Construction Of Photosensitizer/LDHs Pheotoelectrocatalyst And Research On Oxygen Reduction Reaction Performance

Oxygen reduction reaction（ORR）has always received high attention from people for it is a significant process in energy storage devices.The process of 4-electron ORR reduction is particularly important.Therefore,more and more studies have been conducted on ORR process to improve its catalytic activity and selectivity,and then explore its electrocatalytic mechanism.Inspired by the sensitization of O₂molecules to generate reactive oxygen species（ROS）in photodynamic therapy by photosensitizers,this article focuses on the key issue of substrate molecule activation in the ORR electrocatalytic process and carries out the design of photocatalysts.Based on the adjustable composition and solid alkalinity of layered composite hydroxides（LDHs）materials,composite catalysts with metal porphyrin based photosensitizers loaded on LDHs was designed and constructed.The kinetics of photoelectric ORR catalytic reactions based on such catalysts were explored.The structure and composition characterization research confirmed that the composite system was successfully constructed,and its electrochemical performance was comprehensively characterized.The photoelectric catalytic ORR performance was explored,and then photo-assisted zinc air battery with it as a photocathode was constructed,realizing the improvement and optimization of the battery performance.Finally,the mechanism of the photocatalytic ORR reaction using composite catalysts was explored.This study introduces photosensitizers into the photocatalytic ORR reaction,providing new ideas and methods for the design and construction of new ORR catalysts and the development of new concept energy storage devices for photo-assisted metal air batteries.The results and content of this research are as follows:1.Fe TPPCl/NiCoFe-LDHs nanocatalyst was constructed by combining photosensitizer 5,10,15,20-Tetraphenyl-21H,23H-porphine iron（III）chloride（Fe TPPCl）with NiCoFe-LDHs through impregnation method,achieving the activation of substrate O₂molecules to generate reactive oxygen species（ROS）under photocatalytic conditions,and exploring the performance of the catalyst as the photocathode in zinc air batteries.The successful loading of the photosensitizer Fe TPPCl on the surface of NiCoFe-LDHs was demonstrated through various characterization methods such as XRD,UV-vis,and FT-IR.The investigation of the photocatalytic reaction performance of the photoelectric ORR showed that the composite catalyst has O₂reduction ability and better performance under light conditions:oxygen reduction peak potential（0.60V）,Tafel slope(93 m V·dec^-1),starting potential,limiting current density(3.00 m A·cm^-2)and half-wave potential（0.76 and 0.59V vs.RHE）obtained under light conditions.In addition,the discharge voltage of the photo-assisted zinc-air battery was increased from 1.09 V to 1.17 V,the charging voltage was reduced from 1.87 V to 1.84 V,and the round-trip efficiency was increased from 58%to 64%.The battery can continuously charge and discharge for up to 60 hours,with excellent cycle performance.Tests such as electron paramagnetic resonance（EPR）have shown that the composite catalyst fully activates the substrate O₂molecule through synergistic action to participate in the ORR catalytic process as active oxygen species,and the exploration of energy band structure shows that the generation of active oxygen species plays a key role in the 4e^-ORR path selection.The design goal of highly efficient activation substrates for photosensitizer/LDHs materials has been achieved,and the problems of slow kinetic rate,poor selectivity,high overpotential,and high activation energy of ORR have been solved in a collaborative manner.2.The Hemin/NiFe-LDHs nanocatalyst was constructed by combining photosensitizer Hemin with NiFe-LDHs through impregnation method,achieving the activation of substrate O₂molecules to generate reactive oxygen species（ROS）under photocatalytic conditions,and exploring the performance of the catalyst as the photocathode in zinc air batteries.Hemin/NiFe LDHs nanocatalysts were constructed by tightly combining photosensitive molecules Hemin and NiFe LDHs through electrostatic interactions.The successful construction of the composite catalyst was explored using characterization methods such as XRD.The composite catalyst exhibits excellent ORR catalytic performance in photoelectrochemical testing:the starting potential（0.859V）,Tafel slope(66 m V·dec^-1),half-wave potential（0.518V vs.RHE）and limiting current density(3.21 m A·cm^-2),of the nanocatalyst were all improved.In addition,experiments on a photo-assisted zinc-air battery have shown that Hemin/NiFe-LDHs can charge at 1.11V and discharge at 1.93V,with a cycle efficiency of 57.5%,and the battery can continuously charge and discharge for up to 888 hours,with excellent cycling performance.The synergistic effect of Hemin and NiFe-LDHs allows the CB value of the nanocatalyst to be closer to the standard electrode potentials of O₂/H₂O and¹O₂/·O₂^-.The reaction pathway of selective 4-electron generation of H₂O in alkaline electrolytes is realized while the composite catalyst with high activity sensitized the substrate O₂molecule as reactive oxygen species.The results were confirmed by EPR.The optimized preparation method not only effectively strengthens the binding force between photosensitizer and LDHs,but also strengthens the synergistic effect between the two,which further deepens the exploration of the mechanism of activating substrates to promote catalytic performance.This work lays a solid foundation for expanding the research of photosensitizers in the field of photoelectrocatalysis.3.The PPIX@Zn Cr-LDHs was prepared though photosensitizer protoporphyrin（PPIX）with Zn Cr-LDHs by in-situ coordination through impregnation method.PPIX@Zn Cr-LDHs can activate substrate O₂molecules to generate reactive oxygen species（ROS）under photocatalysis conditions for exploring the photocatalytic performance of photoelectrochemical ORR and its application as the photocathode in zinc air batteries:PPIX@Zn Cr-LDHs nanocatalysts were constructed by protoporphyrin（PPIX）without coordination ions in the inner ring with metal ions in Zn Cr-LDHs laminate and characterized by infrared spectroscopy.PPIX@Zn Cr-LDHs shoes excellent ORR catalytic performance in photoelectrochemical testing:the peak potential of the nanocatalyst is 0.57V,the limiting current density is 2.47 m A·cm^-2,the Tafel slope is 98 m V·dec^-1,the initial potential is 0.7530V,the half slope potential is 0.6620V,and the number of transferred electrons approaches 4.The method is suitable not only for the in situ coordination of PPIX with LDHs,but also for the coordination of other macrocyclic molecules with LDHs.This work achieves innovation in the preparation methods of photosensitizer/LDHs nanomaterials,and contributes to improving the catalytic performance of activated substrate molecules.