Spectroscopic and mechanistic surface studies of noble metal hydride cluster synthesis on graphene oxide for hydrogen storage

Graphene and noble metal derivatives represent a crucial class of materials with significant potential for hydrogen storage applications. However, the underlying mechanism of metal hydride formation in a single-step aqueous synthesis is still not fully understood. In this work, an all-aqueous direct chemical reduction synthesis was used to form nanocomposites with Au, Pd, and Pt noble metal nanoclusters utilizing the surface functional groups on graphene. X-ray powder diffraction (XRD) characterization of the resulting nanocomposites showed the presence of PtH and PdH metal clusters on graphene. Gibbs free energy reaction pathways indicate the formation of metal hydride is energetically preferrable through the dissociation of molecular H-2 on the surface of metal clusters. Furthermore, through density functional theory (DFT) calculations, the formation of metal hydride is found to be thermodynamically and kinetically prohibitive on the Au cluster, consistent with the XRD hydride patterns. Since Au has a more positive reduction potential compared to that of Pd and Pt, the direct formation of metal clusters is kinetically more feasible in the presence of NaBH4. Overall, this scalable methodology offers a versatile electrode material-selection for solid-state hydrogen storage and informs an all-aqueous synthesis route for creating noble metal hydride nanocomposites with high surface carbon nanomaterials.