Research Finds New Dimension in Fuel-Cell Efficiency

The possibility of fuel cells that generate electricity from nothing but the hydrogen in the atmosphere is being mulled by University of Manchester researchers as they continue research on graphene, the world’s first 2-dimensional material.

Graphene, a single layer of carbon atoms arranged in a hexagonal lattice, is the world's thinnest material – one atom thick. That’s almost 1 million times thinner than a human hair.

It first was isolated at the university in 2004. Since then, researchers since have found that, contrary to previous thinking, graphene, which is impermeable to all gases and liquids, easily allows protons – hydrogen atoms stripped of their electrons – to pass through it.

A group led by Andre Geim, the scientist involved in first isolating graphene, expected protons would be blocked, as existing theory predicted as little proton permeation as for hydrogen.

It would take the lifetime of the universe for hydrogen, the smallest of all atoms, to pierce a graphene monolayer.

Despite the pessimistic prognosis, the researchers found protons pass through the ultra-thin crystals surprisingly easily, especially at elevated temperatures and if the films were covered with catalytic nanoparticles such as platinum.

The discovery makes monolayers of graphene, and its sister material boron nitride, attractive for possible uses as proton-conducting membranes, which are at the heart of modern fuel-cell technology.

Fuel cells use oxygen and hydrogen as a fuel and convert the input chemical energy directly into electricity. Without membranes that allow a flow only of protons, this technology would not exist.

The discovery could revolutionize fuel cells and other hydrogen-based technologies as they require a barrier that only protons can pass through.

In addition, graphene membranes could be used to sieve hydrogen gas out of the atmosphere, where it is present in minute quantities, creating the possibility of electric generators powered by air.

The University of Manchester research suggests the use of graphene or monolayer boron nitride can allow the existing membranes to become thinner, with less fuel crossover and poisoning and greater efficiency.

The Manchester group also demonstrated their one-atom-thick membranes can be used to extract hydrogen from a humid atmosphere. They hypothesize such harvesting can be combined with fuel cells to create a mobile electric generator that is fueled simply by hydrogen present in air.

“When you know how it should work, it is a very simple setup,” researcher Marcelo Lozada-Hidalgo says in a statement. “You put a hydrogen-containing gas on one side, apply small electric current and collect pure hydrogen on the other side. This hydrogen can then be burned in a fuel cell.

“We worked with small membranes and the achieved flow of hydrogen is, of course, tiny so far. But this is the initial stage of discovery. To build up and test hydrogen harvesters will require much further effort.”

The work is an international collaboration involving groups from China and the Netherlands who supported theoretical aspects of the research.