Graphene Supported MoS₂ Structures with High Defect Density for an Efficient HER Electrocatalysts

Abstract

The development of novel efficient and robust electrocatalysts with sufficient active sites is one of the key parameters for hydrogen evolution reactions (HER) catalysis, which plays a key role in hydrogen production for clean energy harvesting. Recently, two-dimensional (2D) materials, especially those based upon transition metal dichalcogenides such as molybdenum disulfide (MoS2), have gained attention for the catalysis of hydrogen production because of their exceptional properties. Innovative strategies have been developed to engineer these material systems for improvements in their catalytic activity. Toward this aim, the facile growth of MoS2 clusters by sulfurization of molybdenum dioxide (MoO2) particles supported on reduced graphene oxide (rGO) foams using the chemical vapor deposition (CVD) method is reported. This approach created various morphologies of MoS2 with large edges and defect densities on the basal plane of rGO supported MoS2 structures, which are considered as active sites for HER catalysis. In addition, MoS2 nanostructures on the surface of the porous rGO network show robust physical interactions, such as van der Waals and π–π interactions between MoS2 and rGO. These features result in an improved process to yield a suitable HER catalyst. In order to gain a better understanding of the improvement of this MoS2-based HER catalyst, fully atomistic molecular dynamics (MD) simulations of different defect geometries were also performed.

Defects Enhance the Electrocatalytic Hydrogen Evolution Properties of MoS2‐based Materials

“…[25] Defect-rich conductive carbon supports can also prevent the aggregation of MoS 2 particles due to the robust physical interactions (van der Waals [43] and π-π interactions) between MoS 2 and the carbon support. [25] Furthermore, a defective carbon support can stabilize unstable, sensitive Svacancies ( Figure 1a). [28] Overall, a defective, conductive carbon support is essential to enhancing the hydrogen evolution performance of MoS 2 -based catalysts.…”

“…Copyright 2020 American Chemical Society. [25] (d) Synthetic pathways of O, PÀ MoS 2 , and PÀ MoS 2 with different structures. Copyright 2020 Wiley-VCH.…”

“…They explored the effects of the RGOÀ MoS 2 mass ratio and annealing desulfurization on the HER activity of the catalyst (Figure 5c). [25] The sulfurization time tuned the geometry of MoS 2 and created defects to optimize its catalytic activity, and a time of 30 min was optimal when the RGOÀ MoO 2 mass ratio was 1 : 2. The resulting defects increased the number of active sites and triangular structures that increased the active duration of system.…”

“…Considering the disadvantages of 2H-MoS 2 , many researchers have synthesized MoS 2 hydrogen evolution electrocatalysts with defects. [17,[23][24][25][26][27][28][29][30] Some have also used calculations to analyze the role of different defects in catalysis. [17,31,32] Vacancies, particularly S-vacancies, are used to activate the MoS 2 inert basal plane; edge defects, such as holes and cracks, can increase the amount of hydrogen evolution active sites; and defective conductive carbon supports can improve the stability of MoS 2 particles while preventing agglomeration.…”

MoS2-Carbon Inter-overlapped Structures as Effective Electrocatalysts for the Hydrogen Evolution Reaction

“…The FTIR spectra of the OLA-protected monolayer MoS2 compared to the MoS2-carbon interoverlapped structure is shown in Figure 2, and the monolayer MoS2 (before carbonization) showed the presence of characteristic peaks corresponding to the presence of OLA. These included NH2 (722 cm −1 ), C-H (1455 cm −1 ), oily groups (CH2 at 2842 cm −1 and CH3 at 2914 cm −1 ) [37,38], amine (N-H 3402 cm −1 ) and C=C (1631cm −1 ) [21]. However, after carbonization, only the C=C remained, while all the other functional groups were removed, as shown in Figure 2b.…”