A new titanium-oxide-based photocatalytic material could open up a new path for green hydrogen production. Image: Drexel University.
A new titanium-oxide-based photocatalytic material could open up a new path for green hydrogen production. Image: Drexel University.

Clean-energy plans, including the US Infrastructure Investment Act’s ‘Clean Hydrogen Road Map’, are counting on hydrogen as a fuel of the future. But current hydrogen-production technology is still falling short of efficiency and sustainability goals. As part of ongoing efforts to develop materials that could usher in alternative energy sources, researchers in Drexel University’s College of Engineering have developed a titanium oxide nanofilament material that can harness sunlight to unlock hydrogen’s potential as a fuel source.

This discovery offers an alternative to current hydrogen-production methods, which generate greenhouse gas and require a great deal of energy. Photocatalysis, a process that can produce hydrogen by splitting water using only sunlight, has been explored for several decades. But it has remained a distant consideration because the catalytic materials required to boost the process can only survive for a day or two, limiting its long-term efficiency and, as a result, its commercial viability.

Drexel’s group, led by researchers Michel Barsoum and Hussein Badr in collaboration with scientists from the National Institute of Materials Physics in Bucharest, Romania, has now discovered a photocatalytic titanium oxide-based, one-dimensional nanofilament material that can help sunlight glean hydrogen from water for months at a time. As the researchers report in a paper in Matter, this novel material presents a sustainable and affordable path for creating hydrogen fuel.

“Our titanium oxide one-dimensional nanofilaments photocatalyst showed activity that is substantially higher – by an order of magnitude – than its commercial titanium oxide counterpart,” Hussein said. “Moreover, our photocatalyst was found to be stable in water for six months – these results represent a new generation of photocatalysts that can finally launch the long-awaited transition of nanomaterials from lab to market.”

Barsoum’s group discovered hydroxides-derived nanostructures (HDNs) – the family of titanium oxide nanomaterials to which the novel photocatalytic material belongs – two years ago, as it was working on a new process for making MXene materials, which Drexel researchers are exploring for a number of applications. Instead of using caustic hydrofluoric acid to chemically etch out the layered two-dimensional MXenes from a bulk material called a MAX phase, the group used an aqueous solution of a common organic base, tetramethylammonium hydroxide.

But rather than producing MXene, this reaction produced thin, fibrous titanium-oxide-based strands that the team would come to find possessed the ability to facilitate the chemical reaction that produces hydrogen by splitting water molecules when exposed to sunlight.

“Titanium-oxide materials have previously demonstrated photocatalytic abilities, so testing our new nanofilaments for this property was a natural part of our work,” Barsoum said. “But we did not expect to find that not only are they photocatalytic, but they are extremely stable and productive catalysts for hydrogen production from water-methanol mixtures.”

The group tested five photocatalyst materials – titanium-oxide-based HDNs derived from various low-cost and readily available precursor materials – and compared them to Evonik Aeroxide’s titanium oxide material, called P25, which is widely accepted as the photocatalyst material closest to commercial viability.

Each material was submerged in a water-methanol solution and exposed to ultraviolet-visible light produced by a tunable illuminator lamp that mimics the spectrum of the sun. The researchers measured both the amount of hydrogen produced and the duration of activity in each reactor assembly, as well as the number of photons that produced hydrogen when they interacted with the catalyst material — a metric for understanding the catalytic efficiency of each material.

They found that all five titanium-oxide-based HDN photocatalysts were more efficient at using sunlight to produce hydrogen than the P25 material. One of them, derived from binary titanium carbide, is 10 times more efficient than P25 at getting photons to split off hydrogen from water.

This improvement is quite significant on its own, the team reports, but an even more significant finding was that the material remained active after more than 180 days of exposure to the simulated sunlight.

“The fact that our materials appear to possibly be thermodynamically stable and photochemically active in water-methanol mixtures for extended durations cannot be overemphasized,” Hussein said. “Since our material is not costly to make, easy to scale up and incredibly stable in water, its applications in various photocatalytic processes become worth exploring.”

The next step for the research is better understanding why the material behaves this way, so it can be further optimized as a photocatalyst. The team’s current theory posits that the one-dimensional nature and theoretical high surface area of the material contribute to its sustained activity, but additional testing is needed to confirm these suggestions.

The group is also working to find other additives, aside from methanol, to serve as ‘hole quenchers’ – chemicals that prevent the water-splitting reaction from reversing course, which is a common occurrence due to the somewhat chaotic nature of photocatalytic reactions.

The results are so promising that the group has founded a green-hydrogen startup company around the technology and is working with the Drexel Office of Innovation and the US National Science Foundation’s Innovation Corps to move toward commercializing it.

“We are very excited about the possibilities of this discovery,” Barsoum said. “The world needs massive new clean fuels that can supplant fossil fuels. We believe this material can unlock the potential of green hydrogen.”

In addition, the group is exploring several other applications for HDNs, including using them in batteries and solar cells, and for water purification and medical treatments. Their ability to be easily and safely produced in large quantities sets HDNs apart from other nanomaterials, which opens them up to a variety of possible uses, according to Hussein.

“Our HDNs family of nanostructures continue to impress the very different communities with whom we are collaborating. These titanium oxide nanofilaments can be used for number of applications, including water purification, dye degradation, perovskite solar cells, lithium-ion and lithium-sulfur batteries, urea dialysis and breast cancer therapy, among many more.”

This story is adapted from material from Drexel 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.