Study On Electrocatalytic Properties Of Defect-induced Nano-materials

Hydrogen is viewed as an attractive alternative fuel instead of traditional fossil energy.In the previous studies of numerous new energy conversion devices and hydrogen production technologies and approaches,electrochemical water splitting provides an effective and safe way for sustainable energy conversion and storage.However,the HER and OER of various electrochemical water splitting hydrogen devices are slow kinetics.The catalyst material which precious metals platinum and ruthenium oxide/iridium oxide was expressed the best hydrogen and oxygen precipitation reaction activity,respectively.However,they are more problems such as high cost,low reserves and instability in the actual water catalytic cracking reaction process,so it is important to study cheap and new efficient electrocatalyst materials as soon as possible.Therefore,it is the core issues to development a catalyst metal which is characterized by the high efficiency,high stability and low cost.In recent years,two-dimensional materials and transition metal oxide materials have become a promising candidate to replace precious metal catalysts used for electrocatalytic water splitting.However,efficient catalytic properties of nanoscale two-dimensional material is difficult to preparation controllability and mass production;on the other hand,transition metal oxide catalyst material is show need to improve the conductivity and catalytic performance,meanwhile its preparation and mechanism of catalytic OER is not known.All these problems need to be solved.In order to solve these problems,defects-induced effective was be used to optimize the structure of the material.In this paper,our works have demonstrated the two-dimensional materials and transition metal oxide materials which by high energy mechanical ball milling shear force to shear detachment on the two-dimensional material at the same time the heteroatom doping and optimize the regulation of its electronic structure,to effectively increase the electrocatalytic reaction activity of catalyst materials.Using the transition metal oxides as model,the surface electronic structure and crystal structure of spinel Co₃O₄ were regulated by rich oxygen vacancy defects which produced by the low temperature plasma etching technology.On the one hand,the Co₃O₄ materials with high catalytic activity were prepared with the the oxygen vacancy defects which etched and filled impurity atom at the same time in the plasma etching process.On the other hand,the mechanism in the catalytic OER was studied by electrochemical in-situ/quasi-in-situ characterization techniques.The research details of the works as follows:（1）Using commercialization big block of molybdenum disulfide materials as precursors with high energy mechanical ball milling shear stripping processing at the same time the introduction of nitrogen atoms to optimize the structure of electronic materials to enhance the catalytic on the HER activity.The morphological changes of nitrogen doped molybdenum disulfide were observed by SEM and TEM.Its crystallization characteristics and chemical composition were detected by Raman spectroscopy,XRD and XPS.Furthermore,the catalytic activity was analyzed by the electrochemical test method.The results showed that the large block of molybdenum disulfide became thinner and was doped by nitrogen atoms during the process of ball milling.The nitrogen doped molybdenum disulphide had increased the number of active sites of sulfur edge exposed,and the nitrogen atom had optimized the electron structure of molybdenum disulfide.With the material structure were regulated by impurity atoms,the nitrogen doped molybdenum disulfide materials was found lower onset potential and smaller Tafel slope in acidic electrolyte catalytic on the HER,its showing excellent HER catalytic performance,and much better than the pristine and without doping molybdenum disulfide.Therefore,the mechanical ball milling strategy can provide a useful reference for the mass production of green,high efficient and low cost heteroatomic catalyst materials.（2）Commercialization bulk graphite carbon materials was characterized as the intrinsic inert catalytic activity.Under the ball milling shear stripping force for phosphorus atoms controllable doping and optimize its electronic structure,we preparated edge-selective phosphorous-doped graphene materials.The morphological changes of phosphorus-doped graphene materials were observed by SEM,AFM and TEM.Its crystallization characteristics and chemical composition were detected by Raman spectroscopy,BET,XRD and XPS.Meanwhile,various electrochemical test methods were used to investigate the effect of ball milling shearing and phosphorous atom doping on the electrocatalytic OER activity.Results show that the phosphorous selective doped graphene materials（G-P）was proved to be a highly efficient and reliable electrode,which can catalytic oxygen evolution in alkaline solution,and is better than that of without doping graphite/graphene.To deliver 10 mA·cm^-2 for OER,the G-P only requested the overpotential of 0.33 V.And the Tafel slope was only 62mV·dec^-1 for G-P.The G-P was higher than most of the carbon-based electrocatalysts reported so far.In conclusion,the introduction of impurity atomic defects can effectively optimize the electronic structure of the materials,which plays a very important role in improving the catalytic performance.Using the superior catalytic activity of new non-metal carbon-based materials as low-cost catalytic anode to provide large-scale electrochemical production of hydrogen fuel,provides a very good application prospect and research ideas.（3）The spinel Co₃O₄ nanomaterials as researched object.Phosphorous atoms were filled the surface oxygen vacancy defects of Co₃O₄ nanoparticles materials with plasma treated under argon gas transport.The morphology of composite materials were observed by SEM and TEM for investigate the effects of phosphorus atoms filled with Co₃O₄ nanometer films with oxygen vacancy.The crystallization characteristics and chemical composition of the materials were characterized by Raman spectroscopy,XRD,XPS and XAS.The results showed that the phosphorous atoms were effectively filled to the etched oxygen vacancy in the process of argon plasma treatment.In addition,the cobalt ion valence state of the material surface was further regulated and optimized to obtain more tetrahedral Co²⁺（Td）which with superior catalytic activity.Electrochemical tests showed that the Co₃O₄ material in the oxygen vacancy of phosphorous atoms was catalyzed to show enhanced electrocatalytic activity in HER and OER reactions.As the double function features for the electriccatalyst,it can be directly used as the anode and cathode for electriccatalytic water splitting,and showed very good catalytic performance in the simulation of the alkaline cell electriccatalytic water splitting.This electrocatalyst has good application prospect.Furthermore,we calculate the change of electron structure characteristics and the mechanism of catalytic activity enhancement through the theoretical calculation of the material whose electron structure was changed after the oxygen vacancy of phosphorus atom was filled.The theoretical results showed that the oxygen vacancy of Co₃O₄ could were improved the conductivity of the material and the bonding capacity of the intermediates,thus enhancing the catalytic activity of HER and OER reactions.It is helpful for the development of a new bifunctional electrocatalyst material with high efficiency catalytic performance.（4）Using rich oxygen vacancy defects Co₃O₄ as model for OER.The morphology,structure characteristics and chemical composition of materials and electronic characteristics were detected by electrochemical in-situ/quasi-in-situ analysis technique.We researched the reaction mechanism in with/without oxygen vacancy of spinel catalyst materials on the process of OER steps,and in-depth analysis of intermediates(Co^IV)structure transformation process,and the important role of electric catalytic OER.The XRD characterization indicated that the crystal surface and structural transformation of the spinel Co₃O₄ compare with the non-oxygen vacancy Co₃O₄ was different.The Raman and EPR characterization indicated that there is an undetectable CoOOH intermediate structure in the OER process.Further,XPS characterization was analysis of two kinds of material effect on different valence state of cobalt ions structural features as well as the cobalt,oxygen two elements of the valence state evolution and relative content changes.The results showed that the OER process is mainly the relative concentration of oxygen vacancy on the surface of the material,M-O sites and catalytic activity of Co^IV intermediates.Meanwhile,the function and mechanism of rich oxygen vacancy defect structure in catalytic OER the catalytic reaction was comprehensive analysis,simulation and prediction.For with/without rich oxygen vacancy of spinel Co₃O₄ catalyst for oxygen evolution process has two different catalytic way,under the low anode potential,rich oxygen vacancy materials exist induced by oxygen vacancy Co^IV intermediates,which was the key step in the catalytic reaction,while under the high anode potential,the oxygen desorption process of the two surfaces is similar.This work will provide a reasonable understanding of the structure-activity related mechanism of the vacancy-defective electrocatalysts,and as a useful inspiration for the design of metal oxides-based electrocatalysts with optimized defect structures.