Heteroatom Doping Enhance TiO₂ Electrocatalytic Oxygen Reduction For H₂O₂ Synthesis

As one of the most important chemical products in modern society,hydrogen peroxide(H2O2)has been widely applied in the environmental protection,medical and energy fields.However,the current industrial production of H2O2 mainly relies on anthraquinone process,which suffers from serious environmental pollution,highly energy consumption and cumbersome process.The electrocatalytic oxygen reduction production of H2O2 is the most promising new technology with the advantages of renewable energy(solar energy,wind energy,etc.)drive,environmental friendly,safe and reliable,which effectively avoids the problems associated with anthraquinone process and direct synthesis process.However,the existence of competing four-electron side reaction pathways in the electrocatalytic oxygen reduction process significantly restricts the yield efficiency of H2O2.Therefore,it is crucial to exploit highly active and high selectivity electrocatalysts for two-electron oxygen reduction reaction.Among numerous categories of catalysts,titanium dioxide(TiO2)has been investigated extensively in the field of catalysis owing to its advantages of affordability,wide source,structure stability,and environmental friendliness.Nevertheless,the inherent low electroconductivity and poor reactivity of TiO2 prevent it from being an efficient electrocatalyst.To address this problem,we modify the electronic structure of TiO2 and modulate the binding energy of key intermediates in the ORR process to improve the activity and selectivity of TiO2 for two-electron ORR by heteroatom doping.The main research contents and achievements of the dissertation can be summarized as follows:1.Calcium-doping TiO2 was employed for the electrocatalytic oxygen reduction synthesis of H2O2 in alkaline environment.Calcium-doping TiO2(Ca-TiO2)was prepared by strong alkali solution treatment targeting anatase TiO2.The successful doping of Ca into TiO2 lattice was verified by high-resolution transmission electron microscopy(HRTEM)and X-ray photoelectron spectroscopy(XPS),etc.And it was demonstrated that considerable amount of oxygen vacancies and Ti3+ appeared in CaTiO2 that could be the catalytic reaction sites for ORR.The results of the rotating ringdisk electrode(RRDE)experiments indicate that the activity and selectivity for twoelectron ORR of the Ca-TiO2 are dramatically enhanced,with a selectivity up to 85%.In situ spectroscopy experiments and density functional theory(DFT)calculations reveal that Ca doping brings in novel active sites in TiO2 and optimizes the binding energy of*OOH at the active site,making it closer to the optimal theoretical value of 4.2 eV.The H2O2 yield of Ca-TiO2 in alkaline electrolyte was up to 707 mg L-1 h-1.And it performed excellent stability in a long operation time.In addition,the H2O2 electrocatalytically synthesized by Ca-TiO2 enables the complete decolorization of a variety of dye contaminants by Fenton reaction and could efficiently degrade the antibiotic ciprofloxacin(CIP).2.Hydrogen-doping TiO2 for electrocatalytic oxygen reduction synthesis of H2O2 under neutral conditions.Hydrogen-doped TiO2(H-TiO2)were fabricated by acidmetal treatment of TiO2 to achieve efficient electrocatalytic preparation of H2O2 in neutral media.The successful doping of H was demonstrated by high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)and nuclear magnetic resonance(NMR)hydrogen spectroscopy.And the hydrogen-doping only modifies the geometric structure of TiO2 on the atomic scale.Meanwhile,the characterization of electron paramagnetic resonance spectroscopy and hysteresis lines suggest that hydrogen-doping is effective in optimizing the electronic structure of HTiO2,so that it exhibits excellent two-electron ORR activity and selectivity in the RRDE test with a selectivity as high as 97%.According to DFT caculations,H in HTiO2 tends to bind with the O2c site,and the results of the volcano diagram and ORR free energy calculations indicate that hydrogenation facilitates the regulating of the binding energy of*OOH to the catalyst surface to make it closer to the optimal theoretical value.The yield of H2O2 produced by H-TiO2 in neutral electrolyte was up to 331.5 mg L-1 h-1,which is at a comparatively high level compared with other advanced neutral electrocatalysts.In addition,the portable real-time H2O2 production and wastewater treatment platform coupled with the electrocatalytic system based on H-TiO2 as catalyst and Fenton filter can efficiently,rapidly and continuously degrade organic contaminant Rhodamine B with degradation efficiency up to 100%.Meanwhile,the H2O2 electrosynthesized by H-TiO2 is able to effectively sterilize harmful bacteria in the environment with a sterilization rate of 99.9%.