Fabrication Of Cu₂O/TiO₂ Composite Electrode And Its Photoelectrocatalytic Property Of Water Splitting

As an important way of using solar energy to produce hydrogen,photoelectrocatalytic water splitting has aroused people's attention day by day.Compared to one single semiconductor, composite semiconductors fabricated with two semiconductors with different matched bandgaps always show better catalytical performance.In this paper, we studied the fabrication of p-Cu₂O/n-TiO₂ composite electrodes and the performance of the electrode for photoelectrocatalytic water splitting.A two-step anodization method was applied to the fabrication of smooth and orderly TiO₂ nanotube arrays, followed by the exploration of reaction conditions for the preparation of TiO₂ nanotube arrays. The appropriate electrolyte temperature and hydrochloric acid concentration in sonication were confirmed. Characterizations like SEM,XRD,LUV-vis DRS and tests for photoelectrochemical water splitting were employed. The photoconversion efficiencies for TiO₂ nanotube arrays by the first anodization and the second anodization were 0.046% and 0.07%, respectively. The better photoelectrochemical activity of TiO₂ nanotube arrays by the second anodization could be attributed to more smooth and orderly morphology, higher anatase crystallinity and bigger UV-vis absorption.The Cu₂O nanoparticles were deposited on the TiO₂ nanotube arrays via the galvanostatic electrodeposition method. Influences of deposition temperature and charge on the morphology, composition, UV-vis diffuse reflectance and the photoelectrochemical activity of the p-Cu₂O/n-TiO₂ composite electrode was investigated. The suitable deposition temperature was 30 ? and the optimum deposition charge was 0.1 C ?deposition amount of Cu₂O was 5.18×10-7 mol?. Under the optimum conditions,the p-Cu₂O/n-TiO₂ composite electrode revealed a good photoelectrochemical activity with a photocurrent density of 0.8 mA/cm2 at 0 V ?vs.RHE? and corresponding photoconversion effficiency of 0.41% ?0.735 V vs. RHE?,showing 6.2 and 5.8 times that of unloaded TiO₂ nanotube arrays, respectively. The pn junction formed and matched band structure between p type Cu₂O and n type TiO₂ are the reasons resulting in the good photoelectrochemical activity of the p-Cu₂O/n-TiO₂ composite electrodes.The activity of the composite electrodes at the beginning of the test was low,which was increased gradually with the number of scanning, then became stable and started to decrease with the repeated use. Under the measurements like SEM, XRD,XPS,an outer layer of Cu?OH?₂ was formed on the deposited Cu₂O due to the hydroxy adsorption in the basic electrolyte. The falling off of the Cu?OH?₂ and the following exposure of the Cu₂O as the result of the constantly scanning leaded to the improved photoelectrochemical activity and the further dissolved Cu₂O in the electrolyte caused the reduction of the photoelectrochemical activity, which are the activation and reduction of the Cu₂O/TiO₂ composite electrode.The Cu₂O/TiO₂ was annealed to enhance the photoelectrochemical performance at low temperatures in air.The results showed by annealing at 100? for 0.5h in air,The photocurrent density of CT-100 reached 1.18 mA/cm2 at 0 V ?vs. SCE? and photoconversion efficiency of the annealed sample is up to 0.65% ?0.759 V vs. RHE?,showing an increased photoelectrochemical activity compared to the unannealed sample. In the meantime,the annealed sample remained a better photoconversion efficiency of 0.64% ?0.762 V vs. RHE? after 100 scans of linear sweep voltammetry?LSV? and stabilized to 1.90 mA/cm2 during the continuous reaction at 1.23 V ?vs.RHE? for 1 h, showing improved stability compared to the unannealed sample.