Two-Dimensional Materials Get Into Hydrogen Gas Production

One of the inconvenient truths about fuel cells for powering automobiles—a key to the establishment of the so-called hydrogen economy—is that it is extremely costly and energy intensive to isolate hydrogen gas.

The last couple of years have produced research using different nanomaterials that can do the job. Last year, University of Buffalo researchers created silicon nanoparticles that generated hydrogen gas nearly instantaneously when water was added to them. In that process, the nanomaterial didn’t need light or electricity to produce the hydrogen. Of course, the downside was that producing the silicon nanoparticles required a fair amount of energy itself, so it wasn’t clear whether this was a viable solution to overcoming the energy costs of hydrogen production.

The main push in nanomaterials for hydrogen gas separation has been artificial photosynthesis approaches in which sunlight rather than electricity is used to split the hydrogen from a water molecule. These efforts stood in contrast to other nanomaterial solutions that entailed simply replacing the platinum catalyst in the standard electrocatalytic process with a nanomaterial.

Now researchers at North Carolina State University (NCSU) have demonstrated that molybdenum sulfide (MoS2) can be used as an effective catalyst for producing hydrogen gas in a solar water-splitting process.

In research published in the journal Nano Letters (“Layer-Dependent Electrocatalysis of MoS2 for Hydrogen Evolution”), the NCSU team demonstrated that while MoS2 it is not as effective a catalyst as platinum, its relative low cost could make it an attractive alternative.

“We found that the thickness of the thin film is very important,” says Dr. Linyou Cao, an assistant professor of materials science and engineering at NCSU, in a press release. “A thin film consisting of a single layer of atoms was the most efficient, with every additional layer of atoms making the catalytic performance approximately five times worse.”

The researchers also have indicated that MoS2 thin films have an ideal band gap for solar water splitting. In a Q&A with an NCSU blog, Cao said:

"The band gap 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 band gap, about 1.8eV, nicely matches the spectrum of solar radiation."

It should be interesting to see if this discovery that MoS2 makes for an ideal material in solar water splitting compares favorably to other nanomaterials used in artificial photosynthesis approaches.

Photo: North Carolina State University

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