Stacking design in photocatalysis: synergizing cocatalyst roles and anti-corrosion functions of metallic MoS2 and graphene for remarkable hydrogen evolution over CdS

Abstract

CdS has been regarded as a promising visible-light-response photocatalyst in H₂ production while its practical application is often limited by low photoactivity and serious photocorrosion. To tackle these problems, traditional CdS based core–shell and supported photocatalysts have been widely developed but they also suffer from intrinsic structural drawbacks. Herein, a novel stacked nanostructure with CdS embedded at interfaces between graphene supports and metallic MoS₂ overlayers has been designed to eliminate the shortages and achieve outstanding photocatalytic performance, which reaches an optimum H₂ production rate of 14.4 mmol g_cat⁻¹ h⁻¹ and realizes an apparent quantum efficiency of 23.7% at 420 nm without obvious deterioration of activity in 20 h cyclic testing, far exceeding that of pure CdS by a factor of 17.9 times. The enhanced photocatalytic performance is mainly ascribed to the synergistic effects of MoS₂ and graphene: (1) the intimate contact between the CdS core and MoS₂ shell with a large interfacial area favors the transfer of photogenerated electrons to MoS₂ cocatalysts, while a high-percentage 1T-phase provides an excellent electron mobility in the MoS₂ cocatalysts and a high density of active sites for H₂ evolution; (2) CdS cores are protected by MoS₂ and graphene from photocorrosion, in which photogenerated holes are quickly transferred to the MoS₂ shell and isolated from the sulfide surface, while excessive electrons in CdS are shuttled to adjacent MoS₂ outer layers by graphene supports for H₂ evolution in reducing their recombination with holes in the MoS₂ shell and increasing the number of MoS₂ sites available for the proton reduction reaction. The stacking design can be extended to the fabrication of other highly efficient photocatalytic systems.