A mechanistic study of Pt particle electrodeposition and growth on a self-assembled monolayer as an active template

Abstract

• Application of monolayers on gold as templates for deposition of Pt particles. • Evaluation of particle growth using cyclic voltammetry and chronoamperometry. • Evaluation of growth mechanism with SH model using chronoamperometric deposition. • Evaluation of growth mechanism using time dependant image J analysis of the SEM. • Comparing mechanism of growth evaluated using SH model with SEM analysis. Platinum is an essential component in many commercial catalytic processes. However, due to its cost and availability considerable effort is made to control the amount, location, and accessibility of the platinum species on an electrode surface. The current study investigates a low-cost, and versatile method for the deposition of Pt particles using a self-assembled monolayer (SAM) as an active assisted template on a gold electrode. Alkane (HSCH 2 (CH 2 ) 8 CH 3 ), alcohol (HSCH 2 (CH 2 ) 9 CH 2 OH) and carboxylate (HSCH 2 (CH 2 ) 8 CH 2 COOH) terminated monolayers were used to probe the impact of hydrophobicity on particle size, population density and growth mechanism. Cyclic voltammetry (CV) and chronoamperometry (CA) were employed to induce particle growth. From the CA data a dimensionless theoretical plot was calculated based on the Scharifker and Hills model to establish the mechanism as either progressive or instantaneous. The time-dependent study revealed a progressive nucleation mechanism for Pt particles synthesized on all three electrode surfaces, whereas microscopy and image analysis revealed an instantaneous nucleation mechanism for the alkane template only and progressive nucleation pathways for the alcohol and carboxylate SAM surfaces. The results indicated that SAM templating could be used to effectively control particle growth in a predictable fashion, however there is a limitation in application of the existing model due to a combination of factors including the migration of the SAM monomers on the electrode surface, the hydrophobicity of the terminal moieties and the occurrence of secondary and subsequent nucleation and growth phases. In addition, post-particle deposition CV was used to determine the impact of the SAM template on the active area of the Pt particles available for catalysis and showed that the hydrophobic SAM coatings gave significantly higher activity.