Design And Preparation Of Carbon-based Electrocatalysts And Their Electrocatalytic Oxygen Reduction To Synthesize Hydrogen Peroxide

Hydrogen peroxide(H₂O₂)is an environmentally friendly oxidant with a wide range of applications in healthcare,chemical industry and environmental treatment.The global annual value of hydrogen peroxide is expected to reach$5.5 billion by 2023.Currently,hydrogen peroxide is mainly produced by the anthraquinone method,accounting for about95%of the production,but this method has many disadvantages:high energy consumption,the reaction process generates a large amount of organic by-products and requires large chemical equipment for centralized production,in addition,buffers need to be added to avoid the decomposition of H₂O₂ during storage and transportation,and additional costs and time are required to remove the stabilizer before practical application.Electrochemical oxygen reduction reactions(ORR)offer a simple method for H₂O₂ production with mild reaction conditions.With the development of renewable energy sources(hydro,wind,geothermal,solar),it makes sense to use electricity from renewable sources to generate H₂O₂ via electrocatalytic oxygen reduction reactions.ORR can proceed through two pathways,including a four-electron pathway for H₂O production and a two-electron pathway for H₂O₂ production,so obtaining efficient,stable,and highly selective electrocatalysts for H₂O₂ synthesis is very is very important.So far,precious metals(Au,Pt,Pd)and their alloys are still the best performing catalysts for the synthesis of H₂O₂,but the high cost have seriously hindered their application in industrial development.As a kind of electrocatalyst with abundant sources,low cost and good stability in use,carbon-based catalysts have shown promising applications in many reactions,Carbon based catalysts are receiving more and more attention because they show excellent performance as 2e^-ORR electrocatalysts in H₂O₂ production.In this thesis,the following studies were carried out with the aim of improving the catalytic activity and selectivity of the catalysts by modulating the morphological structure and active sites of the carbon-based materials.(1)This paper presents a strategy for the synthesis of metal-doped carbon-based catalysts using sodium alginate,a marine brown algae extract,as the precursor.The metal-doped carbon-based catalysts(Ni SAs/Ni NPs@C)with core-shell structure were formed by ion-exchange of sodium alginate and metal ions(Ni²⁺),which were thermally annealed to form an"egg box"structure.and the H₂O₂ selectivity can reach up to 92%.Density functional theory(DFT)calculations confirmed that the core-shell structure formed by Ni doping and the synergistic effect between Ni nanoparticles(Ni NPs)and Ni single atoms(Ni SAs)promoted the H₂O₂ production.(2)PAQS/CNT nanocatalysts were prepared by loading long-chain organic polymers of poly(anthraquinone sulfide)(PAQS)onto the surface of carbon nanotubes through a polymerization reaction.Under alkaline conditions,PAQS/CNT exhibited excellent ORR electrocatalytic performance and stability with high H₂O₂ selectivity.The quinone functional group was found to be the key to improve the H₂O₂ selectivity by characterization.The loading of organic polymer should not be too high,and the catalytic activity of the catalyst will be affected when the content of PAQS loaded by CNT is too high,leading to the decrease of selectivity.