Surface-Limited Platinum Electrodeposition on Highly Ordered Pyrolytic Graphite

Abstract

Recently we reported an overpotential electrodeposition method to deposit contiguous Pt nanoplatelets/thin films directly onto the surface of self-standing electrospun carbon nanofiber mats, leading to Carbon Nanofibrous Electrodes (NFEs) [1]. We demonstrated the high electrocatalytic activity and improved stability over high-potential prolonged cycling compared to conventional Pt nanoparticles on carbon. In order to study more in detail the Pt growth and the morphology of the obtained Pt surfaces as a function of the experimental parameters, we investigated such surface-limited electrodeposition employing Highly Ordered Pyrolytic Graphite (HOPG) as a model surface.We studied Pt deposition on HOPG by contact-mode AFM imaging. Pt interconnected particles and Pt networks can be grown directly onto the substrate at high overpotential as a function of the deposition time, with no significant variation in thickness and size of the connected particles. A progressive coverage of the substrate surface is clearly present, eventually leading to the formation of Pt thin islands below 2 nm in thickness. We also show by TEM analysis that Pt(111) facets are preferentially deposited and grown on the substrate.We studied the deposition mechanism at high overpotential. We will show that the Pt deposition is not diffusion-limited and that it overlaps with other processes. We will discuss the effects of these other processes (H2 evolution on Pt and HOPG) on the Pt deposition. Additional indications can be derived from computer simulations (e.g. DigiElch®) that approximate the experimental conditions. The rate constants used for the simulations were obtained experimentally and their variation with HOPG surface preparation will also be presented.In this work we will present our advances towards understanding the nature of this surface-limited electrodeposition. The morphological and structural characterization of these Pt features on HOPG will be presented and discussed, along with some early insights on their growth mechanism.[1] G. Ercolano, F. Farina, S. Cavaliere, D.J. Jones, J. Rozière, J. Mater. Chem. A 5 (2017) 3974-3980.