Measuring the Effects of Tunable Alkanethiol Monolayers on the Adsorption and Collision Dynamics of Platinum Nanoparticles

Platinum nanoparticles (PtNPs) catalyze the Hydrogen Evolution Reaction upon colliding at a catalytically inactive electrode surface when sufficient potential is applied, and in the presence of adequate hydrogen ion concentration. Here, we investigated nanoscale interactions of PtNPs at alkanethiol modified gold electrode surfaces and examined the effects of monolayer hydrophilicity/hydrophobicity on single particle collision dynamics. After colliding with and adsorbing onto the modified electrode surface, PtNPs generate measurable cathodic current arising from the reduction of hydrogen. Each single particle collision is indicated by a spike-step or spike of current in the current time trace. The shape, frequency, and size of these current steps are dependent on the terminal chemistry of the alkanethiol covalently bound to the electrode surface. Using the collisional frequency as a function of PtNP concentration, we determined the rate of particle adsorption, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mrow><mml:mi>k</mml:mi></mml:mrow> <mml:mrow><mml:mtext>ads</mml:mtext></mml:mrow> </mml:msub> </mml:math> , to be 2.23 × 10^-6 cm/s and 8.85 × 10^-6 cm/s for -CH₃ and -OH terminated surfaces, respectively. Electrodes modified with a mixture of alkanethiols (-CH₃/-OH) exhibited collision frequencies that scale linearly with the ratio of hydrophilicity of the alkanethiol immobilized on the electrode surface. The results indicate the dependence of intermolecular effects on PtNP collision dynamics at the electrode surface, with hydrophobic-dominating surfaces having the least observed collisions. This study provides insights into the influence of surface chemistry on single nanoparticle interactions, which could advance the designs of biosensors and more efficient nanocatalysts by offering a deeper understanding of the interfacial mechanism of PtNPs on modified electrode surfaces.