alternatives to Li‐ion batteries. While extensive investigations have examined various transition metal oxides and chalcogenides as anode materials for NIBs, few of these have been able to utilize their high specific capacity in sodium‐based systems because of their irreversibility in a charge/discharge process. Here, the mixed Sn–S nanocomposites uniformly distributed on reduced graphene oxide are prepared via a facile hydrothermal synthesis and a unique carbothermal reduction process, producing ultrafine nanoparticle with the size of 2 nm. These nanocomposites are experimentally confirmed to overcome the intrinsic drawbacks of tin sulfides such as large volume change and sluggish diffusion kinetics, demonstrating an outstanding electrochemical performance: an excellent specific capacity of 1230 mAh g^?1, and an impressive rate capability (445 mAh g^?1 at 5000 mA g^?1). The electrochemical behavior of a sequential conversion‐alloying reaction for the anode materials is investigated, revealing both the structural transition and the chemical state in the discharge/charge process. Comprehension of the reaction mechanism for the mixed Sn–S/rGO hybrid nanocomposites makes it a promising electrode material and provides a new approach for the Na‐ion battery anodes.     

NiS2/三维多孔石墨烯复合材料作为超级电容器电极材料的电化学性能

选用合适的软模板,通过简便的一步溶剂热法成功制备了NiS₂/三维多孔石墨烯（3D rGO）复合材料。利用FESEM、TEM、XPS和电化学工作站对样品的表面形貌、元素价态和电化学性能进行表征。结果表明:制备的NiS₂/3D rGO复合材料存在石墨烯三维堆叠的孔道结构,且具备较大的比表面积,为57.51 m2g-1。电化学测试表明,在1 Ag-1的电流密度下NiS₂/3D rGO复合材料的比电容高达1 116.7 Fg-1,而且当电流密度增加到5 Ag-1时NiS₂/3D rGO复合材料的比电容为832.2 Fg-1,比电容保持率为1 Ag-1时的74.5%。在4 Ag-1电流密度下,经过1 000次循环后,NiS₂/3D rGO复合材料的比电容仍能保持91.2%。因此,NiS₂/3D rGO复合材料可作为一种理想的超级电容器电极材料。      

Nontopotactic Reaction in Highly Reversible Sodium Storage of Ultrathin Co9Se8/rGO Hybrid Nanosheets

Transition metal chalcogenide with tailored nanosheet architectures with reduced graphene oxide (rGO) for high performance electrochemical sodium ion batteries (SIBs) are presented. Via one‐step oriented attachment growth, a facile synthesis of Co₉Se₈ nanosheets anchored on rGO matrix nanocomposites is demonstrated. As effective anode materials of SIBs, Co₉Se₈/rGO nanocomposites can deliver a highly reversible capacity of 406 mA h g^?1 at a current density of 50 mA g^?1 with long cycle stability. It can also deliver a high specific capacity of 295 mA h g^?1 at a high current density of 5 A g^?1 indicating its high rate capability. Furthermore, ex situ transmission electron microscopy observations provide insight into the reaction path of nontopotactic conversion in the hybrid anode, revealing the highly reversible conversion directly between the hybrid Co₉Se₈/rGO and Co nanoparticles/Na₂Se matrix during the sodiation/desodiation process. In addition, it is experimentally demonstrated that rGO plays significant roles in both controllable growth and electrochemical conversion processes, which can not only modulate the morphology of the product but also tune the sodium storage performance. The investigation on hybrid Co₉Se₈/rGO nanosheets as SIBs anode may shed light on designing new metal chalcogenide materials for high energy storage system.     

Porous Hybrid Network of Graphene and Metal Oxide Nanosheets as Useful Matrix for Improving the Electrode Performance of Layered Double Hydroxides

Mesoporous hybrid network of reduced graphene oxide (rG‐O) and layered MnO₂ nanosheets could act as an efficient immobilization matrix for improving the electrochemical activity of layered double hydroxide (LDH). The control of MnO₂/rG‐O ratio is crucial in optimizing the porous structure and electrical conductivity of the resulting hybrid structure. The immobilization of Co‐Al‐LDH on hybrid MnO₂/rG‐O network is more effective in enhancing its electrode activity compared with that of on pure rG‐O network. The Co‐Al‐LDH?rG‐O?MnO₂ nanohybrid deliveres a greater specific capacitance than does MnO₂‐free Co‐Al‐LDH?rG‐O nanohybrid. The beneficial effect of MnO₂ incorporation on the electrode performance of nanohybrid is more prominent for higher current density and faster scan rate, underscoring the significant enhancement of the electron transport of Co‐Al‐LDH?rG‐O. This is supported by electrochemical impedance spectroscopy. The present study clearly demonstrates the usefulness of the porously assembled hybrid network of graphene and metal oxide nanosheets as an effective platform for exploring efficient LDH‐based functional materials.     

Reduced graphene oxide supersonically sprayed on wearable fabric and decorated with iron oxide for supercapacitor applications

We demonstrate the fabrication of wearable supercapacitor electrodes.The electrodes were applied to wearable fabric by supersonically spraying the fabric with reduced graphene oxide(rGO)followed by decoration with iron oxide(Fe2O3)nanoparticles via a hydrothermal process.The integration of iron oxide with rGO flakes on wearable fabric demonstrates immense potential for applications in high-energy-storage devices.The synergetic impact of the intermingled rGO flakes and Fe2O3 nanoparticles enhances the charge transport within the composite electrode,ultimately improving the overall electrochemical performance.Taking advantage of the porous nature of the fabric,electrolyte diffusion into the active rGO and Fe2O3 materials was significantly enhanced and subsequently increased the electrochemical interfacial activities.The effect of the Fe2O3 concentration on the overall electrochemical performance was investigated.The optimal composition yields a specific capacitance of 360 F g-1 at a current density of 1A g-1 with a capacitance retention rate of 89％after 8500 galvanostatic cycles,confirming the long-term stability of the Fe2O3/rGO fabric electrode.     

PVA-assisted hydrated vanadium pentoxide/reduced graphene oxide films for excellent Li+and Zn2+storage properties

Low-cost,high safety and environment-friendly aqueous energy storage systems(ESSs)are huge poten-tial for grid-level energy storage,but the(de)intercalation of metal ions in the electrode materials(e.g.vanadium oxides)to obtain superior long-term cycling stability is a significant challenge.Herein,we demonstrate that polyvinyl alcohol(PVA)-assisted hydrated vanadium pentoxide/reduced graphene oxide(V2O5·nH2O/rGO/PVA,denoted as the VGP)films enable long cycle stability and high capacity for the Li+and Zn2+storages in both the VGP//LiCl(aq)//VGP and the VGP//ZnSO4(aq)//Zn cells.The binder-free VGP films are synthesized by a one-step hydrothermal method combination with the filtration.The extensive hydrogen bonds are formed among PVA,GO and H2O,and they act as structural pillars and connect the adjacent layers as glue,which contributes to the ultrahigh specific capacitance and ultralong cyclic performance of Li+and Zn2+storage properties.As for Li+storage,the binder-free VGP4 film(4 mg PVA)electrode achieves the highest specific capacitance up to 1381 F g-1 at 1.0 A g-1 in the three-electrode system and 962 F g-1 at 1.0 A g-1 in the symmetric two-electrode system.It also behaves the outstanding cyclic performance with the capacitance retention of 96.5％after 15000 cycles in the three-electrode system and 99.7％after 25000 cycles in the symmetric two-electrode system.As for Zn2+storage,the binder-free VGP4 film electrode exhibits the high specific capacity of 184 mA h g-1 at 0.5 A g-1 in the VGP4//ZnSO4(aq)//Zn cell and the superb cycle performance of 98.5％after 25000 cycles.This work not only provides a new strategy for the construction of vanadium oxides composites and demonstrates the potential application of PVA-assisted binder-free film with excellent electrochemical properties,but also extends to construct other potential electrode materials for metal ion storage cells.     

Ultrathin Co3O4 nanosheets highly dispersed on reduced graphene oxide: An efficient bi-functional catalyst for Li-O2 battery

Ultrathin Co₃O₄ nanosheets grown on the reduced graphene oxide (Co₃O₄/rGO) was synthesized by a simple hydrothermal method and was investigated as a cathode in a Li-O₂ battery. Benefited from the synergistic effect between Co₃O₄ and rGO, the hybrid exhibits a high initial capacity of 10,528 mAh g^?1 along with a high coulombic efficiency (84.4%) at 100 mA g^?1. In addition, the batteries show an enhanced cycling stability and after 113 cycles, the cut-off discharge voltage remains above 2.5 V. The outstanding performance is intimately related to the high surface area of rGO, which not only provide carbon skeleton for the uniform distribution of Co₃O₄ nanosheets but also facilitate the reversible formation and decomposition of insoluble Li₂O₂. The results of electrochemical tests confirm that the Co₃O₄/rGO hybrid is a promising candidate for the Li-O₂ batteries.     

Two-Dimensional Interlayer Space Induced Horizontal Transformation of Metal–Organic Framework Nanosheets for Highly Permeable Nanofiltration Membranes

Laminar membranes comprising graphene oxide (GO) and metal–organic framework (MOF) nanosheets benefit from the regular in-plane pores of MOF nanosheets and thus can support rapid water transport. However, the restacking and agglomeration of MOF nanosheets during typical vacuum filtration disturb the stacking of GO sheets, thus deteriorating the membrane selectivity. Therefore, to fabricate highly permeable MOF nanosheets/reduced GO (rGO) membranes, a two-step method is applied. First, using a facile solvothermal method, ZnO nanoparticles are introduced into the rGO laminate to stabilize and enlarge the interlayer spacing. Subsequently, the ZnO/rGO membrane is immersed in a solution of tetrakis(4-carboxyphenyl)porphyrin (H₂TCPP) to realize in situ transformation of ZnO into Zn-TCPP in the confined interlayer space of rGO. By optimizing the transformation time and mass loading of ZnO, the obtained Zn-TCPP/rGO laminar membrane exhibits preferential orientation of Zn-TCPP, which reduces the pathway tortuosity for small molecules. As a result, the composite membrane achieves a high water permeance of 19.0 L m⁻² h⁻¹ bar⁻¹ and high anionic dye rejection (>99% for methyl blue).     

In Situ Intercalation of Bismuth into 3D Reduced Graphene Oxide Scaffolds for High Capacity and Long Cycle‐Life Energy Storage

Metal anodes, such as zinc and bismuth have been regarded as ideal materials for aqueous batteries due to high gravimetrical capacity, high abundance, low toxicity, and intrinsic safety. However, their translation into practical applications are hindered by the low mass loading (≈1 mg cm^?2) of active materials. Here, the multiscale integrated structural engineering of 3D scaffold and active material, i.e., bismuth is in situ intercalated in reduced graphene oxide (rGO) wall of network, are reported. Tailoring the rapid charge transport on rGO 3D network and facile access to nano‐ and microscale bismuth, the rGO/Bi hybrid anode shows high utilization efficiency of 91.4% at effective high load density of ≈40 mg cm^?2, high areal capacity of 3.51 mAh cm^?2 at the current density of 2 mA cm^?2 and high reversibility of >10 000 cycles. The resulting Ni‐Bi full battery exhibits high areal capacity of 3.13 mAh cm^?2 at the current density of 2 mA cm^?2, far outperforming the other counterpart batteries. It represents a general and efficient strategy in enhancing the battery performance by designing hierarchically networked structure.     

Synthesis of cuprous oxide nanoparticles on graphitic carbon nitride and reduced graphene oxide and their catalytic performance toward the reduction of 4-nitrophenol

In this work, a desired Cu₂O catalyst supported on graphitic carbon nitride and reduced graphene oxide hybrid (Cu₂O/g-C₃N₄–rGO) with excellent catalytic performance in the reduction of 4-nitrophenol (4-NP) by NaBH₄ has been fabricated. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), N₂ adsorption/desorption and Fourier-transform infrared (FTIR) techniques as well as catalytic test using the reduction of 4-NP by NaBH₄ as probe reaction have been used to investigate the structure–properties relationship of the as-prepared Cu₂O/g-C₃N₄–rGO composites. The results demonstrate that ultrafine Cu₂O nanoparticles can be stably anchored on g-C₃N₄–rGO hybrid by tuning the initial ratio of rGO (reduced graphene oxide) to g-C₃N₄, where homogeneous dispersion of g-C₃N₄ on sheet-like rGO plays a very important role in confining the ultrafine Cu₂O nanoparticles and excellent catalytic performance is noticed on Cu₂O/g-C₃N₄–rGO composite for the reduction of 4-NP by NaBH₄ with an activity parameter up to 6330 s^-1g^-1.

Graphical abstract

     

PdCu alloy nanoparticles supported on reduced graphene oxide for electrocatalytic oxidation of methanol

PdCu nanoparticles supported on reduced graphene oxide nanosheets (PdCu/rGO) with uniform size distribution and dispersion are fabricated by a facile two-step reduction method. During the whole synthesis procedure, no capping agent or surfactant has been used. By varying the Pd/Cu molar ratio, electrocatalysts with different size distribution and dispersion of nanoparticles on graphene are prepared, and their electrocatalytic performance toward methanol oxidation reaction has been studied. It is concluded that the as-prepared electrocatalyst of Pd₂Cu₂/rGO, of which the Pd/Cu molar ratio is 1:1, exhibits the highest mass activity and most stable electroactivity. Compared to commercial Pd/C, the as-prepared Pd₂Cu₂/rGO also demonstrates 2.49 times higher mass activity and much more stable electroactivity. The excellent performance of the Pd₂Cu₂/rGO electrocatalyts is mainly due to the advantages of bimetallic synergistic effects and the supporting material of graphene. Owing to the advantages of high electroactivity, long stability, and cost-effectiveness, the as-prepared Pd₂Cu₂/rGO nanocomposites are promising anode electrocatalysts for direct methanol fuel cells.     

Capillarity Composited Recycled Paper/Graphene Scaffold for Lithium–Sulfur Batteries with Enhanced Capacity and Extended Lifespan

An effective strategy to tackle the twin crises of global deforestation and fossil fuel depletion is to recycle biomass materials for energy storage devices. This study reports a unique and innovative solution to capitalize on a currently overlooked resource to produce high‐performance lithium–sulfur (Li–S) batteries from recycled paper. The recycled paper fibers are creatively composited with graphene oxide sheets via a capillary adsorption method. The recycled paper/graphene oxide hybrid is then converted to activated paper carbon/reduced graphene oxide (APC/graphene) scaffold for sulfur infiltration. The assembled Li–APC/graphene/S battery exhibits a superior lifespan of 620 cycles with an excellent capacity retention rate of 60.5%. An APC interlayer is sandwiched between the Li anode and the separator to suppress the degradation of Li anode by preventing the nonhomogeneous growth of mossy Li whiskers, stretching the battery lifespan up to 1000 cycles with a capacitance retention rate of 52.3%. The capillary adsorption method coupled with the porous carbonaceous anode interlayer configuration creates a new opportunity for the development of batteries derived from porous biomass materials.     

Experimental and computational investigation of reduced graphene oxide nanoplatelets stabilized in poly(styrene sulfonate) sodium salt

The production of large-area interfaces and the use of scalable methods to build up designed nanostructures generating advanced functional properties are of high interest for many materials science applications. Nevertheless, large-area coverage remains a major problem even for pristine graphene, and here we present a hybrid, composite graphene-like material soluble in water that can be exploited in many areas such as energy storage, electrodes fabrication, selective membranes and biosensing. Graphene oxide (GO) was produced by the traditional Hummers’ method being further reduced in the presence of poly(styrene sulfonate) sodium salt (PSS), thus creating stable reduced graphene oxide (rGO) nanoplatelets wrapped by PSS (GPSS). Molecular dynamics simulations were carried out to further clarify the interactions between PSS molecules and rGO nanoplatelets, with calculations supported by Fourier transform infrared spectroscopy analysis. The intermolecular forces between rGO nanoplatelets and PSS lead to the formation of a hybrid material (GPSS) stabilized by van der Waals forces, allowing the fabrication of high-quality layer-by-layer (LbL) films with poly(allylamine hydrochloride) (PAH). Raman and electrical characterizations corroborated the successful modifications in the electronic structures from GO to GPSS after the chemical treatment, resulting in (PAH/GPSS) LbL films four orders of magnitude more conductive than (PAH/GO).     

液相制备石墨烯/硫复合材料及其在锂硫电池正极中的应用

采用氧化石墨烯(grapheneoxide,GO)作为制备石墨烯的前驱体,通过液相还原自组装过程与硫纳米颗粒进行复合,获得了高性能的还原氧化石墨烯/硫(r GO/S)复合正极材料。利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射仪(XRD)、拉曼光谱、X射线光电子能谱分析(XPS)等对材料微观形貌与结构进行表征。结果表明:硫纳米颗粒均匀分布在石墨烯片层间,并且硫纳米颗粒被石墨烯片层有效地封装,硫在35-r GO/S复合物中的质量分数高达83.6%。该35-r GO/S复合正极在0.2C电流密度下初始放电容量可达1197.3mAh·g^-1,经过200次循环后容量仍保持在730mAh·g^-1左右,表现出优异的循环性能。     

ZnCo2O4及ZnCo2O4/rGO复合材料的制备与电化学性能

采用一步水热法制备尖晶石型钴酸锌(ZnCo_2O_4)及钴酸锌/石墨烯(ZnCo_2O_4/rGO)复合材料,通过XRD,SEM和RST5000电化学工作站对材料的组分、表面形貌及电化学性能进行表征。通过改变水热温度,制备出具有辐射状花簇团结构、褶皱片层结构和表面光滑的球体结构的ZnCo_2O_4电极材料。结果表明:加入石墨烯后,ZnCo_2O_4呈规则的多边形结构,附着在石墨烯片上,两者的协同作用可有效改善电极材料的电化学性能;钴酸锌与氧化石墨烯的质量比为6∶1时得到的ZnCo_2O_4/rGO复合材料的比电容为205F/g,比纯ZnCo_2O_4的比电容提升了约114%。     

Tailor made exfoliated reduced graphene oxide nanosheets based on oxidative-exfoliation approach

This study presents a versatile and scalable strategy of ‘oxidation controlled exfoliation’ of rGO nanosheets synthesized from both Hummers and modified Hummers method. A co-relation between degree of oxidation of graphite oxide (GO) sheets and exfoliation of resulting synthesized rGO nanosheets has been successfully developed which in turn reflects in various properties of rGO sheets. The extent of exfoliation of rGO sheets has been well analyzed by XRD, SEM, BET and TEM techniques. Moreover, the quantitative analysis of degree of oxidation of GO has been estimated from FTIR spectra using quotient law method. The variations in number of rGO layers, defect density and sp² domain size have been investigated in detail by Raman spectroscopic technique. Both qualitative-quantitative analysis of rGO nanosheets have been discussed from their SAED pattern and HR-TEM images. The optical characterization of GO and corresponding rGO nanosheets has been studied in detail by UV- Vis spectroscopic technique.     

Monolithic Graphene Trees as Anode Material for Lithium Ion Batteries with High C‐Rates

Monolithically structured reduced graphene oxide (rGO), prepared from a highly concentrated and conductive rGO paste, is introduced as an anode material for lithium ion batteries with high rate capacities. This is achieved by a mixture of rGO paste and the water‐soluble polymer sodium carboxymethylcellulose (SCMC) with freeze drying. Unlike previous 3D graphene porous structures, the monolithic graphene resembles densely branched pine trees and has high mechanical stability with strong adhesion to the metal electrodes. The structures contain numerous large surface area open pores that facilitate lithium ion diffusion, while the strong hydrogen bonding between the graphene layers and SCMC provides high conductivity and reduces the volume changes that occur during cycling. Ultrafast charge/discharge rates are obtained with outstanding cycling stability and the capacities are higher than those reported for other anode materials. The fabrication process is simple and straightforward to adjust and is therefore suitable for mass production of anode electrodes for commercial applications.