Efficient and stable photo-oxidation of water by a bismuth vanadate photoanode coupled with an iron oxyhydroxide oxygen evolution catalyst

BiVO(4) films were prepared by a simple electrodeposition and annealing procedure and studied as oxygen evolving photoanodes for application in a water splitting photoelectrochemical cell. The resulting BiVO(4) electrodes maintained considerable photocurrent for photo-oxidation of sulfite, but generated significantly reduced photocurrent for photo-oxidation of water to oxygen, also decaying over time, suggesting that the photoelectrochemical performance of BiVO(4) for water oxidation is mainly limited by its poor catalytic ablity to oxidize water. In order to improve the water oxidation kinetics of the BiVO(4) electrode, a layer of FeOOH was placed on the BiVO(4) surface as an oxygen evolution catalyst using a new photodeposition route. The resulting BiVO(4)/FeOOH photoanode exhibitied significantly improved photocurrent and stability for photo-oxidation of water, which is one of the best among all oxide-based phoatoanode systems reported to date. In particular, the BiVO(4)/FeOOH photoanode showed an outstanding performance in the low bias region (i.e., E < 0.8 V vs RHE), which is critical in determining the overall operating current density when assembling a complete p-n photoelectrochemical diode cell. The photocurrent-to-O(2) conversion efficiency of the BiVO(4)/FeOOH photoanode is ca. 96%, confirming that the photogenerated holes in the BiVO(4)/FeOOH photoanode are indeed excusively used for O(2) evolution.     

Photocurrent response of the passive film on iron in a high-temperature aqueous electrolyte

An experimental setup for in situ photoelectrochemical measurements of passive films in high-temperature, high-pressure electrolytes are described. The setup enables photovoltammetric and photocurrent spectroscopic measurements at temperatures up to 300 °C and at pressures up to 10 MPa. The first results on the photocurrent response of the passive film on Fe in 0.05 M Na₂B₄O₇ (pH 9.3) are presented. The dependences of the photocurrent on photon energy and electrode potential are explored. The results are discussed in terms of the effect of temperature and potential on the nature of the photoactive layer in the passive film on Fe. It can be concluded that despite the increase in the overall thickness of the film on Fe with increasing temperature, the thickness of the photoactive layer seems to remain constant.     

有机化合物表面光电压谱的研究

<正> 半导体与金属接触处产生表面势垒,当光照射在样品与金属的接触界面上时,在光照面和非光照面之间建立起电位差,记录这个电位差和入射光波长的关系得到表面光电压谱。表面光电压谱反映材料的光吸收性质和电子的带-带跃迁,同时又受到光生载流子寿命的影响。应用表面光电压技术已经测量了单晶半导体的光伏效应,少数载流子的扩散长度以及表面态等。近来,王德军等用表面光电压谱的方法研究了无机半导体粉末光催化剂的活性。     

Optical Sensing by Silica/Titania Thin Films Doped with Oxacarbocyanine Dye

Photocurrent responses of sol-gel films of silica/titania doped with oxacarbocyanine dye were investigated with a sandwich-type photocell constructed with polymer electrolyte membrane and indium-tin-oxide glass electrodes. At an equilibrium and positive bias voltages, a typical photocell exhibited negative and positive current peaks when the visible light illumination was on and off, respectively. The wavelength dependence of the photocurrent responses well matched to the absorption band of the doped dye. This differential photocurrent response was attributed to trapping of carriers photoexcited in the dye molecules at the defect states in the matrix film. At negative bias voltages, on the other hand, the cell exhibited constant, negative photoelectrochemical currents under illumination. These differential and linear photocurrent responses were affected by the SiO₂/TiO₂ matrix structures depending on the Si : Ti ratio.     

TiO_2光电化学电池催化氧化甲基红

以钛基TiO2薄膜为光阳极,研究了光电化学电池中阳极光催化降解偶氮染料甲基红的动力学.结果表明,短接光电化学电池分隔了光催化过程的阴、阳极反应,有利于抑制光生载流子的复合,提高光催化氧化速率.相同实验条件下短路光电流越大,则甲基红降解速率越高.在基底和TiO2薄膜之间夹层SnO2得到组装电极Ti/SnO2/TiO2,进一步提高了光生载流子的分离效率;同时采用电化学阻抗谱(EIS)评价了电极的光催化性能.     

Carboxyphenyl metalloporphyrins as photosensitizers of semiconductor film electrodes. A study of the effect of different central metals

Free-base (P), Zn(II) (P(Zn)), Cu(II) (P(Cu)), Pd(II) (P(Pd)), Ni(II) (P(Ni)), and Co(II) (P(Co)) 5-(4-carboxyphenyl)-10,15,20-tris(4-methylphenyl) porphyrins were designed and synthesized to be employed as spectral senzitizers in photoelectrochemical cells. The dyes were studied adsorbed on SnO(2) nanocrystalline semiconductor and also in Langmuir-Blodgett film ITO electrodes in order to disclose the effect of molecular packing on the studied properties. Electron injection yields were obtained by fluorescence quenching analysis comparing with the dyes adsorbed on a SiO(2) nanocrystalline insulator. Back electron-transfer kinetics were measured by using laser flash photolysis. The unmetallized and metallized molecules have different singlet state energies, fluorescence quantum yields, and redox properties. The quantum yields of sensitized photocurrent generation are shown to be highly dependent on the identity of the central metal. It is shown that P(Ni) and P(Co) do not present a photoelectric effect. The other porhyrins present reproducible photocurrent, P(Pd) being the one that gives the highest quantum yield even in closely packet ITO/LB films. Photocurrent quantum yields increase as the dye ground-state oxidation potential becomes more anodic, which is in agreement with the observation, obtained by laser flash photolysis, that back electron-transfer kinetics decrease with the increase in the driving force for the recombination process. This effect could be exploited as a design element in the development of new and better sensitizers for high-efficiency solar cells involving porphyrins and related dyes.     

TiO2光电化学电池催化氧化甲基红

以钛基TiO₂薄膜为光阳极，研究了光电化学电池中阳极光催化降解偶氮染料甲基红的动力学. 结果表明，短接光电化学电池分隔了光催化过程的阴、阳极反应，有利于抑制光生载流子的复合，提高光催化氧化速率. 相同实验条件下短路光电流越大，则甲基红降解速率越高. 在基底和TiO₂薄膜之间夹层SnO₂得到组装电极Ti/SnO₂/TiO₂，进一步提高了光生载流子的分离效率；同时采用电化学阻抗谱（EIS）评价了电极的光催化性能.     

Photoelectrochemical reaction and H2 generation at zero bias optimized by carrier concentration of n-type GaN

The authors studied the photoelectrochemical properties dependent on carrier concentration of n-type GaN. The photocurrent at zero bias became the maximum value at the carrier concentration of 1.7x10(17) cm-3. Using the sample optimized carrier concentration, the authors achieved H2 gas generation at a Pt counterelectrode without extra bias for the first time. The authors also discussed the mechanism of the dependence of photocurrent on the carrier concentration of GaN.     

Anomalous photoconductivity effects of poly-N-epoxypropylcarbazole films with a high concentration of an anionic polymethine dye

Photoluminescence quenching in an external electric field increases and a long-wavelength photoluminescence band and photoconductivity appear in the visible spectrum with increasing concentration of anionic polymethine dye in poly-N-epoxypropylcarbazole films. Associated species containing dye ion pairs are formed with increasing dye concentration. The kinetics found for the growth and relaxation of the photocurrent in these composite films is anomalous for photosemiconductor materials: the time required for growth of the photocurrent is much greater than the time for its relaxation after switching off the light. A prior irradiation memory effect of the films was discovered.     

后处理对TiO_2纳米晶膜电极光电性能的改善(英文)

利用TiCl4 水溶液处理TiO2 纳米晶膜电极 ,可以提高光电流 ,改善电极的光电转换性能 .对未经处理和处理后电极的比表面、孔分布 ,以及瞬态光电流分析表明 ,后处理改善了电荷在电极中的传输 ,从而提高了光电流     

Study of the influence of substituents on spectroscopic and photoelectric properties of zinc phthalocyanines

In this paper we describe conversion of light energy into electric energy in a photoelectrochemical cell containing zinc phthalocyanine (ZnPc) dyes. For all dyes investigated in liquid polyvinyl alcohol with dimethyl sulfoxide solution and located in the photoelectrochemical cell the following measurements have been done: absorption, fluorescence, photoacoustic spectra, photovoltaic spectra, kinetics of photocurrent and current–voltage characteristics. It has been shown that all dyes located in the photoelectrochemical cell are able to convert light into electric energy but with different effectiveness. The influence of substituted different peripheral groups to ZnPc core and the correlation between the molecular structure and effectiveness of solar to electric energy conversion were observed and described. The unique behavior of ZnPc substituted with fluorines was indicated.     

Study on photoconductivity of dye-polymer-based solid-state thin film

In this article, we describe a solid-state photoelectrochemical cell for light detection. Safranine-T dye mixed with polyvinyl alcohol (PVA) solution was deposited on a conducting and transparent indium-tin-oxide (ITO)-coated glass that was used as one electrode and another ITO-coated glass as the counterelectrode. A solid polymeric electrolyte consisting of polyethylene oxide-ammonium perchlorate-ethylene carbonate and propylene carbonate with suitable weight ratio was prepared and sandwiched between these two ITO-coated glass electrodes, which were separated by a Teflon spacer about 50 μm thick. The cell was biased with a direct current source to make the dye and PVA-coated ITO as the anode and the other ITO as the cathode. On illumination by a tungsten lamp, from the cathode side, the change of photocurrent was measured. The dark current-voltage characteristics and the growth and decay of the photocurrent for steady and pulsed illumination were studied.     

五甲川菁染料敏化p-NiO纳米结构电极的光电化学

研究了NiO纳米结构电极及五甲川菁染料敏化NiO纳米结构电极的光电化学行为。结果表明,NiO纳米结构电极在光照下产生阴极光电流,为p-型半导体,其禁带宽度为2.8eV,使用五甲川菁染料敏化可以显著地提高NiO纳米结构电极的阴极光电流,使NiO纳米结构电极吸收波长红移至可见光区,光电转换效率得到明显改善。研究了OTE/TiO~2/Ru(bpy)~2(SCN)~2和OTE/NiO/PMC作为光阳极和光阴极组成电池的电池特性,结果表明复合电池的光电压提高,但光电流的大小受光电流小的电极限制。     

Role of nanochemical environments in porous TiO2 in photocurrent efficiency and degradation in dye sensitized solar cells

Elongated dye sensitized solar cells with a thickness gradient of the nanoporous TiO2 front electrode were used to assess the impact of the layer thickness on photocurrent and degradation. The photocurrent efficiency passes through a maximum (in our case at about 12 microm). Interestingly, the degradation rate also strongly depends on the layer thickness and is about 3 times faster for a 15-microm cell (in comparison with a 1-microm cell). To explain these nonanticipated results, a model to describe the I3(-)/I- concentration within a typical dye sensitized solar cell under steady-state conditions was derived. It includes the nanoporous TiO2 layer and a bulk solution with their different mobilities for the electrolyte species. Using typical parameters from the literature, it turned out that, despite the fact that the initial I- concentration is about 1 order of magnitude larger and the assumed diffusion coefficient is 1.3 times higher, the depletion of the I- concentration at the TiO2/FTO front contact happens to be in the same range as the depletion of the I3(-) concentration at the back contact. This stresses the importance of iodide in nanoporous environments for both the maximum attainable photocurrent and its role in the regeneration of the oxidized dye. Enhanced degradation rates might be related to poor iodide supply, since the oxidized state cannot be regenerated efficiently.     

Photoelectrochemical cells with tungsten trioxide/Mo-doped BiVO4 bilayers

Mo-doped BiVO(4) nanocrystals with low bandgap energy were embedded into the surface of WO(3) film, resulting in WO(3)/BiV(0.95)Mo(0.05)O(4) photoanodes, which were tested in photoelectrochemical cells for water splitting. Bilayer photoelectrochemical cells showed enhanced photocurrent density: three times that shown by a cell with a pure WO(3) photoanode and 1.5 times that of a cell with a WO(3)/BiVO(4) bilayer photoanode. BiVO(4) showed poor charge carrier mobility; the performance of photoelectrochemical cells can be improved only when BiVO(4) is combined with a WO(3) bottom layer, even after Mo doping and tailoring its transition energies by atomic doping.     

Photoinduced interaction of thionine with phospholipid and cholesterol in artificial membranes

The photoinduced interaction of thionine dye with phosphatidylcholine (PC) (and its components, e.g. lysoPC, phosphorylcholine and choline) and oxidized cholesterol was studied in artificial membranes using spectrophotometric and photoelectrochemical methods. The results show that the dye (electron acceptor) in its singlet excited state forms 1:1 electron donor-acceptor (EDA) complexes with the lipids (electron donor). The electrode kinetics of the photoinduced redox reactions in the cell were also studied to confirm the mechanism of photoinduced interaction between the dye and the lipid.     

Photoelectrochemical Behavior of Poly(3,4-ethylenedioxythiophene) in Acetonitrile Solutions during Cathodic Reduction of Oxygen

The photoelectrochemical behavior of a polymer electrode based on poly(3,4-ethylenedioxythiophene) (PEDT) is studied in acetonitrile solutions during the cathodic reduction of oxygen. The measurements are taken on PEDT films 490 nm thick deposited onto a platinum support in oxygen-saturated 0.1 M Bu₄NBF₄ solutions. The electrode was illuminated with a light of a wavelength 487 nm from a helium–cadmium laser in conditions of modulated illumination, and in doing so, the real and imaginary components of an alternating photocurrent were measured at different modulation frequencies. The peculiarity of the photoelectrochemical behavior of PEDT manifests itself in the emergence of an anodic photocurrent, which increases with a change in potential in the cathodic direction. At low modulation frequencies, the real and imaginary components are of the same sign, whereas at high modulation frequencies the components have opposite signs (photocurrent lags behind a change in the light intensity). The emergence of an anodic photocurrent is connected with the cathodic reduction of oxygen and the formation in a near-electrode layer of radical anion O^– ₂. Such a behavior of PEDT, which makes it different from other polymers of the thiophene series, is explained by different potentials of their anodic oxidation, to which a conductive state of the polymer is related.     

Harvesting infrared photons with tricarbocyanine dye clusters

The absorption of 4,5-benzoindotricarbocyanine dye (IR125) in the infrared can be tuned by controlling the type of aggregation in different media. Molecular clusters of this dye formed in a mixed solvent show broad absorption in the 550-950 nm region as compared to the absorption bands of J- and H-type aggregates. The molecular clusters of the carbocyanine dye are electrophoretically deposited as thin film on optically transparent electrodes using a dc electric field. These tricarbocyanine dye cluster films are photoactive in the infrared region and produce cathodic current when employed as photocathode in a photoelectrochemical cell. Transient absorption spectroscopy of the molecular clusters show short-lived singlet state in the picosecond time scale (lifetime 6 ps) and a charge separated state in the nanosecond time scale. Implication of such dye cluster films for harvesting infrared photons in a photoelectrochemical cell is discussed.     

3D Tungsten Trioxide Nanosheets as Optoelectronic Materials for On-chip Quantification of Global Antioxidant Capacity

The photoelectrochemical properties of semiconductors mainly depend on the size and shape of the corresponding nanoparticles. Herein, 3D WO₃ nanosheets were controllably synthesized with the aid of polyethyleneimine, which presents enhanced photocurrent responses. Based on this excellent photoelectrochemical property, a photoelectrochemical chip was prepared by lithography technology for the smart monitoring of the antioxidant capacity(AC) in red wine and exhibits a series of advantages inclu-ding rapid response time, high sensitivity, and long-lasting stability. The mechanism of the present photoelectrochemical sensing was explored and shows a single electron transfer reaction. Furthermore, only 200 μL of samples are required for one testing, which demonstrates that the present photoelectrochemical chip can be potentially integrated with a portable commercial device(such as a mobile phone) for further research and development of food and drug supervision.     

Non-radiative deactivation pathways of subphthalocyanine and subnaphthalocyanine dyes and of their mixture

Subphthalocyanine and subnaphthalocyanine dyes and their mixture were investigated by means of the spectroscopic and photoelectric methods. Absorption, fluorescence, steady-state and time-resolved photothermal measurements for the dyes and their mixture were done in order to get information about the radiative and non-radiative deactivation processes as competetive processes to charge separation. It was shown that energy transfer between the dyes improved the photocurrent generation in photoelectrochemical cells (PEC) based on In(2)O(3) and SnO(2) as an electrode. The possible participation of the dye triplet states in non-radiative processes was discussed.