2D materials show promise for green technologies:
The Manchester researchers led by Professor Andre Geim and Dr. Marcelo Lozada-Hidalgo found that one-atom thick materials like graphene are highly permeable to protons, nuclei of hydrogen atoms. However, they also found that other 2-D materials such as molybdenum sulphide (MoS2), that were just three atoms thick, were completely impermeable to protons. These results suggested that only one-atom thick crystals could be permeable to protons. Protons can easily permeate through few-layered micas despite the fact that they are 10 times thicker than graphene. Micas, like graphite, consist of crystal layers stacked on top of each other and can be sliced down to a single layer. The team isolated one of these layers and found that it was 100 times more permeable to protons than graphene. At first glance, this result seems impossible because micas are too thick for protons to permeate—they are much thicker than monolayer MoS2 that is completely impermeable to protons. However, micas can be thought of as crystal slabs pierced by tubular channels. These channels aren't empty but filled with hydroxyl groups that are like the proton-conducting one-dimensional chains in water. Protons jump along these chains, turning the material into an excellent proton conductor.
The research team found that proton conductivity in atomically-thin micas is 10 to 100 times higher than in graphene. It is encouraging because graphene is already being considered as a promising proton conducting material. Research results show micas could be even more promising—not least because they are abundant and inexpensive. The researchers also found that micas become particularly highly conductive in a temperature range that has been notoriously inaccessible for the related technologies.
Source: Nano Magazine