Study On Preparation,(Photo)-electrochemical Properties And Applications Of Iron Series Metal Oxides

The(photo)-electrochemical technology is a scientific technology closely related to human production and life.It is widely used in the fields of chemical industry,metallurgy,electronics,metal corrosion and protection,energy,machinery,biology and so on.Especially the applications in biomedicine,environment and energy are paid more and more attention.In the field of biomedicine,the rapid and accurate detection of glucose level by(photo)-electrochemical method is of great significance in clinical diagnosis and treatment of diabetes.In terms of environment and energy,the(photo)-electrochemical method of water splitting to produce hydrogen is considered to be an effective way to solve global environmental pollution and energy crisis.The preparation of electrode materials is one of the key issues in the(photo)-electrochemical method,whether it is used to detect glucose or to split water for hydrogen production.Many materials have been used to construct(photo)-electrodes,such as carbon materials,metal oxides,nitrides,hydroxides,sulfides,etc.Among them,transition metal oxides are ideal and the most widely studied of(photo)-electrocatalytic materials due to their abundant reserves,low prices and good stability.However,the(photo)-electrochemical performance and practical application of oxide are limited due to its poor intrinsic conductivity.So,enhancing the conductivity of the oxide is the key to improving the(photo)-electrochemical performance.In addition,the specific surface area of oxides is also an important factor affecting the catalytic activity.Since the iron series metal oxides in transition metal oxides have the advantages of low cost,simple preparation process and so on,the iron series metal oxides are selected as electrode materials in this paper.Meanwhile,the preparation process of iron series metal oxides are studied,and the influence on(photo)-electrochemical performance and biosensor detection performance were further explored through the analysis of the crystal structure,morphological structureand defects of the material.The main research contents and conclusions are as follows:In chapter one,the first is the basic introduction to iron series metal oxides and(photo)-electrochemical,including the composition elements,application fields and preparation methods of iron series metal oxides,as well as the application and development of(photo)-electrochemical.Then,the research background and working principle of(photo)-electrochemical water splitting to produce hydrogen were introduced,and it was pointed out that enhancing the performance of OER is the key to improving the efficiency of hydrogen production.Besides,the research progress of(photo)-electrochemical water splitting and the index parameters for evaluating the performance of the catalyst were analyzed and summarized.It was followed by an introduction of(photo)-electrochemical sensors,and the basic principle and research progress of the sensor used to detect glucose.Finally,the significance of the topic selection and the main research content of this thesis were proposed.The second chapter was the preparation of iron oxide(?-Fe2O3)electrode and its application in photo-electrochemical water splitting and non-enzyme glucose sensor.Firstly,?-Fe2O3 electrodes were synthesized by a simple hydrothermal method by changing the hydrothermal reaction time and the cooling rate during the annealing process.Then,the application of these electrodes in the photo-electrochemical decomposition of water was explored,and the preparation conditions of the ?-Fe2O3 photo-electrode with the best photoelectric performance were found.Then,the Co-Pi co-catalyst was further loaded on the surface of ?-Fe2O3.Not only the onset potential was reduced,but the photocurrent density was also increased.This is mainly because the surface-loaded Co-Pi facilitated the separation of photo-generated carriers,thereby improving the ?-Fe2O3 photo-electrochemical performance.In the process of preparing electrodes,it was accidentally discovered that the cooling rate during annealing treatment had a great influence on the photoelectric activity of ?-Fe2O3.The photocurrent density increased significantly with the increase of the cooling rate.But the onset potential did not change significantly,which may be mainly due to the fact that changing the cooling rate did not cause an obvious change in the energy gap.A variety of characterization and analysis methods showed that when the cooling rate was increased,the surface particles of the ?-Fe2O3 photo-electrode gradually became larger,the content of oxygen vacancies and carrer concentration increased,the charge transfer resistance at the electrode/electrolyte interface decreased.Therefore,the enhanced conductivity of the ?-Fe2O3 photo-electrode is the main reason for the improvement of the photoelectric performance.It provided a new strategy for improving the photoelectric performance of the ?-Fe2O3 electrode.Moreover,Sn doping of ?-Fe2O3 by thermal evaporation method increased the photocurrent density of ?-Fe2O3 photo-electrode by 1.67 times.So,Sn element doping is also an effective method to improve the photochemical properties of ?-Fe2O3.The ?-Fe2O3 thin film photo-electrodes with different thicknesses and surface particle sizes were prepared by spin-coating method.The surface particle size and film thickness were adjusted by changing the concentration of the precursor solution and the number of spin-coating,and the effects on photoelectric properties of ?-Fe2O3 were investigated.The photocurrent density of the ?-Fe2O3 photo-electrode increased first and then decreased with the increase of the spin-coating cycle number.This is because when the cycle number of spin coatings increased,the content of the ?-Fe2O3 photoactive material on the electrode increased,and the photo-generated carriers generated by light excitation increased,which further increased the photocurrent density.However,considering that the diffusion free path of hole of ?-Fe2O3 is relatively short,it will not be conducive to the separation of photo-generated carriers when the film is too thick.So the photocurrent density of ?-Fe2O3 reduced later.The surface particle size of the ?-Fe2O3 electrode increased with the increase of the precursor solution concentration.When the ?-Fe2O3 film composed of relatively small particles covered on the electrode surface uniformly and completely.It was not only beneficial increasing the light absorption area,but also could shorten the distance from the photo-generated holes to the ?-Fe2O3/electrolyte interface,and reduce the probability of photo-generated carrier recombination.Thus the photoelectric performance was further improved.Finally,the precursor solution concentration and the number of spin coatings for the ?-Fe2O3 photoelectrode with the best photoelectric properties were obtained.Besides,the ?-Fe2O3 electrode prepared under this condition had the best response to glucose,and it had a good linear relationship when the glucose concentration was 0.05 mM-6.0 mM.At the same time,the ?-Fe2O3 electrode also had high sensitivity,low detection limit,fast response time,good selectivity and stability,and had good reliability and practicability in the actual detection.The third chapter was the preparation of Co3O4 electrode and its application in electrochemical water splitting and glucose detection.Firstly,a porous Co3O4 nanosheets electrode was prepared on the C cloth.Then,the morphology of Co3O4 was adjusted by adding NH4F during the hydrothermal reaction process,and its influence on the electrochemical performance of the Co3O4 electrode was explored.The Co3O4 nanosheets electrode with a special porous structure could increase the electrochemically active specific surface,and had a higher glucose response than C.Moreover,the use of conductive scaffolds to enhance conductivity was also an important reason for its excellent performance in glucose detection.The non-enzyme glucose electrochemical sensor constructed by this Co3O4 electrode had high sensitivity,wide linear range,low detection limit,short response time,good anti-interference and stability.Afterwards,in order to explore the influence of the electrode morphology on the performance of glucose detection,the morphology of Co3O4 was changed by adjusting the concentration of NH4F during the hydrothermal reaction.With the addition of NH4F,the morphology of Co3O4 was transformed from nanosheets to nanowires,and completely became a uniform porous nano wire structure composed of nanorods and nanoparticles at the end.The Co3O4 nanowires with a larger electrochemical specific surface area and better conductivity exhibited better glucose detection performance than Co3O4 nanosheets,such as increased sensitivity,wider linear range,and lower detection limit.The results showed that it was a very effective way to enhance the performance of the non-enzyme glucose electrochemical sensors by adjusting the morphology structure of the electrode.The morphology of electrode also had a remarkable effect on the OER performance of electrochemical water splitting.The overpotential of Co3O4 nanowires electrode was lower than of Co3O4 nanosheets electrode at a current density of 10mA/cm2.This was mainly due to the small Tafel slope,large electrochemical specific surface area(ECSA)and enhanced conductivity of Co3O4 nanowires.In addition,the Co3O4 nanowires electrode had good stability,which laid a foundation for the practical application of Co3O4 electro-catalytic materials.The fourth chapter was the preparation of self-supporting NiO nanosheets and its application in electrochemical water splitting and glucose detection.Using nickel foam with high porosity,good conductivity and low cost as the conductive support,a self-supporting NiO nanosheets electrode was prepared by hydrothermal method.The influence of hydrothermal time on the electrochemical performance and the growth process of the electrode were explored and analyzed.NiO first formed a honeycomb-like structure on the surface of the nickel foam,and then transformed into an interlaced nanosheets structure.In the process of electrochemical water splitting,the overpotential of the self-supporting NiO nanosheets with the best OER performance was much lower than the overpotential of Ni.And this electrode had a large electrochemical active specific surface area,small Tafel slope and impedance.These characteristics were conducive to the transfer of charges during the reaction and increase the electrochemical active sites,which were important reason for the good performance of OER.On the other hand,the self-supporting NiO nanosheets also had the highest response to glucose,and had excellent glucose detection performance under optimal detection conditions.This work provides a method and idea for preparing other electrode materials with high electrocatalytic activity.In the fifth chapter,the research works of this thesis were comprehensively summarized,and then the main innovations were listed.Finally,the shortcomings and existing problems in the research were put forward,and the future research work was prospected.In summary,the electrochemical specific surface area and conductivity of electrode materials are closely related to(photo)-electrochemical performance.The(photo)-electrochemical performance can be improved by morphology adjustment,doping,co-catalysts,and the using of conductive supports.And,our research is of great significance and value for improving the efficiency of(photo)-electrochemical water splitting and the performance of non-enzyme glucose electrochemical sensors.