Preparation And Electrocatalytic Performance Of Transition Metals And Their Compounds

At present,it has become the consensus of the whole society to vigorously develop clean energy and create a more livable living environment.Obtaining hydrogen energy and high value-added industrial products through such as oxygen evolution reaction,hydrogen evolution reaction,carbon dioxide electroreduction reaction,etc.is undoubtedly an important road to the sustainable development goal.Nowadays,the research on the electrode materials of the above-mentioned reactions is vigorously developing,and people hope to obtain catalytic materials as close to their thermodynamic potential as possible to reduce the energy loss in the electrolysis process.Transition metals and their compounds exhibit good catalytic performance due to their abundant orbital electrons.Among them,Fe-,Co-,Ni-based materials have a good performance in the water splitting reaction,while silver-based materials are more likely to have carbon dioxide electroreduction reactions on the surface.Therefore,this dissertation designed and prepared several transition metals and their compounds comprehensively,and carried out a series of characterizations of their microstructure,composition,and specific electrochemical properties,in order to provide a certain reference for the design and development of high-performance of various catalysts in the future.The main work is as follows:1.With the help of spray pyrolysis,which has the advantages of precise ratio and uniform distribution of the elements in the product,amorphous Fe Co,Co Ni,Fe Ni,and Fe Co Ni oxide microspheres are synthesized by this method in one step.oxide microspheres in one step.It is found that the synergistic effect of multi-components promotes iron-cobalt-nickel microspheres to have higher surface element valences than bimetallic microspheres,showing extremely strong hydrophilicity,and also makes the material easier to transform into active substances in OER.Therefore,it exhibits an overpotential of 277 m V at 10 m V cm^-2,which is much lower than that of binary metal oxide microspheres.Simultaneously,it also showed excellent stability.After 18 hours of constant current stability,the response voltage value only increased by 1.3%.2.The spray pyrolysis method was used to synthesize iron-cobalt-nickel oxide microsphere as precursors.Then,the sodium hypophosphite is decomposed at a high temperature to participate the gas-solid reaction that occurred on the surface of the microspheres,resulting in the formation of metal phosphorus oxides on the surface.The coordination of positively charged metal ions and negatively charged phosphorus atoms facilitates the formation of M-H and the desorption of hydrogen,thereby promoting the decrease of the overpotential of the material on the HER.The materials with different phosphating ratios show regular changes in the electrochemical test.Under the optimal phosphating ratio,its overpotential(under 10 m V cm^-2)is 179 m V lower than that without phosphating treatment,at the same time,due to the change of inherent conductivity caused by phosphating,its OER overpotential dropped to 262m V.Finally,when the material is applied to the water-splitting,it shows an overpotential of 1.65 V and an excellent stability.3.The silver bromide particles obtained by the hydrothermal method was used as the precursor,the coral-like porous silver microsphere structure adsorbed by bromide anions was synthesized by in-situ electrochemical method.The structure is synthesized by in-situ electrochemical method,with silver bromide particles as the precursor,and the material is obtained after a short period of low voltage electrolysis.Since the transformation of silver cations to elemental silver occurs in situ,the resulting structure is similar in size to the original microspheres,and the pores are uniformly distributed,the microstructure is stable,not easy to collapse and aggregate,which increases the electrochemical specific surface area.In addition,the bromide anions will not be completely released from the microspheres,there are still some bromide anions that are uniformly and completely adsorbed on the surface of the elemental silver,which increases the activity of the outermost electrons of the silver atoms that on the surface and makes the adsorption with the intermediate COOH_adsmore stable,enhanced the material’s selectivity to CO products,result in the window of high Faradaic efficiency is enlarged,and the onset potential is reduced.The Faradaic efficiency of material jumps to a high value（96.5%）at a low voltage like-0.4 V,reaching the highest value of 98.7%at-0.6 V,until-0.9 V,this high selectivity was maintained.