A Better Way to Make Hydrogen Fuel?

Energy bills got you in a bind?  A new technology discovered nearly by accident may help reshape our energy future, and help make hydrogen a cost effective fuel source.

Titanium dioxide (titania) is probably one of the most widely used and least known substances in the world. It’s found in everything from sunblock to solar cells and even toothpaste. Perhaps more interestingly though, is the fact that titania can be used to release hydrogen from water.

It’s been known since the late nineteen sixties, due to the work of Akira Fujishima , that titania functions as a photocatalyst , decomposing water into hydrogen and oxygen in the presence of light and electricity, in a process known as the Honda-Fujishima effect . For some time researchers have been investigating better ways to harness this effect to produce hydrogen from sunlight and water in an economically viable way. Now, a research team from Northeastern University and the National Institute of Standards and Technology (NIST) may have accidentally discovered how to make that possible.

Why Hydrogen?

Hydrogen is combustible in oxygen, just like fossil fuels. The difference is that hydrogen burns cleanly. When burnt it combines with oxygen to form water and nothing else. Hydrogen is also readily available as a constituent of water. Most of our planet is covered in water. The problem thus far has being releasing hydrogen from water in an economically viable way. Hydrolysis is one way of harvesting hydrogen from water. However, more energy is required to release the hydrogen than can be recovered from using the released gas as a fuel. That’s where a photocatalyst like titania (TiO2) comes in. Titania is the naturally occurring form of titanium oxide and under ultraviolet light it acts as a hydrolysis catalyst, reducing the amount of electricity required for hydrolysis to occur.

nanotubes The team at Northern University had been studying ways to increase the performance of titania as a catalyst by combining it with carbon to form tiny nanotube arrays. Nanotubes are typically between ninety and one hundred nanometers in diameter and have an extremely high surface to volume ratio.

The high surface to volume ratio allows more water to come into contact with the titania catalyst and improves hydrogen production. Combining it with carbon helps titania absorb visible light. Pure titania absorbs light at the ultraviolet wavelength, but a lot of ultraviolet light is absorbed by the atmosphere. Astonishingly, it was almost by chance that the team discovered that a residue of the process used to build the nanotube arrays was responsible for improving performance of the nanotubes in solar cells that release hydrogen from water.

The nanoscopic nature of their work necessitated extremely sensitive equipment that could measure the presence of elements at super low concentrations. The NIST X-ray spectroscopy beamline at the National Synchrotron Light Source (NSLS,) uses X-rays that can be precisely adjusted to measure the minute chemical bonds between individual elements. Spectroscopic analysis of the nanotube arrays revealed a surprising result. The analysis had been intended to measure the carbon atoms in the configuration, but it also revealed that tiny amounts of potassium ions had bonded with the surface of the titania. The presence of the potassium could only have been an accidental bi-product of the fabrication process, which used potassium salts. Potassium had never before been detected on titania nanotubes, but previous instruments used were not sensitive enough to detect it.

syncrotron At first the team thought the results were merely an interesting artifact of the production process. Then, they had the foresight to compare the output from the potassium-laced nanotubes to the output from nanotubes constructed in a potassium-free environment. The results were astonishing. “The result was so exciting that we got sidetracked from the carbon research.” says Northeastern physicist Latika Menon. Indeed, the team recorded that the nanotubes containing potassium bonds required only about one-third the electrical energy to produce the same amount of hydrogen as an equivalent array of potassium-free nanotubes.

The team admit that potassium probably has played a role in many experimental water-splitting cells that use titania nanotubes in the past. Potassium hydroxide is commonly used in such cells, but this is the first time that the part that potassium plays in the reaction has been measured. By controlling it solar cell designers could use it to boost performance. Titania is already used in the Graetzel cell , a type of thin film solar cell.

So what does this mean for the average person, struggling to pay the bills?  Well, hydrogen has long been touted as the fuel of the future. Hydrogen powered cars have been in existence for many years. Imagine if, instead of having to fill up tour tank every few days with expensive, environmentally harmful, petrol (or gasoline if you live in the U.S.) you could power your vehicle with clean, inexpensive hydrogen. What if you could power your home and vehicle on hydrogen you produce at home? Now wouldn’t that be something.