Caltech's latest "artifical leaf" design to crack water into H2 & O2. IEEE Spectrum

[gary]

In a September 1 2015 article at the Institute or Electrical and Electronic
Engineering (IEEE) Spectrum Magazine web site, Evan Ackerman reports on
the development of a new passive "artificial leaf" design developed
at Caltech that when immersed in water and exposed to sunlight cracks
the water into oxygen and hydrogen.

Originally Posted by Evan Ackerman, IEEE Spectrum

People have been working on these, but Caltech has just made an enormous amount of progress with an artificial leaf that, according to the researchers, "shatters all of the combined safety, performance, and stability records for artificial leaf technology by factors of 5 to 10 or more."

Originally Posted by Evan Ackerman, IEEE Spectrum

The Caltech design uses two electrodes (a photoanode and a photocathode) separated by a membrane. The photoanode is made of gallium arsenide, which is an excellent light absorber, but tends to oxidize when exposed to water. A layer of titanium dioxide helps keep the photoanode stable and protected, and a layer of nickel on top of that acts as a catalyst. When exposed to sunlight, the photoanode oxidizes water molecules, generating oxygen (O2) as well as protons and electrons, which pass through the membrane and are recombined by the photocathode into hydrogen (H2). Put all of this together, and you end up with a single, fully integrated system that cracks water into oxygen and hydrogen when you put it in the sun:

...

It's all one piece, there's no wiring, and the active electrocatalysts are all “earth abundant” (another way of saying affordable).

...

Having said that, it's important to note that right now, you can get significantly more energy from sunlight (about 20 percent efficiency) by using a conventional solar cell to convert it into electricity rather than hydrogen. It's also way cheaper to do this, since solar cells are an established industry. But, using that electricity to make hydrogen through electrolysis isn't particularly efficient: with a non-concentrator silicon photovoltaic cell and a commercial electrolyzer, you're looking at a complex system that can convert sunlight into hydrogen with an efficiency of about 12 percent. An artificial leaf that could approach the efficiency of existing sunlight-to-hydrogen converters in a much simpler (and eventually cheaper) way is appealing.

Article and video here -
http://spectrum.ieee.org/energywise/...-from-sunlight