Detection of Aqueous Solvated Electrons Produced by Photoemission from Solids Using Transient Absorption Measurements

Abstract

Solvated electrons in water have long been of interest to chemists. While readily produced using intense multiphoton excitation of water and/or irradiation with high-energy particles, the possible role of solvated electrons in electrochemical and photoelectrochemical reactions at electrodes has been controversial. Recent studies showed that excitation of electrons to the conduction band of diamond leads to barrier-free emission of electrons into water. While these electrons can be inferred from the reactions they induce, direct detection by transient absorption measurements provides more direct evidence. Here, we present studies demonstrating direct detection of solvated electrons produced at diamond electrode surfaces and the influence of electrochemical potential and solution-phase electron scavengers. We further present a more detailed analysis of experimental conditions needed to detect solvated electrons emitted from diamond and other solid materials through transient optical absorption measurements.

Early dynamics of the emission of solvated electrons from nanodiamonds in water

“…[28] In any case, the electron emission from hydrogen-terminated diamond is more efficient due to the larger energy difference between diamond and water CBM, ensured by a negative EA, as well as the possibility to emit electrons through surface C-H states. [14] Nevertheless, the H-terminated surface alone cannot explain electron emission upon VIS excitation, as it would only allow electron emission for excitation with photon energies above 4.5 eV. [14] Another absorption process must therefore take place on ND-H upon VIS excitation.…”

“…[14] Nevertheless, the H-terminated surface alone cannot explain electron emission upon VIS excitation, as it would only allow electron emission for excitation with photon energies above 4.5 eV. [14] Another absorption process must therefore take place on ND-H upon VIS excitation. The negative ultrafast TA signal only observed for the ND-H under DUV illumination suggests that an additional process occurs for ND-H during the first picosecond.…”

“…Electron emission was recently shown for hydrogenated nanodiamonds (NDs) in aqueous suspensions under X-ray irradiation. [13] Indirect demonstration were provided on boron doped diamond electrodes, [7,14] NDs [15] and silverdoped diamond thin films. [16] In a seminal work, Zhu et al demonstrated that upon DUV light excitation, a transient signal at 633 nm was observed in water above a diamond single crystal which was assigned to solvated electrons.…”

“…[7] It was recently completed by a detailed study of transient absorption in the ns-µs range, showing sub-bandgap electron emission for excitation down to 4.5 eV (275 nm). [14] Nevertheless, the time evolution over the early stages (< 2 ns) of the electron emission under DUV light remains unexplored to our knowledge. Achieving electron emission with visible (VIS) light excitation instead of DUV light would also be required for a larger significance of diamond in the field of photocatalysis.…”

Early dynamics of the emission of solvated electrons from nanodiamonds in water

“…It was recently shown for hydrogenated nanodiamonds (NDs) in aqueous suspensions under X-ray irradiation. 12 Indirect demonstration were provided on boron doped diamond electrodes, 7,13 NDs 14 and silver-doped diamond thin films. 15 In a seminal work, Zhu et al demonstrated that upon DUV light excitation, a transient signal at 633 nm was observed in water above a diamond single crystal which was assigned to solvated electrons.…”