(Oxy)Sulfide-based Phocatalysts For Photoelectrochemical Water Splitting:Construction,Performance And Mechanism Study

Semiconductor photocatalytic technology can convert the low density and renewable solar energy into high density chemical energy,which is one of the most effective methods to solve energy and environmental issues.Sulfur(Oxygen)Compounds have unique advantages in photoelectrochemical water splitting(PEC)due to its narrow band gap,appropriate band positions.However,it suffer from the limitations of rapid recombination of photogenerated carriers and poor PEC stability,even in the presence of a sacrificial reagent.To this end,in this thesis,we designed and fabricated a CdS/Au/Ti/Pb(Mgi/3Nb2/3)0.7T10.3O3 photocatalyst with ferroelectric spontaneous polarization electric field to separate charge carriers,a cobalt phosphate cocatalyzed CdS nanorod photoanode and Z-scheme photocatalyst in La5Ti2AgS5O7-based powder suspension system for photoelectrochemical water splitting and investigated their PEC performances and reaction mecharnism.The intrinsic relationship between semiconductor interface and the transfer of photogenerated carriers were exploded.This thesis mainly consists of the following three chapters:Chapter 2 we report that the spontaneous ferroelectric polarization in a single domain for efficient charge separation over a representative semiconductor CdS,in the form of CdS/Au/Ti/Pb(Mgi/3Nb2/3)o.7Ti0.3O3(CdS/Au/Ti/PMN-PT),for water splitting in absence of any cocatalyst or external voltage.The photocurrent value of the positive polarized CdS/Au/Ti/PMN-PT yields 1.70 mA·cm-2,which is about 20 times higher than the value of the non-polarized sample.In addition,a biphotoelectrode cell composed of a positively and a negatively polarized CdS/Au/Ti/PMN-PT was constructed.A considerable solar-to-hydrogen conversion efficiency of 0.19%was achieved.Chapter 3 CdS nanorod photoanodes cocatalyzed by cobalt phosphate(CoPi)were synthesized by a facile two-step route using a hydrothermal method followed by photo-assisted electrodeposition of CoPi.The optimal CdS/CoPi photoanode showed a maximum photocurrent of 4.7 mA/cm2 at 0 V vs RHE,which is 5.5-fold higher than the bare CdS photoanode.Based on structure investigation and theoretical simulation,it was found that forming intimate junctions in the form of Co-S bonds between CoPi and CdS nanorods effectively facilitated the charge separation by trapping holes in CoPi sites and lowered the activation energy of the water oxidation reaction.Chapter 4 We report that among La5Ti2CuxAg1-xS5O7,La5Ti2AgS5O7 was found to have the highest performance on Z-scheme overall water splitting in conjunction with PtOx-WO3 as an oxygen evolution photocatalyst(OEP),and a triiodide/iodide(I3-/I-)redox couple as a shuttle electron mediator in powder suspension system.Loading Pt/NiS on LasTi2AgSsO7 benefits the Z-scheme to achieve an apparent quantum yield of 0.12%at 420 nm.