Structural and activity comparison of self-limiting versus traditional Pt electro-depositions on nanopillar Ni films

We report the fabrication, characterisation, and electro-catalytic activity of <0.3 mg cm^-2 platinum deposits onto ∼ 500 nm long nickel nanopillar substrates (NiNP) synthesised by glancing angle deposition (GLAD). This is the first reported study of GLAD-based PteNi electro-catalysts and the first alcohol oxidation study on any GLAD based electro-catalyst. The Pt was deposited onto NiNP via either 1) an unconventional, self-limiting, relatively high current density galvanostatic deposition, with a Pt counter electrode as the source of Pt, or 2) via a conventional potentiostatic deposition from Pt salts dissolved in acidic electrolytes. X-ray Diffraction (XRD) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) confirm the successful deposition of Pt onto NiNP, while Scanning Electron Microscopy (SEM) shows that the nanopillar morphology is preserved but the Pt morphology is significantly different between the two methods. The galvanostatic procedure resulted in a conformal Pt deposition over the entire surface of the NiNP. The conventional procedure appeared to be mass-transfer limited, with most of the Pt being deposited on the tops of the NiNP Cyclic voltammetry in 1 M KOH shows an enhancement of the surface area of the catalysts upon Pt deposition and corroborates the presence of Pt on the NiNP surface. Both prepared catalysts show high electro-catalytic activity towards 2-propanol oxidation in the KOH electrolyte at 60 °C. The activity enhancement below 300 mV vs. RHE (RHE = reversible hydrogen electrode) was attributed to the combined activity of the Pt and Ni components in the catalysts. At higher potentials, a bifunctional mechanism was suggested. Finally, a geometric/composition effect may be at work in the traditionally deposited catalyst, and requires further investigation.