Abnormal Cathodic Photocurrent Generated on an n‐Type FeOOH Nanorod‐Array Photoelectrode

A simple, wet‐chemical method for the synthesis of an FeOOH nanorod‐array photoelectrode on fluorine‐doped tin oxide (FTO) glass is reported. Nanorods of diameter about 35 nm and length about 300 nm have been vertically grown on an FTO substrate. Upon calcination, the FeOOH phase could be easily converted to a hematite structure while maintaining the shape of the nanorod array. An interesting abnormal cathodic photocurrent is generated on the FeOOH nanorod‐array photoelectrode under illumination, which is totally different from that obtained on a calcined hematite photoelectrode under the same experimental conditions. The cathodic photocurrent density generated on the FeOOH photoelectrode can also be tuned by applying an electrochemical anodic or cathodic treatment. Detailed analysis has revealed that higher valence state Fe^IV species in the FeOOH photoelectrode play an important role in sacrificing the photoexcited electrons for generation of the cathodic photocurrent. Comparison between the FeOOH and hematite photoelectrodes allows for a better understanding of the interplay between crystal structure, surface reactions, and photocurrent. The findings on this new abnormal phenomenon could also provide guidance for the design of new types of semiconducting photoelectrochemical devices.     

CdS量子点敏化ZnO纳米棒阵列电极的制备和光电化学性能

采用连续式离子层吸附与反应法制备了CdS量子点敏化的ZnO纳米棒电极.应用扫描电子显微镜(SEM)、X射线衍射(XRD)和透射电子显微镜(TEM)对CdS量子点/ZnO纳米棒电极的形貌、晶型和颗粒尺寸进行了分析和表征;采用光电流-电位曲线和光电流谱研究了不同CdS循环沉积次数及不同沉积浓度对复合电极的光电性能影响.结果表明,前驱体浓度都为0.1mol·L-1且沉积15次敏化后的ZnO纳米棒阵列电极光电性能最好.与单纯的ZnO纳米棒阵列电极和单纯的CdS量子点电极相比,其光电转换效率显著提高,单色光光子-电流转换效率(IPCE)在380nm处达到76%.这是因为CdS量子点可以拓宽光的吸收到可见光区,并且在所形成的界面上光生载流子更容易分离.荧光光谱实验进一步说明了光电增强的原因是,两者间形成的界面中表面态大大减少,有利于减少光生电子和空穴的复合.     

Hematite Surface Activation by Chemical Addition of Tin Oxide Layer

In this study, the effect of tin (Sn⁴⁺) modification on the surface of hematite electrodes synthesized by an aqueous solution route at different times (2, 5, 10, 18, and 24 h) is investigated. As confirmed from X‐ray diffraction results, the as‐synthesized electrode exhibits an oxyhydroxide phase, which is converted into a pure hematite phase after being subjected to additional thermal treatment at 750 °C for 30 min. The tin‐modified hematite electrode is prepared by depositing a solution of Sn⁴⁺ precursor on the as‐synthesized electrode, followed by thermal treatment under the same abovementioned conditions. This modification results in an enhancement of the photocurrent response for all hematite electrodes investigated and attains the highest values of around 1.62 and 2.3 mA cm^?2 at 1.23 and 1.4 V versus RHE, respectively, for electrodes obtained in short synthesis times (2 h). Contact angle measurements suggest that the deposition of Sn⁴⁺ on the hematite electrode provides a more hydrophilic surface, which favors a chemical reaction at the interface between the electrode and electrolyte. This result generates new perspectives for understanding the deposition of Sn⁴⁺ on the hematite electrode surface, which is in contrast with several studies previously reported; these studies state that the enhancement in photocurrent density is related to either the induction of an increased donor charge density or shift in the flat‐band potential, which favors charge separation.     

Evaluation of electroactive surface area of CdSe nanoparticles on wide bandgap oxides (TiO2, ZnO) by cadmium underpotential deposition

Underpotential deposition of cadmium was applied for in situ determination of electroactive surface area (ESA) of CdSe nanoparticles deposited by successive ionic layer adsorption and reaction (SILAR) onto TiO₂ nanotubes and porous ZnO films. The sensitized photocurrent on CdSe/TiO₂ and CdSe/ZnO electrodes was normalized for ESA, and the ESA normalized photocurrent was compared with the photocurrent normalized for geometric area of electrodes. Significantly different types of dependences were observed with the two methods of normalization for the surface area. The efficiency of CdSe as sensitizer appeared to be higher on ZnO when normalized for CdSe ESA, though the photocurrent normalized for geometric area of electrode was an order of magnitude higher on CdSe/TiO₂ electrodes. Also, notable maxima in the photocurrent dependences on the number of SILAR cycles disappeared after the normalization for the ESA, showing a gradual increase in the efficiency of the sensitizer unit surface area with the number of SILAR cycles. This simple experimental procedure can be a helpful tool in the investigation and development of quantum dot-sensitized solar cells.     

Hybrid polymer/zinc oxide photovoltaic devices with vertically oriented ZnO nanorods and an amphiphilic molecular interface layer

We report on the effect of nanoparticle morphology and interfacial modification on the performance of hybrid polymer/zinc oxide photovoltaic devices. We compare structures consisting of poly-3-hexylthiophene (P3HT) polymer in contact with three different types of ZnO layer: a flat ZnO backing layer alone; vertically aligned ZnO nanorods on a ZnO backing layer; and ZnO nanoparticles on a ZnO backing layer. We use scanning electron microscopy, steady state and transient absorption spectroscopies, and photovoltaic device measurements to study the morphology, charge separation, recombination behavior and device performance of the three types of structures. We find that charge recombination in the structures containing vertically aligned ZnO nanorods is remarkably slow, with a half-life of several milliseconds, over 2 orders of magnitude slower than that for randomly oriented ZnO nanoparticles. A photovoltaic device based on the nanorod structure that has been treated with an amphiphilic dye before deposition of the P3HT polymer yields a power conversion efficiency over four times greater than that for a similar device based on the nanoparticle structure. The best ZnO nanorod:P3HT device yields a short circuit current density of 2 mAcm(-2) under AM1.5 illumination (100 mW cm(-2)) and a peak external quantum efficiency over 14%, resulting in a power conversion efficiency of 0.20%.     

CdS nanocrystallites sensitized ZnO nanorods with plasmon enhanced photoelectrochemical performance

A novel architecture of CdS/ZnO nanorods with plasmonic silver (Ag) nanoparticles deposited at the interface of ZnO nanorods and CdS nanocrystallites, was designed as a photoanode for solar hydrogen generation, with photocurrent density achieving 4.7 mA/cm² at 1.6 V (vs. RHE), which is 8 and 1.7 times as high as those of pure ZnO and CdS/ZnO nanorod films, respectively. Additionally, with optical absorption onset extended to ～660 nm, CdS/Ag/ZnO nanorod film exhibits significantly increased incident photo-to-current efficiency (IPCE) in the whole optical absorption region, reaching 23.1% and 9.8% at 400 nm and 500 nm, respectively. The PEC enhancement can be attributed to the one-dimensional ZnO nanorod structure maintained for superior charge transfer, and the extended visible-light absorption of CdS nanocrystallites. Moreover, the incorporated plasmonic Ag nanoparticles could further promote the interfacial charge carrier transfer process and enhance the optical absorption ability, due to its excellent plasmon resonance effect.     

CdS nanocrystallites sensitized ZnO nanorods with plasmon enhanced photoelectrochemical performance

A sandwiched structure of CdS/Ag/ZnO nanorod photoanode exhibits greatly enhanced photoelectrochemical activity for solar hydrogen generation, due to synergistic effect of CdS nanocrystallites and plasmonic Ag nanoparticles for the enhanced optical absorption and the promoted charge carrier separation.     

Enhanced Photoelectrochemical Property of Zn Loaded TiO2 Nanotube Arrays Electrode

TiO₂ nanotube arrays (TNTs) electrode loaded with Zn nanoparticles was prepared by anodization and the size of Zn nanoparticle loaded on TNTs electrode was controlled bychronoamperometry deposition time. Results of SEM and XRD analysis show that Zn nanoparticles had a diameter of about 15-25 nm when the deposition time was 3-5 s. The UV-Vis diffuse reflectance spectra show the Zn loaded harvest light with 480-780 nm more effectively than the unloaded sample. The photocurrent response of Zn loaded TNTs electrodes were studied, the results showed that TNTs electrodes loaded with Zn nanoparti-cles has 50% increased photocurrent response under high-pressure mercury lamp irradiation compared with unloaded TNTs electrode.     

Ag/ZnO Catalysts with Different ZnO Nanostructures for Non‐enzymatic Detection of Urea

Silver coated ZnO nanorods and nanoflakes with different crystallographic orientations were synthesized by a combination of sputter deposition and solution growth process. Catalytic properties of morphology‐dependent Ag/ZnO nanostructures were then investigated for urea sensors without enzyme. Ag/ZnO nanorods on carbon electrodes exhibit a higher catalytic activity and an improved efficiency than Ag/ZnO nanoflakes on carbon electrodes. Ag/ZnO nanorod catalysts with more electrochemically surface area (169 cm² mg^?1) on carbon electrode facilitate urea electrooxidation due to easier electron transfer, which further promotes the urea electrolysis. The Ag/ZnO nanorod catalysts also show a significant reduction in the onset voltage (0.410 V vs. Ag/AgCl) and an increase in the current density (12.0 mA cm^?2 mg^?1) at 0.55 V vs Ag/AgCl. The results on urea electrooxidation show that Ag/ZnO nanostructures can be a potential catalyst for non‐enzymatic biosensors and fuel cells.     

Photovoltaic properties of graphene oxide sheets beaded with ZnO nanoparticles

A hybrid material of graphene oxide (GO) sheets beaded with ZnO nanoparticles was prepared. The material extends over a few hundred square nanometers, in which the ZnO nanoparticles (average diameter (∼5 nm)) are dispersed evenly on the GO sheet. Both the surface photovoltage or surface photocurrent intensity for the material are much stronger than for pure ZnO nanoparticles, meaning that the free charge carriers can effectively be transferred from ZnO nanoparticles to GO sheets, which can serve as a probe to monitor the electron transfer from excited ZnO to GO. Anchoring ZnO nanoparticles on two dimensional carbon nanostructures such as GO can pave a way towards the design of ordered nanostructure assemblies that can harvest light energy efficiently.     

Novel ZnO nanostructured electrodes for higher power conversion efficiencies in polymeric solar cells

1-Dimensional nanostructured ZnO electrodes have been demonstrated to be potentially interesting for their application in solar cells. Herein, we present a novel procedure to control the ZnO nanowire optoelectronic properties by means of surface modification. The nanowire surface is functionalized with ZnO nanoparticles in order to provide an improved contact to the photoactive P3HT:PCBM film that enhances the overall power conversion efficiency of the resulting solar cell. Charge extraction and transient photovoltage measurements have been used to successfully demonstrate that the surface modified nanostructured electrode contributes in enhancing the exciton dissociating ratio and in enlarging the charge lifetime as a consequence of a reduced charge recombination. Under AM1.5G illumination, all these factors contribute to a considerably large increase in photocurrent yielding unusually high conversion efficiencies over 4% and external quantum efficiencies of 87% at 550 nm for commercially available P3HT:PCBM based solar cells. The same approach might be equally used for polymeric materials under development to overcome the record reported efficiencies.     

Ti基ZnO纳米棒阵列的制备及其光催化性能研究

采用两电极体系中恒电流电沉积在Ti基底上制得较均一的ZnO纳米棒阵列,利用SEM和XRD观察表征样品,研究Zn(NO₃)₂浓度及电流密度对ZnO纳米棒阵列微观形貌的影响. 以甲基橙为目标降解物,考察该电极光催化性能. 结果表明,Zn(NO₃)₂浓度和电流密度对纳米棒阵列的形貌有显著影响;与ITO玻璃等其他基底相比,在Ti基底上也可沉积较好均一取向的ZnO纳米棒阵列;紫外灯照射下,ZnO/Ti电极对甲基橙（10 mg·L^-1）模拟印染废水降解2.5 h,降解率达到83.3%,光催化活性较佳;无光照时ZnO纳米棒的降解率仅7%.     

Three-Dimensional Nickel-Nickel Oxide Core-Shell Nanorod Array for Nonenzymatic Glucose Sensing

Nickel-nickel oxide core-shell nanorod array electrodes were fabricated and a preliminary application for nonenzymatic glucose determination exhibited excellent performance. The nanorod array electrode was synthesized for the first time by an anodic aluminum oxide template assisted electrochemical deposition technique. Facile oxidation was employed to convert nickel at the outer surface of the nanorods to nickel oxide, resulting in a nickel-nickel oxide core-shell nanorod array. The successful conversion was confirmed by x-ray diffraction, cyclic voltammetry, and scanning electron microscopy. The modified electrode possessed high surface area contributed by the nanorods, and efficient mass transfer due to the wide internanorod gap. The electrode provided high sensitivity (127 microampere square centimeter per millimolar), a low limit of detection (～0.5 micromolar), and a long linear dynamic range (up to 14 millimolar) for the determination of glucose. Accurate determination of glucose in human serum was performed. This synthetic strategy may have further application for the preparation of high surface area thin-film electrodes for a variety of applications.     

Spectroelectrochemical Evaluation of a ZnO Optically Transparent Electrode Prepared by the Spin‐spray Technique

We present a novel zinc oxide (ZnO) optically transparent electrode (OTE) prepared by the spin‐spray technique for spectroelectrochemistry. The spin‐spray technique can deposit ZnO film at a low cost, high rate deposition, and at a low temperature (<100 °C) in a single step. This new technique provides good optical transparency and electrical conductivity for ZnO. The electrochemical and spectroelectrochemical properties of the ZnO electrode were investigated for varying thicknesses of ZnO using methylene blue as a redox indicator. A ZnO OTE chip that includes three electrodes on a glass chip was developed for thin‐layer spectroelectrochemistry. Moreover, the ZnO films were successfully applied in an electrochemical‐localized surface plasmon resonance (LSPR) method for methylene blue detection by using them as a transparent conducting substrate for loading gold nanoparticles.     

ZnO/BiVO4-V2O5异质结构光生电荷性质及可见光下表面光电流行为

利用水热法合成了花状和球状ZnO微纳材料,并与硝酸铋和偏钒酸铵溶液体系反应构筑了ZnO/BiVO4-V2O5复合体系.利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)及X射线衍射(XRD)对材料进行了系统的表征.利用表面光伏(SPV)、表面光电流(SPC)和瞬态光伏(TPV)技术研究了ZnO/BiVO4-V2O5表面光生电荷的产生和传输机制.结果显示该复合材料在可见区产生了良好的光电响应,获得了较高的光生载流子的分离效率,光生电荷的寿命也同时增加.在单色弱可见光(波长500 nm)照射下,复合材料产生良好重复性的表面光电流响应.     

Gold(Core)–Lead(Shell) Nanoparticle‐Loaded Titanium(IV) Oxide Prepared by Underpotential Photodeposition: Plasmonic Water Oxidation

Underpotential photodeposition of Pb yields an ultrathin shell layer on the Au(111) surface of Au nanoparticle(NP)‐loaded TiO₂ (Au/TiO₂) with heteroepitaxial nanojunctions. The localized surface plasmon resonance of Au/TiO₂ undergoes no damping with the Pb‐shell formation, and the Pb shell offers resistance to aerobic oxidation. Mesoporous films comprising the Au(core)–Pb(shell) NP‐loaded TiO₂ and unmodified Au/TiO₂ were formed on fluorine‐doped tin oxide (FTO) electrode. Using them as the photoanode, photoelectrochemical cells were fabricated, and the photocurrent was measured under illumination of simulated sunlight. The photocurrent for water splitting is dramatically enhanced by the Pb‐shell formation. The photoelectrochemical measurements of the hot‐electron lifetime and density functional theory calculations for model clusters indicate that the Pb‐shell effect originates from the charge separation enhancement.     

Coating Polymeric Carbon Nitride Photoanodes on Conductive Y:ZnO Nanorod Arrays for Overall Water Splitting

Polymeric carbon nitride (PCN) photosensitizers are proposed replacements for their inorganic counterparts in solar‐to‐fuel conversion via photoelectrochemical water splitting. However, intense charge recombination, primarily because of surface defects, limits the use of PCN in PEC systems. Now, photoanodes are designed by coating PCN films onto highly conductive yttrium‐doped zinc oxide (Y:ZnO) nanorods (NRs) serving as charge collectors. The generation of charge carriers can therefore be promoted by this type II alignment. The charge collectors would be kept nearby for charge separation and transport to be used in the interfacial redox reactions. The photocurrent density of the polymer electrode is improved to 0.4 mA cm^?2 at 1.23 V vs. the reversible hydrogen electrode in a Na₂SO₄ electrolyte solution under AM 1.5 illumination. The result reveals a more than 50‐fold enhancement over the PCN films achieved by powder; the efficiency can be preserved at 95 % for 160 minutes.     

Photoelectrochemical sensing for hydroquinone based on gold nanoparticle-modified indium tin oxide glass electrode

Gold nanoparticles (GNPs) were deposited directly onto the surface of indium tin oxide (ITO) thin film-coated glass by electrochemical method. It was used as a photoanode in a photoelectrochemical (PEC) cell for sensitive detection of hydroquinone (HQ) at an applied bias potential of 0.15 V vs. saturated calomel electrode. This heterostructure showed dramatically enhanced PEC properties due to the introduction of the Au/ITO interface. Under the irradiation, the marked photocurrent response was observed at the GNPs/ITO photoelectrode compared with bare ITO electrode. The anodic photocurrent could be further largely enhanced by HQ. A new PEC strategy for sensitive detection of HQ at a relative low potential was developed. The linear range for HQ determination was 0.25 to 150 μM, with a detection limit of 0.1 μM. The sensitivity on the GNPs/ITO electrode at the irradiation was ~ 3.3 times higher than that in dark. These results demonstrate that the simple GNPs/ITO electrodes have great potential for PEC analysis application.     

ZnO及其含锌混合氧化物薄膜的充放电性能研究

从充放电性能、晶体结构等方面考察了包括粉末状的ZnO、脉冲激光沉积方法制备的ZnO薄膜和含锌混合氧化物薄膜的电化学性质.结果表明,ZnO粉末制备的电极的嵌入容量随退火温度的升高而增大,掺入其他氧化物可以明显改善ZnO薄膜的电化学性能,在Ar气氛中,基片温度为400℃时,沉积的靶子成分为Zn:B:P:Al=1:1:0.5:0.5(摩尔比)的含锌混合氧化物薄膜具有较高的可逆容量,且循环性能良好.     

A semiconductor/molecular catalyst hybrid photoanode with FeOOH as an electron transfer relay

A Fe₂O₃/FeOOH/poly-Ru(bda)(vpy) (bda = 2,2’-bipyridine-6,6’-dicarboxylate,vpy = 4-vinylpyridine) photoanode has been fabricated by electropolymerization of molecular Ru(bda)(vpy) catalyst on FeOOH modified Fe₂O₃, in which a thin layer of FeOOH replicates the role of tyrosine residue in PSII as an efficient electron transfer mediator. The ternary hybrid photoanode produced a 2.4 times higher photocurrent density than that of previously reported Fe₂O₃/poly-Ru(bda)(vpy) under AM 1.5 G illumination and displayed a negative shift on the onset potential by 100 mV. In addition, the Fe₂O₃/FeOOH/poly-Ru(bda)(vpy) exhibited long-term stability for at least 10 h with a Faraday efficiency of ∼96%. The high performance shown here was attributed to the improved charge separation between excited semiconductor and the catalyst caused by FeOOH mediated electron transfer on the electrode surface.