The problem of releasing the accumulating heat in graphene and carbon nanotube junctions has been addressed with a novel solution.

The solution mooted by Rice University researchers involves knocking out the barrier that traps the heat by creating a cone-like 'chimney' between graphene and carbon nanotubes.

It involves tweaking of graphene to insert cones between it and nanotubes that grow out of its surface. The cones would vent the heat as 'nano-chimneys.'

The experiment by Rice scientists can be a way forward in pushing out harmful heat from new generation nano-electronics.

When nanotubes are formed from graphene, heptagonal rings that get formed block the heat from escaping. With cones in place, there will be a clear path for hexagons to race up heat toward the chimney as the heptagons are now placed sparsely.

Simulations of Rice researchers revealed that taking out atoms from here and there from the two-dimensional graphene base would solve the issue as cones are created as outlets to release the heat.

"The tunability of such structures is virtually limitless, stemming from the vast combinatorial possibilities of arranging the elementary modules," said study co-author Alex Kutana.

Adjustments On Graphene

The experiments were conducted at the Rice lab of theoretical physicist Boris Yakobson.

Yakobson said the interest in advancing new applications for low-dimensional carbon — fullerenes, nanotubes and graphene — has become broad.

Findings of the research were published in the American Chemical Society's Journal of Physical Chemistry. The paper was authored by Ziang Zhang, a graduate student, and the co-author is Ajit Roy, a materials research engineer.

Process wise, placing of cones between graphene and carbon nanotubes allows phonons to act as better carriers of heat by spreading out the heptagons required for the faster graphene-to-nanotube transition.

In terms of structure, both graphene and carbon nanotubes carry rings of six atoms, giving a chicken-wire appearance and can function as rapid carriers of electricity and phonons.

The problem, however, was the nanotube growing out of graphene coming with heptagonal rings. Though the array of nanotubes growing from graphene is great in storing hydrogen for energy applications it is not good for electronics, as the heptagons disperse phonons and block the escape of heat through the pillars.

Energy Storage

Meanwhile, Rice University's nanomaterial research for applications in energy is making the news.

Fuel cells are emerging as a new solution for powering vehicles after the era of internal combustion engines. This is despite Lithium-ion (Li-ion) batteries enthusiasts, like electric car maker Tesla, projecting the Li-ion battery as the best option.

In the new guidelines by the U.S. Department of Energy (DoE) benchmarks for fuel storage materials for the post-fossil fuel vehicles era have been spelled out.

That is where the nanomaterials, developed by Rice University researchers for fuel cells using layers of graphene and separated by nanotube pillars of boron nitride, emerges.

The 3D architecture of the hybrid nanomaterial shows that it can store as much hydrogen to work as a practical fuel for light-duty vehicles.

The benchmark figures of DoE insist that a medium must store at least 5.5 percent of its weight in hydrogen to be economically viable.

In fact, the team at Rice has exceeded that target. It is modeled on a material that can store 12 percent of its weight in hydrogen at room temperature. More interesting is that storage of hydrogen can be scaled up to 15 percent when the temperature is lowered to -196ºC.

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