Synthesis Of Organic Polymer Interlayer/Bismuth Vanadate Composite Photoanode And Its Catalytic Properties For Water Oxidation

With the environmental pollution and irreversible consumption of fossil fuels,energy shortage has become a serious challenge,which has aroused more and more attention of human society.Photochemical water cracking provides an attractive strategy for obtaining oxygen and hydrogen by converting solar energy directly into chemical energy,which could solve energy shortages and environmental pollution.Bismuth vanadate（Bi VO₄）is one of the most widely used photoelectrode materials due to its excellent light absorption ability,low cost and suitable band gap.Although Bi VO₄has a high theoretical photocurrent density,its actual photocurrent density is very small due to its slow photogeneration carriers and difficult hole separation.However,through structural modulation,defect construction,and heterojunction engineering,there is still a lot of room to optimize the photochemical water decomposition（PEC）efficiency of Bi VO₄.Due to the high cost and scarce resources of precious metal catalyst,it is very important to select suitable cocatalyst.At present,cheap,efficient and stable layered dihydroxides（LDHs）have been widely used in the study of co-catalysts.In conclusion,we chose to introduce the intermediate layer of organic polymer with bimetallic layered hydroxide as a cocatalyst to adjust the ability of charge separation and transfer to improve the water oxidation performance of PEC.Specific work is as follows:（1）Heptazine organic polymer（TM）was prepared by hot solvent method with Melleamine（melem）and 1,3,5-trimethylaldehyde resorcinol（TP）monomers.Then TM was uniformly coated on bismuth vanadate（BVO）substrate by spiral coating method,and combined with bimetallic cocatalyst（Co Mn LDHs）.The photoanode BVO/TM/Co Mn LDHs was constructed by using TM as the intermediate layer.The current density of the BVO/TM/Co Mn LDHs electrode at 1.23 V is 2.7 times higher than that of the BVO electrode（vs.RHE）.The open circuit voltage decay rate of BVO/TM/Co Mn LDHs is slower and the time required for hole transfer is shorter,indicating that the photogenerated electrons and the holes on the surface can be separated more efficiently.The introduction of TM organic polymer interlayers can extend the carrier lifetime by time-resolved photoluminescence（TRPL）and fluorescent photoluminescence（PL）spectra.By density functional theory calculation（DFT）,it is obtained that the free energy barrier of BVO/TM/Co Mn LDHs electrode is minimum after the introduction of TM organic polymer as the intermediate layer,indicating that the introduction of TM intermediate layer can accelerate the separation of charge,promote the transfer of holes,and optimize the PEC performance of water decomposition.（2）Based on the previous chapter,a new three-layer composite photoanode（BVO/Co PP/Ni Fe LDHs）was designed and prepared using the cobalt porphyrin polymer Co PP as the organic polymer interlayer.Through UV-vis diffuse reflection,it was confirmed that the introduction of Co PP into the BVO surface improved the light absorption ability of BVO.Moreover,the photovoltaic performance study shows that the BVO/Co PP/Ni Fe LDHs exhibit the maximum photocurrent density of 3.5 m A/cm²（vs.RHE）at a voltage of 1.23 V under AM 1.5G light irradiation.Their charge transfer resistance(R_ct)was only 217.3Ω,much lower than that of the other four composite electrodes.It was demonstrated experimentally that the enhanced PEC activity can be attributed to the introduction of the Co PP interlayer,which accelerates the transfer of holes.Therefore,the experimental design method in this work provides a reasonable design strategy for enhancing the hole separation and PEC water decomposition system of photoanode.