Drexel scientists discover titanium nanomaterial that is an extremely efficient hydrogen fuel photocatalyst.

Much like many of Mankind's discoveries, such as those that happened through some serendipitous result contrary to the predicted outcome, Drexel University researchers may have stumbled on the method of producing hydrogen fuel – with a photocatalyst 10 times more efficient than the closest commercially viable material.

Sustainable technologies produce electricity as their primary output, as it does not generate harmful emissions when powering their various loads. However, one area presents a difficult challenge, transportation.

As is popularly discussed, electric vehicle manufacturers are attempting to economically commercialize batteries that can compete with fossil fuels. However, the strength and longevity of batteries are just not up to snuff for much of the transportation world – military, space, aeronautics, and shipping that require torque and RPMs that batteries have a tough time delivering, at least at this time.

In light of that, clean energy goals are counting on hydrogen as the fuel of the future.

While it would be used widely as a fuel for electronic systems, the energy would not be supplied by batteries but by hydrogen fuel cells.

According to the Department of Energy, the energy in 2.2 pounds (1 kilogram) of hydrogen gas is about the same as in 1 gallon (6.2 lb, 2.8 kg) of gasoline.

However, current hydrogen separation technologies that would unlock this fuel for widespread use fall short of efficiency and sustainability goals.

Enter Drexel University, renowned for its ongoing work on 2D materials like MXenes.

As they were working out a new process for creating MXene materials, Drexel researchers discovered hydroxide-derived nanostructures (HDNs).

Instead of using the standard caustic hydrofluoric acid to chemically etch out the layered two-dimensional MXenes, the group used an aqueous solution of a common organic base. But rather than producing a new MXene variant, the reaction produced thin, fibrous titanium oxide-based strands.

It was from these strands that the team would come to find they possess the ability to facilitate the chemical reaction that can split hydrogen out of water molecules when exposed to sunlight.

Substantial catalyst

Led by College of Engineering researchers Michel Barsoum and Hussein Badr, in collaboration with scientists from the National Institute of Materials Physics in Bucharest, Romania, the team reported its newest discovery of photocatalytic titanium oxide-based, one-dimensional nanofilament material.

What separates this announcement from the usual hydrogen hopefuls is its efficiency as well as longevity.

"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."

Published in the journal Matter, the authors state that the newest material presents a sustainable and affordable path for creating hydrogen fuel.

"Titanium-oxide materials have previously demonstrated photocatalytic abilities, so testing our new nanofilaments for this property was a natural part of our work," he 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 Drexel team 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 portion was submerged in a water-methanol solution and exposed to ultraviolet-visible light that mimics the spectrum of the sun. The researchers measured both the amount of hydrogen produced and duration of activity in each reactor assembly, as well as the number of photons from the light that produced hydrogen when they interacted with the catalyst material – a metric for understanding the catalytic efficiency of each material.

The researchers learned that all five of their titanium oxide-based HDNs photocatalysts produced hydrogen from the simulated sunlight more efficiently than the P25 material.

One of them, derived from binary titanium carbide, was 10 times more efficient than P25 at enabling photons to split off hydrogen from the water.

While this achievement is quite momentous on its own, the team reported that 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."

As for the next step, the Drexel team is now seeking to understand why the material behaves the way it does so that it can be further optimized as a photocatalyst. The researchers' 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 obviously needed to confirm these ideas.

Hydrogen startup

With results so promising, the group immediately founded a green hydrogen startup around the technology and is working with the Drexel Office of Innovation and the National Science Foundation's Innovation Corps to move it toward commercialization.

"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."

Additionally, the group is exploring a number of other applications for HDNs, including using them in batteries, solar cells, 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 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," said Hussein.