Effects of para-substituents of styrene derivatives on their chemical reactivity on platinum nanoparticle surfaces

Abstract

Stable platinum nanoparticles were successfully prepared by the self-assembly of para-substituted styrene derivatives onto the platinum surfaces as a result of platinum-catalyzed dehydrogenation and transformation of the vinyl groups to the acetylene ones, forming platinum-vinylidene/-acetylide interfacial bonds. Transmission electron microscopic measurements showed that the nanoparticles were well dispersed without apparent aggregation, suggesting sufficient protection of the nanoparticles by the organic capping ligands, and the average core diameter was estimated to be 2.0 ± 0.3 nm, 1.3 ± 0.2 nm, and 1.1 ± 0.2 nm for the nanoparticles capped with 4-tert-butylstyrene, 4-methoxystyrene, and 4-(trifluoromethyl)styrene, respectively, as a result of the decreasing rate of dehydrogenation with the increasing Taft (polar) constant of the para-substituents. Importantly, the resulting nanoparticles exhibited unique photoluminescence, where an increase of the Hammett constant of the para-substituents corresponded to a blue-shift of the photoluminescence emission, suggesting an enlargement of the HOMO-LUMO band gap of the nanoparticle-bound acetylene moieties. Furthermore, the resulting nanoparticles exhibited apparent electrocatalytic activity towards oxygen reduction in acidic media, with the best performance among the series of samples observed with the 4-tert-butylstyrene-capped nanoparticles due to an optimal combination of the nanoparticle core size and ligand effects on the bonding interactions between platinum and oxygen species.

Organically Capped Iridium Nanoparticles as High-Performance Bifunctional Electrocatalysts for Full Water Splitting in Both Acidic and Alkaline Media: Impacts of Metal–Ligand Interfacial Interactions

“…For example, it has been shown that the electronwithdrawing/donating property of the para-substituent groups of phenyl ligands can manipulate the nanoparticle's surface electronic structure and hence the electrocatalytic activity, because of effective metal−ligand interfacial charge transfer. 41,42 In the present study, we demonstrate that by surface functionalization of Ir nanoparticles with acetylene derivatives, the resulting Ir nanoparticles can be used as high-performance electrocatalysts toward both HER and OER in both acidic and alkaline media (with the alkaline HER and OER activity significantly better than that of commercial Pt/C and Ir/C). This is ascribed to the formation of conjugated Ir−C metal−ligand interfacial bonding interactions that reduces the electron density of the Ir nanoparticles and the interactions with critical reaction intermediates, in comparison to the mercapto-(Ir−S) and nitrene-capped (IrN) counterparts.…”

Well-Defined Nanoparticle Electrocatalysts for the Refinement of Theory

“…Additionally, because small metal NPs are inherently unstable, they are usually covered with a monolayer or sub-monolayer of monomeric or polymeric ligands. In addition to providing stability, the ligands or capping agents used during NP synthesis can also be used to control the structure and composition of the resulting NP; − however, the ligands themselves can alter the electrocatalytic activity of the underlying metal NP. − Keeping these limitations in mind, a brief introduction to the principal synthetic techniques currently used for preparing metal nanoscale electrocatalysts with a high level of synthetic control is provided next.…”

Surface Modification for Promoting Durable, Efficient, and Selective Electrocatalysts

“…The presence of organic ligands at the Pt surfaces is likely to impact the adsorption and dissociation energetics of O 2 and oxygenated intermediates (O*, OH*, OOH*, HOO*) that govern the activity and selectivity of the electrocatalytic processes, whatever the underlying associated mechanisms . A wide range of organic compounds such as surfactants, polymers, capping ligands or adsorbed macrocycles were demonstrated to tune the reactivity of Pt nanoparticles.…”

“…It is further interesting to consider another work of Chen's group that balances impact of surface modification with the structure of the nanoparticles . The chemisorption of para ‐substituted styrene derivatives onto Pt nanoparticles surfaces allows the formation of strongly stabilized Pt nanoparticles through platinum‐vinylidene/or platinum‐acetylide interfacial bonds, hence with strong electronic coupling (Figure ) . The electrocatalytic activity towards ORR in acidic media decreases sharply with para substituents in the order methoxy≪trifluoromethyl<‐ tert‐ butyl .…”

“…The chemisorption of para ‐substituted styrene derivatives onto Pt nanoparticles surfaces allows the formation of strongly stabilized Pt nanoparticles through platinum‐vinylidene/or platinum‐acetylide interfacial bonds, hence with strong electronic coupling (Figure ) . The electrocatalytic activity towards ORR in acidic media decreases sharply with para substituents in the order methoxy≪trifluoromethyl<‐ tert‐ butyl . Although that tert ‐butyl group has a lower Hammett constant (σ=−0.20) than the trifluoromethyl group (σ=+0.54), these nanoparticles have the best performance.…”