A High-Pressure System for Studying Oxygen Reduction During Pt Nanoparticle Collisions

Abstract

Here we report measurements of the oxygen reduction reaction (ORR) at single Pt nanoparticles (NPs) through their collision with a Au microdisk electrode of lower electrocatalytic activity. Performing measurements at an elevated pressure (10-atm, pure O2) raises the O2 concentration ∼50-fold over air-saturated measurements, allowing the ORR activity of smaller Pt NPs to be resolved and quantified, compared to measurements taken at atmospheric pressure. Single-NP ORR current vs potential measurements for 2.6, 16, and 24 nm radius citrate-capped Pt NPs, show the catalytic activity of the smallest Pt NPs to be roughly one order of magnitude greater than the activity of the larger NPs. The particle-by-particle nature of our measurement quantifies the distribution of electrocatalytic activities of individual particles, which we determine to be larger than can be explained by the distribution of particle sizes. Additionally, we report that some of the observed ORR current transients contain multiple sharp peaks per single-NP measurement, indicating multiple collisions of a single Pt NP at the electrode surface.

Utilizing the Oxygen Reduction Reaction in Particle Impact Electrochemistry: A Step toward Mediator-Free Digital Electrochemical Sensors

“…31,46 A slight shift in the half-wave potential is also observed, which has been attributed to insufficient buffer capacity when the O 2 concentration becomes too high. 31 In order to confirm the voltammogram shape and the dependency of the limiting-current level on oxygen concentration, the PBS solution was fed with pure O 2 and degassed with N 2 . The red and blue curves in Figure 1 show the increased and decreased limiting-current levels upon oxygen saturation and depletion, respectively.…”

“…29,30 Faradaic impact electrochemistry has been employed to study the ORR at catalysts such as Pt nanoparticles 31−34 and multiwalled carbon nanotubes. 35 Resolving heterogeneity in catalytic activity within nanoparticle populations can be addressed in this manner 31 under different conditions, including alkaline 35 and acidic 33 solutions as well as high pressures. 31 Here, we employ the ORR in blockade impact electrochemistry for detecting microparticles under physiological salt conditions.…”

On-Chip Electrokinetic Micropumping for Nanoparticle Impact Electrochemistry

“…Thus, we conclude that a purely electrostatic approach oversimplifies the situation, as the steady ME current is nonzero throughout the experiment; see Figure 2a. In fact, we most likely induce the reduction of dissolved oxygen at the platinum ME 38,39,44…”

Electronic Circuit Simulations as a Tool to Understand Distorted Signals in Single-Entity Electrochemistry

“…The emerging field of “single-entity electrochemistry” (SEE) refers to measurement and interpretation of the electrical transient signals generated when a single entity, e.g., a nanoparticle, a single molecule, a droplet, a micelle, or a living cell, undergoes electrochemical processes at suitable interfaces, including micro- and nano-electrodes or -pipets, nanopores, etc. − The technique’s capability to probe a signal from single entities makes it powerful for delivering both individual and statistical information on these entities. This makes it beneficial for a broad range of investigations, including nanoparticle characterizations and dynamic transformations, − agglomeration study, ion diffusion and solvation studies, , detection and identification of single bacteria or viruses, − catalytic activity investigation of single enzymes, detection of conformation changes of a single DNA, single-molecule detection, battery material characterization, and investigation of the catalytic activity of individual nanoparticles. − …”

“…This makes it beneficial for a broad range of investigations, including nanoparticle characterizations and dynamic transformations, 6 − 9 agglomeration study, 10 ion diffusion and solvation studies, 11 , 12 detection and identification of single bacteria or viruses, 13 − 15 catalytic activity investigation of single enzymes, 16 detection of conformation changes of a single DNA, 17 single-molecule detection, 18 battery material characterization, 19 and investigation of the catalytic activity of individual nanoparticles. 20 − 23 …”