Manganese oxide at cadmium sulfide (MnOx@CdS) shells encapsulated with graphene: A spatially separated photocatalytic system towards superior hydrogen evolution

Abstract

Exploring novel, high-efficiency and durable catalysts is of vital importance to expedite current research on photocatalytic H2 evolution and address the energy and environmental issues. Herein, we rationally designed and synthesized a novel MnOx@CdS@GR photocatalyst with spatially separated dual co-catalysts for efficient visible-light-driven hydrogen production activity. In this spatially separated photocatalytic system, reduced graphene oxide (GR) and MnOx nanoparticles were anchored on the outer and inner surfaces of CdS shells acting as electron and hole collectors, respectively. The composition, microstructure and optical properties of the samples were thoroughly investigated. Photoluminescence spectra and photocurrent response as well as electrochemical impedance spectra were employed to reveal the separation and transfer ability of photo-generated charge carriers in the spatially separated MnOx@CdS@GR catalyst. Benefit from the synergistic effect including boosted light absorption capacity, enlarged specific surface area and increased separation and transfer efficiency of electron/hole pairs, the MnOx@CdS@GR exhibited superior H2 evolution performance, and the optimized H2-evolution rate reached a value of 5.45 mmol h−1 g−1, which is approximately 7.2 times than that of bare CdS. Moreover, this novel catalyst also displayed a long-term stability without apparent debasement in H2 evolution activity. Finally, the photocatalytic mechanism was proposed and discussed.