Optimizing the precursor of sulfur source for hydrothermal synthesis of high performance CdS for photocatalytic hydrogen production.

Hui Li,Xianliang Fu,Xiuzhen Zheng,Sugang Meng,Ziqun Wang,Lihua Liu,Shifu Chen

doi:10.1039/c8ra00250a

Abstract

Although the CdS photocatalyst has been extensively investigated, a rational hydrothermal synthesis route is still required to prepare highly active CdS for H2 evolution reaction (HER). To optimize the precursor of the sulfur source, three prevalent organic sulfur sources of thiourea (TA), thioacetamide (TAA) and l-cysteine (l-Cys) were used for hydrothermal synthesis of CdS. Their effects on the crystallographic structure, morphology, optical property, band structure, and photocatalytic HER performance of the products were then investigated systematically. The results indicated that hexagonal branched dendritic structure CdS (S-TA) could be produced in TA solution and showed the highest HER activity due to the branched 1D structure, the smallest interfacial electron transfer resistance and the most negative conduction band bottom (Ecb). Whereas in TAA, spherical CdS (S-TAA) with a mixed phase of hexagonal and cubic was obtained. The mixed phase structure and the more positive Ecb of S-TAA lead to a considerably lower HER activity than that of S-TA. Poorly crystallized hexagonal CdS nanoparticles (S-Cys) were prepared in l-Cys and showed the lowest HER performance as its Ecb is very near to H+ reduction potential. Thus, compared to T-AA and l-Cys, TA is a more suitable sulfur source for hydrothermal preparation of highly active CdS for HER.

Highlights

As a clean and high density energy carrier, H2 has been considered as an ideal alternative to fossil fuel to solve the increasing energy demands and the serious environmental issues caused by extensive use of fossil fuels.[1]
It indicates that the samples prepared in TA and L-Cys solutions (S-TA and S-Cys) have a wurtzite structure and the diffraction patterns can be indexed to hexagonal CdS (h-CdS) with lattice constants of a 1⁄4 4.14 and c 1⁄4 6.71 A, which agree well with the values of JCPDS No 77-2306
When TAA was used as the sulfur source, the resulted sample (S-TAA) was a mixture of h-CdS and metastable cubic CdS (c-CdS)[30] (JCPDS No 89-440), which is consistent with Dai's work.[50]

Summary

Introduction

As a clean and high density energy carrier, H2 has been considered as an ideal alternative to fossil fuel to solve the increasing energy demands and the serious environmental issues caused by extensive use of fossil fuels.[1] at present H2 is mainly produced by steam reforming of nonrenewable fossil fuel or electrolysis of water. These high-energy consumption processes are unsustainable, environmentally unfriendly, and cost-expensive. The key challenge for photocatalytic HER is to develop a highly efficient visible light photocatalyst which essentially determines the harvesting of light and the conversion efficiency of solar to H2

Objectives

Results

Conclusion