Pennsylvania State University and Florida State University researchers are contributing to the hydrogen Molecular models representing a 2-D heterostructure made of graphene (gray background hexagonal lattice), and islands on top of hexagonal tungsten and molybdenum disulfide as well as an alloy of the two. (Source: Terrones Group/Penn State)economy with a lower cost, industrially scalable catalyst that drives a low-energy water-splitting process.

Production of hydrogen by steam reforming of methane releases carbon dioxide into the atmosphere. Other routes use waste heat from advanced nuclear power plants or concentrated solar power, both of which face technical challenges for commercial feasibility. Reliance on platinum catalysts is economically unattractive.

Molybdenum disulfide offers potential as a platinum replacement, but it is a semiconductor in its stable phase, with limited ability to conduct electrons. By adding reduced graphene oxide, a highly conducting form of carbon, and alloying the molybdenum disulfide with tungsten, the researchers solved this problem and reduced the Gibbs free energy of the molybdenum compound. The addition of tungsten lowers the electrical voltage required to split water by half, from 200 millivolts with pure molybdenum disulfide, to 96 millivolts with the tungsten-molybdenum alloy.

The catalytic activity of the alloy, formed as a thin film with alternating graphene and tungsten-molybdenum disulfide layers, is stable over time. The enhanced hydrogen evolution achieved with the new catalyst is mainly due to the lower energy barrier created by a favorable overlap of the d-orbitals from the transition metals and the s-orbitals of hydrogen.