Two Photoelectrochemical Processes for TiO2 Electrode under UV Illumination

TiO2 thin film electrode was prepared by a sol-gel method on ITO substrates. Cyclic voltammetric behavior of the ITO/TiO2 electrode under ultraviolet (UV) illumination was investigated in the solution of Na2SO4.There are two photoelectrochemical processes for TiO2 electrode under UV illumination.One is a fast process,which results in the appearance of anodic photocurrent.The anodic photocurrent will appear and disappear with the light on and off.The other is a slow process,which will be responsible for the appearance of an oxidative peak. When the electrode is illuminated under UV light for a long time,a new oxidative peak can be observed.The peak current increases with the increase of UV illumination time.It is assumed that the new peak belongs to the oxidation of Ti^3 ,which formed and accumulated on the electrode surface during the UV illumination.A detailed mechanism is proposed on the base of these two photoelectrochemical processes.It is assumed that the change of hydrophilicity of TiO2 thin film may be related to the slow process while the film irradiated by UV light.     

Effect of Sn content on the properties of passive film on PbSn alloy in sulfuric acid solution

The effect of Sn content on properties of anodic film formed on PbSn alloys in sulfuric acid solution was investigated using linear sweeping voltage (LSV), cyclic voltammetry (CV), and a.c. voltammetry (ACV), based on the Mott-Schottky analysis. The results revealed that the addition of Sn into lead alloys can promote the corrosion resistance property and could decrease the impedance of anodic film; these results were more remarkable with enhancing the Sn content. The over potential of oxygen evolution on lead alloys enhanced with the increase of Sn content. The Mott-Schottky analysis indicated that the passive film appeared an n-type semiconductor, and the donor density of passive film increased with increasing Sn content. The increased vacancies in the passive film with Sn content increasing could illustrate this trend.     

Effect of antimony on the reduction of anodic Pbo_2 film on Pb-Sb alloys in sulfuric acid solution

The reduction processes of anodic PbO2 films formed on Pb-Sb alloys in 4.5mol·dm-3 H2SO4 solution at 1.4 V(vs.Hg/Hg2SO4) for 1 h have been investigated by pho-tocurrent method,chronoamperometry,linear sweep voltammetry as well as X-ray diifractornetry.It was found that the reduction of most of the β-PbO2 and part of the α-PbO2 to PbSO4 can be completed within I s between 0.9 V and 1.0 V(vs.Hg/Hg2SO4) and proceeds much faster than that of the remaining a-PbO2 into photoactive α·PbOx (1相似文献   

WO_3 Anodic Oxide Film——I.Electrochromism and Auto-bleaching mechanism

Electrochromic and auto-bleaching processes at the WO2 anodic film in 0. 5 mol/L H2SO4 solution were investigated by cyclic voltammetry, a. c. impedance technique and photocurrent spectrometry. The colouration mechanism consists of hydrogen adsorption on the WO2 surface and the transport of H atoms in the WO, lattice. The bleaching process involves at least two steps: transport of interstitial H atoms and hydrogen desorption on the W surface, resulting in interstitial H+ ions; then extration of the H+ ions driven by the external electric field. The auto-bleaching arises from the hydroxylation due to both partial interstitial H atoms and a little of water contained in the film.     

Applied bias photon-to-current conversion efficiency of ZnO enhanced by hybridization with reduced graphene oxide

The role of reduced graphene oxide(rGO) in the enhancement of photo-conversion efficiency of ZnO films for photoelectrochemical(PEC) water-splitting applications was analyzed. ZnO and rGO-hybridized ZnO(rGO/ZnO) films were prepared via a two-step electrochemical deposition method followed by annealing at 300 °C under argon gas flow. The physical, optical and electrochemical properties of the films were characterized to identify the effect of rGO-hybridization on the applied bias photon-to-current efficiency(ABPE) of ZnO. Scanning electron microscopy and X-ray diffraction indicated the formation of verticallyaligned, wurtzite-phase ZnO nanorods. Diffuse-reflectance UV–visible spectroscopy indicated that rGO-hybridization was able to increase the light absorption range of the rGO/ZnO film. UPS analysis showed that hybridization with rGO increased the band gap of ZnO(3.56 eV) to 3.63 eV for rGO/ZnO sample,which may be attributed to the Burstein–Moss effect. Photoluminescence(PL) spectra disclosed that rGOhybridization suppressed electron-hole recombination due to crystal defects. Linear sweep voltammetry of the prepared thin films showed photocurrent density of 1.0 and 1.8 m A/cm~2 for ZnO and rGO/ZnO at+0.7 V, which corresponded to an ABPE of 0.55% and 0.95%, respectively. Thus, this report highlighted the multi-faceted role of rGO-hybridization in the enhancement of ZnO photo-conversion efficiency.     

铝阳极氧化膜的半导体特性

The semiconductor properties of anodic oxide film formed on commercial pure aluminum were analyzed usingMott-Schottky theory and point defect model (PDM). The donor density, oxygen vacancy diffusion coefficient and flat-band potential were measured for the oxide films sealed by boiling water and K2Cr2O7, respectively. The results indicated that the anodic oxide films showed the n-type semiconductor property and the donor density decreased exponentially with the voltage elevating. The value of oxygen vacancy diffusion coefficient is about (1.12-5.53)伊10-14 cm-2·s-1. The flat-band potential of anodic oxide filmdeclined after sealing.     

Electrochemical characteristics of poly(ophenylendiamine) film electrodes in phosphatic solution

The electrochemical characteristics of poly(o-phenylendiamine) (POPD) film modified electrodes have been investigated using different electrochemical techniques.The main interest is focused on the effect of potential and film thickness on the electrode process.Good agreement has been found for the apparent diffusion coefficient estimated by chronocoulometry and impedance spec-troscopy.The charge transfer process within POPD films is diffusion processes at negative and positive overpotentials and electron hopping mechanism at formal potential.The POPD film conductivity of the oxidized state is better than that of the reduced state.For all electrode processes,the H+ may penetrate the film/electrolyte interface and take part in charge transfer or protonation-deprotonation of phenazine rings.     

Influence of Annealing on Properties of ZnO Films Grown via Plasma－enhanced MOCVD

The structural and the optical properties of ZnO films with high quality grown via plasma-enhanced met-al-organic chemical vapour deposition(MOCVD) on C-plane sapphire substrate were studied. The crystallini-ty and the optical properties of the films are greatly improved having been annealed in oxygen plasma atmo-sphere. The structure, the band gap and the binding energy of O1s electrons, and the molar ratio of O to Zn were determined by X-ray diffraction (XRD), photoluminescence (PL) and X-ray photoelectron scan meth-ods. For both the annealed and the as-grown films, the exciton peak features were observed at room temper-ature. The band-edge photolof the annealed film is much stronger than that of the as-grown film, and the exciton peak relating to the deep level at 439 nm disappears. The molar ratio of O to Zn in the annealed film is 0. 91, while it is 0. 78 for the as-urown film.     

Photophysical and Photoelectric Properties of 2—{[4—（N—Hexadecyl—N—methylamino）phenyl]methylene}—propanedinitrile

2-{[4-(N-Hexadecyl-N-methylamino)phenyl]methylene}-propanedinitrile(HMAPN) with typical donor-π-acceptor(D-π-A）structure was synthesized.It could be easily assembled into stable films by LB technique.The photophysical properties of HMAPN were investigated in solution and on LB films.The photoelectric properties of HMAPN were examined and the anodic photocurrent of the ITO electrode modified by the monolayer LB film of HMAPN was measured as 835 nA/cm^2 under the white light of 218.2 mW/cm^2 without bias voltage.The effects of light intensity,bias voltage on the photocurrent were discussed.The possible mechanism of the photocurrent formation was given.     

Covalentely Attached Multilayer Films Comprising Phthalocyanine and Their Photoelectron Conversion Properties

The photosensitive multilayer films from sulfonated metal-free, sulfonated copper-, and sulfonated nickel-phthalocyanines were fabricated with diazoresin layer by layer on a substrate via electrostatic interaction by the self-assembly technique. Under UV irradiation, the linkage nature between the layers of the film is converted from the electrostatic bonding to covalent bonding. The covalently attached multilayer films are very stable towards polar solvents and salt aqueous solutions. The photovoltaic properties of the covalently attached film can be determined by means of a traditional three-electrode photoelectrochemical cell in aqueous solutions with KCI as the supporting electrolyte. The photocurrent determination has shown that the sulfonated copper-containing phthalocyanine films possess a higher photocurrent value than sulfonated metalfree and sulfonated nickel-containing phthaloeyanine films.     

铈降低在硫酸溶液中生长的阳极Pb(II)氧化物膜的电阻的研究

应用电化学阻抗频谱法、线性电位扫描法和光电流技术研究了在4.5 mol· dm~(-3) H_2SO_4溶液中Pb-1%(at.)Ce（简称Pb-1Ce）合金在0.9 V (vs. Hg/Hg_2SO_4电极)生长的阳极Pb(II)氧化物膜的电阻较纯铅的低的原因。实验结 果表明,Ce阻抑阳极Pb(II)氧化物膜的生长并增加其孔率,从而降低其电阻。     

VA族元素对阳极铅(II)氧化物膜半导体性质的影响(II)

用光电化学电流法研究了铅、铅砷、铅锑和铅铋合金在4.5 mol·L~(-1) H_2SO_4溶液(22 ℃)中，以0.9 V(vs．Hg/Hg_2SO_4)极化7 h而形成的阳极膜中的氧化铅的半导体性质，合金添加剂砷、锑和铋对t-PbO(四方氧化铝)和o-PbO(斜方氧化铝)的禁带宽度没有影响，从量子效率和电位的关系可求Pb，Pb-lat％As(at％表示原子百分比，全文同)，Pb-lat％Sb和Sb－lat％Bi上膜中t－Pbo的施主密度(N_D)分别为9.3×10~(15)，1.0×10~(16)，3.1×10~(16)和1.3×10~(17) cm~(-3)，平带位分别为-0.20，－0.22，－0.28和-0.08 V(vs．Hg/Hg_2SO_4)．比较VA元素砷、锑和铋对上述膜中t-PbO的N_D(从而自由电子密度)和膜中t-PbO的生长速率的影响，可认为法添加剂砷、锑和铋对阳极膜中t-PbO的作用符合Hauffe规则．     

Photocurrent spectroscopy of semiconducting anodic films on mercury

Cyclic voltammetry and photocurrent epectroscopy have been used to study the growth and properties of HgO and HgS fimls mercury. The band-gap of the film formed on mercury in NaHCO₃ was found to be 1.9 eV, in good agreement with values determined by the other methods. The black HgS layers formed on mercury are photoactive in the visible and near infrared and an apparent band-gap of 0.9 eV has been determined by photocurrent spectroscopy. The implications of this surprising result are discussed.     

阳极二氧化铅膜的阴极还原为硫酸铅的机理

应用旋转环盘电极, 和静止电极线性电位扫描法(LSV)研究铅上阳极PbO~2膜的阴极还原为PbSO~4的机理。实验结果表明相应于Pb盘上阳极膜中PbO~2还原时所产生的Pb-7w/oSb环电流是原先PbO~2膜生长时析出的氧扩散入膜中以及膜内的PbO~2微粒中的品种逸出而被还原所致。无可溶性中间体可被检出。扫速对静止Pb上阳极膜中PbO~2的LSV法还原的影响符合薄膜反应的规律。本文提出了上述反应机理。     

低锑—铅合金的耐蚀性能对铅酸蓄电池循环寿命的影响

铅酸蓄电池板栅合金的组成和性质影响电池的使用寿命及维护特性。无锑的铅钙合金有利于电池维护,但存在着强度差及铸造上的困难;高锑的铅锑合金有利于提高板栅的强度及电池的深充放能力,但不利于电池的维护。本文研究了两种不同添加剂的低锑合金,以弥补无锑或高锑合金各自的不足,测量了两种低锑合金在试验电池充放中的失重腐蚀率,并结合     

Effects of Samarium on the Properties of the Anodic Pb（Ⅱ） Oxides Film Formed on Pb in Sulfuric Acid Solution

The effects of samarium on the properties of the anodic Pb(II) oxides films formed on lead at 0.9 V (vs. Hg/Hg₂SO₄) in 4.5 mol/L H₂SO₄ solution were studied using linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and scanning electron micrographs (SEM). The experimental results show that adding Sm to lead metal can inhibit the growth of the Pb(II) oxides film effectively, and reduce the resistance of the PbO oxides film obviously. The addition of Sm increases the porosity of the anodic film, which may cause the increase of the ionic conductance produced by the interstitial liquid among the PbO particles in the film and lead to the decrease of the resistance of the anodic film.     

Capacitance and photocurrent study of electronic properties of anodic oxide films on Nb and Ta. Evaluation of the ionized donor concentration profile in Nb2O5 film

Electronic properties of electrochemically formed oxide films on Nb were studied by photocurrent and differential capacitance measurements in 0.025 M KH₂PO₄+0.025 M Na₂HPO₄ electrolyte, pH 6.9. Oxide films of n-type conductivity were formed galvanostatically for final potentials ranging from 4 to 230 V. Measurements were performed in two potential regions, which correspond to formation of a depleted layer of variable thickness at relatively low potentials, and to complete depletion of oxide films of electronic charge carriers at higher potentials. In the first potential region the behavior of both capacitance and photocurrent, was governed by a build up of a depleted layer of potential dependent thickness. In the second, high potential, region, which extends up to the oxide film formation potential, the photocurrent and capacitance of oxide films in most features followed the trends typical of dielectric films containing defects and traps. The photocurrent and capacitance measurements on presumably dielectric oxide films formed on Ta were staged for comparison. The capacitance–potential measurements performed in the first potential region enabled us to construct the ionized donor concentration profile across the Nb₂O₅ film width. The limitations on the use of the C–E profiling method for electrochemically formed oxide layers are considered.     

Study of the electrosynthesis of poly(3-butylthiophene) and its semiconductor properties

The mechanism of the electrosynthesis of poly(3-butylthiophene) (PBuT) was studied by cyclic voltammetry and potential step methods in comparison with polybithienyl. The anodic oxidation polymerization of the 3-butylthiophene underwent two steps: oligomer formation and further polymerization to form the polymer. The doping level of the PBuT increases with the cycle number of the potential sweeps during polymerization. The current responses to the potential steps indicate a nucleation and nuclei growth process which is repeated layer to layer. The differential capacity (C _d) and photocurrent were measured at the PBuT films in the aqueous electrolyte solution. The C _d ⁻² vs. E plot shows two regions of linearity, one with a negative slope and the other with a positive slope in different potential regions, which give the same flat-band potential. This indicates that the PBuT film exhibits both p-type and n-type features of a semiconductor at differrent potential regions. The cathodic photocurrent spectrum was analysed by the (j _ph hν)^{2/ n} vs. hν plots, giving band gap energies of 2.41 eV for n=1 and and 2.01 eV for n=4. Received: 29 July 1999 / Accepted: 15 November 1999     

阳极Pb(II)氧化物膜的阴极还原

采用X射线衍射、光电流谱、线性电位扫描和开路电位衰退等方法研究了Pb电 极在0.9 V(vs.Hg/Hg_2SO_4), 4.5 MOL/l h_2so_4溶液中生长2 h所得的阳极Pb (II)氧化物膜的阴极还原行为。实验结果表明;阳极Pb(II)氧化物膜主要由PbO微 粒和PbO·PbSO_4微粒组成,微粒间液膜可供离子输运;在LSV负向扫描过程中,阳 极Pb(II)氧化物膜是按溶解－沉积机理还原的,首先PbO微粒借助该微粒间的液膜 还原为金属铅,而待PbO微粒表面层转化的金属铅与PbO·PbSO_4微粒接触后,则 PbO·PbSO_4就和PbO一起还原,而以PbO·PbSO_4的还原进程略快。