A new system for detecting the production of hydrogen gas, developed by Penn State researchers, may play a key role in the quest to develop hydrogen as an environmentally friendly and economical alternative to fossil fuels.
“We have built a new system for detecting hydrogen evolution that is the most sensitive in the world,” said Professor Venkatraman Gopalan. “This tackles a problem that had not been addressed but that is important going forward for materials discovery.”
The tool can be used to screen promising photocatalysts, materials that when placed in water and exposed to sunlight facilitate reactions that split water molecules into hydrogen and oxygen gases. The process, called water splitting, offers a clean and renewable source of hydrogen, but it is inefficient, and finding the right photocatalysts to boost hydrogen production has been challenging.
In a study, the team found they could test smaller amounts of photocatalyst material than previously possible and detect very small amounts of hydrogen gas produced, or hydrogen evolution, in the range of tens of nanomoles per hour per tens of milligrams of material. They recently published their findings in the Review of Scientific Instruments.
“If you ranked low in both the categories of hydrogen evolution rate and the mass of the photocatalyst needed, it means it's a really sensitive system for discovering new photocatalytic materials,” said Huaiyu “Hugo” Wang, a graduate student who led the study and built the system. “And it turns out that our work ranked the best in both categories.”
At Penn State, scientists led by Professor Ismaila Dabo recently used a supercomputer to narrow a list of more than 70,000 different compounds down to six promising candidates. Another team led by Raymond Schaak, DuPont Professor of Materials Chemistry, synthesized the materials in their laboratory.
However, typical photocatalysts use rare and precious metals such as platinum, which are immensely expensive, so making them in large quantities is impractical, time-consuming, and costly.
When it came time to test samples, the researchers found commercial equipment was not sensitive enough, so Gopalan and Wang built their own. Gopalan said their new system will allow scientists to test smaller amounts of these materials and focus efforts on the most promising candidates.
Unlike the commercial units, the new design can test photocatalysts in their bare state, the scientists said. To be effective, photocatalysts require co-catalysts and other techniques that further improve their efficiency. The gold standard, for example, is titanium dioxide with platinum particles added as a co-catalyst. Photocatalysts without these add-ons are considered bare.
“When we are looking at new materials, we don't know what the correct co-catalysts will be,” Wang said. “Detecting the bare form is the quickest way to help guide the direction of this materials discovery process.”
Two of the photocatalyst materials tested as part of the study performed better than titanium dioxide did in its bare state, the scientists said. The findings suggest that further study of those materials could yield promising photocatalysts.
“If you have a bare compound that behaves much better than titanium dioxide then we know this is a potential material to optimize,” Wang said. “If we find the right co-catalysts for those materials, we can improve them by orders or magnitude and these materials could eventually be useful in water splitting.”
The team said the system is and easy to build from commercially available components. It features a low leakage rate and a small reaction chamber volume size, which allows three orders of magnitude higher detection sensitivity for hydrogen evolution than a conventional gas chromatography system.