Electrodeposition of two-dimensional Pt nanostructures on highly oriented pyrolytic graphite (HOPG): the effect of evolved hydrogen and chloride ions

Abstract

We discuss the electrodeposition of two-dimensional (2D) Pt-nanostructures on HOPG achieved under constant applied potential versus a Pt counter electrode (Eappl = ca. - 2.2 V vs RHE). The deposition conditions are discussed in terms of the electrochemical behavior of the electrodeposition precursor (H2PtCl6). We performed cyclic voltammetry (CV) of the electrochemical Pt deposit on HOPG and on Pt substrates to study the relevant phenomena that affect the morphology of Pt deposition. Under conditions where the Pt deposition occurs and H2 evolution is occurring at the diffusion-limited rate (- 0.3 V vs RHE), Pt forms larger structures on the surface of HOPG, and the electrodeposition of Pt is not limited by diffusion. This indicates the need for large overpotentials to direct the 2D growth of Pt. Investigation of the possible effect of Cl- showed that Cl- deposits on the surface of Pt at low overpotentials, but strips from the surface at potentials more positive than the electrodeposition potential. The CV of Pt on HOPG is a strong function of the nature of the surface. We propose that during immersion of HOPG in the electrodeposition solution (3 mM H2PtCl6, 0.5 M NaCl, pH 2.3) Pt islands are formed spontaneously, and these islands drive the growth of the 2D nanostructures.

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

“…It should be noticed that the obtained morphologies and trends are reproducible, while the current densities obtained for Pt electrodeposition can be slightly different from one sample to another. This is due to the different conditions of the HOPG surface exposed by cleavage of the C–C stacking [ 28 ].…”

“…Indeed, spontaneous electroless deposition on HOPG has been observed from Pt solutions, indicating the presence of metal seeds before the overpotential electrodeposition. The reducing agents for this spontaneous deposition are likely HOPG step edges that get oxidized in solution [ 28 ].…”

“…Spontaneous deposition of Pt agglomerates, nanoparticles, and networks on HOPG was induced from water as well as non-aqueous polar solvents [ 24 , 25 , 26 ] and was explained in terms of the reduction of Pt by oxidized defect sites on the surface and step-edges [ 24 ]. However, the mechanism appears to be more complex, involving not only graphite step-edges, but also hydrogenated sites [ 27 , 28 ]. As a consequence, Pt nuclei may be already present before the application of the overpotential to the electrode [ 28 ].…”

“…However, the mechanism appears to be more complex, involving not only graphite step-edges, but also hydrogenated sites [ 27 , 28 ]. As a consequence, Pt nuclei may be already present before the application of the overpotential to the electrode [ 28 ].…”

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 ].…”