Abstract
We discuss the electrodeposition of two-dimensional (2D) Pt-nanostructures on Highly Oriented Pyrolytic Graphite (HOPG) achieved under constant applied potential versus a Pt counter electrode (Eappl = ca. −2.2 V vs. NHE, normal hydrogen electrode). 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. NHE), 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. The reducing agents for the spontaneous deposition of Pt from solution are proposed as step edges that get oxidized in the solution. We discuss the possible oxidation reactions for the edge sites.
Highlights
The use of Pt is of interest in many renewable energy applications, namely, in the use of technologies that convert chemical energy to electricity, such as proton exchange membrane fuel cells (PEMFCs)
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The rates of deposition vary widely, and we propose that this is due to the different conditions of the surface exposed by cleavage of the C–C stacking with tape
Summary
The use of Pt is of interest in many renewable energy applications, namely, in the use of technologies that convert chemical energy to electricity, such as proton exchange membrane fuel cells (PEMFCs). Bi- or tri-metallic particles, alloys [3,4,5,6] and successively de-alloyed [7] structures where Pt is associated with other transition metals (e.g., Ni, Co, Cu) have been prepared and demonstrated high ORR activity and durability Another very promising class of tailored electrocatalysts is represented by core@shell nanostructures with a thin Pt skin covering a transition metal core in 0D (particle-like) [8,9,10] and 1D (fiber-like) morphologies [11,12,13,14,15,16,17]. Among the methods being investigated to produce Pt conformal thin films, atomic layer deposition (ALD), electrochemical atomic layer deposition (EC-ALD), pulsed laser deposition, surface-limited redox replacement (SLRR), galvanic displacement [18,21,23,24] and other vacuum techniques, such as magnetron sputtering are employed [25]
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