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 asodium 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 the Apr. 10th, 2014 issue of Nature Communications.