Wednesday, July 30, 2008

Cheaper Splitting of Water to H2 and O2

Brian Westenhaus at NewEnergyandFuel describes a new and improved approach to splitting water into its constituent gases, H2 and O2. Using titanium dioxide nanotubes plus copper titanium nanotubes, the splitting is done cheaply and in an orderly fashion:
The clever innovation is a “photoelectrochemical” diode that does a “photolysis” of water. New words now. The diode part comes from the light entering on one side, doing one part of the job, continuing across the substrate and energizing the other side to do the other part of the job, a one way only process. A light wave thus stimulates the light facing side, which is titanium dioxide with a doping of iron soaking up the ultraviolet light in the 300-to 400-nanometer range. Passing over to the other side the light in the 400 to 885 nanometer range energizes the copper titanium side. The two materials thus use the full spectrum of the light segment of the electromagnetic spectrum.

The titanium dioxide layer produces oxygen and the copper titanium layer produces hydrogen. Very neat indeed. So when you hear its only 0.30% efficient one isn’t so disappointed as it’s from a very wide range of light, it’s a first effort, and very low cost. Grimes suggests that perhaps as high as 10% efficiency is possible as no optimization has taken place. But the proof of concept works; the materials and construction offer that the devices are photo stable so lasting a very long time.

The other outstanding point is the device separates the oxygen and hydrogen in the course of operation. Grimes’ process is far more sophisticated than just the innovative materials and construction. The building up process itself is quite interesting. In Grimes’ photoelectrochemical diode, one side is a nanotube array of electron donor material – n-type material – titanium dioxide, and the other is a nanotube array that has holes that accept electrons - p-type material – cuprous oxide titanium dioxide mixture. P and n-type materials are common in the semiconductor industry. Grimes has been making n-type nanotube arrays from titanium by sputtering titanium onto a surface, anodizing the titanium with electricity to form titanium dioxide and then annealing the material to form the nanotubes as used in other solar applications. He makes the cuprous oxide titanium dioxide nanotube array in the same way and can alter the proportions of each metal. _NEF
This is an early example of the clever use of the nanorealm to combat macro-stupidity in the everyday world.

Hydrogen has many uses in various industrial processes, and will be used more often in the renewable bio-energy field to process next generation biodiesels and renewable natural gas. If the splitting of water becomes efficient enough, photovoltaics/H2 fuel cells combinations may be a viable approach to 24 hour home energy. In fact, if the process is efficient enough, it may scale up to industrial levels of energy storage.

Hydrogen is not the best fuel for motor vehicles. Methanol, for example, is far better. But a clever innovator could probably think of at leas a million and one good uses for hydrogen, given the time.

Labels: ,


Blogger Snake Oil Baron said...

Whenever a means for producing a chemical like molecular hydrogen or ethanol using less energy or money it is often derided by those who are worried about it distracting from their favorite energy source of the future but like you said in regards to hydrogen, they are important industrial chemicals. As they become more available at lower costs they can be used for applications which would otherwise involve more expensive and energy intensive methods or using more hazardous chemical intermediates or waste products.

4:03 PM  

Post a Comment

Subscribe to Post Comments [Atom]

<< Home

Newer Posts Older Posts