From Nanoparticle Ensembles to Single Nanoparticles: Techniques for the Investigation of Plasmon Enhanced Electrochemistry

Abstract

Plasmon enhanced electrochemistry (PEEC), where specific electrochemical reactions are promoted due to the reduced energy barrier of the reaction processes by the light excited "hot carriers" of the plasmonic nanoparticles, has aroused tremendous interest in recent years. A deep understanding of the PEEC process becomes a key issue for facilitating PEEC catalyst design and improving PEEC performance. This concept article begins with a brief discussion of the macroscopic electrochemical method of PEEC study of the plasmonic nanoparticle ensembles. Following that, we highlight two electrochemical techniques that may possess single nanoparticle sensitivity, i. e., scanning electrochemical microscope and nano-impact electrochemistry. The pros and cons of each technique are discussed and an outlook is given. We hope to provide the readers with the current status of PEEC to evoke reflections regarding the reaction mechanisms, performance improvement, and the utilizations to important systems. Figure 2. Macroscopic PEEC measurement. (a) Schematic diagram of Macroscopic PEEC measurement. (b) and (c) PEEC of CO 2 RR at pure plasmonic nanomaterial (CuÀ Ag) modified electrode. Reproduced with permission. [22] Copyright 2020, Royal Society of Chemistry. (d) and (e) PEEC of hydrogen evolution reaction (HER) at a plasmonic nanomaterial (Au nanorods)/semiconductor (MoS 2 ) hybrid modified electrode. Reproduced with permission.

Carbon Nanotubes as Controllable Electric-Field-Induced Bipolar Electrodes for Efficient Water Purification

“…Interestingly, in addition to electric-field-induced electrochemical polarization of CNTs, part of CNTs might be transformed to form monopolar electrodes through electrochemical collision with feeding anode or cathode that played a significant role in the degradation of CIP. ,,, The in situ electrochemical behavior of CNTs near the feeding electrode was recorded using the nanoimpact electrochemistry (NIE) method (details shown in SI Appendix, Text S7). A series of spiked transient currents, including typical oxidative or reductive current signals, were observed at different applied potentials, clearly demonstrating the occurrence of a single CNT collision with the electrode (Figure C,D). ,, Consequently, a monopolar electrode of CNTs­(+) or CNTs(−) was generated via the charge transfer step through the collision of single CNTs with a feeding anode or cathode, respectively. Hence, enhanced redox reactions took place on the surface of CNTs­(+) via electron transfer from CIP to CNTs or PM or direct PM reduction from CNTs(−) with the simultaneous formation of RMnS; simultaneously, the charged CNTs promoted their electrostatic interaction with CIP that mainly existed as a cationic state at pH = 5.0 (p K a1 = 5.9 for CIP) and also facilitated their interaction with negatively charged PM, contributing to the degradation of CIP in the E­(CNTs)/PM process.…”

“…A series of spiked transient currents, including typical oxidative or reductive current signals, were observed at different applied potentials, clearly demonstrating the occurrence of a single CNT collision with the electrode (Figure 4C,D). 25,26,42 Consequently, a monopolar electrode of CNTs(+) or CNTs(−) was generated via the charge transfer step through the collision of single CNTs with a feeding anode or cathode, respectively. Hence, enhanced redox reactions took place on the surface of CNTs(+) via electron transfer from CIP to CNTs or PM or direct PM reduction from CNTs(−) with the simultaneous formation of RMnS; simultaneously, the charged CNTs promoted their electrostatic interaction with CIP that mainly existed as a cationic state at pH = 5.0 (pK a1 = 5.9 for CIP) and also facilitated their interaction with negatively charged PM, contributing to the degradation of CIP in the E(CNTs)/PM process.…”

Single Entity Electrocatalysis

“…In reality, quantifying electrocatalysis at adsorbed nanoparticles is complicated, requiring an understanding of the nanoscale geometry and the mass transfer to/around the nanostructures, which can be dynamic in stochastic electrochemistry. , However, when examined carefully, tracking the electrocatalytic response of a nanoparticle collision is rife with information, previously being used to determine the shape (nonspherical), dynamic rotation, and resulting potential distribution of the colliding nanoparticle. Correlated techniques have emerged to further understand the dynamic movement and spatiotemporal reactivity of these systems, including creative optical − correlated experiments and enabling plasmon-enhanced electrocatalysis, which couples a localized surface plasmon resonance excitation with the electrochemical bias for imaging or enhanced electrocatalysis. − Electrochemistry has the inherent sensitivity required to make single-entity measurements, but is limited by shot noise . Although it is beyond the scope of this review, here we provide resources that explain filtering considerations for stochastic electrochemistry experiments. − …”

Nano-impact single-entity electrochemistry enables plasmon-enhanced electrocatalysis

“…There are only a few reports where PEEC on single nanoparticles was investigated. 20,21 For example, Willets group used scanning electrochemical microscopy (SECM) to monitor hot carrier generation on single gold nanoparticles (AuNPs) attached to an indium tin oxide electrode directly or with an intermediate layer of semiconducting TiO2. 22,23 They were able to quantify the relative contribution of thermal effects and hot carriers in plasmon-enhanced electrooxidation 22 and assess the thermalized hot carrier energy distribution after the electron injection to the semiconductor layer.…”