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Optical microscopy unveils rapid, reversible electrochemical oxidation and reduction of graphene
摘要： We unveil the reaction dynamics of monolayer graphene in electrochemical oxidation and reduction processes through interference reflection optical microscopy. At 300-nanometer spatial resolution and 200-millisecond temporal resolution, we reveal rapid electrochemical oxidation of graphene, as well as its efficient electrochemical reduction back to the unoxidized state. We identify 1.4 V (vs. Ag/AgCl) as the onset voltage for oxidation, and show that the process is driven by free radicals generated in the electrolysis of water and so fully suppressible by a radical-trapping molecule. Moreover, we find the oxidation process to be spatially heterogeneous at the nanoscale, defect- and history-dependent, and characterized by a self-limiting effect unique to the two-dimensional system. We further demonstrate that electrochemical reduction rapidly reverses the oxidized graphene back to the unoxidized state in a controlled manner, and find strong dependency of reduction speed on the reduction voltage and pH, from which we conclude a one-to-one relationship between protons and electrons in the reduction process. Besides elucidating the electrochemical reaction mechanisms of graphene, our results point to new pathways to the controlled generation and fine-tuning of graphene derivatives through electrochemistry.
关键词： Graphene,reversible reduction,electrochemistry,oxidation,optical microscopy
更新于2025-09-19 17:15:36
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Enhanced visible-light-photoconversion efficiency of TiO2 nanotubes decorated by pulsed laser deposited CoNi nanoparticles
摘要： The pulsed laser deposition (PLD) technique has been used to decorate TiO2 nanotubes (NTs) with cobalt-nickel (CoNi) nanoparticles (NPs). The TiO2 NTs were produced beforehand through the controlled anodic oxidation of titanium substrates. The effect of the nature of the PLD background gas (Vacuum, O2 and He) on the microstructure, composition and chemical bondings of the CoNi-NPs deposited onto the TiO2-NTs has been investigated. We found that the PLD CoNi-NPs have a core/shell (oxide/metal) structure when deposited under vacuum, while they are fully oxidized when deposited under O2. On the other hand, by varying the CoNi-NPs loading of the TiO2-NTs (through the increase of the number of laser ablation pulses (NLP)), we have systematically studied their photocatalytic effect by means of cyclic-voltammetry (CV) measurements under both AM1.5 simulated solar light and filtered visible light. We show that depositing CoNi-NPs on the substrate under vacuum and He increases the photo-electrochemical conversion effectiveness (PCE) by 600% (at NLP = 10,000) in the visible light domain, while their overall PCE degrades with NLP under solar illumination. In contrast, the fully oxidized CoNi-NPs (deposited under O2) are found to be the most effective catalyst under sunlight with an overall increase of more than 50% of the PCE at the optimum loading around NLP ~1000. Such catalytic enhancement is believed to result from both an enhanced light absorption by CoO (of which bandgap is of ~2.4 eV) and the formation of a heterojunction between NiO/CoO nanoparticles and TiO2 nanotubes.
关键词： TiO2 nanotubes,Pulsed laser deposition,Cobalt/nickel nanoparticles,Photo-electrochemistry,Water-splitting
更新于2025-09-19 17:13:59
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Bis-Cyclometalated Iridium Complexes Containing 4,4a?2-Bis(phosphonomethyl)-2,2a?2-bipyridine Ligands: Photophysics, Electrochemistry, and High-Voltage Dye-Sensitized Solar Cells
摘要： In this report, the synthesis and characterization of two bis-cyclometalated iridium(III) complexes are presented. Single-crystal X-ray diffraction shows [Ir(ppy)2(4,4′-bis(diethylphosphonomethyl)-2,2′-bipyridine)]PF6 adopts a pseudo-octahedral geometry. The complexes have an absorption feature in the near-visible?UV region and emit green light with excited-state lifetimes in hundreds of nanoseconds. The redox properties of these complexes show reversible behavior for both oxidative and reductive events. [Ir(ppy)2(4,4′-bis(phosphonomethyl)-2,2′-bipyridine)]PF6 readily binds to metal oxide supports, like nanostructured SnIV-doped In2O3 and TiO2, while still retaining reversible redox chemistry. When incorporated as the photoanode in dye-sensitized solar cells, the devices exhibit open-circuit voltages of >1 V, which is a testament to their strength of these iridium(III) complexes as photochemical oxidants.
关键词： high-voltage,dye-sensitized solar cells,bis-cyclometalated iridium(III) complexes,electrochemistry,photophysics
更新于2025-09-19 17:13:59
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Organic Electropolymerized Multilayers for Light-Emitting Diodes and Displays
摘要： In electrochemistry, the carbazole generally coupled to dimer but not polymer. This work has reported that organic electropolymerzation (OEP) of 4,4',4"-Tri(N-carbazolyl)triphenylamine (TCTA) would form high crosslinked carbazole polymer by its high activity/reversibility and a synchronous viscosity control. It has significantly improved the OEP film quality of both holes transporting and electroluminescent layers in organic light emitting diodes. As a result, the conductivity and power efficiency of the organic light emitting diodes with TCTA are eight and four times of that without TCTA. A prototype display device with 1.7 inch monochrome passive matrix of 58 ppi under driving chip is successfully fabricated with accurate pixel size and uniform electroluminescence, which makes the big potential of organic electropolymerzation in the electroluminescent application.
关键词： TCTA,Polymerization,Electrochemistry,Carbazole,Organic Light emitting diodes
更新于2025-09-19 17:13:59
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Laser Marked and Textured Biomaterial Evaluated by Mott- Schottky Technique
摘要： The effect of an optical fiber laser marking and texturing techniques on the surface of the ISO 5832-1 stainless steel via the Mott-Schottky approach was evaluated in this work. This is one of the most commonly used biomaterial for permanent implants manufacture. It was found that the pulsed laser treatment increases the susceptibility to corrosion by changes on the roughness, microstructure and surface chemical composition; which affect the surface passivity, comparatively to the non treated biomaterial. In this study, the Mott-Schottky technique was very sensitive to identify the effect of the type of surface treatment, marking and texturing, according to the laser pulse frequency modification on the electronic properties of the oxide layer. The change in the semiconductors behavior was the main procedure proposed to explain the increased susceptibility to localized corrosion associated to the areas affected by the Yb optical fiber laser engraving and texturing process.
关键词： electrochemistry,laser,texturing,Biomaterial,marking
更新于2025-09-12 10:27:22
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Bifunctional nanoscale assemblies: multistate electrochromics coupled with charge trapping and release
摘要： We demonstrate controlled charge trapping and release, accompanied by multiple color changes in a metallo-organic bilayer. The dual functionality of the metallo-organic materials provides a fundamental insight into the metal-mediated electron transport pathways. The electrochemical processes are accompanied by distinct, four color–to–color transitions: red, transparent, orange, and brown. The bilayer consists of two elements: (i) a nanoscale gate consisting of a layer of well-defined polypyridyl ruthenium complexes bound to a flexible transparent electrode, and (ii) a charge storage layer consisting of isostructural iron complexes attached to the surface of the gate. This gate mediates or blocks electron transport in response to a voltage. The charge storage and release depend on the oxidation state of the layer of ruthenium complexes (= gate). Combining electrochemistry with optical data revealed mechanistic information: the brown coloration of the bilayer directly relates to the formation of intermediate ruthenium species, providing evidence for catalytic positive charge release mediated through the gate.
关键词： Thin films,Charge storage,Electrochromism,Metallo-organics,Electrochemistry
更新于2025-09-12 10:27:22
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9,9′-bifluorenylidene derivatives as novel hole-transporting materials for potential photovoltaic applications
摘要： Novel 9,9’-bifluorenylidene derivatives were designed to study the effect of alkyl chain length on selected physical properties. The structure of the synthesized compounds was confirmed by using NMR spectroscopy (1H, 13C, H-H COSY, H-C HMQC, H-C HMBC) and elemental analysis. They showed high thermal stability and undergo decomposition in the range of 388-400°C. As was revealed by DSC investigations, they can be converted from crystalline to amorphous materials with relatively high glass transition temperature. The replacement of the alkyl chains from ethyl to butyl resulted in a significant negative impact on melting and glass transition temperatures. The synthesized derivatives undergo reversible electrochemical oxidation and reduction and showed a very low energy band gap (1.47 and 1.79 eV). They intensively absorb the light up 550 nm and also exhibited a week absorption band in the range of 550-750 nm. Their hole transporting ability was tested in perovskite solar cells. Additionally, the effect of the doping concentration of Li+ on photovoltaic device performance for these compounds was investigated. It should be stressed found that 9,9’-bifluorenylidene derivative substituted with ethyl units applied as hole transporting materials in perovskite solar cells demonstrated the highest device efficiency of 7.33 % higher than of the spiro-OMeTAD utilized for preparation of the reference cell (4.40 %).
关键词： Buchwald-Hardwig reaction,electrochemistry,perovskite solar cells (PSC),holes transporting materials,9,9’-bifluorenylidene derivatives
更新于2025-09-12 10:27:22
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Tunable Optical Metamaterial-Based Sensors Enabled by Closed Bipolar Electrochemistry
摘要： Enabled by the proliferation of nanoscale fabrication techniques required to create spatially-repeating, sub-wavelength structures to manipulate the behavior of visible-wavelength radiation, optical metamaterials are of increasing interest. Here we develop and characterize a chemical sensing approach based on electrochemical tuning of the optical response function of large-area, inexpensive nanoaperture metamaterials at visible and near-IR wavelengths. Nanosphere lithography is used to create an ordered array of sub-wavelength apertures in a Au film. The spacing of these apertures is established during fabrication, based on the size of the polystyrene nanospheres. Tunable shifts in the transmission spectrum can be produced post-fabrication by electrodeposition of a dissimilar metal, Ag, using the nanoaperture film as one electrode in a 2-electrode closed bipolar electrochemical (CBE) cell, altering hole size, film thickness, and film composition while maintaining hole spacing dictated by the original pattern. Optical transmission spectra acquired under galvanostatic conditions can be expressed as a linear combination of the initial and final (saturated) spectra, and the resulting response function exhibits a sigmoidal response with respect to the amount of charge (or metal) deposited. This architecture is then used to perform optical coulometry of model analytes in a CBE-based analyte-reporter dual cell device, thus expanding the capability of CBE-based sensors. Increasing the exposed electrode area of the analyte cell increases the response of the device, while modifying the circuit resistance alters the balance between sensitivity and dynamic range. These tunable nanoaperture metamaterials exhibit enhanced sensitivity compared to CBE electrochromic reporter cells to the μM to nM concentration range, suggesting further avenues for development of CBE-based chemical sensors as well as application to inexpensive, point-of-care diagnostic devices.
关键词： nanosphere lithography,electrodeposition,closed bipolar electrochemistry,chemical sensing,optical metamaterials
更新于2025-09-11 14:15:04
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Molecular Engineering of Simple Metal‐Free Organic Dyes Derived from Triphenylamine for Dye‐Sensitized Solar Cell Applications
摘要： Two new metal-free organic sensitizers, L156 and L224, were designed, synthesized, and characterized for application in dye-sensitized solar cells (DSCs). The structures of the dyes contain a triphenylamine (TPA) segment and 4-(benzo[c][1,2,5]thiadiazol-4-yl)benzoic acid as electron-rich and -deficient moieties, respectively. Two different π bridges, thiophene and 4,8-bis(4-hexylphenyl)benzo[1,2-b:4,5-b’]dithiophene, were used for L156 and L224, respectively. The influence of iodide/triiodide, [Co(bpy)3]2+/3+ (bpy = 2,2’-bipyridine), and [Cu(tmby)2]2+/+ (tmby = 4,4’,6,6’-tetramethyl-2,2’-bipyridine) complexes as redox electrolytes and 18 NR-T and 30 NR-D transparent TiO2 films on the DSC device performance was investigated. The L156-based DSC with [Cu(tmby)2]2+/+ complexes as the redox electrolyte resulted in the best performance of 9.26 % and a remarkably high open-circuit voltage value of 1.1 V (1.096 V), with a short-circuit current of 12.2 mA cm?2 and a fill factor of 0.692, by using 30 NR-D TiO2 films. An efficiency of up to 21.9 % was achieved under a 1000 lx indoor light source, which proved that dye L156 was also an excellent candidate for indoor applications. The maximal monochromatic incident-photon-to-current conversion efficiency of L156–30 NR-D reached up to 70 %.
关键词： electrochemistry,donor–acceptor systems,dyes/pigments,sensitizers,solar cells
更新于2025-09-11 14:15:04
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TEM Sample Preparation of Patterned Quantum Dots
摘要： Electrochemistry and heterogeneous catalysis continue to attract enormous interest. In situ surface analysis is a dynamic research field capable of elucidating the catalytic mechanisms of reaction processes. Shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) is a non-destructive technique that has been cumulatively used to probe and analyze catalytic-reaction processes, providing important spectral evidence about reaction intermediates produced on catalyst surfaces. In this perspective, we review recent electrochemical- and heterogeneous-catalysis studies using SHINERS, highlight its advantages, summarize the flaws and prospects for improving the SHINERS technique, and give insight into its future research directions.
关键词： Catalytic mechanisms,In situ surface analysis,SHINERS,Heterogeneous catalysis,Reaction intermediates,Electrochemistry,Shell-isolated nanoparticle-enhanced Raman spectroscopy
更新于2025-09-11 14:15:04