Preparation Of Semiconductive Nanorod Arrays And Their Photoelectrochemical Properties

Making full use of the enormous solar energy on the Earth is a promising solution toresolve the energy crisis and energy-related environmental problems. Nowadays, there arestill numbers of obstacles to achieve efficient capture, conversion, and storage of the solarenergy. Photoelectrochemical(PEC) water splitting offers an ideal route to realize theconversion of solar energy to renewable and clean hydrogen fuel. At present, the crux of thisenergy conversion process lies in seeking highly efficient and stable photoelectrodes. Avariety of semiconductor materials have been investigated as candidates. However, thehighest energy conversion efficiency achieved so far can hardly meet the minimumrequirement for industrial applications. This efficiency is basically determined by the intrinsicproperties of the semiconductor photocatalysts. It is necessary to use different approaches tomodify those as-known photocatalysts in addition to searching for new candidates. Thesemodifications include bandgap engineering, deposition of cocatalyst, construction ofheterostructures, etc. And the properties like crystalline, electrical structure and morphologyof photocatalysts which dominate their photocatalytic properties should be modified in thesynthetic processes at nanoscale.In this thesis, Zn O nanorod arrays are chosen as the object of research. Via sequentialhydrothermal and ion exchange processes, the Zn O/Zn S/Cd S/Cu In S2 andZn O/Zn Se/Cd Se/Cux S core-shell nanorod arrays with high photocatalytic activity and goodstability were fabricated. The influences of core-shell heterostructures and specific functionallayers on the photoelectrochemical performances were explored, also the mechanisms for theimprovements of photoelectrochemical properties were proposed. The details are outlined asfollows:(1) Regular and perpendicular Zn O nanorod arrays were fabricated on FTO substrates bya hydrothermal method. After a series of ion exchange processes, the Zn O samples react andconverse to Zn O/Zn S/Cd S/Cu In S2 nanorod arrays. Zn O/Zn S/Cd S/Cu In S2 samples withdifferent chemical compositions were fabricated via the modifications of reaction conditions.The optimized Zn O/Zn S/Cd S/Cu In S2 sample demonstrates much higher visible-lightphotocatalytic activity(10.5 m A/cm2) and better stability than the Zn O(0.14 m A/cm2),Zn O/Zn S(0.36 m A/cm2), Zn O/Zn S/Cd S(2.40 m A/cm2), Zn O/Cd S/Cu In S2(2.40 m A/cm2),and Zn O/Zn S/Cu In S2(0.59 m A/cm2) samples. The relationship between the improvement ofphotoelectrocatalytic properties and the core-shell heterostructures as well as specificfunctional layers was inspected.(2) Originated from the Zn O nanorod arrays, the Zn O/Zn Se/Cd Se nanorod arrays weresynthesized via continuous hydrothermal and ion exchange processes. A Cux S layer wasdeposited on the surface by a SILAR(successive ion layer absorption and reaction) techniqueto form the Zn O/Zn Se/Cd Se/Cux S sample. As demonstrated in the photoelectrochemical tests,the visible-light photocatalytic activities of the Zn O/Zn Se/Cd Se sample(37.8 m A/cm2) aremuch higher than those of the Zn O(0.14 m A/cm2), Zn O/Zn Se(0.27 m A/cm2) and Zn O/Cd Se(30.9 m A/cm2) samples, while it suffers from severe photocorrosion. Upon the deposition ofthe Cux S layer, its photocatalytic activity(43.6 m A/cm2) is further improved, and the stabilityis significantly enhanced. The mechanism for the improvement of photoelectrochemicalproperties was explored.