Hydrogen Spillover and Storage on Graphene with Single-Site Ti Catalysts

Hydrogen spillover and storage for single-site metal catalysts, including single-atom catalysts (SACs) and single nanocluster catalysts, have been elucidated for various supports but remain poorly understood for inert carbon supports. Here, we use synchrotron-radiation-based methods to investigate the role of single-site Ti catalysts on graphene for hydrogen spillover and storage. Our in situ angle-resolved photoemission spectra results demonstrate a band gap opening, and X-ray absorption spectra reveal the formation of C–H bonds, both indicating partial graphene hydrogenation. With increasing Ti deposition and H2 exposure, the Ti atoms tend to aggregate to form nanocluster catalysts and yield 13.5% sp3-hybridized carbon atoms corresponding to a hydrogen-storage capacity of 1.11 wt % (excluding the weight of the Ti nanoclusters [Bhowmick, R. et al. J. Am. Chem. Soc. 2011, 133 (14), 5580]). Our results demonstrate how a simple spillover process at Ti SACs can lead to covalent hydrogen bonding on graphene, thereby providing a strategy for the rational design of carbon-supported single-site catalysts.