MIT Artificial Leaf Produces Hydrogen Fuel

Science magazine reported this week on a revolutionary new technology that uses a catalyst-coated silicone “leaf” to produce hydrogen and oxygen gas. A group of researchers led by Daniel Nocera at MIT have been working on the problem for the past several years. Nocera founded the company Sun Catalytix to commercialize the technology. Sun Catalytix is currently seeking a patent for the invention.

Science reports:

The new device is a silicon wafer about the shape and size of a playing card coated on either side with two different catalysts. The silicon absorbs sunlight and passes that energy to the catalysts to split water into molecules of hydrogen and oxygen. Hydrogen is a fuel that can be either burned or used in a fuel cell to create electricity, reforming water in either case. This means that in theory, anyone with access to water can use it to create a cheap, clean, and available source of fuel.

Splitting water into its components of hydrogen and oxygen requires orchestrating two chemical reactions at the same time. Electrons must be stripped from hydrogen atoms in water, which causes water molecules to fracture into positively charged hydrogen ions, or protons, and negatively charged oxygen atoms. One catalyst then must knit together two oxygen atoms to form O2, while a second catalyst welds two hydrogen atoms with two electrons to make H2.

To make its artificial leaf, the MIT team spread its catalysts on opposite sides of a silicon wafer. The silicon absorbs sunlight and passes energetic, negatively charged electrons and positively charged electron vacancies to the catalysts on opposite sides that use them to make H2 and O2.

The solar collector is actually slightly more complex than a uniform slab of silicon. That was necessary because splitting water requires at least 1.23 volts, but a single silicon cell provides only about 0.5 volts. So the MIT team used a commercially available material with three silicon cells layered atop one another, giving them enough voltage to drive the water-splitting reaction.

When the device is placed in a clear jar and exposed to sunlight, it produces a steady stream of oxygen and hydrogen bubbling up to the surface. According to Nocera, the setup converts 5.5% of the energy in sunlight into hydrogen fuel. “You literally walk outside, hold it up, and it works,” Nocera says.

While the technology needs some more tweaking before it’s marketable, the potential uses are quite staggering. The artificial leaves could foreseeably be installed on the roofs of carports and attached to pressurized collection tanks. Fueling a hydrogen-compatible vehicle could become a fairly simple process — and most importantly, sustainable and carbon neutral (unlike fossil fuels). With rising fuel costs, the economic viability of fossil fuels from a household-expense perspective is quickly declining.

Tagged in: artificial leaves, hydrogen fuel, sustainability