Insight into Interfacial Charge Transfer during Photocatalytic H₂ Evolution through Fe, Ni, Cu and Au Embedded in a Mesoporous TiO₂@SiO₂ Core‐shell

Abstract

The efficiency of charge transfer at the interface of transition metals loaded on TiO 2 as well as the active reduction site undoubtedly define the kinetics of H 2 production. Here, we report the interfacial charge process of various transition metals (Fe, Ni, Cu, and Au) embedded in mesoporous coreshell nanostructures, which provides further insight into the photocatalytic H 2 evolution. Au was found to be the most active cocatalyst for the H 2 evolution. Au nanoparticles (NPs) collect electrons and become a very efficient reduction site, promoting both charge separation and H 2 evolution. The scavenging capacity of Au was found to be the highest compared to other NPs. Cu(I), which is as active as Au, but at a higher loading, also shows an ability for electron scavenging and acts as an active site under UV excitation, or rather injects electrons into the TiO 2 conduction band under visible excitation. Ni(II) NPs were found to be involved in chargecarrier separation through hole collection and their contribution to hydrogen evolution is expected to be limited to visible absorption and electron injection. The same behavior occurs with Fe(III), however, it is less efficient for H 2 generation due to the weak charge-carrier lifetime. We show that only Cu(I) could compete with noble metals such as Au, presenting electronscavenging behavior. Understanding the charge-carrier dynamics will help design a very efficient system for photocatalytic H 2 generation system.

Effects of Solvent Treatment on the Formation of Oxygen Vacancy in TiO2 via Vacuum Annealing

“…Photocatalysts of metal oxide semiconductors have the potential to make use of solar energy for various photocatalytic applications. − Among a variety of metal oxide photocatalysts, titanium dioxide (TiO 2 ) has been widely investigated due to its excellent chemical stability, nontoxicity, and cost-effectiveness. − However, the intrinsic wide band gap of TiO 2 (>3.0 eV) and fast recombination of photoexcited charge carriers , limit its absorption and usage of solar light. Many attempts have been successfully performed to improve the visible light absorption of TiO 2 by doping , and avoid the recombination of photogenerated charge carriers by constructing heterojunction structures. − Moreover, defect structures such as oxygen vacancy (Vo) not only adjust the response to solar light , but also alter the charge carrier concentration, − playing an important role in determining the photocatalytic activity of a photocatalyst. ,, Thus, tailoring the Vo in TiO 2 offers an effective approach for improving its photocatalytic performance. , …”

Nanostructured TiO2for improving the solar-to-hydrogen conversion efficiency

“…To further understand the charge carrier dynamics on the surface of the core–shell structure, a mesoporous SiO 2 @TiO 2 core–shell nanostructure was synthesized, and a series of transition metals, including Fe, Ni, Cu, and Au, were embedded in the pores. 135 The charge carrier dynamics was studied via the time-resolved microwave conductivity technique, showing that Au NPs have the highest scavenging ability for electrons, followed by Cu. At the same time, Ni and Fe NPs participated in charge carrier separation through hole collection.…”

Strong Metal‐support Interactions in Photocatalysis: Fundamentals and Design Methods

“…Heterogeneous photocatalysts mediated by metallic nanoparticles, especially plasmonic metals, have shown superior properties and higher efficiency in the solar-to-energy conversion yield. [1][2][3][4][5][6] The metallic nanoparticles have been reported for boosting the photocatalytic efficiency of variable reactions, such as CO 2 reduction, [7][8][9][10] CO 2 methanation, [11][12][13] hydrogeneration, [14][15][16] and alcohol conversion. [17,18] However, further investigations are expected to understand the effect of photocatalyst design, the intrinsic activities of metallic nanoparticles, and the benefits of constructing strong interaction with reducible oxides as supports on the photocatalytic performance.…”

“…Heterogeneous photocatalysts mediated by metallic nanoparticles, especially plasmonic metals, have shown superior properties and higher efficiency in the solar‐to‐energy conversion yield [1–6] . The metallic nanoparticles have been reported for boosting the photocatalytic efficiency of variable reactions, such as CO 2 reduction, [7–10] CO 2 methanation, [11–13] hydrogeneration, [14–16] and alcohol conversion [17,18] .…”