▎ 摘　　要

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 H-2 exposure, the Ti atoms tend to aggregate to form nanocluster catalysts and yield 13.5% sp(3)-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.