Hollow microspheres consisting of uniform ZnxCd1-xS nanoparticles with noble-metal-free co-catalysts for hydrogen evolution with high quantum efficiency under visible light

Abstract

Utilizing solar energy in order to produce hydrogen from water is one of the key technologies to deal with energy and environment issues. A photocatalyst with a small band gap, good charge separation, and high stability plays an important role in this process. Recently, zinc cadmium sulfide (ZnxCd1-xS) has caught researchers’ attention due to its unique photocatalytic properties such as the wide range of visible light energy absorption and strong stability during water splitting. Moreover, a unique feature of this semiconductor is the capability of modifying its band gap structure by changing the Zn/Cd ratio. Herein, a series of ZnxCd1-xS solid solutions was synthesized by utilizing metal-glycerate followed by calcination in air and sulfuration under flowing H2S. As a result, a homogeneous hexagonal wurtzite ZnxCd1-xS solid solution could produce hydrogen in a wide range of visible light region. Moreover, using MoS2 as a cocatalyst resulted in the same amount of hydrogen as Pt. The best result was obtained for the Zn30Cd70S solid solution that showed a hydrogen evolution of 12 mmol h−1 g−1 under solar simulator. The calculated quantum efficiencies (QE) in visible light region are: 46.6% at 400 nm to 23.4% at 500 nm as well as 11.3% at 550 nm. There are among the highest QE that have been ever reported for this kind of material under visible light region.