Evaluating the Effects of Surfactant Templates on the Electrocatalytic Activity and Durability of Multifaceted Platinum Nanostructures

Abstract

High-surface-area multifaceted platinum (Pt) nanoparticles (NPs) exhibit promising electrocatalytic properties for various electrochemical reactions. Effective structural and morphological control is a key factor in attaining improved electrocatalytic activities. Herein, we use low concentrations of surfactants (≲ critical micelle concentration) as templates during Pt electrodeposition to produce multifaceted Pt NPs and evaluate their electrochemical active surface area (Aecsa) and activity for the oxygen reduction reaction (ORR). The electrodeposition potentials for the nucleation and growth stages were optimized through an evaluation of the surface coverage and uniformity of the size of the electrodeposited particles. The electrodeposition was performed in the presence of a cationic (i.e., cetyltrimethylammonium bromide, CTAB), anionic (i.e., sodium dodecyl sulfate, SDS), or non-ionic [i.e., polyoxyethylene (20) stearyl ether, Brij 78] surfactant. The deposited Pt NPs have the mean diameter of 49 ± 11 nm for Brij 78, 54 ± 9 nm for CTAB, and 57 ± 14 nm for SDS, with faceted crystallites exposed on their surfaces as observed using high-resolution transmission electron microscopy. The Aecsa of these Pt nanostructures increased when using surfactants as templates during electrodeposition; the Aecsa increased in the order of non-templated Pt (12.4 m2 g–1) < Pt-CTAB (16.2 m2 g–1) < Pt-SDS (17.1 m2 g–1) < Pt-Brij 78 (20.4 m2 g–1). The mass activities of Pt-CTAB, Pt-SDS, and Pt-Brij 78 toward the ORR were also calculated to be, respectively, ∼1.5, 1.6, and 2.0 times higher than that of non-templated Pt at 0.8 V (vs RHE). The Pt NPs electrodeposited in the presence of surfactants exhibited structural durability when subjected to a test of 5000 cycles of the applied potential in a square wave form between 0.6 and 0.95 V (vs RHE). This comparative study offers several insights into the design of surfactant-assisted electrodeposition techniques for creating multifaceted Pt with enhanced surface area and activity toward the ORR and electrocatalytic stability.