Design And Application Of Palladium-based Alloy Catalyst For Oxygen Reduction To Produce Hydrogen Peroxide

As an important inorganic chemical product,hydrogen peroxide has been used in many areas of human society and life.However,the traditional ways of hydrogen peroxide production cost high energy,produce a large number of harmful substances in the production process and lead safety problems in the transportation process,which make it imperative to develop and find new production methods.The production of hydrogen peroxide by electrocatalysis two-electron oxygen reduction reaction（2e^-ORR）has recently attracted a lot of attention because of its green,efficient,energy-saving and environmentally friendly features.Most of the catalysts reported so far are applied under alkaline conditions,but it is easy to make hydrogen peroxide decompose in alkaline solution,which is not conducive to subsequent storage and use.Therefore,the production of hydrogen peroxide under acidic conditions is more suitable for practical applications.However,most of the catalyst materials for producing hydrogen peroxide under acidic conditions have poor stability,high cost and toxicity,which limit their large-scale development and application.Based on the advanced design strategies of existing catalysts,this thesis explores the performance of palladium-based alloys on2e^-ORR,and finds that oxidized species on their surface are conducive to improving the selectivity and activity of the reaction,and further reveal their internal mechanism,the main content of the thesis can be divided into two parts:（1）According to the difference in the binding ability of metal Pd and Cu to O,a Pd Cu nanoalloy catalyst with a one-dimensional linear structure was synthesized by liquid phase reduction,and the material showed high selectivity in 0.1 M HCl O₄（hydrogen peroxide selectivity is as high as 98%at 0.6 V,hydrogen peroxide selectivity in the whole reaction voltage range is more than 85%）and higher Faraday Efficiency and hydrogen peroxide yield(up to 1866 mol/kg_cat h yield at 0.3 V).In addition,according to the construction of the model material,the deposited few amount of Cu on the Pd disk with an underpotential deposition way confirmed that the addition of Cu improved the 2e^-ORR selectivity of Pd.Compared with metal Pd,it has extremely high hydrogen peroxide selectivity（Pd has less than 10%selectivity）and compared to metal Cu,it has high activity（0.6 V starting potential,pure Cu starting potential is only 0.2V）.Through in situ Raman experiment,the Pd-O bond existing in the reaction process of Pd Cu nanoalloy catalyst was observed,which proved that the addition of Cu improved the binding strength of Pd to O.Furthermore,through theoretical calculation,it is proved that the existence of Pd-O optimizes the adsorption of^*OOH,a key reaction intermediate,and then improves the selectivity of 2e^-ORR.（2）Based on the excellent 2e^-ORR catalytic performance of Pd Cu nanowires,Pd Ni catalysts were designed according to the principle of different O-binding abilities of different metals.Because the metal Ni has strong adsorption of O,the principle is similar to that of Pd Cu nanowires,and the hydrogen peroxide selectivity of Pd is improved by the introduction of Ni.Pd Ni alloy nanoparticles were also synthesized using liquid phase reduction.Pd Ni nanoparticles showed good performance in 0.1 M HCl O₄ and the selectivity of hydrogen peroxide is up to 86%,starting potential of 0.6V.1 h stability test of ring current and H₂O₂ selectivity were stable on RRDE and H-cell test showed H₂O₂ selectivity consistent with RRDE test,so it proved that Pd Ni alloy nanoparticles also have high H₂O₂ yield in actual production.This chapter follows the ideas of the previous chapter to design,prepare and test Pd Ni alloy nanoparticles,which once again proves that the alloy formed between aerophilic metal and metal Pd has a promoting effect on the production of H₂O₂ by 2e^-ORR.