CdS with tunable crystalline phase structures: controllable preparation and enhanced photocatalytic properties

The crystal structure of CdS influences the energy band gap; therefore, its suitability as a semiconductor photocatalyst for solar-to-hydrogen energy conversion. By simply adjusting the temperature of the hydrothermal reaction, CdS samples with different crystal phases were prepared, and their photocatalytic hydrogen production performance was tested. XRD confirmed the successful preparation of the two catalysts. TEM results revealed that the (111) and (100) crystal planes corresponded to the cubic and hexagonal CdS structures of the two catalysts. The band gap values of cubic phase and hexagonal phase CdS were 2.24 eV and 2.17 eV, respectively. Cubic CdS exhibited excellent activity, which was considerably higher than that of hexagonal CdS, for the photocatalytic hydrogen evolution reaction. Electrochemical impedance spectroscopy results showed that cubic CdS exhibits a smaller arc radius and lower resistance. The conduction potential of the two CdS phases was further calculated based on the Mott–Schottky plots, revealing that the conduction potential of cubic CdS is more negative than that of hexagonal CdS. Therefore, cubic CdS exhibits higher carrier migration rate and charge separation efficiency than hexagonal CdS, resulting in higher photocatalytic activity.