Study On Electrocatalytic Oxygen Reduction Of Doped Titanium Dioxide Into Hydrogen Peroxide

Hydrogen peroxide（H₂O₂）as a green strong oxidant was widely applied in industries such as wastewater treatment,paper manufacturing,and chemical synthesis.Its production still uses expensive anthraquinone process in industry,which also involves great transportation risks and serious waste problems.Two-electron oxygen reduction reaction（2e^-ORR）provides a safe,sustainable,and energy-saving way for on-demand production,but ORR generally favors four-electron reduction to water.This poses a severe challenge for catalyst to follow 2e^-pathway,and requires the design of low-cost,high activity and high selectivity catalysts.Titanium dioxide（Ti O₂）has the advantages of low-cost,non-toxicity and good stability,but its low electrical conductivity and weak activation ability hinder its catalytic activity.Heteroatomic doping can introduce oxygen vacancy in Ti O₂ lattice and generate Ti³⁺,which is an effective strategy to improve the selectivity and activity of Ti O₂ to catalyze oxygen reduction generating H₂O₂.In this thesis,nonmetallic element N and transition metal element Cu doped Ti O₂ were studied for the preparation of H₂O₂ by catalytic cathodic reduction of oxygen.Pristine Ti O₂ nanotubes were synthesized by hydrothermal method and the N-doped Ti O₂（N-Ti O₂）nanotubes were synthesized by solid state dispersion method.The morphology,crystal structure and elemental valence of N-Ti O₂ were characterize by XRD,TEM,EDX and XPS.N-Ti O₂ maintained the previous nanotube structure well,and the N doping possessed more oxygen sites,resulting in the formation of oxygen vacancies,which enabled N-Ti O₂ to have a good 2e^-ORR catalytic activity.Electrochemical test results show that the maximum H₂O₂ selectivity can be 92.2%in 0.1 M KOH electrolyte.In addition,at 0.10 V,the highest H₂O₂ yield is 36.1 mg L^-1 h^-1,and the Faraday efficiency is up to 86%.Meanwhile,N-Ti O₂ nanotubes show good durability and stability.To further investigate the influence of transition metal doping on the performance of Ti O₂ catalyzed 2e^-ORR,Cu-doped Ti O₂（Cu-Ti O₂）nanoparticles were synthesized by hydrothermal method by adding metal salts as raw materials.The morphology,crystal structure,elemental valence state and oxygen vacancy of Cu-Ti O₂ were characterize by XRD,TEM,EDX,XPS and EPR.The morphology of the material has no obvious change before and after doping.The doping of Cu leads to the distortion of Ti O₂ lattice.Abundant oxygen vacancies are introduced into the lattice,and Ti⁴⁺is locally reduced by electron to form Ti³⁺,which makes Cu-Ti O₂ possess higher conductivity and catalytic activity than Ti O₂.Under alkaline conditions,Cu-Ti O₂ has a positive onset potential of 0.79 V,and its2e^-ORR dynamics and selectivity are significantly enhanced.Cu-Ti O₂ can achieve a maximum H₂O₂ selectivity of 91.2%.In addition,Cu-Ti O₂ achieves a high H₂O₂ yield of52.5 mg L^-1 h^-1 at 0.1 V,and the Faraday efficiency is up to 96%,which is better than many reported catalysts.Meanwhile,Cu-Ti O₂ nanoparticles also shows good electrochemical stability.DFT theoretical calculations confirm that Cu doping not only improves the conductivity,but also reduces the*OOH adsorption energy of the active site.The synergistic role of Ti³⁺_4c-5c,the active site of Cu-Ti O₂,shows high 2e^-ORR activity.