Mar 7, 2010

Breakthrough Producing Hydrogen from Water + Sunlight

solar hydrogen breakthrough image
Image: Angewandte Chemie, Wiley

Sunlight + Water = Hydrogen Gas
Scientists at the University of East Anglia, led by Dr. Thomas Nann, report a breakthrough in the production of hydrogen from water using the energy of sunlight. Amidst all the hype about a potential hydrogen economy, which would rely upon the highly energetic and clean burning hydrogen atom, one of the big questions has been whether sufficient hydrogen can be produced without using yet more energy to create the hydrogen. Typical production methods include stripping hydrogen from other fuels like methane or using electrolysis to split the hydrogen out of water. But with efficiencies between 20 and 40% for producing energy from traditional photovoltaic processes, the hydrogen economy cannot be solar powered. Or can it?

The Hydrogen Tipping Point?
In fact, producing H2 is so energy intensive that some have even referred to hydrogen as more "battery" than fuel. Breakthroughs in the generation of hydrogen from solar power could tip the balance in favor of hydrogen fuel cell technologies. Enter Thomas Nann and colleagues. They report 60% efficiency for a process in which hydrogen is produced from water by the photons in light that strike a specially designed submersed electrode.

The concept of water + sunlight = hydrogen is not new. But turning 60% of the energy in light into hydrogen power is. The trick lies in the nanophotocathode used by Nann's team. A gold electrode coated with nanoclusters of indium phosphide absorb incoming photons of light (that is the wavy line marked "hv" in the image). The nanoclusters then pass electrons liberated by the sun's energy into an iron-sulfur complex which acts like a match-maker between the negatively charged electron and a hydrogen proton in the surrounding water molecules. Gaseous hydrogen results.

Better Net
The team credits the "better net" effect for the efficiency breakthrough. The indium phosphide nanoclusters are 400 times more likely to grab a photon passing through them than some organic molecules that have been used to split water. Another breakthrough is the durability of the gold-nanocluster electrodes. Other materials have deteriorated under the bombarding rays of sunlight, limiting their utility for an industrial hydrogen generation process.

The next step is to demonstrate the process with cheaper materials. The scientists report there is no special reason to use gold (nor platinum which was used as the second electrode to complete the circuit) -- other than that these nobel metals happened to be lying about the lab.

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