Metal Catalyzed Electrochemical Synthesis of Hydrocarbons from Epitaxial Graphene

Abstract

Pt/Au transition metal catalysts are shown to significantly improve the electrochemical hydrogenation of low defect density epitaxial graphene (EG) layers ∼2ML thick on Si-face 6H-SiC Initial experiments using Pt nanoparticles deposited from aqueous solution showed large increases in hydrogenation, however, this method demonstrated large variability, attributed to the aqueous nature of the catalyst deposition, known to change the conductivity and reactivity of graphene, as well as clustering of Pt nanoparticles. To reduce process variability, 20 nm thick evaporated metals were used. From Raman, the average observed hydrogen cluster density ∼1011 cm−2 was similar to the average densities of intrinsic defects (1010,11 cm−2) and charge impurities (1011 cm−2) consistent with recent reports that these sites play a crucial role in the hydrogenation of EG. Au catalysts (3.23 ± 0.22%wt) showed slightly better H-incorporation than Pt (2.81 ± 0.03%wt), an observation we attribute to the fact that H2 dissociation is no longer the rate-limiting step, as H+ is readily available in the aqueous state. The electrochemical enablement of these hydrogenation pathways using catalysts offers new routes to carbon chemistries for hydrogen storage, bandgap engineered hydrocarbons as well as EG-based battery electrodes.