Birch-Type Hydrogenation of Few-Layer Graphenes: Products and Mechanistic Implications

Few-layer graphenes, supported on Si with a superficial oxide layer, were subjected to a Birch-type reduction using Li and H₂O as the electron and proton donors, respectively. The extent of hydrogenation for bilayer graphene was estimated at 1.6-24.1% according to Raman and X-ray photoelectron spectroscopic data. While single-layer graphene reacts uniformly, few-layer graphenes were hydrogenated inward from the edges and/or defects. The role of these reactive sites was reflected in the inertness of pristine few-layer graphenes whose edges were sealed. Hydrogenation of labeled bilayer (¹²C/¹³C) and trilayer (¹²C/¹³C/¹²C) graphenes afforded products whose sheets were hydrogenated to the same extent, implicating passage of reagents between the graphene layers and equal decoration of each graphene face. The reduction of few-layer graphenes introduces strain, allows tuning of optical transmission and fluorescence, and opens synthetic routes to long sought-after films containing sp³-hybridized carbon.