Quantifying Hot Electron Energy Contributions in Plasmonic Photocatalysis Using Electrochemical Surface-Enhanced Raman Spectroscopy

Abstract

Due to the challenge in measuring hot electron energy under reaction conditions, very few studies focus on experimental determination of hot carrier energy. Here, we adjust the energy state of free electrons in Au nanoparticles to quantify the hot electron energy in plasmonic photocatalysis. Reactant molecules with different reduction potentials such as 4-nitrothiophenol (4-NTP), 4-iodothiophenol (4-ITP), etc. are chosen as molecular probes to investigate the reducing ability of hot electrons. By comparing the voltage required to achieve the same conversion of photo- and electro-reaction pathways, we calibrate the maximum energy efficiency of hot electrons in 4-NTP reduction to be 0.32 eV, which is much lower than the excitation photon energy of 1.96 eV. Our work provides insight into the energy distribution of hot electrons and will be helpful for rational design of highly efficient plasmon-mediated chemical reactions.

Determining Quasi-Equilibrium Electron and Hole Distributions of Plasmonic Photocatalysts Using Photomodulated X-ray Absorption Spectroscopy

“…Using the MSE fit, the TiO 2 lattice temperature is found to be hotter than for the Au@SiO 2 @TiO 2 nanoparticles, attributed to the larger plasmon intensity that leads to a greater level of hot electron thermalization in TiO 2 (Figure S3). Further, the 0.3 eV hot electron quasi-equilibrium distribution is consistent with recent studies, as steady-state and ultrafast Raman measurements estimate that hot electrons exceeding 0.32 and 0.34 eV, respectively, transfer from Au nanoparticles to nearby molecules. , An approximate calculation comparing the electron excitation and relaxation rates in the amorphous TiO 2 is given in the Supporting Information, but the main conclusions of Figure are that photothermal and hot electron effects can be differentiated within a relatively noisy spectrum.…”

“…Further, the 0.3 eV hot electron quasi-equilibrium distribution is consistent with recent studies, as steady-state and ultrafast Raman measurements estimate that hot electrons exceeding 0.32 and 0.34 eV, respectively, transfer from Au nanoparticles to nearby molecules. 52,53 An approximate calculation comparing the electron excitation and relaxation rates in the amorphous TiO 2 is given in the Supporting Information, but the main conclusions of Figure 6 are that photothermal and hot electron effects can be differentiated within a relatively noisy spectrum. Further light-intensity-dependent control experiments would be necessary to quantify the hot electron concentration and would also be useful to clarify the nonlinear change with hot carrier concentration versus the temperature-induced shift.…”

Quantifying the Ultrafast and Steady-State Molecular Reduction Potential of a Plasmonic Photocatalyst

“…energies exceeding 340 meV (Fig.3D, S12). Notably, the ensemble average plasmon generated potential measured in this study is approximately two orders of magnitude less than measured values in other recent work (32,46,47). For example, Yu and coworkers have recently reported a hot electron energy of 0.32 eV generated from continuous wave excitation of a gold nanosphere array.…”

“…(30) The combination of electrochemical techniques and SERS has been used widely for the identification of electrochemically generated surface species, and found unique applications toward quantifying electrochemical heterogeneity, site specificity, and plasmon-generated potentials for nanostructures in the steady state. (31,32) Here, we apply spectroscopic methods to characterize how the vibrational modes of MV change -in both the ultrafast and steady state -when photochemically reduced on an AuFON surface. When we excite the plasmon resonance in the AuFON-MV system, electrons required to drive the reduction process are generated rapidly and we observe non-equilibrium changes to these MV vibrational markers using ultrafast SERS.…”

Raman Monitoring of the Electro-Optical Synergy-Induced Enhancements in Carbon–Bromine Bond Cleavage, Reaction Rate, and Product Selectivity of p-Bromothiophenol

“…Particularly, dehalogenation of halogenated hydrocarbons followed by C–C coupling is of great interest in organic synthesis. Initially, the photoinduced single-electron transfer heterolysis of carbon–halogen (C–X) bonds was catalyzed using transition metals (Au, Ag, Ni, Pd, and Rh), semiconductors, and organic dyes. ,− Relative to other metals, Ag nanoparticles unexpectedly showed a higher plasmonic activity toward the C–C coupling reactions. , Even though plasmon-mediated dehalogenation of C–X into C–C coupling can be achieved, the catalytic efficiency and its selectivity is still lower than their theoretical value due to the ultrafast relaxation process, since the plasmon-generated hot carriers possess ultrashort lifetimes (in the range of fs–ps). ,,, …”