Basically Studies Of Charge Separation And Oxidation Kinetics In Photoelectrochemical Application

Environment and energy is the major problems in 21st century that the human face and development of the clean and efficient new energy technology has become the consensus all over the world.However,the photoelectrochemical?PEC?water splitting system can directly use the solar energy to drive the redox reactions by a semiconductor,and therefore become a clean energy production technology for pollution control.In order to develop the commercial application photoelectrocatalyst technology and numerous studies are focus on the PEC performance and mechanism,including charge separation efficiency and oxidation kinetics efficiency.Here,we combine the new tendency in PEC research area,to improve the separation of photogenerated electron-holes and charge migration,and investigate some nanostructured semiconductors for PEC applications,such as BiVO₄ and Fe₂O₃.We use the electrodeposition,hydrothermal method,solvothermal method,and annealing calcination to synthesize the semiconductor,and control the structure,morphology and composition.In all,the main research contents of this paper are as follows:1.Here,we developed a facile fabrication of BiVO₄ double layer photoanode on the fluorine-doped tin oxide substrate by electrodeposition.The BiVO₄ double layer photoanode is composed by a dense BiVO₄ film as the inner layer and a nanoporous BiVO₄ film as the outer layer.Compared to the BiVO₄ single layer photoanode,the optimized BiVO₄ double layer photoanode produced a much higher photocurrent of 1.15mA/cm² at 0.6 V vs.Ag/AgCl under AM 1.5G?100 mW/cm²?illumination.The results of the photoelectric conversion kinetics for different samples revealed that the charge separation and oxidation kinetics efficiencies for the BiVO₄ double layer are 47.2%and51.6%at 0.6 V vs.Ag/AgCl,while the values for BiVO₄ single layer are 32.3%and35.8%,respectively.The improved photoelectrochemical performance for BiVO₄double layer is mainly ascribed to the decrease of defect state at the interface after inserting a dense BiVO₄ as an inner layer to prevent the recombination of photogenerated electron-hole pairs.2.We developed a facile fabrication of Mo doped BiVO₄ photoanode on the fluorine-doped tin oxide substrate by electrodeposition method and used these samples to better understand the doping effect for charge separation and charge oxidation kinetics.Compared with the undoped BiVO₄ photoanode,the optimized Mo doped BiVO₄?3AMo:BV?produced a much higher photocurrent of 1.91 mA/cm² at 1.23 V vs.RHE under AM 1.5G illumination for water oxidation.The results of the photoelectric conversion kinetics for various samples revealed that the charge separation and oxidation kinetics efficiencies for 3AMo:BV sample are 74.42%and 49.25%at 1.23 V vs.RHE,while the values for undoped BiVO₄ are 48.04%and 32.98%,respectively.The improved PEC performance for Mo doped BiVO₄ is mainly ascribed to the crystal deformation caused by larger tetrahedral ionic VO₄ and higher photovoltage generated by the interface of photoanode and electrolyte.3.We overcome these challenges by coated dual-metal oxide oxygen evolution catalyst on the pristine photoanode.We demonstrate that the photocurrent is enhanced from 0.85?BV?to 2.34 mA/cm²?NiCoO₂/BV?with water oxidation,which can effortless surpass 175%enhancement.Moreover,the NiCoO₂/BV photoanode achieve the simultaneously enhanced charge separation and oxidation kinetics efficiencies?61.9%and 72.7%?at 1.23 V vs.RHE compared with BV?36.5%and 43.6%?,and the charge transport time reduced by 35%due to the NiCoO₂ has a lower work function.The upward energy band is induced by NiCoO₂ particles,which has a positive work to accelerate the charge separation and migration under the outside direction built-in electric field.The highly efficiency of photo to current is attributed to the NiCoO₂ can absorb holes to form Ni⁴⁺and Co⁴⁺species,and suggest that select a cocatalyst with lower work function can promote the photogenerated electron-hole separation and transfer.4.Ultrafast charge recombination in hematite?Fe₂O₃?severely limits its applications in solar energy conversion and utilization in photoelectrochemical water splitting.Here,we report the studies of charge separation and oxidation kinetics efficiencies with Fe₂O₃ nanorod?40 nm?decorated by FeP?5 nm?core-shell structure.By selecting the appropriate time to phosphorization?20 min?,the photocurrent result reveal that the FeP@Fe₂O₃-20 photoanode?0.86 mA/cm²?enhanced by 3.10 folds compared with pristine Fe₂O₃?0.21 mA/cm²?for water oxidation under AM 1.5G illumination at 1.23 V vs.RHE.Further,the efficiencies of charge separation and oxidation kinetics for FeP@Fe₂O₃-20?24.8%and 50.6%?are higher than Fe₂O₃?11.6%and 26.6%?,and the charge transport time reduced by 30%due to the FeP shell served as the hole transport layer.The upward energy band is induced by FeP shell,which has a positive work to accelerate the charge separation and migration ascribe to the built-in electric field.Our studies provide a detailed understanding of carrier dynamics in Fe₂O₃,and rationalized the experimentally reported activation of FeP@Fe₂O₃ core-shell structure by one step phosphorization,demonstrating a new method to exploring high-efficiency approaches for solar harvesting.5.Manipulation the charge transport and energy band of a semiconductor is always an important theme for photoelectrochemistry.Here we design and fabricate a ferroelectric-semiconductor hybrid structure for photoelectrochemical applications.By selecting the appropriate poled bias,the polarization direction of ferroelectric could be conveniently manipulated for n-type semiconductors?TiO₂ and ZnO?and p-type semiconductors?g-C₃N₄ and Bi₂Mo₂O₉?.The photocurrents of the hybrid photoanodes?at 1.23 V vs.RHE?and photocathodes?at 0 V vs.RHE?enhanced by 60±5%and 85±15%with water oxidation and reduction respectively under the illumination of a monochromater??=365 nm?.Further,the efficiency of oxidation kinetics for hybrid photoanodes increased by 1.5 fold,and the charge transport time reduced 10%¹5%for photoanodes and photocathodes.The polarized ferroelectric blended in semiconductor may have an effect on the space charge region by the semiconductor,further,bending the energy band and accelerate the charge transport at the photoelectrode surface.This research has a certain reference for developing hybrid photoelectrodes relevant to the large-scale application of ferroelectric materials in solar water splitting,photovoltaic,and solar fuels devices.Our research can provide a certain method for the synthesis the new energy device with PEC applications for the material design,preparation,characterization,and properties test.Further,we can give a hand for the design concept and theoretical basis with of materials research and construction.