| Photocatalytic technology utilizes solar energy through semiconductor materials to solve energy depletion crisis and ecological crisis.On the one hand,solar energy is inexhaustible fundamental source of all earth's energy:the sun transmits 1.74×10^17 J to the earth per seconds,about half amount of energy cost by human every day.Among them,only half of it can pass through the atmosphere and arrive to the earth's surface,which means solar energy in 4 seconds can satisfy the demand of energy in one day.So far,however,the total power that humans can use is 1.75 ×10^13 J/s,which takes only 0.01%of the solar energy earth accept;therefore,using solar energy have extremely great potential in the future.The success of improving solar energy utilization efficiency will supply available inexhaustible energy resources to human,and solve energy crisis we are facing now.Indirectly,the demand for high-pollution and low-efficiency energy sources such as fossil fuels will decrease sharply.As a result,ecological pollution and degradation will be greatly alleviated.On the other hand,the use of solar energy is advantageous in some ways,such as low energy consumption,less pollution,mild reaction conditions,and technically feasibility.At present,the technologies with low solar energy utilization efficiency have been industrialized,such as current solar cells and photovoltaic power generation.However,the efficiency is still unsatisfying,and need to be improved in a large extend.Photocatalytic technology is a new direction to further improve the utilization efficiency.Transition metal Group VI compounds have been extensive researched in past decades,but they are facing problems of low efficiency and insufficient stability even they are advantageous in photocatalytic degradation of pollutants and reduction of CO2 Therefore,it is necessary to continue the exploration about facile cheap,stable and efficient catalysts for degrading pollutants and reducing CO2.Supercapacitors are a new solution to the break the bottleneck of energy density.Capacitors work by using electric layer formed on the surface of an electrode or a two-dimensional/quasi-two-dimensional Faraday reaction occurring to store charges.Since several centuries ago,humans have begun to explore ways to store electric charges,like Leiden bottles.People are still using glass plates as dielectric materials with metal foils covering on the surface as capacitors to store electrical energy by storing charge.The capacitance behavior of traditional capacitors is not ideal,such as the bad reversibility of charge and discharge process,insufficient cycle stability.The new type of electrochemical supercapacitor possess excellent energy density that is ten times more than that of traditional capacitors.The application scenarios of supercapacitors are much broader than traditional capacitors,which means it is promising in many fields in the future.Carbon-based electrochemical capacitors and transition metal oxide capacitors are two kinds of capacitors wildly used nowadays.Carbon-based capacitors have a suitable power density,but energy density is relatively low compared to transition metal oxides,which limited the practical application.In contrast,reversible redox reaction occurs on the surface of the transition metal oxide electrode material,which generates a pseudo-capacitor.The faster redox reaction happens,the better performance transition metal oxides capacitors obtains compare with carbon-based capacitor.In the application of photocatalysis,this paper selects the appropriate transition metal oxide and combines with other metal compounds to create facile materials with energy band coupling effect.The material possess more active sites than traditional materials,possess greatly improved photocatalytic efficiency.In the application of capacitors,this paper synthesized diferent three-dimensional nanomaterial based on one dimension.The active specific surface area of the material is significantly improved.Furthermore,we prepared solid symmetric supercapacitor.These measures increase the power density and energy density of electrochemical energy storage equipment,and expand its application prospects.The main work and innovations of this dissertion are listed as follows:(1)Aiming at the shortcomings of insufficient solar energy utilization efficiency,low quantum efficiency,and limited degradation ability of pure Bi2O3,we combined AgBr with Bi2O3 to improve absorption efficiency,increase the number of electron/hole pairs,and reduce the electron/hole recombination rate.The catalytic degradation ability was greatly improved,and the reaction mechanism was further studied.First,the BiOBr precursor was prepared by a solvothermal method,then the combination of AgBr and formation of Bi2O3 happened at the same time.The solar energy utilization efficiency and degradation efficiency of the product were greatly improved.A series of optical performance characterization and physical and chemical properties test results show that the AgBr/Bi2O3 composite has good light absorption and has a larger specific surface area than pure Bi2O3 nanoparticle,thereby providing more active sites.Under the optimal reaction conditions,the degradation rate of pollutants was 10.7 times higher than of pure Bi2O3 nanoparticles.It is inferred from the radical quenching experiments that the AgBr/Bi2O3 radicals are superoxide radicals and hydroxyl radicals with strong oxidative properties.(2)Two-dimensional CuSe nanosheets were prepared in one step by solvothermal method.As a transition metal selenide,CuSe is a promising semiconductor material.A series of optical performance characterization and physical and chemical properties test demonstrates that it possesses advantageous specific surface area and good adsorption capacity,and nanosheet can provide enough active sites to guarantee the efficient CO2 reduction efficiency.The reduction product of CO2 is CO,maximum yield of CO is 14.9?mol·h-1·g-1.The stability of the material was tested.The reduction efficiency kept 88%of original efficiency after several cycles.Shortly speaking,our method is simple,environmentally friendly,low cost,and has great potential in relative area.(3)By using elemental doping method,we combined the hydrothermal method and annealing process and successfully doped Ru into NiCo2O4.The materials were grown on the surface of nickel foam with high specific surface area,and its application as an electrode material in supercapacitors was also explored.The results show that the material possess a high specific capacitance,and the constructed solid capacitor successfully achieves higher power density,energy density,and stability.Electrode possess 1526.8 F·g-1 at 1 1 A·g-1,Rct is 0.42 ? and Rs is 1.05?;after 3000 charge/discharge cycles,the electrode kept 94.3%of original capacitance.Solid symmetric supercapacitor have 8.44 Wh·kg-1 at 15000 W·kg-1,and still perform 2000 W·kg-1 at 48.5 Wh·kg-1.Firstly,the metal oxides have high electrochemical activity,low resistance,and high specific capacitance.Secondly,the morphology of NiCo2O4 ensures a large specific surface area,which provided many active sites for redox reactions.Thirdly,nickel foam itself is hollow inside and the diffusion distance is short enough to swiftly transport the electron and fully utilize the material.Finally,Ru-doped NiCo2O4 effectively accelerates the ion transfer rate,suppressed the volume change among the embedded/desorbed process of ion in the electrolyte,thereby obtaining excellent cycle stability.(4)We combined a simple hydrothermal process and post-annealing process to prepare Co3O4.Three-dimensional structure electrode composed of one-dimensional porous Co3O4 nanorods is directly grown on nickel foam,and its application in solid capacitors wass explored.The results show that Co3O4 porous needle-like nanorod arrays(PANRA)with NH4F have better performance than Co3O4 porous sea urchin-like structures(PULS)without NH4F.PANRA have higher than capacitors,better stability,and solid-state capacitor performance.To optimize the PANRA structure,we adjust the amount of NH4F to find the best composition,which is CO1.The electrode kept 1486 F·g-1 at 1 A·g-1;after 5000 charge/discharge cycles,it kept 98.8%of original capacitance.Solid symmetric supercapacitor composed by these electrodes perform 4,8.63 Wh·kg-1 at 600 W·kg-1 and kept 19 Wh·kg-1 at 6000 W·kg-1.A series of physical and chemical properties tests show that the excellent performance can be attributed to a larger specific surface area and a shorter electron transport path.Nickel foam provides a larger contact area,helping the active material Co3O4 to be more fully utilized,and alleviating volume expansion.The assembled solid capacitors show promising energy and power density,with great potential in the future,and it will play an important role in future energy storage devices. |
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