Hydrogen Peroxide Electrosynthesis Via Regulating The Oxygen Reduction Reaction Pathway On Pt-based Noble Metal Ion Poisoning

Hydrogen peroxide（H₂O₂）,one of the most eco-friendly chemicals,is widely used in wastewater treatment,pulp bleaching,medical disinfection,chemical synthesis,electronic devices and aerospace.It was reported that the globle demand of H₂O₂ would reach 12 million tonnes by 2025.Up to now,more than 95%H₂O₂ is produced by the industrial anthraquinone auto-oxidation process with palladium（Pd）as the catalyst.However,the waste-intensive process requires centralized infrastructure.Further purification and transportion processes not only increase the cost but also bring safty issus.Therefore,there is an urgent need for a simple and environmentally friendly method for the synthesis of controlled concentrations of H₂O₂under mild conditions.The electrochemical 2e^-oxygen reduction reaction（ORR）synthesis of H₂O₂ has drawing broad attention.However,it limites by the lack of electrocatalysts with high activity selectivity and stability.At present,the most active 2e^-ORR catalysts are still based on the precious metals.For instance,Pt-Hg alloy and Pt single-atom catalysts could effectively regulate the ORR to 2e^-pathway to produce H₂O₂.However,the highly toxic mercury limits its practical use.And the stability of single-atom catalysts needs for further improvement.In the thesis,based on the concept of isolating active sites of precious metals,we develope an efficient and highly stable 2e^-ORR catalysts.The main works are summaried below:（1）A simple ion poisoning strategy was proposed by virtue of the strong ion coordination effects between SCN^-and Pt,the as prepared Pt/C-SCN catalysts could successfully regulate the ORR to 2e^-pathway to produce H₂O₂ in acid media.The electrochemical evaluation of the SCN^-poisoned Pt/C catalyst display high activityan（an onset potential of 0.70 V vs.RHE,which is close to theoretical values）and selectivity for over 90%faraday efficiency at a wide range of potentials.The stability tests show negligible performance lost after 30 hours.This work offers a promising poisoning strategy to regulate precious catalysts for selectively electrochemical production of H₂O₂.（2）Based on the above work,we propose a direct chemical one-step synthesis of surface ion isolated platinum-thiocyanate（Pt SCNx）catalyst as a promising electrocatalyst for the H₂O₂electrosynthesis in acidic media.The SCN^-binding remarkably weakens the absorption of crucial*OOH intermediate on the Pt surface,leading to the change of ORR electron transfer pathway.The carbon supported Pt SCNx exhibits an onset potential of 0.68 V（vs.RHE）and～90%selectivity.Significantly,the Pt SCNx/C shows a continual and stable electrolysis over130 h,which outperforms the state-of-the-art 2e^-ORR catalysts.Moreover,an on-site electro-chemical rapid removal of organic pollutant is achieved through an electro-Fenton process.（3）Combing the DFT calculations and experiments,a series of Pt Sx/C catalyst was prepared with different S coverage degree（_Xandθ（S）both are the coverage of S）.Whenθ（S）≤1/4,the 2e^-ORR selectivity of Pt S_X is positively correlated with S coverage.However,forθ（S）>1/4,the 2e^-ORR selectivity is decreased steeply.Thus,Pt S_0.26/C has the optimum（?）G（*OOH）,activity（0.70 V vs.RHE）and selectivity（～90%）.The stability（180 h）and mass activity of Pt S_0.26/C for electrosynthesis H₂O₂(66 A g^-1 atη=50 m V)also outperform other reported 2e^-ORR electrocatalysts.The Pt S_0.26/CP as a cathode of electro-Fenton process further enables in-situ degradation of toxic and persistent organic pollutants,such as rhodamine B and phenol,which is expected to achieve practical applications.