Aqueous proton transfer across single-layer graphene

• Published in: Nature communications Vol. 6; no. 1; p. 6539
• Main Authors: Achtyl, Jennifer L., Unocic, Raymond R., Xu, Lijun, Cai, Yu, Raju, Muralikrishna, Zhang, Weiwei, Sacci, Robert L., Vlassiouk, Ivan V., Fulvio, Pasquale F., Ganesh, Panchapakesan, Wesolowski, David J., Dai, Sheng, van Duin, Adri C. T., Neurock, Matthew, Geiger, Franz M.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 17.03.2015; Nature Publishing Group; Nature Pub. Group
• Subjects: 119/118; 140/125; 140/133; 639/638/298/918; 639/638/440; catalysis (heterogeneous); charge transport; electrodes - solar, mechanical behavior; energy storage (including batteries and capacitors); Helium; Humanities and Social Sciences; hydrogen and fuel cells; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; materials and chemistry by design; MATERIALS SCIENCE; multidisciplinary; PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; Science; Science (multidisciplinary); Silica; solar (fuels); synthesis (novel materials)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms7539

Proton transfer across single-layer graphene proceeds with large computed energy barriers and is therefore thought to be unfavourable at room temperature unless nanoscale holes or dopants are introduced, or a potential bias is applied. Here we subject single-layer graphene supported on fused silica to cycles of high and low pH, and show that protons transfer reversibly from the aqueous phase through the graphene to the other side where they undergo acid–base chemistry with the silica hydroxyl groups. After ruling out diffusion through macroscopic pinholes, the protons are found to transfer through rare, naturally occurring atomic defects. Computer simulations reveal low energy barriers of 0.61–0.75 eV for aqueous proton transfer across hydroxyl-terminated atomic defects that participate in a Grotthuss-type relay, while pyrylium-like ether terminations shut down proton exchange. Unfavourable energy barriers to helium and hydrogen transfer indicate the process is selective for aqueous protons. Proton transfer across graphene is associated with large computed energy barriers and is thought to be generally unfavourable. Here, the authors observe aqueous proton transfer through graphene subjected to pH cycling, suggesting that it is due to transfer through rare, naturally occurring atomic defects.