Surface-Limited Electrodeposition of Continuous Platinum Networks on Highly Ordered Pyrolytic Graphite

Abstract

Continuous thin platinum nanoplatelet networks and thin films were obtained on the flat surface of highly ordered pyrolytic graphite (HOPG) by high overpotential electrodeposition. By increasing the deposition time, the morphology of the Pt deposits can be progressively tuned from isolated nanoplatelets, interconnected nanostructures, and thin large flat islands. The deposition is surface-limited and the thickness of the deposits, equivalent to 5 to 12 Pt monolayers, is not time dependent. The presence of Pt (111) facets is confirmed by High Resolution Transmission Electron Microscopy (HRTEM) and evidence for the early formation of a platinum monolayer is provided by Scanning Transmission Electron Microscopy and Energy Dispersive X-rays Spectroscopy (STEM-EDX) and X-ray Photoelectron Spectroscopy (XPS) analysis. The electroactivity towards the oxygen reduction reaction of the 2D deposits is also assessed, demonstrating their great potential in energy conversion devices where ultra-low loading of Pt via extended surfaces is a reliable strategy.

Electrodeposition of Two-Dimensional Pt Nanostructures on Highly Oriented Pyrolytic Graphite (HOPG): The Effect of Evolved Hydrogen and Chloride Ions

“…However, under the conditions of high overpotentials (E = −2 V vs. Ag/AgCl), the loading is expected to be much lower based on the size of the Pt features: the Pt NPs in Figure 8 (E = −0.5 V) are much larger than the nanostructures on Figure 10 (E = −2 V) are mostly below 2 nm in high. This sample prepared at high overpotentials shows the nanoplatelets previously described [ 19 , 28 , 29 ], together with some larger Pt aggregates. The latter are smaller than those seen above obtained at lower overpotentials ( Figure 8 ) (ca.…”

“…In addition to platelets 40 nm in diameter and 3–4 nm thick, larger Pt aggregates (ca. 120 × 30 nm) appears, which are not observed when the sample is prepared at larger overpotentials (−2.0 V) [ 19 , 29 ].…”

“…Pt/HOPG Electrode preparation: Full details are given elsewhere for the preparation of the Pt electrode on HOPG and [ 19 , 29 ]. Briefly, the HOPG was exposed to the solution, and the deposition was performed either on a 2- or 3-electrode cell.…”

“…The resulting self-supported nanofibrous electrode (NFE) was demonstrated to be an efficient and stable ORR material. The understanding of the mechanistic aspects that yield the electrodeposition of a Pt thin film on a carbonaceous model surface, such as Highly Oriented Pyrolytic Graphite (HOPG), is crucial for the deposition of ultra-low and continuous coverage of Pt on carbon supports of different morphology and porosity [ 29 ].…”

Ultra-Thin Platinum Deposits by Surface-Limited Redox Replacement of Tellurium

“…The preparation of Pt thin films to achieve ultra-low Pt loaded electrodes with high performance and stability is a challenge however, due to the complexity of several fabrication techniques and the difficulty in tailoring thickness and continuity of the deposits [ 11 , 12 , 13 ]. For this purpose, electrochemical fabrication methods are often considered, due to their ease of use and overall cost effectiveness [ 14 , 15 , 16 ]. Conventional overpotential electrodeposition results in preferential growth at areas with high surface energy, such as step edges and surface defects, leading to incomplete substrate coverage at low thicknesses and non-uniform deposits [ 17 , 18 ].…”