High Sensitive Microsensor Based on Organic‐Inorganic Composite for Two‐Dimensional Mapping of H2O2 by SECM

The present work describes the development of a selective, sensitive and stable sensing microsensor for scanning electrochemical microscopy (SECM) to measure H₂O₂ during electrochemical reduction of oxygen. The microsensor is based on graphene and Poly(3,4‐ethylenedioxythiophene) composite as support to iron (III) hexacyanoferrate (II) (PEDOT/graphene/Fe^III₄[Fe^II(CN)₆]₃ microsensor). The electrochemical properties of the PEDOT/graphene/Fe^III₄[Fe^II(CN)₆]₃ microsensor were investigated by cyclic voltammetry (CV) and scanning electrochemical microscopy (SECM). The PEDOT/graphene/Fe^III₄[Fe^II(CN)₆]₃ microsensor showed an excellent electrocatalytic activity toward hydrogen peroxide (H₂O₂) reduction with a diminution of the overpotential of about 500 mV in comparison to the process at a bare gold microelectrode. The microsensor presented excellent performance for two dimensional mapping of H₂O₂ by SECM in 0.1 mol L^?1 phosphate buffer solution (pH 7.0). Under optimized conditions, a linear response range from 1 up to 1000 µmol L^?1 was obtained with a sensitivity of 0.08 nA L µmol^?1 and limit of detection of 0.5 µmol L^?1.     

Synthesis of Carbon/Sulfur Nanolaminates by Electrochemical Extraction of Titanium from Ti2SC

Herein we electrochemically and selectively extract Ti from the MAX phase Ti₂SC to form carbon/sulfur (C/S) nanolaminates at room temperature. The products are composed of multi‐layers of C/S flakes, with predominantly amorphous and some graphene‐like structures. Covalent bonding between C and S is observed in the nanolaminates, which render the latter promising candidates as electrode materials for Li‐S batteries. We also show that it is possible to extract Ti from other MAX phases, such as Ti₃AlC₂ , Ti₃SnC₂ , and Ti₂GeC, suggesting that electrochemical etching can be a powerful method to selectively extract the “M” elements from the MAX phases, to produce “AX” layered structures, that cannot be made otherwise. The latter hold promise for a variety of applications, such as energy storage, catalysis, etc.     

Ultrafast Electron Transfer Kinetics of Graphene Grown by Chemical Vapor Deposition

High electrochemical reactivity is required for various energy and sensing applications of graphene grown by chemical vapor deposition (CVD). Herein, we report that heterogeneous electron transfer can be remarkably fast at CVD‐grown graphene electrodes that are fabricated without using the conventional poly(methyl methacrylate) (PMMA) for graphene transfer from a growth substrate. We use nanogap voltammetry based on scanning electrochemical microscopy to obtain very high standard rate constants k⁰≥25 cm s^?1 for ferrocenemethanol oxidation at polystyrene‐supported graphene. The rate constants are at least 2–3 orders of magnitude higher than those at PMMA‐transferred graphene, which demonstrates an anomalously weak dependence of electron‐transfer rates on the potential. Slow kinetics at PMMA‐transferred graphene is attributed to the presence of residual PMMA. This unprecedentedly high reactivity of PMMA‐free CVD‐grown graphene electrodes is fundamentally and practically important.     

Photocatalytically Renewable Micro‐electrochemical Sensor for Real‐Time Monitoring of Cells

Electrode fouling and passivation is a substantial and inevitable limitation in electrochemical biosensing, and it is a great challenge to efficiently remove the contaminant without changing the surface structure and electrochemical performance. Herein, we propose a versatile and efficient strategy based on photocatalytic cleaning to construct renewable electrochemical sensors for cell analysis. This kind of sensor was fabricated by controllable assembly of reduced graphene oxide (RGO) and TiO₂ to form a sandwiching RGO@TiO₂ structure, followed by deposition of Au nanoparticles (NPs) onto the RGO shell. The Au NPs‐RGO composite shell provides high electrochemical performance. Meanwhile, the encapsulated TiO₂ ensures an excellent photocatalytic cleaning property. Application of this renewable microsensor for detection of nitric oxide (NO) release from cells demonstrates the great potential of this strategy in electrode regeneration and biosensing.     

Electro‐oxidation and reduction of H2 on platinum studied by scanning electrochemical microscopy for the purpose of local detection of H2 evolution

Electrochemical detection of H₂ using scanning electrochemical microscopy (SECM) has shown to hold great promise as a sensitive characterization method with high spatial resolution for active surfaces generating H₂. Herein, the factors contributing to the current that is measured by SECM in generation/collection mode for H₂ detection are studied. In particular, the concentration gradient of H₂ at the substrate, the H₂/H⁺ recycling between the SECM tip and substrate and hemispherical profile of H₂ diffusion has been discussed. It was postulated that H₂/H⁺ recycling plays a dominant role in the oxidative current measured in generation/collection mode of SECM when the microelectrode is positioned in close vicinity of substrate. Copyright © 2015 John Wiley & Sons, Ltd.     

Electrodes/Electrolyte Interfaces in the Presence of a Surface‐Modified Photopolymer Electrolyte: Application in Dye‐Sensitized Solar Cells

Since hundreds of studies on photoanodes and cathodes show that the electrode/electrolyte interfaces represent a key aspect at the base of dye‐sensitized solar cell (DSSC) performances, it is reported here that these interfaces can be managed by a smart design of the spatial composition of quasi‐solid electrolytes. By means of a cheap, rapid, and green process of photoinduced polymerization, composition‐tailored polymer electrolyte membranes (PEMs) with siloxane‐enriched surfaces are prepared, and their properties are thoroughly described. When assembled in DSSCs, the interfacial action promoted by the composition‐tailored PEMs enhances the photocurrent and fill factor values, thus increasing the global photovoltaic conversion efficiency with respect to the non‐modified PEMs. Moreover, the presence of the siloxane‐chain‐enriched surface increases the hydrophobicity and reduces the water vapor permeation into the device, thus enhancing the cell′s durability.     

In Situ Detection of Particle Aggregation on Electrode Surfaces

Partially blocked electrodes (PBEs) are important; many applications use non‐conductive nanoparticles (NPs) to introduce new electrode functionalities. As aggregation is a problem in NP immobilization, developing an in situ method to detect aggregation is vital to characterise such modified electrodes. We present chronoamperometry as a method for detection of NP surface aggregation and semi‐quantitative sizing of the formed aggregates, based on the diffusion limited current measured at PBEs as compared with the values calculated numerically for different blocking feature sizes. In contrast to voltammetry, no approximations on electrode kinetics are needed, making chronoamperometry a more general and reliable method. Sizing is shown for two modification methods. Upon drop casting, significant aggregation is observed, while it is minimized in electrophoretic NP deposition. The aggregate sizes determined are in semi‐quantitative agreement with ex situ microscopic analysis of the PBEs.     

Non‐destructive Patterning of Carbon Electrodes by Using the Direct Mode of Scanning Electrochemical Microscopy

Patterning of glassy carbon surfaces grafted with a layer of nitrophenyl moieties was achieved by using the direct mode of scanning electrochemical microscopy (SECM) to locally reduce the nitro groups to hydroxylamine and amino functionalities. SECM and atomic force microscopy (AFM) revealed that potentiostatic pulses applied to the working electrode lead to local destruction of the glassy carbon surface, most likely caused by etchants generated at the positioned SECM tip used as the counter electrode. By applying galvanostatic pulses, and thus, limiting the current during structuring, corrosion of the carbon surface was substantially suppressed. After galvanostatic patterning, unambiguous proof of the formation of the anticipated amino moieties was possible by modulation of the pH value during the feedback mode of SECM imaging. This patterning strategy is suitable for the further bio‐modification of microstructured surfaces. Alkaline phosphatase, as a model enzyme, was locally bound to the modified areas, thus showing that the technique can be used for the development of protein microarrays.     

Photoluminescence properties of a cationic trinuclear zinc(II) complex with the tetradentate Schiff base ligand 6‐methyl‐2‐({[(pyridin‐2‐yl)methyl]imino}methyl)phenolate

Metal complexes with Schiff base ligands have been suggested as potential phosphors in electroluminescent devices. In the title complex, tetrakis[6‐methyl‐2‐({[(pyridin‐2‐yl)methyl]imino}methyl)phenolato‐1:2κ⁸N,N′,O:O;3:2κ⁸N,N′,O:O]trizinc(II) hexafluoridophosphate methanol monosolvate, [Zn₃(C₁₄H₁₃N₂O)₄](PF₆)₂·CH₃OH, the Zn^II cations adopt both six‐ and four‐coordinate geometries involving the N and O atoms of tetradentate 6‐methyl‐2‐({[(pyridin‐2‐yl)methyl]imino}methyl)phenolate ligands. Two terminal Zn^II cations adopt distorted octahedral geometries and the central Zn^II cation adopts a distorted tetrahedral geometry. The O atoms of the phenolate ligands bridge three Zn^II cations, forming a dicationic trinuclear metal cluster. The title complex exhibits a strong emission at 469 nm with a quantum yield of 15.5%.     

化学探头法与荧光光谱法测定水中溶解氧量

探讨了化学探头法和荧光光谱法测定水中溶解氧的关系。分别用F检验和t检验对两组数据进行了比较,结果表明两组数据的精密度和系统误差都没有显著差异,两种方法测定溶解氧的相对标准偏差(RSD,n=9)分别为0.35%,0.33%。进而又探讨了溶解氧与NaCl含量、温度之间的关系,结果表明溶解氧含量随NaCl含量的增加、温度的升高而逐渐降低。