The Goldilocks Zone For Graphene-Coated Nanoparticles

Scientists in Japan have identified the precise number of graphene layers that would help to stabilize nanoparticles without compromising their catalytic ability.

AsianScientist (Jul. 12, 2018) – In a study published in ACS Energy Letters, a team of scientists in Japan has devised a method to increase the stability of catalysts for the generation of hydrogen fuel.

Hydrogen is an attractive clean fuel source and can be produced from water by the hydrogen evolution reaction. For hydrogen fuel to become widely adopted, it is important to be able to generate hydrogen on a large scale and at low cost. To achieve this goal, durable, inexpensive catalysts are required.

However, most existing catalysts based on non-precious metals are unstable under the acidic solutions formed during the hydrogen evolution reaction. Simply protecting the catalyst from the acidic solution tends to lower its activity.

To overcome these constraints, researchers led by Dr. Hu Kailong at the University of Tsukuba, Japan, found that coating catalyst nanoparticles with an optimal number of layers of graphene—a sheet of carbon atoms organized into a honeycomb lattice with high conductivity and mechanical strength—raised nanoparticle durability while allowing the nanoparticles to retain their catalytic activity.

The researchers fabricated and characterized a series of nanoparticle samples coated with different numbers of graphene layers, then determined the catalytic activity of the coated nanoparticles.

“We optimized the balance between the number of graphene layers coating the nanoparticles and their catalytic activity,” said Hu. “We had to precisely control the number of graphene layers coating the nanoparticles, which we achieved by carefully regulating the deposition time of graphene on the nanoparticles.”

They found that when the catalyst nanoparticles were coated with just three to five layers of graphene, their activity in the hydrogen evolution reaction was similar to that of an expensive platinum-based catalyst. Importantly, these nanoparticles also exhibited high stability—the graphene coating prevented the metal nanoparticles from dissolving in the acidic reaction solution.

Furthermore, the scientists conducted theoretical calculations to support their experimental findings, showing that the nanoparticles coated with fewer than three graphene layers showed higher catalytic activity than those coated with three to five layers, but this came at the expense of durability.

“Our results pave the way for rational design of stable, cheap catalysts for large-scale hydrogen production at hydrogen stations by on-site polymer electrolyte membrane electrolysis under acidic conditions,” said co-author Associate Professor Yoshikazu Ito of Tohoku University, Japan.

The team’s findings bring us a step closer to the realization of a clean sustainable future using hydrogen as a fuel source.


The article can be found at: Hu et al. (2018) Graphene Layer Encapsulation of Non-Noble Metal Nanoparticles as Acid-Stable Hydrogen Evolution Catalysts.

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Source: University of Tsukuba; Photo: Shutterstock.
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