Carbon Allotropes Accelerate Hydrogenation via Spillover Mechanism

Solid-phase hydrogenation kinetics can be substantially increased by utilizing hydrogen spillover phenomenon. Carbonaceous allotropes are considered as promising spillover agents (SOAs) for improved hydrogen transport rate. We studied the effect of carbon-based SOA properties on irreversible hydrogenation. We divided the reaction into two major stages, near- and far-field hydrogenation (with respect to a catalyst), and determined their rate-limiting steps. The hydrogenation kinetics was analyzed for hydrogen originating from either catalyst on activated carbon or catalyst-decorated carbon nanotubes. The far-field hydrogenation is investigated for three types of loaded nanocarbons: 1D (nanotubes), 2D (graphene), and 3D (activated carbon). We found that the kinetics acceleration is strongly correlated with the nanocarbon dimension, 1D > 2D > 3D, and could reach almost 2 orders of magnitude. These findings are useful for the study of reversible hydrogen storage applications.