Preparation And Electrochemical Properties Of Rare Earth Metal Composite Biomass Carbon Based Catalyst For Oxygen Reduction Reaction

With the acceleration of urbanization,industrialization and agricultural modernization,it has led to a large variety and concentration of pollutant in our water.Therefore,it is urgent to find a water pollution treatment technology with high oxidation efficiency,green and simple process.Electrochemical oxidation among advanced oxidation technologies has attracted the attention of a large number of researchers due to its advantages of non-selective oxidation of organic pollutants,rapid reaction.This method uses strong oxidizing sbustances produced on the electrode surface to remove organic pollutants from the wastewater,where the more common oxidant is hydrogen peroxide（H₂O₂）.The source of H₂O₂ is mainly oxygen generated through the 2-electron oxygen reduction reaction（2e^-ORR）and direct injection from outside the system.Considering the price of H₂O₂ and the danger of its transportation and storage,2e^-ORR production of H₂O₂ in situ is more valuable for research.At present,2e^-ORR catalysts are mainly based on noble metals and noble precious metal alloys,but the disadvantages of expensive precious metals and their alloys and the low ability of carbon materials to produce H₂O₂ are limited in the large-scale of industry.Therefore,the search for an efficient and inexpensive 2e^-ORR catalyst has become a top priority to solve the water pollution problem.In recent years,many scholars have focused on rare-earth metals,which are rich in d-orbital electrons,and its introduction can improve the oxygen storage capacity and lattice oxygen activity of catalysts.However,rare earth metals have poor electrical conductivity,so they need to be laminated on a carbon substrate.Hohhot as the dairy capital of China,accounts for more than half of the dairy production in the whole country,among which a certain amount of waste milk will remain during the production and pretreatment process.The factory usually uses acid and alkali washing process to clean the pipeline,and the end product is the salt and waste milk obtained after acid and alkali neutralization,and the waste milk can be used as a biomass carbon source to improve the conductivity of the catalyst.In this paper,we proposed to synthesize biomass carbon based catalysts with rare earth by high temperature calcination using milk as biomass based carbon material and Na Cl as template agent,and rare earth salt as metal source.The experimental results demonstrate that the addition of rare earth improves the electrochemical performance of the 2e^-ORR.Synthesized biomass carbon based catalysts compounded with rare earth elements were examined as electrode materials for in situ ORR of H₂O₂ production,and a series of characterizations were performed as follows:1.In part one,the 2e^-ORR electrocatalyst with CeO₂ composite biomass carbon material was successfully fabricated and characterized by physical characterization and electrochemical testing,and the analysis showed that the catalyst has a three-dimensional layered structure and the successful composite of Ce O₂ facilitates the 2e^-ORR process.The electrochemical performance show that the catalyst doped with Ce O₂ has certain 2e^-ORR performance.In addition,the metal raw material of this material is cheap and easy to obtain and the carbon source can be obtained by waste reuse.The result shows that the H₂O₂ yield of this catalyst reaches 66.7%at the mass ratio of milk to Na Cl of 1:10 and the mass ratio of metal compound of 2.5%.The results of physical characterization and electrochemical testing concluded that the surface oxygen content of the catalysts and the content of Ce O₂ and nitrogen and phosphorus have significant effects on the ORR reaction pathway.2.In part two,a series of different rare-earth metal-doped biomass carbon-based catalysts were prepared for physical characterization as well as2e^-ORR testing using the same preparation method as in part one.The results of the physical characterization showed that the catalysts doped with La,Pr,and Nd as chlorine oxides.The electrochemical characterization revealed that this series of carbon-based catalysts compounded with chlorine oxides of rare earth metals all have good 2e^-ORR performance in alkaline electrolytes.The catalyst was optimized by varying different metals and different carbon sources.The La OCl-NPC catalyst was determined to have an H₂O₂ yield close to 70%at a milk to Na Cl ratio of 1:10,a metal percentage of 6%,and a calcination temperature of 1200°C.Therefore,it was tested and proved that its ability to treat pollutants in water is certain by adding the dye rhodamine B to the electrolytic cell as organic pollutants in water.