Abstract
Solar-driven hydrogen peroxide (H
2
O
2
) production presents unique merits of sustainability and environmental friendliness. Herein, efficient solar-driven H
2
O
2
production through ...dioxygen reduction is achieved by employing polymeric carbon nitride framework with sodium cyanaminate moiety, affording a H
2
O
2
production rate of 18.7 μmol h
−1
mg
−1
and an apparent quantum yield of 27.6% at 380 nm. The overall photocatalytic transformation process is systematically analyzed, and some previously unknown structural features and interactions are substantiated via experimental and theoretical methods. The structural features of cyanamino group and pyridinic nitrogen-coordinated soidum in the framework promote photon absorption, alter the energy landscape of the framework and improve charge separation efficiency, enhance surface adsorption of dioxygen, and create selective 2e
−
oxygen reduction reaction surface-active sites. Particularly, an electronic coupling interaction between O
2
and surface, which boosts the population and prolongs the lifetime of the active shallow-trapped electrons, is experimentally substantiated.
BiOI/TiO2 heterostructures with different Bi to Ti molar ratios were synthesized through a simple soft-chemical method at a temperature as low as 80 °C. The as-prepared powders were characterized by ...X-ray powder diffraction, electron microscopy, UV−vis diffuse reflectance spectroscopy, nitrogen sorption, and X-ray photoelectron spectroscopy. The photocatalytic activities of these BiOI/TiO2 heterostructures were evaluated on the degradation of methyl orange under visible-light irradiation (λ > 420 nm). The results revealed that the BiOI/TiO2 heterostructures exhibited much higher photocatalytic activities than pure BiOI and TiO2, respectively, and 50%BiOI/TiO2 showed the best activity among all these heterostructured photocatalysts. Surface photovoltage spectroscopy and transient photovoltage measurements were used to confirm the formation of heterojunction and probe charge transfer between BiOI and TiO2. The visible-light photocatalytic activity enhancement of BiOI/TiO2 heterostructures could be attributed to its strong absorption in the visible region and low recombination rate of the electron−hole pairs because of the heterojunction formed between BiOI and TiO2.
This paper reports a one-step hydrothermal method of in-situ growing copper selenide (CuSe) nanoparticles on the 2D materials-MXene (Ti3C2) nanosheets to form CuSe/Ti3C2 composite with ...three-dimensional structure. The CuSe/Ti3C2 slurry prepared via a solvothermal method was screen-printied onto graphite sheet to form a counter electrode (CE) in quantum dot-sensitized solar cells (QDSCs). The CuSe/Ti3C2 CE shows the better electrical conductivity for electron transfer, and a larger specific surface area to provide more active sites for polysulfide electrolyte reduction, as compared to the pristine CuSe CE and Ti3C2 CE. Hence, the device with CuSe/Ti3C2-30 mg CE achieves an efficiencies of 5.12%, which much better than that of CuSe CE (3.47%) and Ti3C2 CE (2.04%). The symmetrical dummy cells consisting of two CEs are further designed to confirm the best electrocatalytic activity and the excellent stability of composite CE towards polysulfide electrolyte. Therefore, CuSe/Ti3C2 is very promising as CE for QDSCs and this strategy provides a facile route for the design of the composite with MXene as a CE for QDSCs.
The improvement of photoinduced charge separation is the key for light-harvesting systems in both photovoltaic and photoelectrochemical solar cells. In this study, the charge separation efficiency ...has been modulated through varying the magnitude of interfacial electric field in p–n Cu2O homojunction films prepared by simple electrodeposition method. The photoelectrochemical and surface photovoltage measurements were used to investigate the behaviors of photoinducded charge carriers in different p–n Cu2O homojunction films. The results confirmed that the p–n Cu2O homojunction film which exhibited the highest charge separation efficiency resulted in the highest activity in photocatalytic reduction of methyl viologen. These implied that it is possible to achieve high charge separation efficiency via constructing a large magnitude of interfacial electric field within a semiconductor using a simple electrodeposition method.
A series of different crystalline phases BiVO4 photocatalysts (tetragonal, monoclinic, and monoclinic/tetragonal heterophase) have been prepared by a coprecipitation and molten salt method. ...High-resolution transmission electron microscopy (HRTEM) results show that an interface of intimate contact is formed in monoclinic/tetragonal heterophase and monoclinic phase is mainly on the surface of nanoparticles. Surface photovoltage (SPV) and transient photovoltage (TPV) techniques are used to further investigate the transfer process of photoinduced charge carriers. The results show that the behavior of photoinduced charges markedly depend on the crystalline phases of BiVO4 samples, and the presence of interface in monoclinic/tetragonal heterophase provides a spatial condition for charge transfer, promotes the separation of photoinduced electron–hole pairs, and changes the migration direction of photoinduced carriers. The relationship between behavior of photoinduced charge carriers and photocatalytic activity was discussed in detail, which would provide a greater insight into the intrinsic reasons of the enhancement in photocatalytic activity.
The growth of anatase TiO2 nanowires (NWs) on fluorine doped tin oxide (FTO) substrates through hydrothermal reaction has attracted wide attention and research, especially in the case of the solar ...cells. Actually, the built-in electric field at the anatase TiO2 NWs/FTO interface leads to the photoexcited holes transfer to FTO conductive substrates because the Fermi energy of anatase TiO2 NWs film is higher than that of FTO substrates. Yet efficient transport of photoexcited electron to the FTO conductive substrates is desirable. Hence, the built-in electric field at the pure TiO2 NWs/FTO interface has prevented anatase TiO2 NWs-based solar cells from achieving a higher photoelectric performance. In this work, we elaborately design and construct the N-doped anatase TiO2 NWs/FTO interface with the desirable orientations from FTO toward N-doped anatase TiO2 NWs, which favors the photoexcited electron transfer to the FTO conductive substrates. The surface photovoltage (SPV) and Kelvin probe measurements demostrate that the N-doped anatase TiO2 NWs/FTO interface favors the photoexcited electron transfer to the FTO conductive substrates due to the fact that the orientation of the built-in electric field at the N-doped TiO2 NWs/FTO interface is from FTO toward TiO2. The photoexcited charge transfer dynamics of CdS QD-sensitized TiO2 NWs and N-doped TiO2 NWs electrodes was investigated using the transient photovoltage (TPV) and transient photocurrent (TPC) technique. Benefiting from the desirable interface electric field, CdS-based quantum dot-sensitized solar cells (QDSCs) with the optimal N doping amount exhibit a remarkable solar energy conversion efficiency of 2.75% under 1 sun illumination, which is 1.46 times enhancement as compared to the undoped reference solar cells. The results reveal that the N-doped anatase TiO2 NWs electrodes have promising applications in solar cells.
Highly photocatalytically active cobalt-doped ZnO （ZnO：Co） nanorods have been prepared by a facile hydrothermal process. X-ray diffraction, X-ray photoelectron spectroscopy, Raman scattering and ...UV-vis diffuse reflectance spectroscopy confirmed that the dopant ions substitute for some of the lattice zinc ions, and furthermore, that Co〉 and Co〉 ions coexist. The as-prepared ZnO：Co samples have an extended light absorption range compared with pure ZnO and showed highly efficient photocatalytic activity, only requiring 60 rain to decompose -93% of alizarin red dye under visible light irradiation （λ 〉 420 nm）, The photophysical mechanism of the visible photocatalytic activity was investigated with the help of surface photovoltage spectroscopy. The results indicated that a strong electronic interaction between the Co and ZnO was present, and that the incorporation of Co promoted the charge separation and enhanced the charge transfer ability and, at the same time, effectively inhibited the recombination of photogenerated charge carriers in ZnO, resulting in high visible light photocatalytic activity.
Inverted perovskite solar cells (PSCs) have been extensively studied by reason of their negligible hysteresis effect, easy fabrication, flexible PSCs and good stability. The certified photoelectric ...conversion efficiency (PCE) achieved 23.5% owing to the formed lead−sulfur (Pb−S) bonds through the surface sulfidation process of perovskite film, which gradually approaches the performance of traditional upright structure PSCs and indicates their industrial application potential. However, the fabricated devices are severely affected by moisture, high temperature and ultraviolet light due to the application of organic materials. Depending on nitrogen, cost of protection may increase, especially for the industrial production in the future. In addition, the inverted PSCs are found with a series of issues compared with the traditional upright PSCs, such as nonradiative recombination of carriers, inferior stability and costly charge transport materials. Thus, the development of inverted PSCs is systematically reviewed in this paper. The design and fabrication of charge transport materials and perovskite materials, enhancement strategies (e.g., interface modification and doping) and the development of all−inorganic inverted devices are discussed to present the indicator for development of efficient and stable inverted PSCs.
A WO3/TiO2 heterojunction photoanode was prepared by in situ growth of WO3 on a mesoporous TiO2 electrode. The photoinduced charge‐transfer properties and chargeseparation improvement in this kind of ...type‐II heterojunction were characterized by transient surface photovoltage spectra. By using sulfite oxidation as a hole scavenger, we demonstrated that 72 % of the photo‐generated holes are reaching the surface of the photoanode, but the efficiency of hole injection (ηox) into the electrolyte was only 48 %. For the first time, a NiII meso‐tetra(4‐carboxyphenyl)porphyrin (NiTCPP) was incorporated as a water oxidation catalyst into the WO3/TiO2 heterojunction photoanode, which promoted the value of ηox to 81 %. The maximum applied bias photon‐to‐current efficiency for the WO3/TiO2/NiTCPP photoanode was determined to be 0.2 % at 1.01 V vs. the reversible hydrogen electrode (RHE), under which condition a Faradic efficiency of 89 % for water oxidation was achieved (averaged over 1 h of photolysis).
Stairway to injection: Hole injection from a WO3/TiO2 photoanode into the electrolyte is identified as being only 48 % efficient. Incorporation of a nickel porphyrin into the photoanode results in a 1.7‐fold enhancement in hole injection, improving the photo‐to‐current efficiency and Faradaic efficiency for water oxidation.
Inevitable drawbacks on α-Fe2O3 photoanodes, such as poor conductivity, short hole diffusion length, high electron-hole recombination rate, limit their photoelectrochemical (PEC) performance for ...water oxidation. The construction of heterojunction is an effective approach to improve the PEC performance of photoanodes. Herein, we report the design of the WO3/Ti–Fe2O3 heterojunction photoanodes, which are synthesized by two simple hydrothermal method. The optimized WO3/Ti–Fe2O3 photoanode shows remarkably improved photocurrent of 2.15 mA/cm2 at 1.23 V versus reversible hydrogen electrode (RHE) without additional cocatalyst, which is higher than that of previous literatures. The improvement benefits from reduced charge transfer resistance in the bulk of Ti–Fe2O3 photoanode and improved charge separation efficiency, which can been further confirmed by electrochemical impedance spectroscopy (EIS), the transient photovoltage (TPV) and the work function (WF) measurement. The present work also provide new opportunities in developing high performance photoanodes for PEC water splitting.
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