|
|
|
|
|
|
|
Engineering News |
| Researchers Create Hydrogen with Help of Solar Energy and Water | |
Engineers Edge - Penn State researchers are developing a low cost process to produce fuel hydrogen help of water, solar energy and Nanotube diodes.
"Other researchers have developed ways to produce hydrogen with mind-boggling efficiency, but their approaches are very high cost," says Craig A. Grimes, professor of electrical engineering. "We are working toward something that is cost effective." Currently, reforming of natural gas steam during refining produces most of our hydrogen. This process introduces two problems. The technology uses expensive natural gas and the process introduces carbon dioxide into the atmosphere. Grimes' process separates water into its two components, hydrogen and oxygen, and separates the elements using commonly available titanium and copper cathode and anodes. Splitting water for hydrogen production is well understood and utilized technology, however as typically used requires siginificant amounts electric energy. Grimes and his team are utilizing solar energy to separate the hydrogen and oxygen from water, using two different groups of nanotubes in a photoelectrochemical diode. As reported in the July issue of Nano Letters using incident sunlight, "such photocorrosion-stable diodes generate a photocurrent of approximately 0.25 milliampere per centimeter square, at a photoconversion efficiency of 0.30 percent." "It seems that nanotube geometry is the best geometry for production of hydrogen from photolysis of water," says Grimes In Grimes' photoelectrochemical diode is configured such that 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 electronic materials are commonly used within semiconductor technologies. Grimes has been making n-type nanotube arrays from titanium by sputtering titanium onto a surface, anodizing the titanium to form titanium dioxide and then annealing the material to form the nanotubes. He makes the cuprous oxide titanium dioxide nanotube array in the same way and can alter the proportions of each metal. While titanium dioxide is very absorbing in the ultraviolet portion of the sun's spectrum, many p-type materials are unstable in sunlight and damaged by ultraviolet light, they photo-corrode. To solve this challenge, the Penn State researchers made the titanium dioxide side of the diode transparent to visible light by adding iron and exposed this side of the diode to natural sunlight. The titanium dioxide nanotubes soak up the ultraviolet between 300 and 400 nanometers. The light then passes to the copper titanium side of the diode where visible light from 400 to 885 nanometers is used, covering the light spectrum. The photoelectrochemical diodes function the same way that green leaves do, only not quite as well. They convert the energy from the sun into electrical energy that then breaks up water molecules. The titanium dioxide side of the diode produces oxygen and the copper titanium side produces hydrogen. Although 0.30 percent efficiency is low, Grimes notes that this is just a first go and that the device can be readily optimized. "These devices are inexpensive and because they are photo-stable could last for years," says Grimes. "I believe that efficiencies of 5 to 10 percent are reasonable." Grimes is now working with an electroplating method of manufacturing the nanotubes, which will be faster and easier. Working with Grimes are Gopal K. Mor, Oomman K. Varghese and Karthik Shankar, research associates; Rudeger H. T. Wilke and Sanjeev Sharma, Ph.D. candidates; Thomas J. Latempa, graduate student, all at Penn State; and Kyoung-Shin Choi, associate professor of chemistry, Purdue University. The U.S. Department of Energy supported this research.
Related Resource: Applications & Design Modified by Administrator at Sat, Jul 19, 2008, 10:34:08 |
 |
Email Friend | EMail Author | Current page |
|
