The team’s new analysis shows that efficiencies of 16 percent or more should now be possible
Bringing the concept of an “artificial leaf” closer to reality, a team of researchers at MIT has published a detailed analysis of all the factors that could limit the efficiency of such a system. The new analysis lays out a roadmap for a research program to improve the efficiency of these systems, and could quickly lead to the production of a practical, inexpensive and commercially viable prototype.
Such a system would use sunlight to produce a storable fuel, such as hydrogen, instead of electricity for immediate use. This fuel could then be used on demand to generate electricity through a fuel cell or other device. This process would liberate solar energy for use when the sun isn’t shining, and open up a host of potential new applications.
The new work is described in a paper this week in the Proceedings of the National Academy of Sciences by associate professor of mechanical engineering Tonio Buonassisi, former MIT professor Daniel Nocera (now at Harvard University), MIT postdoc Mark Winkler (now at IBM) and former MIT graduate student Casandra Cox (now at Harvard). It follows up on 2011 research that produced a “proof of concept” of an artificial leaf — a small device that, when placed in a container of water and exposed to sunlight, would produce bubbles of hydrogen and oxygen.
The device combines two technologies: a standard silicon solar cell, which converts sunlight into electricity, and chemical catalysts applied to each side of the cell. Together, these would create an electrochemical device that uses an electric current to split atoms of hydrogen and oxygen from the water molecules surrounding them.
The goal is to produce an inexpensive, self-contained system that could be built from abundant materials. Nocera has long advocated such devices as a means of bringing electricity to billions of people, mostly in the developing world, who now have little or no access to it.
“What’s significant is that this paper really describes all this technology that is known, and what to expect if we put it all together,” Cox says. “It points out all the challenges, and then you can experimentally address each challenge separately.”
Winkler adds that this is a “pretty robust analysis that looked at what’s the best you could do with market-ready technology.”
The original demonstration leaf, in 2011, had low efficiencies, converting less than 4.7 percent of sunlight into fuel, Buonassisi says. But the team’s new analysis shows that efficiencies of 16 percent or more should now be possible using single-bandgap semiconductors, such as crystalline silicon.
“We were surprised, actually,” Winkler says: Conventional wisdom held that the characteristics of silicon solar cells would severely limit their effectiveness in splitting water, but that turned out not to be the case. “You’ve just got to question the conventional wisdom sometimes,” he says.
via Science Daily
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