Preparation And Photoelectrochemical Performance Of α-Fe₂O₃/rGO/NiFe-LDH Composite Photoanode

With the increase of world population and economic development,human beings are relying on the tradition energies,such as fossil fuel.Photoelectrochemical（PEC）water splitting,which converts solar energy into hydrogen,is a promising technology for production of hydrogen energy.For PEC devices,the photoanodes are its core component.Thus,the preparation of high-efficient and stable photoelectrodes is crucial.Photoanode material combined with electron transport layer,hole transport layer and surface cocatalyst can be selected.Hematite（α-Fe₂O₃）as a photoanode material has many advantages,such as suitable visible bandgap（1.9-2.2 e V）,good stability and abundant content of elements.However,the intrinsicα-Fe₂O₃ has short hole diffusion length（～2-4 nm）,low charge separation efficiency and slow water oxidation kinetics.These shortcomings seriously hinder the performance improvement ofα-Fe₂O₃ photoanode,which results in that the actual PEC efficiency ofα-Fe₂O₃ is much lower than its theoretical value（16.9%）.In view of this,in this master’s thesis,we selected reduced graphene oxide（rGO）with electrical conductivity as the charge transport layer,and NiFe-LDH cocatalyst as excellent oxygen evolution catalyst to improve PEC performance ofα-Fe₂O₃photoanode.The synergistic effects of rGO and NiFe-LDH on the photoelectrochemical properties ofα-Fe₂O₃ were deeply explored.The specific research contents are as follows:（1）Theα-Fe₂O₃/rGO/NiFe-LDH composite photoanode was constructed.First,we preparedα-Fe₂O₃ thin films on FTO conductive substrates by hydrothermal-annealing method.Then,the surface ofα-Fe₂O₃ thin films was covered with rGO as a charge transport layer by spin-coating method to enhance charge separation efficiency.Finally,the NiFe-LDH oxygen evolution catalyst was modified by photo-assisted electrodeposition to improve the OER activity.During the experiment,the amount of rGO and NiFe-LDH can be controlled,which obtains the optimal combination on the PEC performance of photoanode in the subsequent studies.（2）The PEC performance of the composite photoelectrodes were explored.The effects of rGO with different cycles and NiFe-LDH with different photo-assisted electrodeposition time on the PEC performance were investigated.Theα-Fe₂O₃/rGO/NiFe-LDH photoanode exhibits a remarkable higher photocurrent density of 1.46 m A/cm² at 1.23 V_RHE photocurrent,which is 2.86 times ofα-Fe₂O₃.Furthermore,the onset potential exhibits a significant cathodic shift of 230 m V,from～0.88 V_RHE forα-Fe₂O₃ to～0.65 V_RHE forα-Fe₂O₃/rGO/NiFe-LDH.The results show that rGO as the charge transport layer and NiFe-LDH as the oxygen evolution catalyst play a synergistic role to promote the separation of photogenerated charges and enhance the performance of photoelectrochemical water splitting.