Probing Hot Electron Flow Generated on Pt Nanoparticles with Au/TiO₂Schottky Diodes during Catalytic CO Oxidation

Abstract

Hot electron flow generated on colloid platinum nanoparticles during exothermic catalytic carbon monoxide oxidation was directly detected with Au/TiO 2 diodes.Although Au/TiO 2 diodes are not catalytically active, platinum nanoparticles on Au/TiO 2 exhibit both chemicurrent and catalytic turnover rate. Hot electrons are generated on the surface of the metal nanoparticles and go over the Schottky energy barrier between Au and TiO 2 . The continuous Au layer ensures that the metal nanoparticles are electrically connected to the device. The overall thickness of the metal assembly (nanoparticles and Au thin film) is comparable to the mean free path of hot electrons, resulting inballistic transport through the metal. The chemicurrent and chemical reactivity of nanoparticles with citrate, hexadecylamine, hexadecylthiol, and TTAB (Tetradecyltrimethylammonium Bromide) capping agents were measured during catalytic CO oxidation at pressures of 100 Torr O 2 and 40 Torr CO at 373~513 K. We found that chemicurrent yield varies with each capping agent, but always decreases with increasing temperature. We suggest that this inverse temperature dependence is associated with the influence of charging effects due to the organic capping layer during hot electron transport through the metal-oxide interface.

Hydrogen-Etched TiO2−x as Efficient Support of Gold Catalysts for Water–Gas Shift Reaction

“…They proposed a possible photocatalytic mechanism: under visible light irradiation the surface plasmon band of Au nanoparticles will be excited and will inject electrons (−) to the conduction band of the TiO 2 , which facilitates water reduction to hydrogen, and the holes (+) remaining on Au nanoparticles will be responsible for the oxidation of adsorbed CO. Furthermore, "hot-electron flow" can be formed between metal-oxide interfaces during exothermic chemical processes, and the "hot-electron flow" plays a key role in determining the catalytic activity of CO oxidation [46,[56][57][58]. Accordingly, correlating traditional and photocatalytic WGS reaction mechanisms with the optoelectronic properties, we try to understand the WGS pathway from the view of electron flow processes, as shown in Figure 10.…”

“…As shown in Figure 10a, since the work function of metal Au (Φ m = 4.8 eV) is smaller than that of semiconductor TiO 2 (Φ s = 5.1 eV) [70], the electrons can diffuse from the metal into the semiconductor when the two phases are in contact [71,72]. This electron transfer was called "hot-electron flow" [56,57,[73][74][75] or "chemicurrent" [76][77][78], which usually happened in exothermic catalytic reactions [56,57,[73][74][75] and low-energy reactions [74] or even nonthermal directions [75]. For example, it has been reported that electron excitation was also involved in atomic/molecular adsorption processes [73,77,78].…”

Conquering Catalyst Complexity: Nanoparticle Synthesis and Instrument Development for Molecular and Atomistic Characterisation Under In Situ Conditions

“…This generates a hot electron, which, if the distance of travel to a Schottky interface is less than the mean free path of the electron, can cross the barrier and end up in the conduction band of the oxide (allowing a current to be measured). This has been done with both Pt films [84][85][86][87][88] and colloidal Pt nanoparticles on a Au/TiO 2 nanodiode, [89,90] the latter is depicted in Figure 6. higher potential than in Au, causing current to flow so a "chemicurrent" can be measured…”

Molekulare Faktoren der katalytischen Selektivität

“…[8,33,101] [40,41,107] Wir detektierten einen Strom "heißer" Elektronen mithilfe einer Schottky-Diode. [38,39,106,108] Werden Metallpartikel [59] oder ein Film [109] mit Durchmessern bzw. einer Dicke ähnlich der mittleren freien Weglänge für Elektronen (ca.…”