Hot electron-driven photocatalytic water splitting

Abstract

We report measurements of photocatalytic water splitting using Au films with and without TiO coatings. In these structures, a thin (3-10 nm) film of TiO is deposited using atomic layer deposition (ALD) on top of a 100 nm thick Au film. We utilize an AC lock-in technique, which enables us to detect the relatively small photocurrents (∼μA) produced by the short-lived hot electrons that are photoexcited in the metal. Under illumination, the bare Au film produces a small AC photocurrent (<1 μA) for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) due to hot electrons and hot holes, respectively, that are photoexcited in the Au film. The samples with TiO produce a larger AC photocurrent indicating that hot electrons are being injected from the metal into the TiO semiconductor where they then reduce hydrogen ions in solution forming H (i.e., 2H + 2e → H). The AC photocurrent exhibits a narrow peak when plotted as a function of reference potential, which is a signature of hot electrons. Here, we photoexcite a monoenergetic source of hot electrons, which produces a peak in the photocurrent, as the electrode potential is swept through the resonance with the redox potential of the desired half-reaction. This stands in contrast to conventional bulk semiconductor photocatalysts, whose AC photocurrent saturates beyond a certain potential (i.e., light limited photocurrent). The photocurrents produced at the metal-liquid interface are smaller than those of the metal-semiconductor system, mainly because, in the metal-semiconductor system, there is a continuum of energy and momentum states that each hot electron can be injected into, while for an ion in solution, the number of energy and momentum states are very small.

Enhanced Photocatalytic Hydrogen Generation by Optimized Plasmonic Hot Electron Injection in Structure-Adjustable Au-ZnO Hybrids

“…Hot electrons, which are generated from the nonradiative relaxation of localized surface plasmons, are more energetic than those generated by direct photoexcitation [11][12][13][14][15]. The maximum utilization of hot electrons is significantly important to improve the photocatalytic performance of metal-semiconductor hybrids [16][17][18][19][20][21][22]. Several strategies have been proposed to optimize the hot electron injection in plasmonic composites, such as enhancing the near field of plasmonic metal nanocrystals [23][24][25], selectively placing a semiconductor on the position, where a strong near field is located [26,27].…”

Plasmonic Nickel–TiO2 Heterostructures for Visible‐Light‐Driven Photochemical Reactions

“…[1][2][3] Specifically,t he plasmon-mediated carrier transfer (PMCT) across interfacial Schottky barriers at metal-semiconductor heterojunctions has been employed to promote various photocatalytic reactions. [1][2][3] Specifically,t he plasmon-mediated carrier transfer (PMCT) across interfacial Schottky barriers at metal-semiconductor heterojunctions has been employed to promote various photocatalytic reactions.…”

“…Plasmonic metal nanostructures combining tunable optical properties with catalytically active surfaces offer intriguing opportunities for solar photocatalysis. [1][2][3] Specifically,t he plasmon-mediated carrier transfer (PMCT) across interfacial Schottky barriers at metal-semiconductor heterojunctions has been employed to promote various photocatalytic reactions. [1,4,5] So far, Au has been commonly used in most PMCT studies due to its plasmonic absorption of visible light and its capability to form Schottky barriers with semiconductors such as TiO 2 and ZnO.…”

“…[1][2][3] Specifically,t he plasmon-mediated carrier transfer (PMCT) across interfacial Schottky barriers at metal-semiconductor heterojunctions has been employed to promote various photocatalytic reactions. [1,4,5] So far, Au has been commonly used in most PMCT studies due to its plasmonic absorption of visible light and its capability to form Schottky barriers with semiconductors such as TiO 2 and ZnO. [6][7][8] Recently,s everal studies have used inexpensive metals such as Al to substitute Au.…”

Resonant and Selective Excitation of Photocatalytically Active Defect Sites in TiO2

“…In our previous work, similar structures consisting of Au films with and without TiO 2 coatings were investigated. 30 For the bare metal electrodes, the mechanism of photocatalysis was attributed to hot electrons photoexcited in the metal. The mechanism of photocurrent generation in TiO 2 -coated Au electrodes was attributed to hot electron injected by the metal film because of our inability to detect these defect states in the UV-vis absorption process.…”