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Graphene-Nanotube Combo Exceeds Benchmarks for Hydrogen Storage in Fuel Cells

Nanomaterial hybrid makes hydrogen storage economically feasible for next-generation vehicles

2 min read
Pink (boron) and blue (nitrogen) pillars serve as spacers for carbon graphene sheets (grey). The researchers showed the material worked best when doped with oxygen atoms (red), which enhanced its ability to adsorb and desorb hydrogen (white).
Illustration: Lei Tao

With lithium-ion (Li-ion) batteries becoming the de-facto energy source for next-generation vehicles, some of us remember that there was a time when fuel cells were thought to be the most viable solution for powering vehicles after the internal combustion engine.

Of course, this is only a perception based on how companies like Tesla have made the Li-ion battery seem to be the best option. However, the US Department of Energy (DoE) has set benchmarks for what storage materials will need to deliver in order to compete for a place in post-fossil fuel vehicles.

Now researchers at Rice University have developed a nanomaterial for fuel cells that consists of layers of graphene separated by nanotube pillars of boron nitride. The material might tick all the boxes established by the DoE for next-generation vehicles.

In research described in the journal Langmuir, the Rice researchers demonstrated in computer models that 3D architecture of the hybrid nanomaterial would be able to store enough hydrogen to become a practical fuel for light-duty vehicles.

According to DoE’s benchmark figures, a medium would need to store at least 5.5 percent of its weight in hydrogen to be economically feasible. The Rice team has modeled a material that can store nearly 12 percent of its weight in hydrogen at room temperature. When the temperature is brought down to -196ºC that percentage bumps up to 15 percent.

To get to these numbers, the researchers juggled a few different combinations of nanomaterials. The models tested pillared structures of boron nitride and pillared boron nitride graphene doped with either oxygen or lithium. The best of these turned out to be oxygen-doped boron nitride graphene.

In the un-doped pillared born nitride graphene, the hydrogen atoms bond to the material because of van der Waals forces, which are forces of attraction or repulsion between molecules that are not based on covalent or ionic bonds.  But when oxygen is used to dope the material the atoms bond very strongly with the hybrid material, leading to a better surface for incoming hydrogen.

“Adding oxygen to the substrate gives us good bonding because of the nature of the charges and their interactions,” said Rouzbeh Shahsavari, a materials scientist at Rice, in a press release. “Oxygen and hydrogen are known to have good chemical affinity.”

This hybrid material allows for a large degree of tunability, according to Shahsavari, making it possible to tailor it for particular operating temperatures and pressures.

With this structure, Shasavari and his colleagues are confident that the material can meet the DoE requirement that a fuel cell be able to withstand 1500 charge-discharge cycles.

The Conversation (0)
This photograph shows a car with the words “We Drive Solar” on the door, connected to a charging station. A windmill can be seen in the background.

The Dutch city of Utrecht is embracing vehicle-to-grid technology, an example of which is shown here—an EV connected to a bidirectional charger. The historic Rijn en Zon windmill provides a fitting background for this scene.

We Drive Solar

Hundreds of charging stations for electric vehicles dot Utrecht’s urban landscape in the Netherlands like little electric mushrooms. Unlike those you may have grown accustomed to seeing, many of these stations don’t just charge electric cars—they can also send power from vehicle batteries to the local utility grid for use by homes and businesses.

Debates over the feasibility and value of such vehicle-to-grid technology go back decades. Those arguments are not yet settled. But big automakers like Volkswagen, Nissan, and Hyundai have moved to produce the kinds of cars that can use such bidirectional chargers—alongside similar vehicle-to-home technology, whereby your car can power your house, say, during a blackout, as promoted by Ford with its new F-150 Lightning. Given the rapid uptake of electric vehicles, many people are thinking hard about how to make the best use of all that rolling battery power.

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