A research team led by Linyou Cao at NC State has shown that a one-atom thick film of molybdenum sulfide (MoS2 ) may work as an effective catalyst for creating hydrogen.
Hydrogen holds great promise as an energy source, but the production of hydrogen from water electrolysis – freeing hydrogen from water with electricity – currently relies in large part on the use of expensive platinum catalysts. The new research shows that MoS2 atomically thin films are also effective catalysts for hydrogen production and – while not as efficient as platinum – are relatively inexpensive. (A release on the work can be found here, the paper can be found here.)
But what sets this apart from previous work on catalysts that are cheaper than platinum? We sat down with Linyou Cao to explain what’s going on.
The Abstract: How are your findings about using MoS2 as a catalyst for hydrogen production different from previous findings about other catalysts that are also cheaper than platinum?
Linyou Cao: It’s very simple. Our work is the first demonstration ever showing that atomic MoS2 thin films can be effective catalysts for hydrogen evolution. The MoS2 thin film is a semiconductor with an ideal bandgap for solar water splitting. In contrast to previous research you mentioned, whose materials are limited for applications in electrocatalytic water splitting (splitting water using electricity), our materials hold great promise for water splitting using solar light, which is the holy grail of the field of solar energy.
The Abstract: But aren’t there other semiconductors that can produce hydrogen from light energy – if coupled to a light absorber – without using electricity?
Cao: In short, monolayer MoS2 provides an unparalleled material platform for solar water splitting.
First, monolayer MoS2 has an ideal bandgap for solar water splitting, which none of the existing materials can compete with. The bandgap of monolayer MoS2 spans over the redox potentials of water. Its valence band is lower than the potential of water oxidation, and the conduction band is higher than that of water reduction. Additionally, its bandgap, ~1.8eV, nicely matches the spectrum of solar radiation.
Second, our work demonstrates that monolayer MoS2 combines the functionality of solar light absorption and catalysis. Unlike all the previous work, which typically requires a combination of two different materials – one for light absorption and the other for catalytic reaction – monolayer MoS2 provides a new platform for solar water splitting with both functions genetically integrated. This integration can dramatically facilitate the efficiency of transferring the photo-generated charges to drive the reactions, which is a huge challenge for the conventional two-material systems.
It’s important to note that this work has not demonstrated the water splitting yet, but points out the promise of monolayer MoS2 in that direction. This work has for the first time demonstrated that monolayer MoS2 is catalytically active for the hydrogen evolution reaction. The result is in stark contrast with the conventional wisdom in the community, which believes that only the edge sites of MoS2 can be catalytically active and that continuous MoS2 atomically thin films with little edges would be catalytically inactive.
The Abstract: Let’s cut to the chase here. Why should people care about this advance? And how far is it removed from commercial application?
Cao: This work is a significant advance in fundamental science. It demonstrates that monolayer MoS2 films are catalytically active for hydrogen evolution, which is in stark contrast with the conventional wisdom in the community.
This work may profoundly impact technological developments in two aspects. First, it paves the way for the development of monolayer MoS2 photocatalysts for solar water splitting, as we discussed above. Second, unlike the conventional strategy, which looks for increasing the number of edge sites to improve catalytic performance for hydrogen evolution, this work suggests that decreasing the thickness of MoS2 materials is a key factor for efficiently catalyzing the hydrogen evolution.
To the best of our knowledge, we are the only group in the world working on the catalysis of monolayer MoS2 films. This is because at this moment we have a unique capability to produce large-area (centimeter-scale) monolayer MoS2 films. This synthetic capability is required for the catalysis study.
This breakthrough is very promising, but is still at the early stage of technical development. We are currently working on using the MoS2 films for solar water splitting, and hopefully can have positive results soon.