| In the present world,human beings are experiencing acute environmental pollution and energy shortage,this severe background makes it vital to develop renewable clean energy to replace the fossil energy.Electrochemical capacitors(supercapacitors)are now being widely investigated benefitting from its fast charge-discharge time,excellent rate capacity and good environmental friendliness as advanced energy storage device.Layered double hydroxides(LDHs)have attracted increasing attentions in supercapacitor fields not only owing to their versatile physical and chemical properties,but also because of their huge potencial applications.LDH materials raised a lot of attention because they can provide large active site for electrochemical reaction benefited by their unique hierarchical structure.However,There are still great challenges to synthesize LDH materials by controlling their structures precisely such as thickness and the ratio of elements.An atomic layer deposition(ALD)is a representative thin film technology with exceptional capabilities in developing atomic-precisely conformal films,designing novel nanomaterials,tuning material compositions,expanding the selection of various crystallinity of materials,and preparing uniform and conformal coatings.In this paper,we applied ALD technology to design and fabricate a series of LDHs and their composite hierarchical nanomaterials,besides,we demonstrated electrochemical performance of these electrodes in supercapacitor.The main contents are as following:1 By using sacrificial template method with NiC2O4 nanowires,hierarchical NiAl LDH nanotubes consisting of ultrathin nanosheets were synthesized by integrating an atomic layer deposition(ALD)technique with a simple hydrothermal treatment.The morphology and structure of NiAl LDH were characterized by SEM and TEM,which show that the NiAl LDH nanotubes were constructed by ultrathin nanosheets whose thickness can be precisely controlled by ALD.Their unique structural features can offer large ion-accessible surface area and efficient ion transport pathways.Besides,XRD,FT-IR and XPS have been employed to analyze their phase composition and element valence state.The developed NiAl LDH nanotubes exhibit an excellent performance in electrochemistry including high specific capacitance,excellent rate performance and outstanding cycling stability as an electrode for supercapacitors.Thereinto,the NiAl-LDH electrodes can provide a high specific capacitance of 2123.7 F/g at a current density of 0.5 A/g,and 91.9%of the initial capacitance was retained after 10000 cycles at a current density of 5 A/g.2.A binder free carbon-coated Ni(OH)2/NiAl layered doubled hydroxide hierarchical nanostructure(Ni(OH)2/NiAl-LDH@C)in situ grown on Ni foam was prepared through a template method by integrating an atomic layer deposition(ALD)technique with a simple hydrothermal treatment.TEM and SEM revealed that Ni(OH)2/NiAl-LDH@C materials have hierarchical nanostructure,in which Ni(OH)2 and NiAl LDH hierarchically grown onto the Ni foam.Such a unique hierarchical structure provides areal capacitance as high as 14.0 F/cm2 at 5 mA/cm2 with excellent rate capability,and maintains 87.2%of the initial capacitance even after 2000 cycles.Such an effective approach to design high-performance integrated electrode has great potential for energy storage and conversion applications.3.Based on the synthesis method of NiAl LDH,CoNiAl LDH hierarchical nanomaterials were fabricated by the introduction of cobalt in the hydrothermal process.SEM and TEM showed that the morphology of CoNiAl LDH is similar to that of the NiAl LDH,and CoNiAl LDH materials performed even better in electrochemistry.The CoNiAl LDH can provide an initial specific as large as capacitance of 2782 F/g(1772 F/g at 20 A/g).Furthermore,an asymmetric supercapacitor is also assembled with the CoNiAl LDH electrode and activated carbon electrode,which exhibited an energy density of 43.7-78.2 Wh/kg at a power density of 800-16000 W/kg. |
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