Efficient Electron Transfer across a ZnO–MoS₂–Reduced Graphene Oxide Heterojunction for Enhanced Sunlight‐Driven Photocatalytic Hydrogen Evolution

Abstract

The development of noble metal-free catalysts for hydrogen evolution is required for energy applications. In this regard, ternary heterojunction nanocomposites consisting of ZnO nanoparticles anchored on MoS -RGO (RGO=reduced graphene oxide) nanosheets as heterogeneous catalysts show highly efficient photocatalytic H evolution. In the photocatalytic process, the catalyst dispersed in an electrolytic solution (S and SO ions) exhibits an enhanced rate of H evolution, and optimization experiments reveal that ZnO with 4.0 wt % of MoS -RGO nanosheets gives the highest photocatalytic H production of 28.616 mmol h g under sunlight irradiation; approximately 56 times higher than that on bare ZnO and several times higher than those of other ternary photocatalysts. The superior catalytic activity can be attributed to the in situ generation of ZnS, which leads to improved interfacial charge transfer to the MoS cocatalyst and RGO, which has plenty of active sites available for photocatalytic reactions. Recycling experiments also proved the stability of the optimized photocatalyst. In addition, the ternary nanocomposite displayed multifunctional properties for hydrogen evolution activity under electrocatalytic and photoelectrocatalytic conditions owing to the high electrode-electrolyte contact area. Thus, the present work provides very useful insights for the development of inexpensive, multifunctional catalysts without noble metal loading to achieve a high rate of H generation.

Dual II Heterojunctions Metallic Phase MoS2/ZnS/ZnO Ternary Composite with Superior Photocatalytic Performance for Removing Contaminants

“…The electrons on the valance band (VB) of MoS 2 , ZnS and ZnO are photoexcited and transferred to the conduction band (CB) under light irradiation. Some of the previous works have reported the CB position of ZnS (−1.04 V) and MoS 2 (−0.55 V) as more negative than that of ZnO (−0.31 V) . Therefore, the photogenerated electrons of MoS 2 and ZnS move to the CB of ZnO due to the different electronic potentials; the holes on the VB of ZnO were injected to the VB of MoS 2 and ZnS, respectively.…”

“…Some of the previous works have reported the CB positiono fZ nS (À1.04 V) and MoS 2 (À0.55 V) as more negative than that of ZnO (À0.31 V). [23,27] Therefore, the photogenerated electrons of MoS 2 and ZnS move to the CB of ZnO due to the different electronic potentials;t he holes on the VB of ZnO were injected to the VB of MoS 2 and ZnS, respectively.B ased on the reactive specie trapping tests (main reactive speciesa re h + and O 2 C À )a nd previous literature, ZnO forms at ype II heterojunction with MoS 2 and ZnS, respectively. [24a, 28] The dual II type heterojunctions play ak ey role in hinderingr ecombination of electron-hole pairs, resultingi nf ast electron transfer and high efficiency of electron-hole separation.…”

Preparation Of ZnO/Co3O4 Hollow Microsphere By Pollen‐biological Template And Its Application In Photocatalytic Degradation

“…The violet emission band at 469 nm can be attributed to the defect of ZnO gap, which is derived from the recombination of the VB hole with electrons. The blue emission band at 485 nm and the green emission band at 495 nm are attributed to surface states and oxygen vacancies in ZnO, respectively . The decrease of emission intensity of PL indicates that the electron‐hole recombination and the transfer of charge from the CB of the ZnO to the active sites are suppressed after the loading of Co 3 O 4 .…”

Ionic Liquid Originated Synthesis of N,P‐doped Graphene for Hydrogen Evolution Reaction

“…Therefore, a low cost and high efficient electrocatalyst for hydrogen evolution reaction (HER) is highly desired to decrease the overpotential and improve the electrolysis rate. Although Nobel metal‐based materials (e. g. Pt‐group metals) are the most frequently used HER catalysts due to their low overpotentials and high current densities, the high cost and scarce abundant have limited their widespread application . Recently, non‐noble metal based HER electrocatalysts, such as Mo 2 C, Co,N‐doped CNTs,, α‐MoB 2 and Co 9 S 8 ,, were prepared to address these issues with good HER activites while some of these materials could lose the catalytic activities during HER conditions and cause the detrimental environmental effects.…”