Design Of One-dimensional Novel Electrode Materials And Their Electrochemical Applications

With the rapid depletion of fossil fuels and the deterioration of environment issues,energy crisis has become one of the most important problems in the 21st century.Development of low-cost,eco-friendly,and efficient energy storage and conversion electrode materials is the key to solve these issues.The flourish of nanotechnology brings new opportunities to design novel materials and therefore researchers have taken advantage of this technology to make much progress in the fabrication and application of energy materials.However,it is highly needed yet challenging to obtain various functional materials by rational design and realize the optimal performances by tuning material structures.One-dimensional?1D?nanostructures with many benefits,such as high surface area,short electron transport pathway,and facile formation of three-dimensional?3D?networks,have been widely utilized as one unique target for serving excellent energy storage and conversion materials.Herein,we focus on the design,fabrication,and electrochemical application of several 1D materials.Firstly,using the extremely uniform carbonaceous nanofiber?CNF?developed by our group as the carbon precursor,we have synthesized the heteroatom-doped CNF for high-performance supercapacitor electrode materials.Furthermore,a series of 1D hollow tube structures have been prepared through two approaches,which are applied as the potential energy storage electrode materials.In addition,by the treatment of nickel molybdate?NiMoO₄?nanorods with carbon coating and direct growth induced by 3D substrate,carbon supported NiMo-based nanoparticles and NiMo-based oxide nanorod arrays can be obtained,respectively.These two bifunctional electrocatalysts exhibit the excellent activity for electrochemical water splitting to produce hydrogen fuels.The main results can be concluded as follows:1.To realize the enhanced electrochemical performance of carbon-based supercapacitors,boron and oxygen co-doped CNF?BO-CNF?films with 3D network structures were developed by the rational heteroatom doping.Employing the uniform CNF developed by our group as the carbon source and boric acid as the dopant,followed by the simple blending and high-temperature carbonization treatment,a series of free-standing BO-CNF films were prepared.Both high gravimetric and volumetric capacitances?192.8 F g-1 and 179.3 F cm-3 at 1 A g-1?can be enabled by an optimized design with regulating the heteroatom content and packing density.The nanostructures of BO-CNF have a distinct effect on their electrochemical properties.The BO-CNF film exhibits an excellent rate capability,which is due to the formation of continuous electrolyte ion diffusion network as well as good electrical conductivity.Meanwhile,to realize the further improvement of performance,such BO-CNF film can act as an excellent platform for depositing polyaniline active materials with the higher specific capacitance.The boron dopant can be recycled to reduce the cost for the possibly scalable application.2.Two simple and effective strategies were demonstrated to fabricate various transition metal oxide and hydroxide hollow micro-/nanotubes.Firstly,CNF was used as the hard template,which was coated by metal precursor and then etched by chemical method at the low temperature,to generate hollow nickel hydroxide?Ni?OH?₂?nanotubes.Ni?OH?₂ nanotube is highly porous and its specific surface area is as high as 221.8 m2 g-1.The etching conditions have a substantial effect on the structures and morphologies of our materials.This universal method can be applied to other transition metal oxide hollow structures,such as cobalt and manganese,and so on.Secondly,various coating thicknesses of metal-organic framework?MOF?core-shell structures were achieved by the in situ step-by-step growth of cobalt-based MOF on the surface of another molybdenum-based MOF.The core-shell MOF structure can generate a mixed metal oxide?CoMoO₄?submicrotube with hierarchical structures when the precursor treated by an annealing process and then alkaline etching.With the advantages of large surface area and high porosity for these metal oxide micro-/nanotube structures,we studied these hollow materials as the electrode materials for supercapacitors and lithium ion batteries.3.A 1D porous carbon-supported transition metal composite material was developed as the efficient catalyst for electrochemical water splitting.This new catalyst,the porous carbon-supported Ni/Mo₂C?Ni/Mo₂C-PC?,was derived by thermal treatment of low-cost NiMoO₄ nanorods coated with polydopamine.This composite material as the bifunctional catalyst can efficiently and robustly catalyse both hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?.Our study demonstrates that the high activity of Ni/Mo₂C-PC is likely due to the electron transfer from Ni to Mo₂C,leading to a higher Ni valence and a lower Mo valence of Ni/Mo₂C-PC catalyst,which are HER and OER active species and thus account for the enhanced activity.Remarkably,the water-splitting alkaline electrolyser assembled with Ni/Mo₂C-PC as both anode and cathode exhibits the high activity and stability,further evidencing the potential application of this catalyst for hydrogen production.4.The direct growth of 1D metal oxide nanorod arrays on nickel foam?NF?substrate was demonstrated to fabricate the urea electrolysis catalysts for hydrogen production.A simple thermal treatment of NF-supported NiMoO₄ nanorod arrays under Ar and H₂/Ar atmospheres can produce two kinds of electrocatalysts.The anodic catalyst consisted of the high oxidation states of Ni and Mo ions can efficiently catalyze the urea oxidation reaction?UOR?,which is used to replace the ordinary anodic OER process and reduce the voltage value substantially.At the same time,the cathodic catalyst with abundant oxidation states of Ni and Mo ions has the multiple HER active sites,exhibiting the comparable HER activity with the best Pt/C catalyst.Assembling an electrolytic cell using our developed UOR and HER catalysts only needs a low cell voltage to reach a high current density,representing the best yet reported noble-metal-free electrolysers.The using 3D catalyst avoids the addition of polymer binder and the coating process of powder catalyst,possessing the high activity and good stability for electrocatalytic reaction,which is very suitable for the practical production of hydrogen.