The new technique combines two previously known methods for producing hydrogen. And although the previous methods have limitations making them impractical when used alone, those drawbacks are overcome when the methods are combined, according to Arvind Varma, the head of Purdue’s
One of the methods was invented by Herbert Brown, who discovered a compound called sodium borohydride during World War II. The compound contains sodium, boron and hydrogen. He later developed a technique for producing hydrogen by combining sodium borohydride with water and a catalyst. The method, however, has a major drawback – it requires expensive catalysts such as ruthenium.
The other method involves a chemical reaction in which tiny particles of aluminium are combined with water in such a way that the aluminium ignites, releasing hydrogen during the combustion process. This method does not require an expensive catalyst, but it yields insufficient quantities of hydrogen to be practical for fuel cell applications.
“Our solution is to combine both methods by using what we call a triple borohydride-metal-water mixture, which does not require a catalyst and has a high enough hydrogen yield to make the method promising for fuel cell applications,” Varma said.
Aluminium particles just 100nm wide are used in the fuel cell as is a gel formed from a mixture of polyacrylamide and water. The combination increases the boiling point of water and decreasing the ignition temperature of aluminium, making the reaction possible.
“So far we have shown in experiments that we can convert 6.7% of the mixture to hydrogen, which means that for every 100 grams of mixture we can produce nearly 7 grams of hydrogen, and that yield is already better than alternative methods on the market.”
The researchers have filed a provisional patent application for the technique and hope to increase the yield to about 10% through additional experiments, according to research scientist Evgeny Shafirovich.
They believe they will be able to safely dissipate the heat produced by the reaction, making the technology practical for portable electronics.