Study On Piezo-Catalysis For Oxygen Reduction Reaction

Piezo-catalytic effect can converse mechanical energy into chemical energy.What's more,small kinetic energies,such as those from sounds,water waves and vibrations,are everywhere as well as solar energy.In a typical piezo-catalytic process,an external force will create a great potential field in piezoelectric materials,then the field can separate the charge carriers?electron-hole pairs?in opposite directions,if the potentials of the charge carriers are large enough,consequently,corresponding chemical reactions will proceed.The mechanism of piezo-catalytic effect is similar to photocatalytic,however,current piezo-catalytic researches focus on the degradation of organic pollutant.With a view to the model reactions and catalyts in the field of piezo-ctalytic effect,we first carry out the researches of piezo-catalytic generation of H₂O₂ and oxidization of CH₄,and the piezo-catalytic performance of bismuth oxychloride,graphitic carbon nitrides and hydroxyapatite are researched.The main contents of this paper include:1.Study on piezo-catalytic effect over BiOCl.The BiOCl microplates were synthesized by hydrothermal method.The piezoelectric response of BiOCl was directly characterized by piezoresponse force microscopy?PFM?.The BiOCl exhibits efficient catalytic performance for generating H₂O₂?28?mol/h?only from O₂ and H₂O,which is above the average level of H₂O₂produced by solar-to-chemical process.A piezo-catalytic mechanism was proposed:with ultrasonic waves,an alternating electric field will be generated over BiOCl,which can drive charge carriers?electrons?to interact with O₂ and H₂O,then to form H₂O₂.With the addition of surfactant,three sizes of samples were synthesized.The results of piezoelectric response microscope demonstrated that the spontaneous polarization increased with increasing size of BiOCl.And the sample with largest size has greatest piezo-catalytic performance.2.Herein,we provide a nonmetal piezo-catalyst of g-C₃N₄,which owns efficient activity of generating H₂O₂ only from H₂O and O₂ under ultrasonic vibration.We synthesized g-C₃N₄ just by one step of sintering.In the dark,KMnO₄ can be efficiently and continuously reduced with ultrasonic waves over g-C₃N₄,which verifies the piezo-catlytic effect of g-C₃N₄.Piezo-ctalytic Au³⁺reduction evidenced that the ultrasonic-derived piezoelectric polarization over g-C₃N₄ is along[001].Without any organics,the ultrasonic-driven generation rate of H₂O₂ can reach to 34?mol/h.To verify that the ultrasonic-assisted catalytic reaction is piezo-catalytic effect,we prepared Cv-C₃N₄ and Nv-C₃N₄?g-C₃N₄ containing C or N vacancies?.The result of piezoelectric response force microscopy?PFM?evidences that g-C₃N₄ owns stronger piezoelectric effect than Cv-C₃N₄ and Nv-C₃N₄.Although Cv-C₃N₄ and Nv-C₃N₄ have larger specific surface area and C or N vacancies can both active O₂,Cv-C₃N₄ and Nv-C₃N₄ exhibit lower catalytic performance with ultrasonic waves than g-C₃N₄,which indicated that the essence of ultrasonic-assisted reaction in suspension of samples is piezo-catalytic effect..3.Herein,we report a piezo-catalytic method of oxidizing CH₄ with ultrasonic waves over hydroxyapatite(Ca₁₀?PO₄?₆?OH?₂)under ambient temperature and pressure.In the piezo-catalytic process of degrading organic pollutant over hydroxyapatite,the main reactive oxygen specie was determined as hydroxyl radical,and photoluminescence technology further confirmed the sustainable generation of hydroxyl radical.Under the atmosphere of air,the piezo-catalytic generation rate of H₂O₂ reaches to 20?mol/h.It has been proven that H₂O₂ and hydroxyl radical can both efficiently promote the activation CH₄.Therefore,piezo-catalytic oxidation of CH₄ was carried out.At the flow of CH₄ and O₂,the piezo-catalytic production of ethyl alcohol can reach 20 mg/L with ultrasonic waves for 3h.