Surface limited redox replacement (SLRR) is an electrochemical technique for depositing metal films monolayers in thickness, typically on other metals. As interest in graphene as a highly conductive, chemically resistant support for metal nanoparticles has risen, some have sought to apply this deposition technique to graphene as an electrochemical alternative to other chemical or vacuum-based deposition techniques. To better understand the nature of the interactions between the metal and graphene, our group has used this technique to deposit Pt on graphene to observe the structure of Pt and its epitaxy with the substrate. We have previously found that Pt prefers to bind to the bridge sites of graphene, preferring to form a simple-cubic-like structure and producing a slight lattice compression. We sought to expand on this study by observing the interactions of Pd with graphene.

Pd was deposited on graphene using Cu-mediated SLRR, however, most Cu-mediated SLRR is performed with CuSO₄ or Cu(ClO₄)₂ dissolved in H₂SO₄ or HClO₄. This does not necessarily produce a strong Cu underpotential deposition feature on graphene, so HCl was used as the electrolyte instead. This produced a substantially more pronounced underpotential deposition feature, but cyclic voltammograms in this solution do not appear to agree with typical Cu-S-Cl Pourbaix diagram.

This also resulted in two different types of structures, primarily Cu-containing films and primarily Pd-containing nanoparticles. The films were always found in the presence of the particles, but the particles did not always have accompanying films. A structural analysis of the particles determined that they preferred to interface with graphene along the (110) planes of Pd and have a slight elongation along the [001] direction of about 1.6% when oriented such that their columns were visible in the scanning transmission electron microscope. Based on an analysis of their orientation, this alignment and elongation appear to be the result of Pd minimizing its interfacial strain with graphene. A structural and compositional analysis of the films determined them to be CuCl, and they prefer to interface with graphene along their (111) plane, although the reason for this particular orientation is unclear as there is weaker evidence for a correlation between the alignment of the graphene and the films.