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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.

This paper reports the synergy between ceramic nanofibers and a polymer, and the enhanced interfacial Li-ion transport along the nanofiber/polymer interface in a solid-state ceramic/polymer composite electrolyte, in which a three-dimensional (3D) electrospun aluminum-doped Li0.33La0.557TiO3 (LLTO) nanofiber network is embedded in a polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) matrix. Strong chemical interaction occurs between the nanofibers and the polymer matrix. Addition of the ceramic nanofibers into the polymer matrix results in the dehydrofluorination of the PVDF chains, deprotonation of the –CH2 moiety and amorphization of the polymer matrix. Solid-state nuclear magnetic resonance (NMR) spectra reveal that lithium ions transport via three pathways: (i) intra-polymer transport, (ii) intra-nanofiber transport, and (iii) interfacial polymer/nanofiber transport. In addition, lithium phosphate is coated on the LLTO nanofiber surface before the nanofibers are embedded into the polymer matrix. The presence of lithium phosphate at the LLTO/polymer interface further enhances the chemical interaction between the nanofibers and the polymer, which promotes the lithium ion transport along the polymer/nanofiber interface. This in turn improves the ionic conductivity and electrochemical cycling stability of the nanofiber/polymer composite. As a result, the flexible LLTO/Li3PO4/polymer composite electrolyte membrane exhibits an ionic conductivity of 5.1 × 10−4 S cm−1 at room temperature and an electrochemical stability window of 5.0 V vs. Li/Li+. A symmetric Li|electrolyte|Li half-cell shows a low overpotential of 50 mV at a constant current density of 0.5 mA cm−2 for more than 800 h. In addition, a full cell is constructed by sandwiching the composite electrolyte between a lithium metal anode and a LiFePO4-based cathode. Such an all-solid-state lithium metal battery exhibits excellent cycling performance and rate capability.

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.

Perovskite Li3x La2/3−x TiO3 (LLTO) nanofibers have been heat-treated in the hydrogen-containing atmosphere and then incorporated with the poly(vinylidene fluoride)-co-hexafluoropropylene (PVDF-HFP) polymer to form a composite electrolyte. Hydrogen treatment has created oxygen vacancies in the LLTO nanofibers, which has reduced the activation energy of Li ion transport along intra-grains and inter-grains, leading to an improvement in the ion conductivity of LLTO nanofibers. Hydrogen treatment of the LLTO nanofibers has also enhanced the chemical interaction between the LLTO nanofibers and the polymer matrix in the composite electrolyte, and favored the Li ion transport at the nanofiber/polymer interface, improving the ion conductivity of the composite electrolyte to 3.4 × 10−4 S/cm at room temperature. As a result, the Li|composite-electrolyte|Li half-cell exhibits good stability during lithium plating/stripping cycling at room temperature, showing an overpotential of ~91 mV at a constant current density of 0.5 mA/cm2. The full-cell battery with the composite electrolyte, lithium metal anode and lithium iron phosphate cathode shows excellent rate capacity and cycling performance.

Previous studies have shown that hydrogen treatment leads to the formation of blue to black TiO_2, which exhibits photocatalytic activity different from that of white pristine TiO_2. However, the underlying mechanism remains poorly understood. Herein, density functional theory is combined with comprehensive analytical approaches such as X-ray absorption near edge structure spectroscopy and transient absorption spectroscopy to gain fundamental understanding of the correlation among the oxygen vacancy, electronic band structure, charge separation, charge carrier lifetime, reactive oxygen species (ROS) generation, and photocatalytic activity. The present work reveals that hydrogen treatment results in chemical reduction of TiO_2, inducing surface and subsurface oxygen vacancies, which create shallow and deep sub-band gap Ti(III) states below the conduction band. This leads to a blue color but limited enhancement of visible light photocatalytic activity up to 440 nm at the cost of reduced ultraviolet photocatalytic activity. The extended light absorption spectral range for reduced TiO_2 is ascribed to both the defect-to-conduction band transitions and the valence band-to-defect transitions. The photogenerated charge carriers from the defect states to the conduction band have lifetimes too short to drive photocatalysis. The Ti(III) deep and shallow trap states below the conduction band are also found to reduce the lifetime of photogenerated charge carriers under ultraviolet light irradiation. The ROS generated by the reduced TiO_2 are less than those generated by pristine TiO_2. Consequently, the reduced TiO_2 exhibits ultraviolet-responsive photocatalytic activity worse than that of pristine TiO_2. This report shows that increasing the light absorption spectral range of a semiconductor by doping or introduction of defects does not necessarily guarantee an increase in photocatalytic activity.

Gold nanoparticles have been deposited on the surface of hematite nanorod array photoanode to improve the photoelectrochemical water splitting performance. The Au nanoparticles induce the Fermi level equilibration, the surface catalysis, and the plasmonic enhancement effects in the Au/hematite photoanode. The Fermi level equilibration effect promotes the extraction of photo-generated charge carriers, suppressing the charge recombination. Surface catalysis effect reduces the overpotential for photoelectrochemical water oxidation. In the Au/hematite sample, the Fermi level equilibration and the surface catalysis effect make major contribution to photocurrent enhancement while the plasmonic effect makes a little contribution. In addition, the Au@SiO2 particle has been immobilized on hematite nanorod array surface that has been passivated. In the Au@SiO2/hematite sample, the photocurrent enhancement originating from plasmonic effects is negligible. Both the Femi level equilibration and the surface catalysis effects were excluded due to the isolated Au and hematite while surface passivation is mainly responsible for the photocurrent enhancement.