Preparation And Electrochemical Properties Of Porous Metal/transition Metal Oxide Composites

Based on its own unique physical and chemical properties,the transition metal oxide material with the advantages of rich storage in earth and adjustable micro/nano structure has been widely favored by many researchers and has the broad application prospects in the field of environment and energy,such as supercapacitor,electrochemical sensors and photocatalysis and so on.However,the transition metal oxide has the disadvantages of poor conductivity,low ion transport kinetics,poor structural stability and so on,which limits its application.Therefore,the design of high performance electrode structure based on transition metal oxide becomes the urgent issue.In this thesis,based on the porous metal,various kinds of transition metal oxide composite electrodes are synthesized by using different methods such as plasma treatment,atomic layer deposition,electrochemical deposition and thermal decomposition of metal organic framework compounds.In addition,we also explore the properties in the area of supercapacitors,biosensors and water oxidation reactions.This is of great significance for elucidating the relationship between the micro/nanostructures and properties of the materials,which is in favor of the extended applications of transition metal oxides.Considering above issues,this paper mainly illustrates creative researches on high-performance electrochemical electrodes based on three-dimensional(3D)porous metal and transition metal oxides nanocomposite materials,including as follows:(1)The hierarchical porous Ni/NiO core-shell structures were prepared by hydrothermal synthesis,thermal annealing and plasma treatment.The microstructure characterization and electrochemical tests were also investigated.The core-shells are composed of highly conductive and interconnected Ni skeleton and NiO shells uniformly covering the surface of nanoporous Ni,which exhibit excellent electrochemical performance in terms of supercapacitors and biosensors.As the pseudocapacitive materials,the electrode exhibits an area capacitance up to 255 mF cm-2.Meanwhile,this conductive electrode also exhibits electrocatalytic activity for glucose oxidation with a sensitivity of 4.49 mA mM-1 cm-2 and a reliable detection limit of 10 ?M.In addition,the hierarchical porosity enhances the rapid diffusion and transport of electrolytes and ions in the interconnected porous channels,which is mainly reflected in a superior storage stability of 4000 cycles and an amperometric response time of 1.5 s.These concepts of the hierarchical porous metal/metal oxide core-shell open an avenue to design high-performance materials for energy storage and electrochemical catalysis.(2)An ultrathin CoO layer is deposited on the skeleton surfaces of a nanoporous gold(NPG)film by using atomic layer deposition,creating a flexible electrode.The morphology characterization and electrochemical tests were also investigated.The NPG/CoO hybrid not only achieves high catalytic activity for glucose oxidation and H2O2 reduction,but also exhibits a linear dependence of the electrical signal on the concentration of glucose and H2O2 molecules in the electrolyte.Meanwhile,the sensitivity of the electrode for H2O2 sensors can be as high as 62.5 ?A mM-1 cm-2 with linear dependence on the concentration in the range of 0.1-92.9 mM.The excellent electrocatalytic performance of this electrode is proposed to result from the synergistic effect of Au and CoO at the interfaces,and the high conductivity of the gold skeleton with a large surface area.(3)Scratching technology at the micron-scale enables construction of the interdigital microelectrode directly based on nanoporous gold films.Both nanoporous channels with high ionaccessible ability and interconnected skeletons with high conductivity enable the design of pseudocapacitive micro-supercapacitors with high performances.Therefore,the planar devices show several excellent capacitive character including ultrafast charge/discharge(high rate ability),large capacitance(1.27 mF cm-2,127 F cm-3),and ultrahigh energy density(0.045 W h cm-3)while maintaining a high power density(22.21 W cm-3).Especially,the superb cyclability and mechanical flexibility give them great potential for future microelectronics.The design concept reported here provides an avenue to integrate planar micro-supercapacitors into large-scale devices.(4)Porous Co3O4/C nanowire arrays(NAs)were configured by thermally annealing a hydrothermal synthesized Co-based metal-organic framework(Co-MOF)in Ar and air,respectively.For electrochemical energy storage,the hybrid Co3O4/C NAs demonstrate a high specific capacitance of 1.32 F cm-2 at a current density of 1 mA cm-2,which is much superior to that of bare Co3O4 NAs.A highly stable symmetric supercapacitor based on Co3O4/C NAs exhibits an excellent durability with only 21.7%capacitance decay after 5000 cycles.In addition,the Co3O4/C hybrids demonstrate an outstanding electrochemical catalysis ability for the oxygen evolution reaction,identified by the high current density of 30 mA cm 2 at low overpotential(?30=318 mV)and a small Tafel slope(81 mV dec-1).The electrical conductivity of the doped carbon and ion diffusion within the hierarchical porosity are intrinsic causes to promote the pseudo-capacitive performance and enhance catalytic activity.The synthesis strategy reported here opens an avenue to design high performance electrodes for energy storage and electrochemical catalysis.