Shell-thickness dependent Fano resonance in molecular catalyst functionalized CdSe/ZnS core/shell QDs.

Hybrid photocatalysts consisting of molecular catalyst functionalized semiconductors have attracted intense recent interest in solar fuel applications. Charge transfer interactions between the molecular catalyst and semiconductor have long been recognized to affect catalyst properties by controlling photoinduced charge separation across the semiconductor/molecule interface. In this paper, we investigate how such an interaction can also affect Fano resonance between the catalyst vibration and the intraband absorption of semiconductors.

Competitive Carbonate Binding Hinders Electrochemical CO Reduction to CO on Cu Surfaces at Low Overpotentials.

The electrochemical reduction of CO to useful chemicals holds promise for a sustainable carbon cycle. However, the key factors that control the pathways to various desired products remain unresolved, partially due to the limited knowledge of reaction intermediates on the electrode surface. To address this, we utilize in situ electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy in combination with density functional theory calculation to examine the potential-dependent composition of adsorbed species during CO reduction on polycrystalline copper.

Engineering Inorganic Perovskite Films by X Values of DMAPbI toward Large Area Photovoltaic Devices by Slot-Die Coating.

Dimethylammonium lead iodide (DMAPbI) has the potential to address the phase stability issue of inorganic perovskite solar cells (PSCs). In this study, the crystallinity, phase structure, defect states, and crystal growth habits of DMAPbI are controlled by adjusting the x value during synthesis, where N,N-dimethylacetamide (DMAC) is used as the solvent to regulate perovskite film growth. Furthermore, large-area CsPbIBr perovskite films with preferred oriented growth are achieved using the optimized x value in DMAPbI through the slot-die coating method.

Contactless EFISH Study of the Rate-Determining Step of Light-Driven Water Oxidation on TiO Photoanodes.

For many slow solar-fuel-forming reactions, the accumulation of photogenerated minority carriers on the photoelectrode surface leads to light-induced band edge unpinning, affecting the junction properties by decreasing band bending in the semiconductor space charge layer and increasing the driving force of surface reactions in the electric double layer. In this study, we demonstrate a contactless electric field-induced second harmonic generation (EFISH) method for measuring the band bending change (δΔΦ) on photoelectrodes upon photoexcitation. For n-doped rutile TiO water oxidation photoanodes at pH 7, δΔΦ increases at more positive potentials or higher illumination power density until it reaches saturation values.

Shell Thickness and Heterogeneity Dependence of Triplet Energy Transfer between Core-Shell Quantum Dots and Adsorbed Molecules.

Quantum dot (QD)-sensitized triplet energy transfer (TET) has found promising applications in photon upconversion and photocatalysis. However, the underlying mechanism of TET in the QD-acceptor complex remains unclear despite the well-developed TET theory for the molecular donor-acceptor systems. Herein, the coupling strength of TET from CdSe/CdS core-shell QDs to 9-anthracene carboxylic acid (ACA) was studied by measuring the TET rate as a function of shell thickness with time-resolved photoluminescence.

In Situ Studies of Multi-Carrier Dynamics in Electrochemically-Charged Colloidal CdSe/CdS Core/Shell Quantum Dots.

The application of semiconductor nanocrystals (NCs) in optoelectronic devices and photocatalysis inevitably involves them in charged states. The carrier and exciton dynamics of electrochemically charged NCs in solutions have yet to be reported. Herein, the electrochemical charging effects in colloidal CdSe/CdS core/shell quantum dots (QDs) are systematically investigated using static spectroelectrochemistry (SEC) and in situ transient absorption (TA) spectroscopy.

Fano Resonance in CO Reduction Catalyst Functionalized Quantum Dots.

Molecular catalyst functionalized semiconductor quantum dots (QDs) are a promising modular platform for developing novel hybrid photocatalysts. The interaction between adsorbed catalyst vibrations and the QD electron intraband absorption can influence the photophysical properties of both the QD and the catalysts and potentially their photocatalysis. In CdSe QDs functionalized by the CO reduction catalyst, Re(CO)(4,4'-bipyridine-COOH)Cl, we observe that the transient Fano resonance signal resulting from coupling of the catalyst CO stretching mode and the QD conduction band electron mid-IR intraband absorption appears on an ultrafast time scale and decays with the electron population, irrespective of the occurrence of photoreduced catalysts.

Control of Reversible Oxidative Addition/Reductive Elimination of Surface-Attached Catalysts by External Electric Fields.

We demonstrate that applied electric fields at interfaces can control the oxidative addition/reductive elimination equilibria of surface-attached molecular catalysts without any synthetic modification. Density functional theory (DFT) calculations show that the oxidative addition of HCl to a Co complex is "field switchable", being favorable under negative fields but unfavorable under sufficiently positive fields. Extending the analysis to different substrates (O, H) and metal centers (Rh, Ir) reveals consistent trends in the magnitude of the electric field effect: Co > Rh ≈ Ir and HCl > O > H.

Electron Transfer Energetics in Photoelectrochemical CO Reduction at Viologen Redox Polymer-Modified p-Si Electrodes.

While redox polymer-mediated catalysis at silicon photoelectrodes has been studied since the 1980s, there have been few detailed studies of these materials in photoelectrochemical CO reduction. Here, we develop silicon photoelectrodes functionalized with a viologen-based polymer that mediates the formation of catalytic gold nanoparticles. The presence of gold was confirmed by X-ray photoelectron spectroscopy (XPS), and the nanoparticles were imaged with high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM).

Efficient Size-Dependent Hot Electron Transfer from Au to TiO Nanoparticles.

Harvesting of plasmon-induced hot carriers at the metal/semiconductor interface offers a promising and innovative avenue for solar energy conversion. However, their practical implementation is often hampered by their limited efficiencies. Herein, we have demonstrated a highly efficient plasmonic hot electron transfer with a quantum efficiency (QE) of up to 57 ± 4% from 5.

The Impact of Electric Fields on Processes at Electrode Interfaces.

The application of external electric fields to influence chemical reactions at electrode interfaces has attracted considerable interest in recent years. However, the design of electric fields to achieve highly efficient and selective catalytic systems, akin to the optimized fields found at enzyme active sites, remains a significant challenge. Consequently, there has been substantial effort in probing and understanding the interfacial electric fields at electrode/electrolyte interfaces and their effect on adsorbates.

Direct and Indirect Interfacial Electron Transfer at a Plasmonic p-CuS/CdS Heterojunction.

Plasmonic semiconductors exhibit significant potential for harvesting near-IR solar energy, although their mechanisms of plasmon-induced hot electron transfer (HET) are poorly understood. We report a transient absorption study of plasmon-induced HET in p-CuS/CdS type II heterojunctions. Near-IR excitation of the p-CuS plasmon band at ∼1400 nm leads to ultrafast HET into the CdS conduction band with a time constant of <150 fs and a quantum efficiency of ∼0.

Molecular catalyst coordinatively bonded to organic semiconductors for selective light-driven CO reduction in water.

The selective photoreduction of CO in aqueous media based on earth-abundant elements only, is today a challenging topic. Here we present the anchoring of discrete molecular catalysts on organic polymeric semiconductors via covalent bonding, generating molecular hybrid materials with well-defined active sites for CO photoreduction, exclusively to CO in purely aqueous media. The molecular catalysts are based on aryl substituted Co phthalocyanines that can be coordinated by dangling pyridyl attached to a polymeric covalent triazine framework that acts as a light absorber.

Oligoyne bridges enable strong through-bond coupling and efficient triplet transfer from CdSe QD trap excitons for photon upconversion.

Polyyne bridges have attracted extensive interest as molecular wires due to their shallow distance dependence during charge transfer. Here, we investigate whether triplet energy transfer from cadmium selenide (CdSe) quantum dots (QDs) to anthracene acceptors benefits from the high conductance associated with polyyne bridges, especially from the potential cumulene character in their excited states. Introducing π-electron rich oligoyne bridges between the surface-bound anthracene-based transmitter ligands, we explore the triplet energy transfer rate between the CdSe QDs and anthracene core.

A contactless in situ EFISH method for measuring electrostatic potential profile of semiconductor/electrolyte junctions.

In photoelectrochemical cells, promising devices for directly converting solar energy into storable chemical fuels, the spatial variation of the electrostatic potential across the semiconductor-electrolyte junction is the key parameter that determines the cell performance. In principle, electric field induced second harmonic generation (EFISH) provides a contactless in situ spectroscopic tool to measure the spatial variation of electrostatic potential. However, the total second harmonic generation (SHG) signal contains the contributions of the EFISH signals of semiconductor space charge layer and the electric double layer, in addition to the SHG signal of the electrode surface.

Electro-inductive Effects and Molecular Polarizability for Vibrational Probes on Electrode Surfaces.

A microscopic understanding of electric fields and molecular polarization at interfaces will aid in the design of electrocatalytic systems. Herein, variants of 4-mercaptobenzonitrile are designed to test different schemes for breaking the continuous conjugation between a gold electrode surface and a nitrile group. Periodic density functional theory calculations predict applied potential dependencies of the CN vibrational frequencies similar to those observed experimentally.

Doping of Colloidal Nanocrystals for Optimizing Interfacial Charge Transfer: A Double-Edged Sword.

Doping of colloidal nanocrystals offers versatile ways to improve their optoelectronic properties, with potential applications in photocatalysis and photovoltaics. However, the precise role of dopants on the interfacial charge transfer properties of nanocrystals remains poorly understood. Here, we use a Cu-doped InP@ZnSe quantum dot as a model system to investigate the dopant effects on both the intrinsic photophysics and their interfacial charge transfer by combining time-resolved transient absorption and photoluminescent spectroscopic methods.

Charge Transfer from Quantum-Confined 0D, 1D, and 2D Nanocrystals.

The properties of colloidal quantum-confined semiconductor nanocrystals (NCs), including zero-dimensional (0D) quantum dots, 1D nanorods, 2D nanoplatelets, and their heterostructures, can be tuned through their size, dimensionality, and material composition. In their photovoltaic and photocatalytic applications, a key step is to generate spatially separated and long-lived electrons and holes by interfacial charge transfer. These charge transfer properties have been extensively studied recently, which is the subject of this Review.

A Resilient Platform for the Discrete Functionalization of Gold Surfaces Based on N-Heterocyclic Carbene Self-Assembled Monolayers.

We describe the synthesis and characterization of a versatile platform for gold functionalization, based on self-assembled monolayers (SAMs) of distal-pyridine-functionalized N-heterocyclic carbenes (NHC) derived from bis(NHC) Au(I) complexes. The SAMs are characterized using polarization-modulation infrared reflectance-absorption spectroscopy, surface-enhanced Raman spectroscopy, and X-ray photoelectron spectroscopy. The binding mode is examined computationally using density functional theory, including calculations of vibrational spectra and direct comparisons to the experimental spectroscopic signatures of the monolayers.

Triplet energy transfer from quantum dots increases Ln(iii) photoluminescence, enabling excitation at visible wavelengths.

Europium(iii) complexes are promising for bioimaging because of their long-lived, narrow emission. The photoluminescence (PL) from europium(iii) complexes is usually low. Thus, the effective utilization of low-energy light >400 nm and enhancement of PL are long-standing goals.

Tailoring Interfaces for Enhanced Methanol Production from Photoelectrochemical CO Reduction.

Efficient and stable photoelectrochemical reduction of CO into highly reduced liquid fuels remains a formidable challenge, which requires an innovative semiconductor/catalyst interface to tackle. In this study, we introduce a strategy involving the fabrication of a silicon micropillar array structure coated with a superhydrophobic fluorinated carbon layer for the photoelectrochemical conversion of CO into methanol. The pillars increase the electrode surface area, improve catalyst loading and adhesion without compromising light absorption, and help confine gaseous intermediates near the catalyst surface.

Electro-inductive Effect Dominates Vibrational Frequency Shifts of Conjugated Probes on Gold Electrodes.

Interfacial electric fields play a critical role in electrocatalysis and are often characterized by using vibrational probes attached to an electrode surface. Understanding the physical principles dictating the impact of the applied electrode potential on the vibrational probe frequency is important. Herein, a comparative study is performed for two molecular probes attached to a gold electrode.

Nanorod length-dependent photodriven H2 production in 1D CdS-Pt heterostructures.

Colloidal quantum confined semiconductor-metal heterostructures are promising candidates for solar energy conversion because their light absorbing semiconductor and catalytic components can be independently tuned and optimized. Although the light-to-hydrogen efficiencies of such systems have shown interesting dependences on the morphologies of the semiconductor and metal domains, the mechanisms of such dependences are poorly understood. Here, we use Pt tipped 0D CdS quantum dots (with ∼4.