| Photoelectrochemical water splitting of the semiconductor-based photoelectrodes is regarded as one of the most effective measures to solve the energy crisis and environmental pollution in the 21st century.In this paper,CdS and TiO2 are used as the substrates due to their excellent properties.A novel three-dimensional CdS@Ni(OH)2 and TiO2@Ni(OH)2 heterostructure photoanode with a p-n junction and a type-II band alignment has been constructed via a simple electrochemical deposition of the hierarchical Ni(OH)2 nanosheets onto the surfaces of the CdS and TiO2 nanorod arrays.During the experiment,the deposition current can be adjusted to control the loadings of Ni(OH)2.Then,the composition,crystal phase,morphology and size of the prepared sample are characterized,and the light absorption properties and the photoelectric properties of the sample are tested.Finally,a reasonable explanation for the enhanced photoelectric performance of the sample is given by studying the separation and transfer process of the photoproduced electrons and holes.The main contents and conclusions are given as follows:(1)Preparation and photoelectric properties of the CdS and TiO2 nanorod arrays.The CdS and TiO2 samples have been synthesized on fluorine-doped tinoxide(FTO)substrate by the hydrothermal method.Characterization results showed that the CdS nanorods of hexagonal wurtzite phase are hexagonal prisms with a cross section diameter of 150-200 nm,while the TiO2 nanorods of rutile structure are quadrilateral prisms with a cross section diameter of about 100 nm.Performance tests show that the CdS photoanode has strong visible light absorption capacity.The photocurrent density of the pure CdS photoanode is 0.22 mA/cm2,the maximum value of the solar-to-hydrogen conversion efficiency is 0.084%when the bias voltage is 0.67 V vs.RHE,and the maximum value of the incident photon to current efficiency is 8.5%at the wavelength of 340 nm.The TiO2 photoanode has excellent ultraviolet light absorption performance.The photocurrent density of the pure TiO2 photoanode is 0.5 mA/cm2,and the solar-to-hydrogen conversion efficiency reaches a maximum of 0.32%when the bias voltage is 0.35 V vs.RHE.(2)Preparation and photoelectric properties of the CdS@Ni(OH)2 nanorod arrays heterostructure.A novel three-dimensional hierarchical CdS@Ni(OH)2 heterostructure with different Ni(OH)2 loadings by adjusting the deposition current has been fabricated through an easy electrochemical deposition process to load the Ni(OH)2 nanosheets onto the surfaces of the CdS nanorods.The characterization results show that the Ni(OH)2 nanosheets self-assemble into a three-dimensional hierarchical structure.The performance tests show that the visible light absorption and photoelectric performance of the heterostructure is significantly improved.The three-dimensional CdS@Ni(OH)2 photoanode fabricated under the optimal deposition current of 2.5 mA obtains a photocurrent density of up to 1.1 mA/cm2,5-fold that of the pure CdS photoanode and achieves a maximum solar-to-hydrogen conversion efficiency of 0.26%at 0.67 V vs.RHE,about 3.3-fold higher than that of the bare CdS photoanode.It also achieves the largest incident photon to current efficiency of 16%at wavelength of 340 nm,2.8-fold higher than that of the bare CdS photoanode.The research shows that the enhanced photoelectrochemical water splitting performance of the sample is ascribed to the efficient charge separation and transport,which is achieved by the cooperative action of the p-n junction and the type-II energy alignment.(3)Preparation and photoelectric properties of the TiO2@Ni(OH)2 nanorod arrays heterostructure.A novel three-dimensional hierarchical TiO2@Ni(OH)2 heterostructure has been constructed via a simple electrochemical deposition of the Ni(OH)2 nanosheets onto the surfaces of the TiO2 nanorod arrays.The characterization results show that the Ni(OH)2 nanosheets self-assemble into a three-dimensional hierarchical structure.The performance tests show that the three-dimensional TiO2@Ni(OH)2 photoanode has significantly enhanced absorption capacity of the ultraviolet light.It obtains a photocurrent density of up to 0.75 mA/cm2,1.5-fold that of the pure TiO2 photoanode and achieves a maximum solar-to-hydrogen conversion efficiency of 0.48%at 0.35 V vs.RHE,about 1.5-fold higher than that of the bare TiO2 photoanode.The research shows that the enhanced photoelectrochemical water splitting performance of the sample is ascribed to the efficient charge separation and transport,which is achieved by the cooperative action of the p-n junction and the type-Ⅱ energy alignment. |
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