The Artificial Leaf

Dean Sigler Electric Powerplants 0 Comments

Daniel Nocera, Henry Dreyfus Professor of Energy and professor of chemistry at Massachusetts Institute of Technology (MIT), has caused a stir in the scientific community and attracted press attention including a recent feature article in the May 14 New Yorker.

MIT’s own press release makes it sound all too simple and immediately appealing. “The artificial leaf — a silicon solar cell with different catalytic materials bonded onto its two sides — needs no external wires or control circuits to operate. Simply placed in a container of water and exposed to sunlight, it quickly begins to generate streams of bubbles: oxygen bubbles from one side and hydrogen bubbles from the other. If placed in a container that has a barrier to separate the two sides, the two streams of bubbles can be collected and stored, and used later to deliver power: for example, by feeding them into a fuel cell that combines them once again into water while delivering an electric current.”

Dr. Nocera created the playing card-sized device to demonstrate the low-budget, relatively inefficient technology that could provide small amounts of hydrogen fuel to be used to generate small amounts of electricity for individuals in developing countries.  For that reason, the leaf’s modest output was ideal for those with modest expectations.

That also seems to be a point of concern for those who would like a more industrial-size program to generate cheap hydrogen.  The playing card form factor is a nice introduction to the technology, and as shown in the video, visually appealing, but requires far larger sizes to make even minimally practical outputs. According to David Owens’ article in the New Yorker, it would take an artificial leaf the size of a door to generate enough hydrogen to power a 100-Watt light bulb through the night.  This is a goal for similar programs, such as those which distribute solar-powered lights to poor regions.  Productivity in a village picks up when light is available beyond sunset, and children can read and study into the night, enhancing their education.

The “leaf” is made of inexpensive materials bound onto a sheet of silicon.  One side has a layer of a cobalt-based catalyst that releases oxygen and the other side has a layer of a nickel-molybdenum-zinc alloy, which release hydrogen.  The device seems to be long-lasting and maintenance free, and can be used in even dirty water, often a given in poor countries.

If the program can develop a way to collect the gases, store them in a relatively low-pressure vessel, and use the output to generate light, or to cook, it would be a breakthrough, since indoor cooking with wood, dung, and other materials causes enormous health problems in poor countries.

Tata Industries is working with Nocera to create a commercial product line for Inda based on the technology, and Nocera’s former student, Steven Reese now works at Sun Catalytix, “a company started by Nocera to commercialize his solar-energy inventions, along with five other researchers from Sun Catalytix and MIT.”

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