Controlled Construction Of Platinum-bismuth-based Three-dimensional Self-supported Monolithic Electrodes And Their Application In Glycerol Electro-oxidation Value Addition

The increasing demand and production of biodiesel has created an imbalance in the supply and demand of glycerol as a by-product.Value-added conversion of cheap glycerol to obtain high-end chemicals has attracted interest.Among the many methods for value-added conversion of glycerol,the replacement of oxidant with electricity for selective electrocatalytic oxidation has the advantages of low energy consumption,green and non-polluting,and low economic cost.However,the problems of poor conversion and selective compatibility of glycerol electrooxidation restrict its practical application.In addition,the problems of easy poisoning of the active center and poor reaction stability are yet to be solved.In this thesis,platinum and bismuth were used as the active species to develop glycerol electrooxidation catalysts with high conversion and specific selectivity.Different carriers were selected to explore the influence of the composition,morphology,crystalline phase and structure of the carriers on the catalytic glycerol electrooxidation,and to reveal the mechanism of the synergistic enhancement of the electrocatalytic glycerol oxidation performance between platinum and bismuth and the carriers,in order to obtain glycerol electrooxidation catalysts with excellent performance.The main research contents and conclusions are as follows:（1）In chapter 2,BiOI microplates and Pt nanoparticles were deposited on the surface of the conductive substrate by two electrodeposition methods,and a three-dimensional self-supported electrode Pt/BiOI/CC with a Pt-BiOI heterogeneous interface was constructed for electrocatalytic glycerol oxidation.The research results show that the construction of Pt-BiOI heterojunction greatly increases the selectivity of products（glyceric acid and lactic acid）,and effectively alleviates the peroxidation problem of Pt catalysts in the electrooxidation of glycerol.In alkaline medium,the Pt/BiOI/CC electrode exhibits excellent electrocatalytic performance for glycerol oxidation,achieving67.6%glycerol conversion during the 8 h electrocatalytic reaction under0.91 V vs.RHE potentiostatic conditions,a remarkably high Compared with BiOI/CC（13.7%）,it is close to that of Pt/C/CC（72.1%）.At the same time,it achieves 38.8%glyceric acid selectivity and 32.1%lactic acid selectivity,which is significantly better than that of BiOI/CC（0%and 1.5%）and Pt/C/CC（21.3%and 0.9%）.In addition,the selectivity of its catalyzed generation of peroxidation products was only 18.9%,which was significantly lower than that of BiOI/CC（98.5%）and Pt/C/CC（44.9%）.Combining in-depth structural characterization and surface electronic state studies,the mechanism of BiOI synergistically enhancing Pt-catalyzed electro-oxidation of glycerol was clearly revealed for the first time.Nanoparticles greatly improve the mass transfer efficiency and increase the contact area between glycerol and the catalytic active center,ensuring the efficient catalytic oxidation of glycerol;on the other hand,BiOI can effectively control the electronic structure of Pt and optimize the catalytic intermediate product and Pt The binding capacity increases the selectivity of glyceric acid and lactic acid,and greatly reduces the selectivity of peroxidation products.（2）In the third chapter of the thesis,based on the second chapter,BiOI was replaced by hollow TiN nanowires with better conductivity and stability and further hybridized Bi nanoparticles in order to further enhance the performance of Pt electrocatalytic glycerol oxidation.Ti O₂nanowires were grown in situ on the surface of carbon cloth by hydrothermal method and treated with high temperature nitridation to obtain titanium nitride nanowires,and further loaded with Pt and Bi nanoparticles by impregnation-reduction method to obtain Pt-Bi hybridized nanoparticles(Pt_1-x-Bi_x)uniformly loaded on the surface of hollow titanium nitride nanowires（TiN HNWs）for the three-dimensional self-supported electrode Pt_1-x-Bi_x/TiN HNWs/CC（0（?）x（?）1）and used for electrocatalytic glycerol oxidation.The Pt_0.95-Bi_0.95/TiN HNWs/CC electrode with optimal catalytic performance was obtained by optimizing the catalyst preparation conditions such as Pt/Bi ratio,reduction temperature,and carrier type.The electrode can achieve 87%glycerol conversion and 36.6%glyceric acid selection after electrolysis in 0.05 M glycerol+1.0 M KOH solution at a constant potential of 0.95 V vs.RHE for 8 h,which is higher than most reported Pt-Bi thermal and electrocatalysts,while maintaining the stability for 8 h.Various characterization and electrochemical test results showed that the excellent electrocatalytic glycerol oxidation performance of Pt_0.95-Bi_0.95/TiN HNWs/CC electrode originated from its unique structure and composition.In the Pt_0.95-Bi_0.95/TiN HNWs/CC electrode,the hollow porous titanium nitride imparts excellent electrical conductivity,fully exposed active sites,efficient mass/charge transfer efficiency and good chemical stability,and the synergistic interaction between Bi nanoparticles and TiN carriers and Pt effectively modulates the electronic structure of Pt and optimizes the adsorption and desorption behavior of reaction intermediates on its surface The three-dimensional self-supporting structure effectively reduces the interfacial resistance and improves the structural stability of the catalyst,thus it exhibits excellent electrocatalytic glycerol oxidation activity and stability.（3）In Chapter 4,based on Chapter 3,the TiN hollow nanowires were replaced by nitrogen-doped carbon nanotubes with larger specific surface area and more defects,and further modified with rare earths（Ce,La,Eu）in order to further enhance the performance of Pt-Bi electrocatalytic glycerol oxidation.Nitrogen-doped carbon nanotubes were grown on the surface of carbon cloth by dicyandiamine-assisted alkali cobalt nitrate pyrolysis catalysis,followed by rare earth（RE=Ce,La,Eu）modification by electrodeposition,and further loaded with Pt and Bi nanoparticles by impregnation-reduction,and Pt-Bi hybrid nanoparticles(Pt_0.95-Bi_0.05)were uniformly loaded on the surface of the rare earth-modified nitrogen-doped carbon nanotubes（RE-NCNTs）on the surface of the three-dimensional self-supported electrode Pt_0.95-Bi_0.05/RE-NCNTs/CC and used for electrocatalytic glycerol oxidation.The optimal Pt_0.95-Bi_0.05/La-NCNTs/CC electrode can achieve 85.7%glycerol conversion and 35.1%oxalate selectivity after 8 h of electrooxidation in0.05 M glycerol+1.0 M KOH solution at 1.10 V vs.RHE voltage,which is higher than most reported Pt-Bi thermal and electrocatalysts,while maintaining stability for 8 hours.The test results indicate that the excellent electrocatalytic glycerol oxidation performance of Pt_0.95-Bi_0.05/La-NCNTs/CC electrode is due to its small charge transfer resistance,large specific surface area,abundant accessible active sites and the synergistic effect between Pt-Bi,RE and NCNTs.