Role of an Inert Electrode Support in Plasmonic Electrocatalysis

Abstract

Direct loading of plasmonic nanostructures onto catalytically inert conductive support materials leads to the Schottky barrier-free architecture of the photocatalytic system. Such systems have recently attracted the attention of the research community as they permit collection of hot carriers independent of their energy when additional charge separation strategies are used. However, a systematic mechanistic investigation and description of the contribution of an inert conductive support to plasmonic electrocatalysis is missing. Herein, we systematically investigated the effect of the supporting electrode material on the observed photoinduced enhancement by comparing the photoelectrocatalytic properties of AuNPs supported on highly oriented pyrolytic graphite (HOPG) and indium tin oxide (ITO) electrodes using electrocatalytic benzyl alcohol (BnOH) oxidation as a model system. Upon illumination, only ∼(3 ± 1)% enhancement in catalytic current was recorded on the AuNP/ITO electrodes in contrast to ∼(42 ± 6)% enhancement on AuNP/HOPG electrodes. Our results showed that the local heating due to light absorption by the electrode material itself independent of localized surface plasmon effects is the primary source of the observed significant photoinduced enhancement on the HOPG electrodes in comparison to the ITO electrodes. Moreover, we demonstrated that an increased interfacial charge transfer at elevated temperatures and not faster reactant diffusion as suggested previously is the main source of the thermal enhancement. This work highlights the importance of the systematic evaluation of contributions of all parts, even if they are catalytically inert, to the light-induced facilitation of catalytic reactions in plasmonic systems.

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

“…The decay of the photocurrent after turning off the illumination is gradual and much slower than the cell time constant (τRC = 30 ms; Figure S1, Note S1), implying that the contribution of hot carriers to glucose electrocatalysis is minimal and that thermal effects are the primary source of electrooxidation rate enhancement. 15 LSVs on AuNP/HOPG electrodes illuminated by a 650 nm laser at which hot carriers can not be generated also show an increase of peak current at 0.2V by 37±6% (Figure 2C). This matches within the error to the increase observed under 532 nm illumination (Figure 2C vs.…”

“…29 The electrocatalytic activity of AuNPs towards glucose oxidation was first examined by conventional ensemble electrochemistry in a three-electrode setup. 15 Highly oriented pyrolytic graphite electrode (HOPG) with immobilized AuNPs (AuNP/HOPG) was used as a working electrode. HOPG was chosen as an electrode support because of its similar properties with a carbon microfibre, which was used as the working electrode for SEE measurements (vide infra).…”

“…8,9 Chronoamperometry measurements under alternating illumination can be used to distinguish hot carriers and temperature contributions in PEEC when the response time of the cell is known, and it is fast. 15,32 Figure 2B shows the photocurrent response of the AuNP/HOPG electrode under alternating illumination in deoxygenated 100 mM NaOH and 30 mM glucose solution. The relative anodic current enhancement in chronoamperometry differs from the values obtained from LSV peak current as both glucose and gluconic acid can be oxidized at the applied potential.…”

“…These differences in electrocatalytic performance and absorption spectra between AuNP/HOPG and AuNP/ITO indicate that photo-induced heating of HOPG rather than the decay of plasmons is the primary source of the electrocatalytic rate enhancement on AuNP/HOPG electrodes in agreement with our previous findings. 15 Heterogeneities in nanoparticle size, shape, and interaction with the support contribute to the observed electrocatalytic properties of plasmonic photoelectrodes in PEEC. 34 To accurately measure intrinsic nanoparticle reactivity and minimize collective heating effects, 35 As the AuNP surface oxidizes and loses its electrocatalytic activity at high potentials (Figure S6, Note S4), 0.2 V vs. Ag/AgCl, corresponding to the peak potential in LSV curves (Figure 2A, C), was chosen for chronoamperometry measurements.…”

“…Elevated temperatures near the plasmonic electrocatalyst facilitate phonon-driven chemical reactions. 14,15 In electrocatalytic systems, plasmonic nanomaterials can act as both light-adsorbing and electrocatalytic sites or be combined with other electrocatalytic materials and/or semiconductors in hybrid systems. Pure plasmon metal-driven electrocatalysis combined with effective charge separation strategies is proposed to be more efficient than electrocatalysis on metal/semiconductor interfaces, as the Schottky barrier limits the collection efficiency of hot carriers.…”