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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.

A metal–organic framework (MOF) single lithium-ion conductor has been synthesized by covalently immobilizing anions to the skeleton of MOF structures. The functionalized UiO-66 MOF exhibits an elec...

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.

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.

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.

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.

The photocatalytic water oxidation activity of hematite (α-Fe2O3) has been greatly enhanced by incorporating hematite nanoparticles on the reduced graphene oxide (rGO) nanosheets. Photoelectrochemical measurement results show that coupling the hematite nanoparticles with the rGO greatly increases the photocurrent and reduces the charge recombination rate. Transient absorption spectroscopy and time-domain terahertz spectroscopy have provided the direct evidence that the photogenerated electrons have transferred as the mobile carriers from α-Fe2O3 to rGO, which enhances the charge separation and suppresses the charge recombination. This work has provided new insight into the mechanism of photocatalysis enhancement by reduced graphene oxide, which has implications in the design of semiconductor/graphene heterojunction photocatalysts.

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...

Photoelectrochemical (PEC) water-splitting remains a promising sustainable technique for hydrogen generation. However, existing photoanode materials for PEC water-splitting suffer from sluggish water oxidation kinetics. Cerium (IV) compounds have historically been used as oxidizers in chemical and are thermodynamically able to oxidize water without additional energy input. In this project, Cerium(III/IV) is used as a regenerable redox mediator for water oxidation. A rutile TiO2 nanorod array (TiO2 NRA) is employed as a photoanode in an acidic electrolyte containing varying concentrations of Ce(III). This presentation demonstrates the roles of Ce(III) in improving the photoelectrochemical performance of TiO2 NRA.

Nowadays, with the crisis of the fossil fuels’ depletion and the pollution from these fuels’ combustion, there is a huge demand for clean and sustainable energy source, which makes solar energy extremely appealing. Using a photoelectrochemical cell (PEC) with the semiconductor as a photoanode, the solar energy could be absorbed, converted and stored in hydrogen via water splitting. One-dimensional (1D) nanostructured semiconductors, as a photoanode, are promising with their advantage in photon absorption and charge transport. The solar fuel efficiency could be increased using the hybridized Quantum Dots-1D nanostructure heterojunction. Herein we report the fabrication of QDs/ZnO 1D heterostructure for solar fuel generation. Such band alignment not only extends the light harvesting up to near infrared region, but also forces the forward transfer of the charge carriers, which improves the charge separation and suppresses the charge recombination, and thus ensures the high efficiency. Such 1D nanostructures provide great opportunities for the realization of the solar cell commercialization.

Earth’s dependence on fossil fuels for providing the majority of the world’s energy is problematic due to the finite nature of fossil fuels and the release of greenhouse gases and other pollutants during their combustion. As such, sustainable, carbon-neutral fuels are needed as a long-term replacement for fossil fuels. One promising approach is direct solar energy-to-chemical fuel conversion by photocatalysis. Examples of fuels produced include H2 from photocatalytic water splitting or photocatalytic reduction of CO2 to methanol or methane. However, current photocatalyst materials suffer from a combination of problems such as poor charge carrier lifetimes and mobility, poor photostability in water, wide bandgaps that allow only UV light absorption, and/or an inactive surface for carrying out redox reactions. Forming heterostructures made of plasmonic metals (i.e. Au, Ag, or Cu) and semiconductor photocatalyst materials can serve to enhance overall photocatalytic performance versus the photocatalyst alone. This enhancement comes from photonic mechanisms like visible or NIR light absorption or scattering by plasmonic metal nanostructures and plasmonic enhancement mechanisms of direct transfer of “hot” electrons from the plasmonic metal to the photocatalyst and plasmon-induced resonant energy transfer from plasmonic metal to photocatalyst through dipole-dipole interactions. This poster summarizes our latest research on determining the nature of these enhancement mechanisms and progress towards high efficiency photocatalytic production of solar-fuels.

As the world’s energy demand increases and the finite supply of fossil fuels is used, clean, renewable energy alternatives are needed to fill the void of fossil fuels for supplying the world’s energy. One potential alternative to fossil fuels is chemical fuels produced through photocatalysis. However, the photocatalyst materials currently used and studied have problems such as poor charge carrier mobility and excitation lifetimes, large bandgaps that limit light absorption to the UV part of the spectrum, poor reaction kinetics at the interface photocatalyst surface and electrolyte. Coupling photocatalysts to nanoparticles and nanostructures made of plasmonic metals such as Au and Ag has been shown to enhance the overall photocatalytic performance of these materials. This enhancement is due to a combination of photonic effects due to enhanced light absorption in the visible and infrared parts of the spectrum and plasmonic effects such as direct electron transfer or a resonant energy transfer from plasmonic metal to the semiconductor photocatalyst. This poster presents our recent research on photocatalyst/plasmonic metal heterostructures and the mechanisms responsible for this enhancement.