A research team, led by The University of Manchester, have reported a way to use light to accelerate proton transport through graphene, which could advance hydrogen generation technologies.
Proton transport is a key step in many renewable energy technologies, such as hydrogen fuel cells and solar water splitting, and it was also previously shown to be permeable to protons. The recent study has shown that light can be used to accelerate proton transport through graphene, despite the fact that it was previously thought that graphene was impermeable to protons. The researchers found that when graphene is illuminated with light, the electrons in the graphene become excited. These excited electrons then interact with protons, accelerating their transport through the material.
"Understanding the connection between electronic and ion transport properties in electrode-electrolyte interfaces at the molecular scale could enable new strategies to accelerate processes central to many renewable energy technologies, including hydrogen generation and utilization," said lead researcher Dr. Marcelo Lozada-Hidalgo.
Graphene is an excellent electronic conductor and, unexpectedly, was also found to be permeable to protons. However, its proton and electronic properties were believed to be completely unrelated. Now, the team measured both graphene’s proton transport and electronic properties under illumination and found that exciting electrons in graphene with light accelerates proton transport.
The evidence of this connection was the observation of a phenomenon known as ‘Pauli blocking’ in proton transport. This is an unusual electronic property of graphene, never observed in proton transport. In essence, it is possible to raise the energy of electrons in graphene to such an extent that graphene no longer absorbs light – hence the ‘blocking’. The researchers demonstrated that the same blocking takes place in light-driven proton transport by raising the energy of electrons in graphene. This unexpected observation demonstrates that graphene’s electronic properties are important to its proton permeation properties.
Dr. Shiqi Huang, co-first author of the work, said: “We were surprised that the photo response of our proton conducting devices could be explained by the Pauli blocking mechanism, which so far had only been seen in electronic measurements. This provides insight into how protons, electrons and photons interact in atomically thin interfaces”.
“In our devices, graphene is being effectively bombarded with protons, which pierce its electronic cloud. We were surprised to see that photo-excited electrons could control this flow of protons”, commented Dr. Eoin Griffin, co-first author.