Research On The Photoelectrochemical Water Splitting By Surface/interface Modification And Device Fabrication Of The Ferrous Oxides

Solar water splitting(SWS)to produce hydrogen and oxygen is one of the most promising strategies to realize the renewable,environmental-friendly and sustainable development.Ferrous oxides(Fe2O3,LaFeO3)are the most desirable SWS materials for their excellent chemical stability,earth abundance and suitable band gaps(?2.0 eV).However,the SWS efficiency still remains low due to the severe carrier recombination within the bulk phase and slow reaction kinetics at the surface.To solve these problems,such methods as doping,surface modification and heterojunction formation are utilized to promote the charge transfer within the bulk,surface and interface of the ferrous oxides.Meanwhile,atomic layer deposition(ALD)is selected to fabricate and modify the micro and nanostructure of the ferrous oxides.Finally,we design and set up a SWS device based on the ferrous oxides with high efficiency and stability,which is in the international peering level.The main research works are shown as below,1.The photoelectrochemical(PEC)testing platform is set up to test the photocurrent density,onset potential,transient photocurrent density and the electrochemical analysis.We also set up the quantum efficiency testing platform to measure the external and internal quantum efficiency ranging in 350?1000 nm.The hydrogen(oxygen)production of the SWS device during the PEC process can also be tested by the drainage and mass spectrograph methods.2.The pristine and transisiton metal(Mn,Co,Cu)doped LaFeO3 flat SWS electrode is fabricated by sol-gel and doctor blade methods.After doping,the PEC performance is found to exhibit the promotion order of LaFe0.9Cu0.1O3>LaFe0.9Co0.1O3>LaFe0.9Mn0.1O3>LaFeO3.Discharge from Fe3+ to Fe4+ is well observed by cyclic voltammetry study,which results in the photocurrent densities promotion.Furthermore,the charge transfer is found to be accelerated by the electrochemical impedance spectroscopy.Finally,the PEC reaction process could be well modified.3.The cathodic photocurrent for p-type characteristics reversing to anodic photocurrent is well observed on the LaFeO3 flat SWS electrode.By hole capturer(Co-Pi)coating,the anodic photocurrent density is promoted and cathodic is suppressed.Based on the reaction kinetics and flat band variation after Co-Pi coating,we construct the band structure bending model of the surface modification.With a view of the limitation of the semiconductor size to the SWS behavior,the nano LaFeO3 flat SWS electrode with-20 nm is fabricated by ALD and exhibits p-type PEC characteristics.4.The p-LaFeO3/n-Fe2O3 nanorod heterojunction SWS electrode is designed and fabricated by ALD.The p-LaFeO3 film is observed to be homogeneous coating on the Fe2O3 nanorod.Based on the flat band and electrochemical impedance spectroscopy analysis,the charge transfer is observed to be accelerated after the heterojunction formed.Furthurmore,co-catalyst(CoOx)is loaded on the heterojunction surface and the PEC performcance exhibits significant improvement(IPCE 25.13%at 400nm).5.By summarizing the systematic research on the charge transport within the bulk,surface and interface of the Fe2O3/LaFeO3 heterojunction,we design and fabricate the ferrous oxide SWS devices with high efficiency and stability.By testing the performance,the device exhibites well stability under illumination.Finally,the IPCE at 400 nm is promoted to be 30.21%and the gas production is obtained of 17 mL/h(?250?mol/h·cm2).This dissertation carries out a systematic research on the charge transference within the bulk,surface and interface of ferrous oxide during SWS.Our results show that the charge transfer would be dramatically effected by the bulk size,surface state and interface formation.We have successfully fabricated the LaFeO3 nano film and p-LaFeO3/n-Fe2O3 nanorod heterojunction by ALD technique.By summarizing the systematic research,the high efficient and stable ferrous oxide SWS devices have been obtained and the IPCE is promoted to be 30.21%(400 nm),which demonstrates the enormous advantage of ALD for the homogeneous thin film deposition,micro/nano structure modification and high efficient ferrous oxide SWS device fabrication.