Defect Engineering Modulate Ternary Sulphides Nanoarray For High Efficient Photoelectrochemical Performance

Photoelectrochemical(PEC)water oxidation based on semiconductor materials plays an important role in the production of clean fuel and value-added chemicals.Defect engineering has proven to be an effective way to construct highly efficient PEC water splitting photoanodes with the construction of catalytically active sites,carrier transport,and water oxidation kinetics.However,from theoretical point of view,the relationship between the defects of photoanode materials and their PEC performance is unclear.Therefore,it has become a key subject for PEC catalysis that construct and modulate the defect state on metal sulfide nanoarray to understand the role of defects in the catalyst.In addition,the ordered nanostructure can not only enhance the utilization of photon energy,but also promote charge transfer.In this dissertation,we intended to explore the influence of defect on metal sulfide catalysts and design of the rational highly active sites.The main contents are as follows:1.We chose the Zn₁₀In₁₆S₃₄ nanotube(ZIS)as the catalyst candidate and introduce the P doping via defect engineering to modulate the electronic structure.We investigated the relationship between the doping and the performance for photocatalytic,indicating that the P defects served as the active sites for PEC water splitting.The photocurrent of the P-ZIS photoanode was as high as 2.2 m A/cm²,approximately 4 times that of undoped ZIS nanotubes.In addition,the performance of P-doped sample after continuous illumination for 1 h in neutral electrolyte almost did not decline,while the ZIS performance decreased obviously,which further indicated that P-doping enhanced the stability of the catalyst,inhibited the photocorrosion of metal sulfides.The doped P sample played a multi-role in facilitating H₂O activation:(1)constructing defect band,which enhanced light capture and charge transfer;(2)Intensity modulated photocurrent spectroscopy(IMPS)disclosed that the P-doped ZIS sample had an increased electron lifetime and charge transfer rate,which is roughly 1.6 times longer than that of the pristine,indicating a significant improvement in the separation efficiency of photoexcited carriers by doping P into the ZIS crystal.2.Based on the results in Part 1,we attempted to modulate the vacancies on catalyst surface to further improve the activity in PEC performance.The gradient oxygen doped ZnxCd1-xS inverse opals with sulfur vacancies(O-ZCS)has been successfully designed and synthesized by combing hydrothermal and low temperature heat treatment.There is little difference between O atoms and S atoms,O atoms have lone pairs of electrons in 2p orbitals,which can attract the local charge density of metal sites,adjust the electronic structure,and stabilize the sulfur vacancies of metal sulfides by compensating the coordination number.Such design takes the advantage of both stability of sulfur vacancy and gradient band structure to facilitate the bulk carrier transport.The investigation indicated that the coordinatively unsaturated metal atoms with sulfur vacancies served as the sites for PEC water splitting and electron transfer.The optimized O-ZCS achieves that the photocurrent density is close to the theoretical value,which is more than twice that of the undoped ZCS.More importantly,photoelectrochemical impedance spectroscopy(PEIS)shows that gradient oxygen doping enhances the surface density of states and band curvature of ZCS with sulfur-rich vacancies.IMPS spectrum analysis displays that the transfer rate constant of electron hole pair in Helmholtz layer of gradient oxygen-doped photoanode is increased,the recombination rate constant is decreased and the photoinduced electron transfer time is shortened.Finally,combined with the density functional theory(DFT)calculation,it is proved that the introduced sulfur vacancy can adsorb and activate water molecules and construct the overpotential of gradient oxygen doping to reduce water oxidation.The synergistic effect of sulfur vacancies and gradient oxygen doped eventually boosted the catalytic activity and lowered the reaction barrier.