Evidence for an Interface of Hybrid Cocatalysts Favoring Photocatalytic Hydrogen Evolution Kinetics

Hybrid cocatalysts have great application potential for improving the photocatalytic hydrogen evolution performance of semiconductors. The interfaces between components of hybrid cocatalysts make a great contribution to the improvement, but the associated mechanisms remain unclear. Herein, we prepared and tested three comparative CdS-based photocatalysts with NiS, NiS/Ni₉S₈, and Ni₉S₈ as the cocatalysts separately. The emphasis is placed on investigating the effect of the NiS/Ni₉S₈ interfaces on the photocatalytic hydrogen evolution performance of CdS. NiS/Ni₉S₈ exhibits a higher ability than NiS and Ni₉S₈ in making CdS a more active photocatalyst for water splitting. It shows that NiS, NiS/Ni₉S₈, and Ni₉S₈ perform similarly in terms of promoting the charge transfer and separation of CdS based on steady-state and time-resolved photoluminescence studies. At the same time, the linear sweep voltammetry and electrochemical impedance spectroscopy tests combined with the density functional theory calculations reveal that the component interfaces of NiS/Ni₉S₈ enable us to lower the water splitting activation energy, the charge-transfer resistance from the cocatalyst to sacrificial agent, and hydrogen adsorption Gibbs free energy. It is evidenced from this work that component interfaces of hybrid cocatalysts play a vital role in accelerating the dynamics of hydrogen evolution reactions.