Heterojunction of Zinc Blende/Wurtzite in Zn_1–xCd_xS Solid Solution for Efficient Solar Hydrogen Generation: X-ray Absorption/Diffraction Approaches

Abstract

In the past decade, inorganic semiconductors have been successfully demonstrated as light absorbers in efficient solar water splitting to generate chemical fuels. Pseudobinary semiconductors Zn1-xCdxS (0≤x≤1) have exhibited a superior photocatalytic reactivity of H2 production from splitting of water by artificial solar irradiation without any metal catalysts. However, most studies had revealed that the extremely high efficiency with an optimal content of Zn1-xCdxS solid solution was determined as a result of elevating the conduction band minimum (CBM) and the width of bandgap. In addition to corresponding band structure and bandgap, the local crystal structure should be taken into account as well to determine its photocatalytic performance. Herein, we demonstrated the correlations between the photocatalytic activity and structural properties that were first studied through synchrotron X-ray diffraction and X-ray absorption spectroscopy. The crystal structure transformed from zinc blende to coexisted phases of major zinc blende and minor wurtzite phases at a critical point. The heterojunction formed by coexistence of zinc blende and wurtzite phases in the Zn1-xCdxS solid solution can significantly improve the separation and migration of photoinduced electron-hole pairs. Besides, X-ray absorption spectra and UV-vis spectra revealed that the bandgap of the Zn0.45Cd0.55S sample extended into the region of visible light because of the incorporation of Cd element in the sample. These results provided a significant progress toward the realization of the photoelectrochemical mechanism in heterojunction between zinc blende and wurtzite phases, which can effectively separate the charge-carriers and further suppress their recombination to enhance the photocatalytic reactivity.

Interface induce growth of intermediate layer for bandgap engineering insights into photoelectrochemical water splitting

“…3d . Beside two sets of clear lattice spacing (0.33 and 0.31 nm) corresponding to the (002) plane of the wurtzite CdS and (111) planes of the zinc blended ZnS, respectively 30 , several sets of lattice spacing of 0.31 and 3.2 nm with different orientations are detected in the interlayer of the css-NRs which caused by the passive diffusion (interface induction from CdS) of Zn ion to the CdS crystal to assemble Zn 1−x Cd x S 31 32 33 intermediate layer during the temperature-rise process. Figure S1 and 2 ( Supporting Information ) display the morphology of intermediate state (ZnS/CdS nanorods) which conforms to our expectation that Zn ion from amorphous ZnS shell can diffuse easily in the interface of ZnS/CdS without the imprisonment from ZnS crystal cell.…”

Nanostructured materials for photocatalysis

“…170 Sulfide-based solid solution photocatalysts have been extensively reported to be synthesized by continuous tuning of both CB and VB for efficient hydrogen production. [171][172][173][174] Binary sulfides including CdS found to be moderately active photocatalysts for H2 production (see section on binary photocatalysts), with inherent issues related to quick recombinations of photogenerated charge carriers and photo-corrosion under visible light (essentially limiting their use at a large scale [175][176][177][178] ).…”

Recent developments and perspectives in CdS-based photocatalysts for water splitting

“…Several other heterojunctions have been also reported, such as hexagonal-cubic CdS, and zinc blende-wurtzite Zn 1Àx Cd x S solid solutions. [232][233][234][235] Others have been formed from two SCs, such as Au-TiO 2 /CdS, CdS/CdSe, CdS/Co 0.85 Se, etc. 201,236 The enhancement in the activity can, therefore, be attributed to the built-in-electric eld thus created, which plays a key role in directing the charge ow.…”