Collision Incidents of Single Tetrahexahedral Platinum Nanocrystals Recorded by a Carbon Nanoelectrode

Abstract

Recently, collision mode has been adopted to study the electrochemical or photoelectrochemical behavior of single particles touching and/or attaching on a biased ultramicroelectrode (UME). However, to correlate the reaction activity to the nanocrystal structure still remains challenging because of: (1) the uncontrolled structure and size of the single nanoparticle;(2) the uncertainty of one particle in each collision incident since the size of UME is much larger than that of the single nanoparticle. To these problems, we synthesized well-defined convex tetrahexahedral platinum nanocrystals (THH Pt NC) with an average size of 30 nm and fabricated a carbon nanoelectrode through pyrolysis of butane. The current fluctuation caused by oxygen reduction reaction (ORR) during the single collision incident of THH Pt NC was detected by the carbon nanoelectrode. It is reasonable to use nanocrystals with well-defined morphology and size in the collision experiments. However, the adoption of nanoelectrode will decrease the collision frequency and shorten the standing time of nanocrystals on the electrode surface. How to figure out the kinetics from the current fluctuations in the single collision incident still remains challenging.

Nanoimpacts at Active and Partially Active Electrodes: Insights and Limitations

“…We noted that particle collisions measured at −660 mV vs. SCE did not produce true steady‐state responses, yet at −750 mV they did. We attributed the decay in current at −660 mV to deactivation of the Pt particles, which has been reported previously (especially in other nano‐impact studies) . Because we also observed deactivation of a Pt microelectrode toward the HER (Supporting Information, Figure S6), we questioned whether Pt particle impacts at a partially‐active Pt electrode could help explain the deactivation mechanism.…”

“…The electrochemical nanoimpact technique has recently emerged as a means of measuring the properties of individual entities rather than ensembles . This method has recently been used to study particle size, porosity, and heterogenous catalytic rates on a single‐particle basis; these parameters are critically important to the performance of an electrocatalyst. While a wide variety of systems have been analyzed through particle‐electrode impacts, several typical schemes have emerged.…”

“…The requirement for an active particle‐inactive electrode in ECA schemes (or vice versa in blocking schemes) limits both the scope of particle‐electrode impact detection and the depth of mechanistic insight such impacts can reveal. ECA schemes have typically required the addition of an inner‐sphere redox probe, such as hydrogen peroxide or hydrazine, or used protons or oxygen already present in solution . Regardless of the redox species, the measurements require that the particle be more active toward the redox reaction than the electrode.…”

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

“…A large number of catalytic particles can be characterized without the need for specialized instrumentation, providing electrochemical insight into catalytic reactions including proton reduction, [26][27][28] hydrazine oxidation, 26 water oxidation, 29 NaBH 4 oxidation, 30 and oxygen reduction. [31][32][33] In this manuscript, we characterize ORR on single citrate-capped Pt NPs with radii ranging from 2−24 nm using EA. Measurable ORR currents at individual particles of ∼2-3 nm radius (a relevant size for particles used in fuel cell cathodes) are achieved by increasing the dissolved O 2 concentration by elevating the pressure.…”

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

“…In contrast, in mediated faradaic impact methods, redox mediators undergo oxidation or reduction on the surface of electroactive particles that collide with an otherwise inert UME, leading to amplified current spikes in the current–time response . Redox mediators such as ferrocene derivatives, potassium ferrocyanide, hydrazine, NaBH 4 , and so forth have been employed in impact measurements for biosensing applications − and for analyzing electrocatalysts. , Faradaic impact electrochemistry has been employed to study the ORR at catalysts such as Pt nanoparticles − and multiwalled carbon nanotubes . Resolving heterogeneity in catalytic activity within nanoparticle populations can be addressed in this manner under different conditions, including alkaline and acidic solutions as well as high pressures …”