Click here for a printer-friendly version of this page.

Discovery of an Unexpected Boost for Solar Water-Splitting Cells

Posted on: Friday April 24, 2009.

Scanning electron microscope image of typical titania nanotubes for a photocatalytic cell to produce hydrogen gas from water. Nanotubes average roughly 90-100 nanometers in diameter.

Credit: Menon, Northeastern University
A research team from Northeastern University and the National Institute of Standards and Technology (NIST) has discovered, serendipitously, that a residue of a process used to build arrays of titania nanotubes—a residue that wasn’t even noticed before this—plays an important role in improving the performance of the nanotubes in solar cells that produce hydrogen gas from water. Their recently published results* indicate that by controlling the deposition of potassium on the surface of the nanotubes, engineers can achieve significant energy savings in a promising new alternate energy system.

Titania (or titanium dioxide) is a versatile chemical compound best known as a white pigment. It’s found in everything from paint to toothpastes and sunscreen lotions. Thirty-five years ago Akira Fujishima startled the electrochemical world by demonstrating that it also functioned as a photocatalyst, producing hydrogen gas from water, electricity and sunlight. In recent years, researchers have been exploring different ways to optimize the process and create a commercially viable technology that, essentially, transforms cheap sunlight into hydrogen, a pollution-free fuel that can be stored and shipped.

Increasing the available surface area is one way to boost a catalyst’s performance, so a team at Northeastern has been studying techniques to build tightly packed arrays of titania nanotubes, which have a very high surface to volume ratio. They also were interested in how best to incorporate carbon into the nanotubes, because carbon helps titania absorb light in the visible spectrum. (Pure titania absorbs in the ultraviolet region, and much of the ultraviolet is filtered by the atmosphere.)

This brought them to the NIST X-ray spectroscopy beamline at the National Synchrotron Light Source (NSLS)**. The NIST facility uses X-rays that can be precisely tuned to measure chemical bonds of specific elements, and is at least 10 times more sensitive than commonly available laboratory instruments, allowing researchers to detect elements at extremely low concentrations. While making measurements of the carbon atoms, the team noticed spectroscopic data indicating that the titania nanotubes had small amounts of potassium ions strongly bound to the surface, evidently left by the fabrication process, which used potassium salts. This was the first time the potassium has ever been observed on titania nanotubes; previous measurements were not sensitive enough to detect it.

The result was mildly interesting, but became much more so when the research team compared the performance of the potassium-bearing nanotubes to similar arrays deliberately prepared without potassium. The former required only about one-third the electrical energy to produce the same amount of hydrogen as an equivalent array of potassium-free nanotubes. “The result was so exciting,” recalls Northeastern physicist Latika Menon, “that we got sidetracked from the carbon research.” Because it has such a strong effect at nearly undetectable concentrations, Menon says, potassium probably has played an unrecognized role in many experimental water-splitting cells that use titania nanotubes, because potassium hydroxide is commonly used in the cells. By controlling it, she says, hydrogen solar cell designers could use it to optimize performance.

* C. Richter, C. Jaye, E. Panaitescu, D.A. Fischer, L.H. Lewis, R.J. Willey and L. Menon. Effect of potassium adsorption on the photochemical properties of titania nanotube arrays. J. Mater. Chem., published online as an Advanced Article, March 27, 2009. DOI: 10.1039/b822501j

** The NSLS is part of the Department of Energy’s Brookhaven National Laboratory.

News Story Origin and Copyright: NIST
Click here for the original news release.

Click here for a printer-friendly version of this page.

Cool products from our online store:
Cyclone Tube

Cyclone Tube

On SALE today:
$3.95 $2.49 /each

2 inch Alnico Horseshoe Magnet

2 inch Alnico Horseshoe Magnet

On SALE today:
$9.95 $4.95 /each

Solar System Placemat

Solar System Placemat

On SALE today:
$5.99 $3.49 /each

Genius of Leonardo da Vinci Poster

Genius of Leonardo da Vinci Poster

On SALE today:
$19.95 $9.95 /each



Click here to get
a FREE ride with Uber!

Click here to
sign up for Birchbox

Science Quote

'As long as men are free to ask what they must; free to say what they think; free to think what they will; freedom can never be lost and science can never regress. '

J. Robert Oppenheimer
Science Sidebar | Science Education Articles
10 Ways to Keep Your Kids Interested In Science

Young children are natural scientists: they ask questions, pick up sticks and bugs outside, and are curious about the world around them. But as they get a bit older, many kids gradually lose their interest in science. They might see it as just another task at school, something that doesn't apply to their lives. Of course nothing could be further from the truth, so here are ten ways you can remind your kids that science is everywhere. Most of these are fun for adults, too! Continue reading ...

Top Selling

Here are our physics & astronomy bestsellers:
Mini Plasma Ball
KonusScience 5 Way Microscope Kit
3D Magnetic Field Tube
Scorpion, Ant, Wasp and Flower Bug
Alnico Bar Magnet - 6 inch Long
Weather Station 4M Kit
Solar Radiometer
Cherry Wood Levitron
12 inch Galileo Thermometer
Revolving Multi-Color Fiberoptic Light


USC University of Southern California Dornsife College Physics and Astronomy Department McMaster University Physics and Astronomy Department