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Role of Pt Loading in the Photocatalytic Chemistry of Methanol on Rutile TiO2(110)
摘要： As a cocatalyst, Pt is well-known for accepting photoexcited electrons and lowering the overpotential of hydrogen production in photocatalysis, being responsible for the enhanced photocatalytic efficiency. Despite the above existing knowledge, the adsorption of reactants on the Pt/photon-absorber (for example, Pt/TiO2) interface, a prerequisite to understand the photocatalytic chemistry, is extremely difficult to investigate mainly due to the complexity of the powdered material and solution environment. Combining ultrahigh vacuum and well-ordered single crystals, we study the photocatalytic chemistry of methanol on Pt loaded rutile TiO2(110) using temperature-programmed desorption (TPD) and ultraviolet photoelectron spectroscopy (UPS). Despite the same photocatalytic chemical products, i.e., formaldehyde and surface hydrogen species, as on Pt-free TiO2(110), the subsequent chemistry of surface hydrogen species and the photocatalytic reaction rate are much different. The bridging hydroxyls desorb as water molecules around 500 K on Pt-free TiO2(110) surface, by contrast, this desorption channel disappears completely and water and molecular hydrogen desorb at much lower temperature (<300 K) after Pt deposition, which can prevent the recombination of hydrogen species with formaldehyde. More importantly, methanol dissociates into methoxy at the Pt/TiO2(110) interface, which is crucial in the photocatalytic chemistry of methanol on TiO2 surfaces since methoxy is a more effective hole scavenger than methanol itself. The photocatalytic chemical reaction rate is increased by nearly one order of magnitude after 0.12 monolayer Pt deposition. This work suggests that Pt loading can promote the dissociation of methanol into methoxy and lower the desorption barrier of molecular hydrogen, which may work cooperatively with separating photoexcited charges to enhance the photocatalytic efficiency. Our work implies the importance of the cocatalysts in affecting the surface structure and adsorption of reactants and products and then improving the photoactivity, in addition to the well-known role in charge separation.
关键词： Titanium Dioxide,Charge Separation,Pt Cocatalyst,Hydrogen Production,Methanol to Methoxy Conversion
更新于2025-09-23 15:21:21
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Transmission-Line Model for Materials with Spin-Momentum Locking
摘要： We provide a transmission-line representation for channels exhibiting spin-momentum locking (SML) that can be used for both time-dependent and steady-state transport analysis on a wide variety of materials with spin-orbit coupling such as topological insulators, Kondo insulators, transition metals, semimetals, oxide interfaces, and narrow band-gap semiconductors. This model is based on a time-dependent four-component di?usion equation obtained from the Boltzmann transport equation assuming linear response and elastic scattering in the channel. We classify all electronic states in the channel into four groups (U+, D+, U?, and D?) depending on the spin index [up (U), down (D)] and the sign of the x component of the group velocity (+, ?) and assign an average electrochemical potential to each of the four groups to obtain the four-component di?usion equation. For normal metal channels, the model decouples into the well-known transmission-line model for charge and a time-dependent version of the Valet-Fert equation for spin. We ?rst show that, in the steady-state limit, our model leads to simple expressions for charge-spin interconversion in SML channels in good agreement with existing experimental data on diverse materials. We then use the full time-dependent model to study spin-charge separation in the presence of SML, a subject that has been controversial in the past. Our model shows that the charge and spin signals travel with two distinct velocities, resulting in well-known spin-charge separation, which is expected to persist even in the presence of SML. However, our model predicts that the lower velocity signal is purely spin, while the higher velocity signal is largely charge with an additional spin component proportional to the degree of SML, which has not been noted before. Finally, we note that our model can be used within standard circuit simulators such as SPICE to obtain numerical results for complex geometries.
关键词： spin-orbit coupling,spin-charge separation,transmission-line model,topological insulators,charge-spin interconversion,spin-momentum locking
更新于2025-09-23 15:21:01
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Charge separation and electron transfer routes modulated with Co-Mo-P over g-C3N4 photocatalyst
摘要： In this case, a novel photocatalyst with visible light harvesting, spatial charge separation and effective electron transfer route is reported, which assemble Co-Mo-P nanoparticle on the surface of g-C3N4. The composite photocatalyst shows high H2 evolution with a yield of 646.4 μmol in 5 h, which is 66.7 times than over the pristine g-C3N4. The AQE measured was reached 5.25% at the wavelength of 475 nm after 1 h. The inner reason was comprehensively studied and understood by means of FESEM, HRTEM, XRD, XPS, UV–vis DRS and BET. Especially the investigation of their photoelectrochemical properties with photocurrent, voltammetric scanning, fluorescence spectra, etc. The characterization results show that CoMoP forms a large number of active sites on the surface of g-C3N4, which improves efficiency of the charge transfer and then accelerates the rate of HER. At the same time, the mechanism of H2 production of photocatalyst in the eosin Y sensitization system was proposed.
关键词： Hydrogen production,Electron transfer,Charge separation,Photocatalysis
更新于2025-09-23 15:21:01
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Asymmetric Electron Acceptors for Higha??Efficiency and Lowa??Energya??Loss Organic Photovoltaics
摘要： Low energy loss and efficient charge separation under small driving forces are the prerequisites for realizing high power conversion efficiency (PCE) in organic photovoltaics (OPVs). Here, a new molecular design of nonfullerene acceptors (NFAs) is proposed to address above two issues simultaneously by introducing asymmetric terminals. Two NFAs, BTP-S1 and BTP-S2, are constructed by introducing halogenated indandione (A1) and 3-dicyanomethylene-1-indanone (A2) as two different conjugated terminals on the central fused core (D), wherein they share the same backbone as well-known NFA Y6, but at different terminals. Such asymmetric NFAs with A1-D-A2 structure exhibit superior photovoltaic properties when blended with polymer donor PM6. Energy loss analysis reveals that asymmetric molecule BTP-S2 with six chlorine atoms attached at the terminals enables the corresponding devices to give an outstanding electroluminescence quantum efficiency of 2.3 × 10?2%, one order of magnitude higher than devices based on symmetric Y6 (4.4 × 10?3%), thus significantly lowering the nonradiative loss and energy loss of the corresponding devices. Besides, asymmetric BTP-S1 and BTP-S2 with multiple halogen atoms at the terminals exhibit fast hole transfer to the donor PM6. As a result, OPVs based on the PM6:BTP-S2 blend realize a PCE of 16.37%, higher than that (15.79%) of PM6:Y6-based OPVs. A further optimization of the ternary blend (PM6:Y6:BTP-S2) results in a best PCE of 17.43%, which is among the highest efficiencies for single-junction OPVs. This work provides an effective approach to simultaneously lower the energy loss and promote the charge separation of OPVs by molecular design strategy.
关键词： asymmetric acceptors,molecular design strategies,nonfullerene acceptors,charge separation,organic photovoltaics
更新于2025-09-23 15:21:01
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Highly Efficient Inorganic-Organic Heterojunction Solar Cells Based on Polymer and CdX (X=Se, Te) Quantum Dots: An Insight from a Theoretical Study
摘要： By using the density functional method, we explore the potentiality of recently synthesized CdX (X=Se, Te)QD/P3HT composites in solar energy conversion devices. Our study reveals that inorganic/organic hybrid CdXQD/P3HT nanocomposites with larger size of CdX QDs exhibit type-II band alignment, suggesting efficient charge separation upon photoexcitation. But for smaller size of QDs, the composites show type-I band alignment which are devoid of charge separation and thus are not suitable for solar cell applications. To remove this obstacle, we focus on chemical modification to polymer P3HT. The substitution of hydrogen at the beta position of each thiophene ring of polymer by electron withdrawing group (CN) results type-II band alignment and yield spatial charge separation even for smaller size of QDs. Finally, we calculated the powerconversion efficiency (PCE) of CdXQD and CN functionalized P3HT nanocomposites. The maximum calculated PCE value of 10.82% is achieved, which makes them immensely competitive with other reported heterojunction solar cells.
关键词： CdX (X=Se, Te)QD/P3HT composites,powerconversion efficiency,solar energy conversion,charge separation,type-II band alignment
更新于2025-09-23 15:21:01
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Construction of nitrogen and phosphorus co-doped graphene quantum dots/Bi5O7I composites for accelerated charge separation and enhanced photocatalytic degradation performance
摘要： Nitrogen and phosphorus co-doped graphene quantum dot-modified Bi5O7I (NPG/Bi5O7I) nanorods were fabricated via a simple solvothermal method. The morphology, structure, and optical properties of the as-prepared samples were investigated by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), and diffused reflectance spectroscopy. The photocatalytic performance was estimated by degrading the broad-spectrum antibiotics tetracycline and enrofloxacin under visible light irradiation. The photodegradation activity of Bi5O7I improved after its surface was modified with NPGs, which was attributed to an increase in the photogenerated charge transport rate and a decrease in the electron-hole pair recombination efficiency. From the electron spin resonance spectra, XPS valence band data, and free radical trapping experiment results, the main active substances involved in the photocatalytic degradation process were determined to be photogenerated holes and superoxide radicals. A possible photocatalytic degradation mechanism for NPG/Bi5O7I nanorods was proposed.
关键词： Charge separation,Photocatalysis,Bi5O7I,N,P co-doped graphene quantum dots,Ionic liquid
更新于2025-09-23 15:21:01
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Enhanced Ferroelectric Photovoltaic Effect in Semiconducting Single-Wall Carbon Nanotubes/BiFeO <sub/>3</sub> Heterostructure Enabled by Wide-Range Light Absorption and Efficient Charge Separation
摘要： The interfacial electronic band structures of photovoltaic heterostructure devices greatly affect their light absorption and charge-transport properties and thus their photovoltaic performance. In this work, we report an enhanced ferroelectric photovoltaic effect in a semiconducting single-walled carbon nanotube (S-SWCNTs)/ferroelectric BiFeO3 (BFO) heterostructure. A wide range of light absorption was possible in this structure owing to the low bandgaps of the S-SWCNTs (0.2–2.1 eV) and BFO (2.2–2.7 eV). The heterostructure also enabled efficient charge separation owing to the strong built-in electric field resulting from the synergic effect of the formation of p–f–n junctions (p-type S-SWCNTs/ferroelectric (f) BFO/n-type Nb:SrTiO3) and the introduction of a polarization-mediated internal field in the ferroelectric BFO layer. Compared with a single-layer device (Pt/BFO/Nb:SrTiO3), the heterostructure device (Pt/S-SWCNTs/BFO/Nb:SrTiO3) exhibited substantial enhancement of the photovoltaic performance. The open-circuit photovoltage and short-circuit photocurrent density reached up to 0.23 V and ?7.52 mA cm?2 (corresponding to a photo-conversion efficiency of 4.40%) under one-sun illumination, respectively, after optimization of the ferroelectric layer thickness and appropriate interfacial band alignment. Moreover, by applying switchable electric polarization, this heterostructure could be tuned, enabling the development of controllable photovoltaic devices. Our findings demonstrate that the synergistic integration of materials with different functionalities is a promising approach for the design of photovoltaic devices with tunable performance.
关键词： BiFeO3,light absorption,single-walled carbon nanotube,heterostructure,charge separation,ferroelectric photovoltaic effect
更新于2025-09-23 15:21:01
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Impact of electrona??phonon coupling on the quantum yield of photovoltaic devices
摘要： In describing the charge carriers’ separation mechanism in the organic solar cell, providing a method, which considers the impact of all parameters of interest on the same footing within an inexpensive numerical effort, could play an essential role. We use here a simple tight-binding model to describe the dissociation of the charge carriers and investigate their dependence on the physical parameters of the system. We demonstrate that the quantum yield of the cell is subtly controlled by the collective action of the Coulomb interaction of the electron–hole pair, electron–phonon coupling, and the geminate recombination of the charge carriers. This approach should help us understand the performance of organic solar cells and optimize their efficiency.
关键词： electron–phonon coupling,quantum yield,organic solar cells,charge separation,photovoltaic devices
更新于2025-09-23 15:19:57
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The Role of Delocalization and Excess Energy in the Quantum Efficiency of Organic Solar Cells and the Validity of Optical Reciprocity Relations
摘要： The photon energy dependence of long-range charge separation is studied for two prototypical polymer:fullerene systems. The internal quantum efficiency (IQE) of PCDTBT:PC61BM is experimentally shown to be independent on the excitation energy. In contrast, for TQ1:PC71BM the IQE is strongly energy-dependent for excitation energies close to CT electroluminescence peak maximum while it becomes energy-independent at higher excitation energies. Kinetic Monte Carlo simulations reproduce the experimental IQE and reveal that the photon energy-dependence of the IQE is governed by charge delocalization. Efficient long-range separation at excitation energies corresponding to the CT electroluminescence peak maximum or lower requires an initial separation of the hole-electron pair by ～4-5nm, whereas delocalization is less important for charge separation at higher photon energies. Our modeling results suggest that a phenomenological reciprocity between CT electroluminescence and external quantum efficiency does not necessarily prove that commonly employed reciprocity relations between these spectra are valid from a fundamental perspective.
关键词： delocalization,optical reciprocity relations,quantum efficiency,organic solar cells,charge separation
更新于2025-09-23 15:19:57
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Strongly coupled 2D-2D nanojunctions between P-doped Ni2S (Ni2SP) cocatalysts and CdS nanosheets for efficient photocatalytic H2 evolution
摘要： Developing low-cost, environment-friendly and highly-active nanocomposites for photocatalytic hydrogen evolution reaction (HER) holds pivotal function in water splitting. Supported cocatalysts on semiconductor can facilitate speedy transfer and separation of photoexcited charge, active interfacial response and suppress photocorrosion. We, for the first time, proposed a novel strategy to formed 2D-2D (two dimensional) nanocomposites by loading 2D P-doped Ni2S (Ni2SP) cocatalysts onto 2D CdS nanosheets (NSs). The as-obtained 2D-2D CdS/Ni2SP nanocomposites exhibited excellent HER activity in 0.25 M Na2S-Na2SO3 sacrificial solution under visible light (λ ≥ 420 nm). The optimal loading of 2 wt% 2D Ni2SP on 2D CdS as a cocatalyst yielded an optimal H2 production rate at 18.96 mmol g-1 h-1, which was approximately 3.26 folds higher than that of bare 2D CdS (5.82 mmol g-1 h-1) without cocatalysts. In the presence of non-precious metal, the highest apparent quantum efficiency of 4.8% was recorded at 420 nm. The enhanced photocatalytic HER activity was attributed to the excellent interfacial coupling effects of Ni2SP NSs cocatalyst with CdS NSs, which was essential for the rapid charge separation and transfer, increased number of active sites and improved H2-evolution kinetics. This study offers a feasible scheme to design efficient photocatalysts system to produce hydrogen.
关键词： Charge separation and transfer,2D-2D nanojunctions,P-doped Ni2S (Ni2SP) cocatalysts,Photocatalytic hydrogen evolution reaction
更新于2025-09-23 15:19:57