May 2, 2011 at 2:32 PM ET
Scientists have found and tested an abundant and inexpensive catalyst needed to make hydrogen fuel from sunlight and water, a necessary step on the road to the elusive clean, green hydrogen economy.
The new catalyst — molybdenum sulfide — is an alternative to platinum, an expensive and rare catalyst used to convert single ions of hydrogen split off from water into hydrogen gas.
"That's the very neat thing here, it is quite inexpensive and abundant," Jens Norskov, a chemical engineer with the Department of Energy's SLAC National Accelerator Laboratory at Stanford University, told me Monday.
The dream of a hydrogen economy stems from the fact that hydrogen is an energy dense and clean fuel — upon combustion, it releases water. The problem is that most hydrogen is produced from natural gas in a process that releases carbon dioxide, a greenhouse gas.
Hydrogen producing enzymes
An alternative method is to make hydrogen fuel from sunlight and water. The current process is called photo electrochemical, or PEC, water splitting. When sun hits the PEC cell, the solar energy is absorbed and used for splitting water molecules into hydrogen and oxygen, the DOE explains in a press release.
Progress, however, in the technology has been limited in part by the lack of cheap catalysts that can speed up the generation of hydrogen and oxygen. Platinum works, it's just expensive and rare.
"We would like to have something that is cheaper and more abundant," Norskov said.
His team used a theoretical approach to look for hydrogen producing enzymes, which are natural catalysts, from certain organisms. This led to molybdenum sulfide.
"This actually works quite well," he said. The second part of the research was combining the catalyst with a solar absorber — a chemical solar cell — to capture solar energy.
The absorber was designed by Norskov's colleagues the Technical University of Denmark. It consists of silicon arranged in closely packed pillars, each dotted with tiny clusters of molybdenum sulfide.
When the pillars were exposed to light, hydrogen gas bubbled up as quickly as if the team had used platinum, according to the DOE. A paper describing the research was published last week in Nature Materials.
This breakthrough addresses only one half of problem. The other is actually splitting the water, which Norskov says is the more difficult half. His group and others are working on finding the catalysts and sunlight absorbers to do that half as well.
Ultimately, this is the type of research that could lead to a clean, green economy.
"We are not there, let me stress that," Norkov told me. "But we are making progress one step at a time."
Many research teams around the world are working on this.
For example, a team led by Daniel Nocera at the Massachusetts Institute of Technology reported at a meeting of the American Chemical Society in March on the development of an artificial leaf technology that splits water.
Details on the makeup of the catalysts this team used are being kept a secret until publication in the scientific literature.
Ultimatley, Norskov said, realizing the goal of the clean, green hydrogen will require "the effort of many groups and the ingenuity of many people to take us there because it is a very hard problem."
More stories on the hydrogen economy: