This is an artist's rendering of P22-Hyd, a new biomaterial created by encapsulating a hydrogen-producing enzyme within a virus shell. Image: Indiana University.
This is an artist's rendering of P22-Hyd, a new biomaterial created by encapsulating a hydrogen-producing enzyme within a virus shell. Image: Indiana University.

Scientists at Indiana University (IU) have created a highly efficient biomaterial for catalyzing the formation of hydrogen – one half of the ‘holy grail’ of splitting H2O to produce hydrogen and oxygen for use in fuel cells.

Comprising the enzyme hydrogenase encased within the protein shell, or ‘capsid’, of a bacterial virus, this new material is 150 times more efficient than the unaltered form of the enzyme. The process of creating the material was recently reported in a paper in Nature Chemistry.

"Essentially, we've taken a virus's ability to self-assemble myriad genetic building blocks and incorporated a very fragile and sensitive enzyme with the remarkable property of taking in protons and spitting out hydrogen gas," said Trevor Douglas, professor of chemistry in the IU Bloomington College of Arts and Sciences' Department of Chemistry, who led the study. "The end result is a virus-like particle that behaves the same as a highly sophisticated material that catalyzes the production of hydrogen."

Other IU scientists who contributed to the research were: Megan Thielges, an assistant professor of chemistry; Ethan Edwards, a PhD student; and Paul Jordan, a post-doctoral researcher at Alios BioPharma, who was an IU PhD student at the time of the study.

The hydrogenase is produced by two genes, hyaA and hyaB, derived from the common bacteria Escherichia coli, which are inserted inside the protective capsid using methods previously developed by the IU scientists. The capsid comes from a bacterial virus known as bacteriophage P22. The resulting biomaterial, called ‘P22-Hyd’, is not only more efficient than the unaltered enzyme but is also produced through a simple fermentation process at room temperature.

The biomaterial is potentially far less expensive and more environmentally friendly to produce than other catalytic materials, such as the costly and rare metal platinum. "This material is comparable to platinum, except it's truly renewable," Douglas said. "You don't need to mine it; you can create it at room temperature on a massive scale using fermentation technology; it's biodegradable. It's a very green process to make a very high-end sustainable material."

In addition, P22-Hyd both breaks the chemical bonds of water to create hydrogen and also works in reverse to recombine hydrogen and oxygen to generate power. "The reaction runs both ways – it can be used either as a hydrogen production catalyst or as a fuel cell catalyst," Douglas said.

Three different forms of hydrogenase occur in nature: di-iron (FeFe)-, iron-only (Fe-only)- and nitrogen-iron (NiFe)-hydrogenase. The third form was selected for the new material due to its ability to easily integrate into biomaterials and tolerate exposure to oxygen.

Unfortunately, NiFe-hydrogenase is highly susceptible to destruction from chemicals in the environment and breaks down at temperatures above room temperature – both of which make the unprotected enzyme a poor choice for use in manufacturing and in commercial products such as cars. Encapsulating NiFe-hydrogenase within a capsid, however, provides it with significantly greater resistance to breakdown from chemicals in the environment and also allows it to retain its catalytic ability at room temperature.

This sensitivity to chemicals and temperature are "some of the key reasons enzymes haven't previously lived up to their promise in technology," Douglas said. Another is their difficulty to produce. "No one's ever had a way to create a large enough amount of this hydrogenase despite its incredible potential for biofuel production. But now we've got a method to stabilize and produce high quantities of the material – and enormous increases in efficiency," he said.

The development is highly significant, according to Seung-Wuk Lee, professor of bioengineering at the University of California, Berkeley, who was not part of the study. "Douglas' group has been leading protein- or virus-based nanomaterial development for the last two decades, " he said. "This is a new pioneering work to produce green and clean fuels to tackle the real-world energy problem that we face today and make an immediate impact in our life in the near future."

Beyond this study, Douglas and his colleagues continue to craft P22-Hyd into an ideal ingredient for hydrogen power by investigating ways to activate catalytic reactions with sunlight, as opposed to introducing elections using laboratory methods. "Incorporating this material into a solar-powered system is the next step," Douglas said.

This story is adapted from material from Indiana University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.