•Increase the redox active site and increase the capacity.•Prepares composites materials and enhances the electrochemical properties.•A compact structure that expands the surface area of the ...material.•The composite material has a stable structure, and the charge carrier conducts it efficiently and quickly.
The exploration of high-performance sodium-ion hosts is an important issue in the field of advanced energy storage and conversions. Herein, MnFe PBA/rGO composite was prepared by simple coprecipitation and in situ synthesis, and realized the fast kinetics and superior stability for sodium storage. The rGO nanosheets were introduced as the framework to encapsulate the MnFe PBA nanocuboids with uniform particle size and well-defined configuration to further enhance their electrical conductivity and electrochemical properties. The prepared MnFe PBA/rGO composite exhibits superior charge/discharge properties than the pristine MnFe PBA nanocuboids, which show a capacity enhancement of over 30%. In addition, the PBA/rGO composite exhibits excellent cycling stability, which retains 80% of the capacity after 1000 cycles at a high rate of 1 A/g. The electrochemical impedance spectroscopy (EIS) results further demonstrate the low resistance, high durability, and ultrahigh stability of the MnFe PBA/rGO composite during high-rate long-term cycling. Therefore, this work not only provides a high-performance sodium host but also gives a new clue to the design and construction of highly efficient electrode materials for advanced electrochemical systems.
Doped carbon-based systems have been extensively studied over the past decade as active electrocatalysts for both the two-electron (2e–) and four-electron (4e–) oxygen reduction reactions (ORRs). ...However, the mechanisms for ORR are generally poorly understood. Here, we report an extensive experimental and first-principles theoretical study of the ORR at nitrogen-doped reduced graphene oxide (NrGO). We synthesize three distinct NrGO catalysts and investigate their chemical and structural properties in detail via X-ray photoelectron spectroscopy, infrared and Raman spectroscopies, high-resolution transmission electron microscopy, and thin-film electrical conductivity. ORR experiments include the pH dependences of 2e– versus 4e– ORR selectivity, ORR onset potentials, Tafel slopes, and H/D kinetic isotope effects. These experiments show very different ORR behavior for the three catalysts, in terms of both selectivity and the underlying mechanism, which proceeds either via coupled proton–electron transfers (CPETs) or non-CPETs. Reasonable structural models developed from density functional theory rationalize this behavior. The key determinant between CPET vs non-CPET mechanisms is the electron density at the Fermi level under operating ORR conditions. Regardless of the reaction mechanism or electrolyte pH, however, we identify the ORR active sites as sp2 carbons that are located next to oxide regions. This assignment highlights the importance of oxygen functional groups, while details of (modest) N-doping may still affect the overall catalytic activity, and likely also the selectivity, by modifying the general chemical environment around the active site.
In this study, a magnetically recyclable Ni1-xCdxCeyFe2-yO4-rGO (x, y = 0.05) (NCCF-rGO) nanocomposite photocatalyst has been prepared by following a facile in-situ co-precipitation method combined ...with ultra-sonication means. The as-synthesized magnetically separable NCCF-rGO nanocomposite photocatalyst efficiently degrades methylene blue (MB) dye in comparison to bare Ni1-xCdxCeyFe2-yO4 (x, y = 0.05) (NCCF) nanoparticles (NPs) under visible light irradiation. The photo-degradation rate of MB with NCCF-rGO was ~9 times higher than NCCF nanoparticles (NPs). This enhanced photocatalytic performance of NCCF-rGO photocatalyst was due to the presence of reduced graphene oxide, which greatly help in production of photoactive species by reducing the rate of electro-hole pair recombination. The role of photoactive species that were responsible for the photocatalytic degradation of methylene blue has also been investigated. The as-synthesized NCCF-rGO photocatalyst expressed superb chemical stability and photocatalytic activity even after seven cycle runs. Moreover, the NCCF-rGO nanocomposite worked at all pH values and showed good acid resistance. In particular, the as-synthesized NCCF-rGO photocatalyst could be collected for the next cycle run by simply applying an external magnetic field. Hence, the NCCF-rGO nanocomposite could have potential use in organic dyes contained wastewater treatment.
•A comparative analysis of graphene produced by natural and synthetic reducing agents.•The reducing ability of various reductants examined using XRD, Raman, FTIR, and XPS.•Lemon-reduced GO (LrGO) ...emerges as the most efficiently reduced option that was further applied for supercapacitor application.•LrGO showed a higher capacitance value of 124F/g at a current density of 2 A/g as compared to GO.
Graphene has emerged as one of the most fascinating materials for the scientific community. The exceptional properties of graphene make it a better candidate than the existing materials. So far, the reduced form of graphene oxide (GO) is the best substitute for large quantity graphene. There are numerous ways of reducing GO via synthetic reducing agents that are not eco-friendly and cost-effective. This investigation aims to expand the scope for the reduction of GO using naturally existing reducing agents. In the present work, a comparative study of the extent of reduction using metal/acids and vitamin C containing green reductants is done. The X-ray diffraction peak for GO was detected at 2θ = 10.8° which gradually shifted to higher 2θ values (24-26°) after reduction, indicating that GO was reduced well using all the reductants. The C/O ratio of GO (calculated by XPS), gradually increased from 2.5 to 4–5 for all the reducing agents. Inspired by the better reduction in lemon reduced GO (LrGO), its electrochemical characterization was performed using cyclic voltammetry (CV). The increased supercapacitive value validates the improved electrochemical behavior of LrGO over GO. Finally, our findings conclude that green reductant (lemon juice) serves as a good, eco-friendly, and economic reducing agent for the synthesis of reduced graphene oxide with improved electrochemical properties.
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•NiS1.03/S-rGO with ultrafine NiS1.03 decorated on and wrapped in S-rGO is prepared.•The hybrid exhibits excellent electrochemical performances for both LIBs and SIBs.•The synergistic ...coupling between NiS1.03 and S-rGO contributes to the performances.
The interest on developing nickel sulfide based dual-role anode materials for both lithium-ion battery (LIBs) and sodium-ion battery (SIBs) has aroused broad attention. However, increasing their lithium and sodium storage performances necessitates smart structure design and fabrication. Herein, we demonstrate a facile strategy for the rational combination of NiS1.03 nanoparticles with sulfur doped reduced graphene oxide (NiS1.03/S-rGO), with the designed structure of ultrafine NiS1.03 nanoparticles uniformly anchored on or even wrapped in S-rGO. The systematic electrochemical studies demonstrate that the NiS1.03/S-rGO exhibits high reversible capacities of 996.1 mAh g−1 after 100 cycles at 0.1 A g−1 and 337.8 mAh g−1 up to 2000 cycles at 4 A g−1 as an anode material for LIBs. As for SIBs, the NiS1.03/S-rGO also displays high reversible capacities of 345.6 mAh g−1 at 0.1 A g−1 after 100 cycles and 242.1 mAh g−1 at 0.5 A g−1 after 200 cycles. Additionally, detailed structure analysis illustrates that the superior electrochemical performances mainly originate from the robust composite architecture where the NiS1.03 nanoparticles and S-rGO are tightly bridged via the doped sulfur atoms at the hetero-interface through a synergistic coupling effect, simultaneously guaranteeing the electrode integrity and fast diffusion kinetics. More importantly, the combination approach and mechanism understanding at the molecular level presented in this study show good promise on transition oxides/sulfides for high-performance alkali metal ion battery.
The microstructures of metal oxide-modified reduced graphene oxide (RGO) are expected to significantly affect room-temperature (RT) gas sensing properties, where the microstructures are dependent on ...the synthesis methods. Herein, we demonstrate the effect of microstructures on RT NO
sensing properties by taking typical SnO
nanoparticles (NPs) embellished RGO (SnO
NPs-RGO) hybrids as examples. The samples were synthesized by growing SnO
NPs on RGO through hydrothermal reduction (SnO
NPs-RGO-PR), which display the advantages such as high reactivity of the SnO
surface with NO
, more oxygen vacancies (O
) and chemisorbed oxygen (O
), close contact between SnO
NPs and RGO, and large surface area, compared to the samples prepared by one-pot hydrothermal synthesis from Sn
and GO (SnO
NPs-RGO-IS), and the assembly of SnO
NPs on RGO (SnO
NPs-RGO-SA). As expected, the SnO
NPs-RGO-PR-based sensor presents high sensitivity towards 5 ppm NO
(65.5%), but 35.0% for the SnO
NPs-RGO-IS-based sensor and 32.8% for the SnO
NPs-RGO-SA-based sensor at RT. Meanwhile, the corresponding response time and recovery time calculated by achieving 90% of the current change of the SnO
NPs-RGO-PR-based sensor for exposure to NO
is 12 s and to air is 17 s, respectively, whereas 74/42 s for the SnO
NPs-RGO-IS-based sensor and 77/90 s for the SnO
NPs-RGO-SA-based sensor. The results can prove the tailoring sensing behavior of the gas sensor according to different structures of materials.
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•A novel La2O3/rGO hybrid composite electrodes were prepared by one step hydrothermal route.•La2O3/rGO composite electrode has a high specific capacitance of 546 Fg−1, which is ...higher than pristine La2O3 (348 Fg−1).•ASC device has a high energy density (80 Whkg−1) and a high power density (2,250 Wk g−1).
In this report, La2O3 nanoparticles decorated reduce graphene oxide nanosheets is synthesized to use it as electrode material in high performance supercapacitor. XRD and SEM results reveal that monoclinic crystalline structure with spherical shaped morphology of La2O3, which is uniformly decorated on the 2D-nanosheets of rGO. The surface area, porous nature and elemental compositions present in hybrids were determined by BET, XPS and EDS. As an application, the synthesized La2O3/rGO hybrids revealed enhanced electrochemical performance as high specific capacitance with excellent cycling stability which was very significant for electrochemical SCs. The La2O3/rGO hybrids electrode fulfills an approving specific capacitance value of 546 Fg−1 at a scan rate of 2 mAg−1 and improved cycling stability of 92.3% capacitance retention after 10,000 cycles in the three-electrode setup. The asymmetric two-electrode system with outstanding energy density was assembled by employing the La2O3/rGO as the positive electrode and the activated carbon as the negative electrode. The two-electrode system displays a high energy density of 80 Whkg−1 at a power density of 2250 Wkg−1 within a potential rage of 0–1.6 V. Furthermore, the system exhibited high cycle stability (90.3 % retention) with only 5.8% loss of its initial capacitance after 10,000 cycles. The enhancement of specific capacitance is explained by the charge transfer effect between rGO and La2O3 at the interface.
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•The synergy effect between oxygen vacancies and high conductivity improves NRR performance.•Oxygen vacancies have been proved to be the active sites of NRR by calcination in O2 or ...oxidation with H2O2.•3%RGO/Cu-doped W18O49 shows high activity for ambient electrocatalytic N2fixation to NH3.
High-performance nitrogen fixation is severely limited by the efficiency and selectivity of a catalyst of electrochemical nitrogen reduction reaction (NRR) under ambient conditions. Here, the RGO/WOCu (reduced graphene oxide and Cu-doping W18O49) composite catalysts with abundant oxygen vacancies are prepared by the hydrothermal method. The obtained RGO/WOCu achieves an enhanced NRR performance (NH3 yield rate:11.4 μg h−1 mgcat-1, Faradaic efficiency: 4.4%) at −0.6 V (vs. RHE) in 0.1 mol L-1 Na2SO4 solution. Furthermore, the NRR performance of the RGO/WOCu still keeps at 95% after four cycles, demonstrating its excellent stability. The Cu+-doping increases the concentration of oxygen vacancies, which is conducive to the adsorption and activation of N2. Meanwhile, the introduction of RGO further improves the electrical conductivity and reaction kinetics of the RGO/WOCu due to the high specific surface area and conductivity. This work provides a simple and effective method for efficient electrochemical reduction ofN2.
Solar-steam generation is one of the most promising technologies to mitigate the issue of clean water shortage using sustainable solar energy. Photothermal aerogels, especially the three-dimensional ...(3D) graphene-based aerogels, have shown unique merits for solar-steam generation, such as lightweight, high flexibility, and superior evaporation rate and energy efficiency. However, 3D aerogels require much more raw materials of graphene, which limits their large-scale applications. In this study, 3D photothermal aerogels composed of reduced graphene oxide (RGO) nanosheets, rice-straw-derived cellulose fibers, and sodium alginate (SA) are prepared for solar-steam generation. The use of rice straw fibers as skeletal support significantly reduces the need for the more expensive RGO by 43.5%, turning the rice straw biomass waste into value-added materials. The integration of rice straw fibers and RGO significantly enhances the flexibility and mechanical stability of the obtained photothermal RGO–SA–cellulose aerogel. The photothermal aerogel shows a strong broad-band light absorption of 96–97%. During solar-steam generation, the 3D photothermal aerogel effectively decreases the radiation and convection energy loss while enhancing energy harvesting from the environment, leading to an extremely high evaporation rate of 2.25 kg m–2 h–1, corresponding to an energy conversion efficiency of 88.9% under 1.0 sun irradiation. The salinity of clean water collected during the evaporation of real seawater is only 0.37 ppm. The materials are environmentally friendly and cost-effective, showing great potential for real-world desalination applications.
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•Raman studies of GO, rGO and t-GO were conducted to assess the degree of reduction.•The C/O ratio is related to the intensity of D* band and I(D*)/I(G) ratio.•Calculations reveal the ...origin of D* band, with its relationship in I(D*)/I(G) ratio.
Reduced graphene oxide (rGO) is a graphene-like material that exhibits high productivity for a wide range of industrial applications. To promote the application of rGO, it is important to not only produce high-quality rGO but also precisely evaluate the output. The intensity ratio of the D to G band in the Raman scattering is commonly used to assess the defect density of the carbon materials; however, this ratio is limited to evaluate the reduction degree of rGO because of the ambiguity arising from the superposition of the bands. In this study, we investigate the relationship between the intensity ratio of D* to G band and the reduction of graphene oxide (GO) to evaluate the degree of reduction of rGO. The spectral analysis of GO and rGO, along with systematic research of the thermally reduced GO synthesized via thermal treatment (100–900 °C) revealed a strong linkage between the D*/G intensity ratio and the C/O atomic ratio. The atomic vibrational relationships were elucidated by the assignment of the D* band, based on the density functional perturbation theory calculations. These findings explain the atomic vibrational properties of rGO and provide an indicator of the quality of rGO to optimize its performance for applications.
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