is like a sheet of paper: a large plain with very little edge. But our material is highly porous. What we see in the images are short, 5- to 6-nanometer planes and a lot of edge, as though the material had bore holes drilled all the way through."

A thin, flexible film developed at Rice University shows excellent potential as a hydrogen catalyst or as an energy storage device. The two-dimensional film could be a cost-effective component in such applications as fuel cells. Credit: Tour Group/Rice University

The new film was created by Tour and lead authors Yang Yang, a postdoctoral researcher; Huilong Fei, a graduate student; and their colleagues. It catalyzes the separation of hydrogen from water when exposed to a current. "Its performance as a HER generator isas good as any molybdenum disulfide structure that has ever been seen, and it's really easy to make," Tour said.

While other researchers have proposed arrays of molybdenum disulfide sheets standing on edge, the Rice group took a different approach. First, they grew a porous molybdenum oxide film onto a molybdenum substrate through room-temperature anodization, an electrochemical process with many uses but traditionally employed to thicken natural oxide layers on metals.

The film was then exposed to sulfur vapor at 300 degrees Celsius (572 degrees Fahrenheit) for one hour. This converted the material to molybdenum disulfide without damage to its nano-porous sponge-like structure, they reported.

The films can also serve as supercapacitors, which store energy quickly as static charge and release it in a burst. Though they don't store as much