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Metal oxides are more inexpensive and abundant as plasmonic materials compared with noble metals. This report shows that chemically reduced WO₃–ₓ nanosheets exhibit a localized surface plasmon resonance (LSPR) band centered at 540 nm and photocatalytic activity toward degradation of methyl orange. The methyl orange is decomposed via the reaction with plasmonic hot holes and superoxide radicals from excitation of LSPR. This work has provided evidence that plasmonic hot holes from oxides can directly react with methyl orange and play a significant role in photocatalysis. In contrast, it is well-known that plasmonic hot holes in metals are seldom reported for involvement of photocatalysis.

Currently plasmonic metal oxides are present in the form of free-standing nanoparticles because they are synthesized with wet chemistry methods. In contrast, this report presents the preparation of...

This paper presents a p–n heterojunction photoanode based on a p-type porphyrin metal–organic framework (MOF) thin film and an n-type rutile titanium dioxide nanorod array for photoelectrochemical water splitting. The TiO2@MOF core–shell nanorod array is formed by coating an 8 nm thick MOF layer on a vertically aligned TiO2 nanorod array scaffold via a layer-by-layer self-assembly method. This vertically aligned core–shell nanorod array enables a long optical path length but a short path length for extraction of photogenerated minority charge carriers (holes) from TiO2 to the electrolyte. A p–n junction is formed between TiO2 and MOF, which improves the extraction of photogenerated electrons and holes out of the TiO2 nanorods. In addition, the MOF coating significantly improves the efficiency of charge injection at the photoanode/electrolyte interface. Introduction of Co(III) into the MOF layer further enhances the charge extraction in the photoanode and improves the charge injection efficiency. As a result, the photoelectrochemical cell with the TiO2@Co-MOF nanorod array photoanode exhibits a photocurrent density of 2.93 mA/cm2 at 1.23 V (vs. RHE), which is ~ 2.7 times the photocurrent achieved with bare TiO2 nanorod array under irradiation of an unfiltered 300 W Xe lamp with an output power density of 100 mW/cm2.

In plasmonic metals, surface plasmon resonance decays and generates hot electrons and hot holes through non-radiative Landau damping. These hot carriers are highly energetic, which can be modulated by the plasmonic material, size, shape, and surrounding dielectric medium. A plasmonic metal nanostructure, which can absorb incident light in an extended spectral range and transfer the absorbed light energy to adjacent molecules or semiconductors, functions as a "plasmonic photosensitizer." This article deals with the generation, emission, transfer, and energetics of plasmonic hot carriers. It also describes the mechanisms of hot electron transfer from the plasmonic metal to the surface adsorbates or to the adjacent semiconductors. In addition, this article highlights the applications of plasmonic hot electrons in photodetectors, photocatalysts, photoelectrochemical cells, photovoltaics, biosensors, and chemical sensors. It discusses the applications and the design principles of plasmonic materials and devices.

The application of safe, high energy-density solid-state lithium (Li) metal batteries is hindered by dendrite growth, poor interfacial contact, and side reactions between the Li metal and the solid-state ceramic electrolyte. The use of a three-dimensional (3D) porous copper (Cu) scaffold has shown to be an effective solution to enabling a Li metal anode. However, it is difficult to fabricate such 3D structures rapidly and controllably. Herein, a 3D printing approach has been developed to fabricate a 3D anode structure with controlled dimension, geometry, and chemical composition. In addition, mixture design-based sequential learning is used to guide design and optimization of the printing ink formula as well as the rheological and operating parameters of the 3D printing process. Inks are patterned directly onto the NASICON-type Li1+xAlx3+M2−x4+(PO4)3 (LATP) electrolyte, yielding scaffolds with a range of pore sizes. The printed scaffolds and the electrode-electrolyte interface are characterized using symmetric cell cycling, X-ray photoelectron spectroscopy, and scanning electron microscopy. The characterization results show that the 3D printed structure benefits both interfacial stability and the suppression of lithium dendrite growth. The Li|Cu@LATP@Cu|Li symmetrical cell with a 3D printed Cu scaffold exhibits a polarization voltage of 60 mV at a current density of 0.05 mA/cm2. This work shows that machine learning based on experimental design and statistical analysis leads to reduced experimental effort in optimizing the 3D printing process.

Plasmonic metals can excite charge carriers in semiconductors through plasmon-induced resonance energy transfer (PIRET) and hot electron injection processes. Transient absorption spectroscopy reveals that the presence of plasmon-induced charge separation mechanisms in metal@TiO2 core–shell nanoparticles can be controlled by tailoring the spectral overlap and the physical contact between the metal and the semiconductor. In Ag@SiO2@TiO2 sandwich nanoparticles, the localized surface plasmon resonance band is overlapped with the absorption band edge of TiO2, enabling PIRET, while the SiO2 barrier prevents hot electron transfer. In Au@TiO2, hot electron injection occurs, but the lack of spectral overlap disables PIRET. In Ag@TiO2, both hot electron transfer and PIRET take place. In Au@SiO2@TiO2, photoconversion in TiO2 is not enhanced by the plasmon despite strong light absorption by Au.

Doping a semiconductor can extend the light absorption range, however, it usually introduces mid-gap states, reducing the charge carrier lifetime. This report shows that doping lanthanum dititinate (La2Ti2O7) with nitrogen extends the valence band edge by creating a continuum of dopant states, increasing the light absorption edge from 380 nm to 550 nm without adding mid-gap states. The dopant states are experimentally resolved in the excited state by correlating transient absorption spectroscopy with a supercontinuum probe and DFT prediction. The lack of mid-gap states is further confirmed by measuring the excited state lifetimes, which reveal the shifted band edge only increased carrier thermalization rates to the band edge and not interband charge recombination under both ultraviolet and visible excitation. Terahertz (time-domain) spectroscopy also reveals that the conduction mechanism remains unchanged after doping, suggesting the states are delocalized.

Compared to pristine Cu2O nanoparticles (NPs), Ag@Cu2O core-shell NPs exhibit photocatalytic activity over an extended wavelength range because of the presence of localized surface plasmon resonance (LSPR) in the Ag core. The photocatalysis action spectra and transient absorption measurements show that the plasmonic energy is transferred from the metal to the semiconductor via plasmon-induced resonant energy transfer (PIRET) and direct electron transfer (DET) simultaneously, generating electron–hole pairs in the semiconductor. The LSPR band of Ag@Cu2O core-shell NPs shows a red-shift with an increase in the Cu2O shell thickness, extending the light absorption of Ag@Cu2O heterostructures to longer wavelengths. As a result, the photocatalytic activity of the Ag@Cu2O core-shell NPs is varied by modulation of the shell thickness on the nanometer scale. This work has demonstrated that the Ag@Cu2O core-shell heterostructure is an efficient visible-light plasmonic photocatalyst, which allows for tunable light ab...