Hot Hole Collection and Photoelectrochemical CO2 Reduction with Plasmonic Au/p-GaN Photocathodes

Hot Holes Assist Plasmonic Nanoelectrode Dissolution

Strong light-absorbing properties allow plasmonic metal nanoparticles to serve as antennas for other catalysts to function as photocatalysts. To achieve plasmonic photocatalysis, the hot charge carriers created when light is absorbed must be harnessed before they decay through internal relaxation pathways. We demonstrate the role of photogenerated hot holes in the oxidative dissolution of individual gold nanorods with millisecond time resolution while tuning charge-carrier density and photon energy using snapshot hyperspectral imaging. We show that light-induced hot charge carriers enhance the rate of gold oxidation and subsequent electrodissolution. Importantly, we distinguish how hot holes generated from interband transitions versus hot holes around the Fermi level contribute to photooxidative dissolution. The results provide new insights into hot-hole-driven processes with relevance to photocatalysis while emphasizing the need for statistical descriptions of nonequilibrium processes on innately heterogeneous nanoparticle supports.

Hot electron-driven photocatalysis and transient absorption spectroscopy in plasmon resonant grating structures

We have developed a method to measure photocurrents produced by photoexcited hot electrons and holes in bulk metal films.

Plasmonic hot carrier-driven oxygen evolution reaction on Au nanoparticles/TiO2 nanotube arrays

The use of hot carriers generated from the decay of localized surface plasmon resonance in noble metal nanoparticles is a promising concept for photocatalysis. Here, we report the enhancement of photocatalytic activity by the flow of hot electrons on TiO₂ nanotube arrays decorated with 5-30 nm Au nanoparticles as photoanodes for photoelectrochemical water splitting. This enhanced photocatalytic activity is correlated to the size of the Au nanoparticles, where higher oxygen evolution was observed on the smaller nanoparticles. Conductive atomic force microscopy and ultraviolet photoelectron spectroscopy were used to characterize the Schottky barrier between Au and TiO₂, which reveals a reduction in the Schottky barrier with the smaller Au nanoparticles and produces an enhanced transfer of photoinduced hot carriers. This study confirms that the higher photocatalytic activity was indeed driven by the hot electron flux generated from the decay of localized surface plasmon resonance.

Recent Progress on Titanium Dioxide Nanomaterials for Photocatalytic Applications

Environmental and energy problems have drawn much attention owing to rapid population growth and accelerated economic development. For instance, photocatalysis, "a green technology", plays an important role in solar-energy conversion owing to its potential to solve energy and environmental problems. Recently, many efforts have been devoted to improving visible-light photocatalytic activity by using titanium dioxide as a photocatalyst as a result of its wide range of applications in the energy and environment fields. However, fast charge recombination and an absorption edge in the UV range limit the photocatalytic efficiency of TiO₂ under visible-light irradiation. Many investigations have been undertaken to overcome the limitations of TiO₂ and, therefore, to enhance its photocatalytic activity under visible light. The present literature review focuses on different strategies used to promote the separation efficiency of electron-hole pairs and to shift the absorption edge of TiO₂ to the visible region. Current synthesis techniques used to elaborate several nanostructures of TiO₂ -based materials, recent progress in enhancing visible photocatalytic activity, and different photocatalysis applications will be discussed. On the basis of the studies reported in the literature, we believe that this review will help in the development of new strategies to improve the visible-light photocatalytic performance of TiO₂ -based materials further.

Role of Heteroatoms in S,N-Codoped Nanoporous Carbon Materials in CO2 (Photo)electrochemical Reduction

Thiourea-modified wood-based activated carbon materials were evaluated as catalysts for the CO₂ electrochemical reduction reaction (CO₂ ERR). The materials obtained at 950 °C showed long-term stability. The results indicated that thiophenic sulfur provides the catalytic activity for CO formation. However, it was not as active for CH₄ formation as was pyridinic N. Tafel plots suggested that the nanoporous structure enhanced the kinetics for CO₂ reduction. The electric conductivity limited the activity for CO₂ ERR in the materials modified at 600, 800, and 900 °C. The effect of visible light on CO₂ ERR was also investigated in this study. Upon irradiation, photocurrent was generated, and the current density increased during the CO₂ reduction process. Combined with a band-gap alignment, the results indicate that thiophenic S in the carbon matrix contributed to the sample's photoactivity in visible light. These species enhance the overall reduction process, promoting both the hydrogen evolution reaction and CO₂ reduction to CO.