KAUST team alters atomic composition of MoS2 to boost performance as water-splitting catalyst for H2 production
Researchers at KAUST have developed and used a novel way of increasing the chemical reactivity of a two-dimensional molybdenum disulfide material to produce a cheap and effective catalyst for water splitting to produce hydrogen. This technique may also have potential benefits for other manufacturing industries.
One route to hydrogen generation is by electrolysis: passing an electrical current through water via two electrodes to cause a chemical reaction that breaks the water molecule into its component hydrogen and oxygen atoms. The speed of this hydrogen evolution reaction can be increased using a catalyst on the electrodes. Platinum is a perfect material for the job, but is it very expensive.
Two-dimensional layered transition metal dichalcogenide (TMD) materials such as Molybdenum disulfide (MoS2) have been recognized as one of the low-cost and efficient electrocatalysts for hydrogen evolution reaction (HER). The crystal edges that account for a small percentage of the surface area, rather than the basal planes, of MoS2 monolayer have been confirmed as their active catalytic sites. As a result, extensive efforts have been developing in activating the basal planes of MoS2 for enhancing their HER activity.
Here, we report a simple and efficient approach—using a remote hydrogen-plasma process—to creating S-vacancies on the basal plane of monolayer crystalline MoS2; this process can generate high density of S-vacancies while mainly maintaining the morphology and structure of MoS2 monolayer. The density of S-vacancies (defects) on MoS2 monolayers resulted from the remote hydrogen-plasma process can be tuned and play a critical role in HER, as evidenced in the results of our spectroscopic and electrical measurements.
The H2-plasma treated MoS2 also provides an excellent platform for systematic and fundamental study of defect-property relationships in TMDs, which provides insights for future applications including electrical, optical and magnetic devices.—Cheng et al.
Molybdenum disulfide is a two-dimensional material very similar to graphene. Previous experimental and theoretical results have verified its excellent catalytic potential and indicated that the hydrogen evolution reaction takes place at its jagged edges, while its flat surface planes remain chemically inert.Lain-Jong Li, Professor of Material Science and Engineering at KAUST, with colleagues from the National Chiao Tung University (Taiwan) and the National Applied Research Laboratories in Taiwan created their molybdenum disulfide using a process called chemical vapor deposition.
A sample was then transferred to a graphite substrate and placed in a vacuum chamber in which the researchers created a hydrogen plasma. This process removed some of the sulfur atoms from the surface of the sample. By adjusting the sample’s time in the plasma, the team could control the density of these sulfur vacancies.
A monolayer of molybdenum disulfide is only reactive for reducing water to hydrogen at its edge. But we discovered an efficient way to create active sites on its planar surface, largely activating surface reactivity.—Lain-Jong Li
The researchers confirmed the changes in catalytic activity and also found a useful offshoot of this process. Controlling the atomic composition of molybdenum disulfide could also lead to the development of electrical, optical and magnetic devices.
Next we hope to move beyond the beaker and put the catalysts in practical flow cell tests.—Lain-Jong Li
Chia-Chin Cheng, Ang-Yu Lu, Chien-Chih Tseng, Xiulin Yang, Mohamed Nejib Hedhili, Min-Cheng Chen, Kung-Hwa Wei, Lain-Jong Li (2016) “Activating basal-plane catalytic activity of two-dimensional MoS2 monolayer with remote hydrogen plasma,” Nano Energy, Volume 30, Pages 846-852 doi: 10.1016/j.nanoen.2016.09.010