Sunlight generates hydrogen in new porous silicon

April 10, 2014

Porous silicon manufactured in a bottom up procedure using solar energy can be used to generate hydrogen from water, according to a team of Penn State mechanical engineers, who also see applications for batteries, biosensors and optical electronics as outlets for this new material.

The surface area of this porous silicon is high," said Donghai Wang, assistant professor of mechanical engineering. "It is widely used and has a lot of applications."

The standard method for manufacturing porous silicon is a subtraction method, similar to making a sculpture.

"Silicon is an important material because it is a semiconductor," said Wang. "Typically, porous silicon is produced by etching, a process in which lots of material is lost."

Wang's team uses a chemically based method that builds up the material rather than removing it. The researchers start with silicon tetrachloride, a very inexpensive source of silicon. They then treat the material with a sodium potassium alloy.

"The bonds between silicon and chlorine in silicon tetrachloride are very strong and require a highly reducing agent," said Wang. "Sodium potassium alloy is such an agent."

Once the bonds break, the chlorine binds with the sodium, potassium and silicon, potassium chloride and sodium chloride -- table salt -- become solid, forming a material composed of crystals of salt embedded in silicon. The material is then heat-treated and washed in water to dissolve the salt, leaving pores that range from 5 to 15 nanometers. The researchers report their results in today's (Apr. 10) issue of Nature Communications.

Because sodium potassium alloy is highly reactive, the entire procedure must be done away from the oxygen in the air, so the researchers carry out their reaction in an argon atmosphere.

"I believe that the process can be scaled up to manufacturing size," said Wang. "There are some processes that use sodium potassium alloy at industrial levels. So we can adapt their approaches to make this new type of porositic silicon."

Because these silicon particles have lots of pores, they have a large surface area and act as an effective catalyst when sunlight shines on this porous silicon and water. The energy in sunlight can excite an electron that then reduces water, generating hydrogen gas. This process is aided by the material's larger-than-normal band gap, which comes from the nanoscale size of the silicon crystallites.

"This porous silicon can generate a good amount of hydrogen just from sunlight," said Wang.

The researchers are also looking into using this porous silicon as the anode in a lithium ion battery.
-end-
Other researchers on this project were Fang Dai, Jiantao Zai and Hiesang Sohn, all postdoctural researchers in mechanical engineering; and Ran Yi, Mikhail L Gordin and Shuru Chen, graduate students in mechanical engineering.

The U.S. Department of Energy and the Defense Threat Reduction Agency funded this work.

Penn State

Related Hydrogen Articles from Brightsurf:

Solar hydrogen: let's consider the stability of photoelectrodes
As part of an international collaboration, a team at the HZB has examined the corrosion processes of high-quality BiVO4 photoelectrodes using different state-of-the-art characterisation methods.

Hydrogen vehicles might soon become the global norm
Roughly one billion cars and trucks zoom about the world's roadways.

Hydrogen economy with mass production of high-purity hydrogen from ammonia
The Korea Institute of Science and Technology (KIST) has made an announcement about the technology to extract high-purity hydrogen from ammonia and generate electric power in conjunction with a fuel cell developed by a team led by Young Suk Jo and Chang Won Yoon from the Center for Hydrogen and Fuel Cell Research.

Superconductivity: It's hydrogen's fault
Last summer, it was discovered that there are promising superconductors in a special class of materials, the so-called nickelates.

Hydrogen energy at the root of life
A team of international researchers in Germany, France and Japan is making progress on answering the question of the origin of life.

Hydrogen alarm for remote hydrogen leak detection
Tomsk Polytechnic University jointly with the University of Chemistry and Technology of Prague proposed new sensors based on widely available optical fiber to ensure accurate detection of hydrogen molecules in the air.

Preparing for the hydrogen economy
In a world first, University of Sydney researchers have found evidence of how hydrogen causes embrittlement of steels.

Hydrogen boride nanosheets: A promising material for hydrogen carrier
Researchers at Tokyo Institute of Technology, University of Tsukuba, and colleagues in Japan report a promising hydrogen carrier in the form of hydrogen boride nanosheets.

World's fastest hydrogen sensor could pave the way for clean hydrogen energy
Hydrogen is a clean and renewable energy carrier that can power vehicles, with water as the only emission.

Chemical hydrogen storage system
Hydrogen is a highly attractive, but also highly explosive energy carrier, which requires safe, lightweight and cheap storage as well as transportation systems.

Read More: Hydrogen News and Hydrogen Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.