Delong Li

Preparation of porous micro–nano-structure NiO/ZnO heterojunction and its photocatalytic property

This paper introduced a novel physical route which combined pulse electrodeposition with thermal oxidation to obtain a porous micro–nano-structure NiO/ZnO heterostructural composite. Because ZnO nanoneedle directly grew from the porous Ni foam or NiO surface, and was accompanied with a short-range atom interdiffusion at the interface between ZnO and NiO, a heterojunction was formed and exhibited a high interfacial adhesion strength and high density. The experimental results revealed this composite had excellent photocatalytic performance, 2.5 times higher than that of pure ZnO. The reason was that the NiO/ZnO heterojunction improved the separation rate of photogenerated electrons and holes, and therefore enhanced photocatalytic efficiency.

Highly porous graphitic biomass carbon as advanced electrode materials for supercapacitors

In this work, we established a one-step strategy to synthesize three-dimensional porous graphitic biomass carbon (PGBC) from bamboo char (BC), and studied its electrochemical performance as electrode materials for supercapacitors. Using potassium ferrate (K2FeO4) to fulfil the synchronous carbonization and graphitization of bamboo carbon, this method is less time-demanding, highly efficient and pollution-free, when compared with a conventional two-step strategy. The as-prepared PGBC sample possessed a porous structure with a large specific surface area (1732 m2 g−1) and abundant micropores, as well as a high graphitization degree demonstrated by XRD and Raman. Further electrochemical measurements revealed that the PGBC electrode exhibited a high specific capacitance of 222.0 F g−1 at 0.5 A g−1, and the solid-state symmetric supercapacitor in an aqueous electrolyte (KOH/PVA) presented considerable synergetic energy–power output properties with an energy density of 6.68 W h kg−1 at a power density of 100.2 W kg−1, and 3.33 W h kg−1 at 10 kW kg−1. Moreover, the coin-type symmetric supercapacitor in an ionic liquid electrolyte (EMIM TFSI) delivered a higher energy density of 20.6 W h kg−1 at a power density of 12 kW kg−1. This approach holds great promise to achieve low-cost, green and industrial-grade production of renewable biomass-derived carbon materials for advanced energy storage applications in the future.

Facile Synthesis of Carbon Nanosphere/NiCo2O4 Core-shell Sub-microspheres for High Performance Supercapacitor.

This paper introduced a process to prepare the carbon nanosphere (CNS)/NiCo2O4 core-shell sub-microspheres. That is: 1) CNSs were firstly prepared via a simple hydrothermal method; 2) a layer of NiCo2O4 precursor was coated on the CNS surface; 3) finally the composite was annealed at 350 °C for 2 hours in the air, and the CNS/NiCo2O4 core-shell sub-microspheres were obtained. This core-shell sub-microsphere was prepared with a simple, economical and environmental-friendly hydrothermal method, and was suitable for large-scale production, which expects a promising electrode candidate for high performance energy storage applications. Electrochemical experiments revealed that the composite exhibited remarkable electrochemical performances with high capacitance and desirable cycle life at high rates, such as: 1) the maximum specific capacitance was up to 1420 F/g at 1 A/g; 2) about 98.5% of the capacitance retained after 3000 charge-discharge cycles; 3) the capacitance retention was about 72% as the current density increase from 1 A/g to 10 A/g.

Facile synthesis of hybrid CNTs/NiCo2S4 composite for high performance supercapacitors.

In this work, a novel carbon nanotubes (CNTs)/NiCo2S4 composite for high performance supercapacitors was prepared via a simple chemical bath deposition combined with a post-anion exchange reaction. The morphologies and phase structures of the composites were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy (Raman), X-ray photoelectron spectroscopy (XPS) and low-temperature sorption of nitrogen (BET). The electro-chemical tests revealed that the CNT/NiCo2S4 composite exhibited high electrochemical performance, because the CNTs were used as a conductive network for the NiCo2S4 hexagonal nanoplates. Compared with pure NiCo2S4 and the mechanically mixed CNTs/NiCo2S4 composite, the CNTs/NiCo2S4 composite electrode material exhibited excellent supercapacitive performance, such as a high specific capacitance up to 1537 F/g (discharge current density of 1 A/g) and an outstanding rate capability of 78.1% retention as the discharge current density increased to 100 A/g. It is therefore expected to be a promising alternative material in the area of energy storage.

Synthesis of nitrogen doped graphene from graphene oxide within an ammonia flame for high performance supercapacitors

This paper introduces a novel process for preparing nitrogen (N) doped graphene by using an ammonia flame treatment under ambient conditions, which is simple, effective, faster and economical. That is, when graphene oxide (GO) was treated in the ammonia flame, GO not only could be reduced to graphene, but also could be doped with nitrogen atoms simultaneously. Furthermore, due to the special atmosphere in the ammonia flame, the N-doped graphene exhibited differences from the N-doped graphene by using other processes, which indicated the special properties and potential applications. The experimental results revealed: (1) the N atom concentration was up to 3.97 at% in the N-doped graphene; (2) various nitrogen species including pyridinic-N, pyrrolic-N and quaternary-N were detected in the N-doped graphene; (3) the specific capacitance of the N-doped graphene was 246.4 F g−1 at a current density of 1 A g−1 with high cycle stability, which was about 2 times higher than that of regular graphene without N-doping. It was indicated that this N-doped graphene could be an excellent electrode material for supercapacitor applications.

Preparation of ZnO/graphene heterojunction via high temperature and its photocatalytic property

This paper introduces a novel electrochemical route for preparing the ZnO/graphene heterojunction composite via high temperature. This process includes: (1) depositing the electrochemically reduced graphene oxide (ERGO) on ITO glass via cyclic voltammetry; (2) pulse plating a zinc (Zn) layer on the ERGO; (3) thermally treating the Zn/ERGO composite and “in situ” to obtain the ZnO/ERGO composite. SEM characterizations revealed that the Zinc Oxide (ZnO) particles were homogenously distributed on the surface of graphene sheets. XRD and Raman spectra found a ZnCO3 phase in the ZnO/ERGO composite, which demonstrated that when the Zn film transformed into ZnO particles during thermal treatment, Zn also reacted with graphene and formed a ZnCO3 intermediate layer at the interface between ZnO and ERGO via short-range diffusion. Compared with the heterojunction formed from regular chemical route, the present process provided a tight contact and combination between ZnO and ERGO, which eventually led to a heterojunction between ZnO and graphene sheets. This heterojunction exhibited great improvement for separation efficiency of photo-generate electron–hole pairs. Experimental results of ultraviolet–visible (UV–Vis) light catalysis demonstrated that the photocatalytic activity of the ZnO/ERGO composite had been greatly improved, and exhibited a value of three times higher than that of pure ZnO.

Conductive enhancement of copper/graphene composites based on high-quality graphene

Copper is a well-known traditional metal and has been widely used for thousands years due to its combination of properties, especially its electrical conductivity. Any efforts to increase copper’s electrical conductivity, by even a small percentage, will make a great contribution to the economic effectiveness of society. In this paper, we report an electrical conductivity enhanced copper/graphene composite based on high-quality graphene (HQG) via processes involving graphene-coated copper powders through ball milling, and subsequent spark plasma sintering (SPS). The HQG is converted from regular reduced graphene oxide (RGO) by using a hot-pressing treatment. The experimental results reveal that: (1) on comparing with the copper/RGO composite, the electrical conductivity of the copper/HQG composites is significantly increased; (2) the highest electrical conductivity of the copper/HQG composite was obtained at the optimal mass percentage, 1 wt%, of HQG, at which an 8% increase was achieved when compared with pure copper. We believe that the electrical conductivity enhancement is related to the high electron mobility of HQG, and the formation of a graphene conductive network in the copper/HQG composites. In addition, the hardness of both the copper/RGO and copper/HQG composites is much higher than that of pure copper, while the copper/HQG composite shows the highest value when the amount of HQG is 0.5 wt%. It is expected that the copper/HQG composites have broad prospects of application in the electrical and electronics industry, light industry, machinery manufacturing, architecture construction, national defense, etc.

Preparation of Au nanoparticle-decorated ZnO/NiO heterostructure via nonsolvent method for high-performance photocatalysis

In this paper, we present a novel physical (or nonsolvent) route to fabricate a kind of Au/ZnO/NiO heterostructure photocatalytic composite. That is, a Zn layer upon Ni foam substrate is prepared by pulse electrodeposition, then the ZnO nanoneedle/NiO heterostructural composite is obtained via thermal oxidation, and at last, the composite is modified with the dispersively deposited Au nanoparticles (Au NPs) by ion sputtering. The surface plasmon resonance effect of the Au NPs significantly enhances the light absorption. Meanwhile, the Au NPs form a Schottky barrier with ZnO nanoneedles and further inhibit the recombination of photogenerated electron–hole pairs. In addition, due to the nonsolvent conditions, the introduction of impurities is avoided, and thus it shows strong photocatalytic stability. The experimental results reveal that, the optimized Au/ZnO/NiO composite exhibits up to two times photocatalytic performance on RB degradation and higher stability than that of regular ZnO/NiO composite. The present experimental strategy can also be used for other noble metals, and it is expected to have important application prospects in the fields of environmental purification, solar cells, hydrogen generation, etc.

Preparation of a ZnO/TiO2 vertical-nanoneedle-on-film heterojunction and its photocatalytic properties

This paper introduces a process to prepare a novel ZnO/TiO2 heterojunction composite with ZnO nanoneedles vertically grown on a TiO2 film via micro-arc oxidation (MAO), pulse plating and thermal oxidation. Firstly a TiO2 thin film was prepared on a titanium substrate using MAO; then a Zn nanocrystalline film was pulse plated on the MAO film; finally the composite film was thermally treated at 380° for several hours, which transformed the Zn film into ZnO nanoneedles. SEM observations revealed that the ZnO nanoneedles were vertically grown on the TiO2 film. The advantage of the ZnO/TiO2 heterojunction was that during heat treatment, in addition to the phase transformation from Zn into ZnO, simultaneous short-range atom diffusion occurred at the interface between the ZnO nanoneedles and the TiO2 layer, which encouraged the formation of a highly efficient, strong and stable heterojunction. Photocatalytic experiments demonstrated that, compared with pure ZnO or TiO2, the as-prepared ZnO/TiO2 composites showed greater efficiency and stability in photogenerated carriers and a significantly improved photocatalytic performance, due to this special heterojunction structure.