Minimization of Ion-Solvent Clusters in Gel Electrolytes Containing Graphene Oxide Quantum Dots for Lithium-Ion Batteries.

This study uses graphene oxide quantum dots (GOQDs) to enhance the Li+ -ion mobility of a gel polymer electrolyte (GPE) for lithium-ion batteries (LIBs). The GPE comprises a framework of poly(acrylonitrile-co-vinylacetate) blended with poly(methyl methacrylate) and a salt LiPF6 solvated in carbonate solvents. The GOQDs, which function as acceptors, are small (3-11 nm) and well dispersed in the polymer framework. The GOQDs suppress the formation of ion-solvent clusters and immobilize PF6- anions, affording the GPE a high ionic conductivity and a high Li+ -ion transference number (0.77). When assembled into Li|electrolyte|LiFePO4 batteries, the GPEs containing GOQDs preserve the battery capacity at high rates (up to 20 C) and exhibit 100% capacity retention after 500 charge-discharge cycles. Smaller GOQDs are more effective in GPE performance enhancement because of the higher dispersion of QDs. The minimization of both the ion-solvent clusters and degree of Li+ -ion solvation in the GPEs with GOQDs results in even plating and stripping of the Li-metal anode; therefore, Li dendrite formation is suppressed during battery operation. This study demonstrates a strategy of using small GOQDs with tunable properties to effectively modulate ion-solvent coordination in GPEs and thus improve the performance and lifespan of LIBs.

Highly efficient gel-state dye-sensitized solar cells prepared using poly(acrylonitrile-co-vinyl acetate) based polymer electrolytes.

Poly(acrylonitrile-co-vinyl acetate) (PAN-VA) is utilized as a gelation agent to prepare gel-state electrolytes for dye-sensitized solar cell (DSSC) applications. Based on the synergistic effect of PAN-VA and TiO(2) fillers in the electrolyte, the gel-state DSSC can achieve a conversion efficiency higher than that of a liquid counterpart. The high performance of the gel-electrolyte is attributed to the in situ gelation property of the gel-electrolyte, the contribution of the PAN-VA to the charge transfer, as well as the enhancement effect of TiO(2) fillers on the charge transfer at the Pt-electrolyte interface. The experimental results show that the efficiencies of the gel-state cells have little dependence on the conductivity of the electrolytes with various contents of PAN-VA, but are closely related to the penetration situation of the electrolyte in the TiO(2) film. For PAN-VA concentrations ≤15 wt%, the electrolyte can be easily injected at room temperature based on its in situ gelation property. For higher PAN-VA concentrations, good penetration of the high viscous electrolyte can be achieved by elevating the operation temperature. By utilizing a heteroleptic ruthenium dye (coded CYC-B11), gel-state DSSCs with an efficiency of above 10% are obtained. Acceleration tests show that the cell is stable under one-sun illumination at 60 °C.

Elucidating the mechanism of photocatalytic reduction of bicarbonate (aqueous CO2) into formate and other organics.

The photocatalytic reduction of CO2 under solar irradiation is an ideal approach to mitigating global warming, and reducing aqueous forms of CO2 that interact strongly with a catalyst (e.g., HCO3-) is a promising strategy to expedite such reductions. This study uses Pt-deposited graphene oxide dots as a model photocatalyst to elucidate the mechanism of HCO3- reduction. The photocatalyst steadily catalyzes the reduction of an HCO3- solution (at pH = 9) containing an electron donor under 1-sun illumination over a period of 60 h to produce H2 and organic compounds (formate, methanol, and acetate). H2 is derived from solution-contained H2O, which undergoes photocatalytic cleavage to produce •H atoms. Isotopic analysis reveals that all of the organics formed via interactions between HCO3- and •H. This study proposes mechanistic steps, which are governed by the reacting behavior of the •H, to correlate the electron transfer steps and product formation of this photocatalysis. This photocatalysis achieves overall apparent quantum efficiency of 27% in the formation of reaction products under monochromatic irradiation at 420 nm. This study demonstrates the effectiveness of aqueous-phase photocatalysis in converting aqueous CO2 into valuable chemicals and the importance of H2O-derived •H in governing the product selectivity and formation kinetics.

Electrodeposition of copper on a Pt(111) electrode in sulfuric acid containing poly(ethylene glycol) and chloride ions as probed by in situ STM.

This study employed real-time in situ STM imaging to examine the adsorption of PEG molecules on Pt(111) modified by a monolayer of copper adatoms and the subsequent bulk Cu deposition in 1 M H(2)SO(4) + 1 mM CuSO(4)+ 1 mM KCl + 88 µM PEG. At the end of Cu underpotential deposition (~0.35 V vs Ag/AgCl), a highly ordered Pt(111)-(√3 × âˆš7)-Cu + HSO(4)(-) structure was observed in 1 M H(2)SO(4) + 1 mM CuSO(4). This adlattice restructured upon the introduction of poly(ethylene glycol) (PEG, molecular weight 200) and chloride anions. At the onset potential for bulk Cu deposition (~0 V), a Pt(111)-(√3 × âˆš3)R30°-Cu + Cl(-) structure was imaged with a tunneling current of 0.5 nA and a bias voltage of 100 mV. Lowering the tunneling current to 0.2 nA yielded a (4 × 4) structure, presumably because of adsorbed PEG200 molecules. The subsequent nucleation and deposition processes of Cu in solution containing PEG and Cl(-) were examined, revealing the nucleation of 2- to 3-nm-wide CuCl clusters on an atomically smooth Pt(111) surface at overpotentials of less than 50 mV. With larger overpotential (η > 150 mV), Cu deposition seemed to bypass the production of CuCl species, leading to layered Cu deposition, starting preferentially at step defects, followed by lateral growth to cover the entire Pt electrode surface. These processes were observed with both PEG200 and 4000, although the former tended to produce more CuCl nanoclusters. Raising [H(2)SO(4)] to 1 M substantiates the suppressing effect of PEG on Cu deposition. This STM study provided atomic- or molecular-level insight into the effect of PEG additives on the deposition of Cu.

Adsorption and desorption of bis-(3-sulfopropyl) disulfide during Cu electrodeposition and stripping at Au electrodes.

The adsorption and desorption of bis-(3-sulfopropyl) disulfide (SPS) on Cu and Au electrodes and its electrochemical effect on Cu deposition and dissolution were examined using cyclic voltammetry stripping (CVS), field-emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS). SPS dissociates into 3-mercapto-1-propanesulfonate when it is contacted with Au and Cu electrodes, producing Cu(I)- and Au(I)-thiolate species. These thiolates couple with chloride ions and promote not only the reduction of Cu(2+) in Cu deposition but also the oxidation of Cu(0) to Cu(+) in Cu stripping. During Cu electrodeposition on the SPS-modified Au electrode, thiolates transfer from Au onto the Cu underpotential deposition (UPD) layer. The Cu UPD layer stabilizes a large part of the transferred thiolates which subsequently is buried by the Cu overpotential deposition (OPD) layer. The buried thiolates reappear on the Au electrode after the copper deposit is electrochemically stripped off. A much smaller part of thiolates transfers to the top of the Cu OPD layer. In contrast, when SPS preadsorbs on a Cu-coated Au electrode, almost all of the adsorbed SPS leaves the Cu surface during Cu electrochemical stripping and does not return to the uncovered Au surface. A reaction mechanism is proposed to explain these results.

In-Situ surface enhanced infrared absorption spectroscopy study of electrocatalytic oxidation of ethanol on Platinum/Gold surface.

The behavior of ethanol oxidation reaction on composite electrodes prepared by deposition platinum on a gold surface (Pt/Au) were studied by cyclic voltammetry and surface enhanced infrared absorption spectroscopy (SEIRAS) analysis. The results show that the Pt electrode has high oxidation activity and significant poison behavior; on the contrary, the Au electrode demonstrates low activity without a poison peak. The SEIRAS analyses reveal that both carbon monoxide (CO) and carbon dioxide (CO2) appear during anode sweeping, and the CO peak density decreases with increasing potential and finally is eliminated. During the cathodic scanning, the CO peak reappears, and the peak intensity increases with scanning cycles, demonstrating a high poison behavior and the C1 reaction route on Pt. On the Au electrode, CO2 and CO peaks were not observed; instead, an acetic acid peak appeared, indicating a C2 reaction path. For the Pt/Au composited electrodes, the electrochemical activities of the electrodes, as well as their poison behavior, increased with the deposition amount of Pt. However, the intensities of the poison peaks are smaller than those of oxidation ones; therefore, a higher tolerance to the CO poison can be achieved. For the 2 m-Pt/Au composite electrode, the activity is close to that of pure Pt, but the poison tolerance is 3 times the value of Pt.

Headgroup effects of template monolayers on the adsorption behavior and conformation of glucose oxidase adsorbed at air/liquid interfaces.

Stearic acid (SA) and octadecylamine (ODA) monolayers at the air/liquid interface were used as template layers to adsorb glucose oxidase (GOx) from aqueous solution. The effect of the template monolayers on the adsorption behavior of GOx was studied in terms of the variation of surface pressure, the evolution of surface morphology observed by BAM and AFM, and the conformation of adsorbed GOx. The results show that the presence of a template monolayer can enhance the adsorption rate of GOx; furthermore, ODA has a higher ability, compared to SA, to adsorb GOx, which is attributed to the electrostatic attractive interaction between ODA and GOx. For adsorption performed on a bare surface or on an SA monolayer, the surface pressure approaches an equilibrium value (ca. 8 mN/m) after 2 to 3 h of adsorption and remains nearly constant in the following adsorption process. For the adsorption on an ODA monolayer, the surface pressure will increase further 1 to 2 h after approaching the first equilibrium pressure, which is termed the second adsorption stage. The measurement of circular dichroism (CD) spectroscopy indicates that the Langmuir-Blodgett films of adsorbed GOx transferred at the first equilibrium state (π = 8 mN/m) have mainly a ß-sheet conformation, which is independent of the type of template monolayers. However, the ODA/GOx LB film transferred at the second adsorption stage has mainly an α-helix conformation. It is concluded that the specific interaction between ODA and GOx not only leads to a higher adsorption rate and adsorbed amount of GOx but also induces a conformation change in adsorbed GOx from ß-sheet to α-helix. The present results indicate that is possible to control the conformation of adsorbed protein by selecting the appropriate template monolayer.

In situ STM imaging of bis-3-sodiumsulfopropyl-disulfide molecules adsorbed on copper film electrodeposited on Pt(111) single crystal electrode.

The adsorption of bis-3-sodiumsulfopropyldi-sulfide (SPS) on metal electrodes in chloride-containing media has been intensively studied to unveil its accelerating effect on Cu electrodeposition. Molecular resolution scanning tunneling microscopy (STM) imaging technique was used in this study to explore the adsorption and decomposition of SPS molecules concurring with the electrodeposition of copper on an ordered Pt(111) electrode in 0.1 M HClO(4) + 1 mM Cu(ClO(4))(2) + 1 mM KCl. Depending on the potential of Pt(111), SPS molecules could react, adsorb, and decompose at chloride-capped Cu films. A submonolayer of Cu adatoms classified as the underpotential deposition (UPD) layer at 0.4 V (vs Ag/AgCl) was completely displaced by SPS molecules, possibly occurring via RSSR (SPS) + Cl-Cu-Pt → RS(-)-Pt(+) + RS(-) (MPS) + Cu(2+) + Cl(-), where MPS is 3-mercaptopropanesulfonate. By contrast, at 0.2 V, where a full monolayer of Cu was presumed to be deposited, SPS molecules were adsorbed in local (4 × 4) structures at the lower ends of step ledges. Bulk Cu deposition driven by a small overpotential (η < 50 mV) proceeded slowly to yield an atomically smooth Cu deposit at the very beginning (<5 layers). On a bilayer Cu deposit, the chloride adlayer was still adsorbed to afford SPS admolecules arranged in a unique 1D striped phase. SPS molecules could decompose into MPS upon further Cu deposition, as a (2 × 2)-MPS structure was observed with prolonged in situ STM imaging. It was possible to visualize either SPS admolecules in the upper plane or chloride adlayer sitting underneath upon switching the imaging conditions. Overall, this study established a MPS molecular film adsorbed to the chloride adlayer sitting atop the Cu deposit.

Effect of chloride ions on the adsorption of 3-mercapto-1-propanesulfonic acid and bis(3-sulfopropyl)-disulfide on a Au(111) surface.

In situ scanning tunneling microscopy (STM) and cyclic voltammetry (CV) were used to study the adsorption of 3-mercapto-1-propanesulfonic acid (MPS) and bis(3-sulfopropyl)-disulfide (SPS) on Au(111) electrode in a HClO(4) aqueous solution. Chloride ions were introduced into the electrolyte solution, and their effect on the adsorption behavior of MPS and SPS was investigated. The CV results show that SPS and MPS molecules preferentially adsorb on the Au(111) surface compared to chloride ions, and furthermore, chloride ion can induce the adsorption of thiol molecules on the Au(111) surface. In the absence of chloride, no adsorption phase of SPS (or MPS) adlayer can be imaged by STM at low potentials. Raising electrode potential leads to the appearance of disordered adsorption phase at ca. 0.4 V (vs RHE) and ordered adlattices at ca. 0.8 V. In the presence of chloride, ordered adsorption structures of SPS and MPS appear at a lower potential (0.2 V), implying the enhancement effect of chloride to the thiol adsorption. It is inferred that the presence of chloride ions triggers a more positively charged gold surface, enhancing the reaction rate of thiol adsorption. Furthermore, the presence of chloride also leads to a decrease in the thiol-electrolyte interaction, due to the high solvation effect of chloride ions, which promotes the adsorption of SPS and MPS onto the Au surface. With further elevation of electrode potential, electrostatic interaction leads to coadsorption of chloride ions into the adlayer, as well as orientation changes of the ad-molecules. As a result, the ordered adlattice was disrupted and disappeared at ca. 0.5 V.

The heat annealing effect on the performance of CdS/CdSe-sensitized TiO2 photoelectrodes in photochemical hydrogen generation.

Heat treatment was utilized to anneal the semiconductor sensitizers (CdS, CdSe and CdS/CdSe) assembled on mesoporous TiO(2) films to enhance the performance of the photoelectrodes in a process of photoelectrochemical hydrogen generation. Various annealing temperatures (150, 300 and 400 degrees C) were employed and the results show that appropriately elevating the temperature (to approx. 300 degrees C) can increase the crystallinity of the CdS and CdSe, improve the charge transport characteristic of a photoelectrode and, therefore, lead to a higher performance of the TiO(2) /CdS and TiO(2) /CdSe electrodes. However, an over-annealing temperature (400 degrees C) may cause serious oxidation and/or decomposition of the sensitizers which is unfavorable to the photoelectrode. For the co-sensitized electrode, counter-diffusion of CdS and CdSe happens at the CdS/CdSe interface when the TiO(2) /CdS/CdSe electrode was co-annealed at 300 degrees C, which significantly decreases the performance of the co-sensitized electrode. This problem was solved by annealing first a TiO(2) /CdS electrode at 300 degrees C, followed by CdSe assembly and a second annealing at 150 degrees C. This electrode appears to have better performance than the others.

Highly Efficient Dye-sensitized Solar Cells Based on Poly(vinylidene fluoride-co-hexafluoropropylene) and Montmorillonite Nanofiller-based Composite Electrolytes.

Highly efficient nanocomposite electrolytes were prepared by mixing the montmorillonite (MMT) clay nanofillers and iodide poly(vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) gel electrolytes for the purpose of measuring the performance of quasi-solid-state dye-sensitized solar cells (QS-DSSCs). The impacts of different amounts of MMT nanofillers on the ion diffusivity, conductivity of the polymer gel electrolytes (PGEs), and the photovoltaic performance of the cells using the PGEs were evaluated. The results indicated that the use of 5 wt.% MMT markedly increase the ion diffusivity and conductivity of the PVDF-HFP PGE. The introduction of 5 wt.% nanofillers considerably reduced the Warburg diffusion resistance, which made to the high performance of the QS-DSSCs. Cells utilizing 5 wt.% MMT nanofillers were shown to obtain a power conversion efficiency (PCE) (6.77%) higher than that obtained for cells using pure PGEs and identical to that obtained using liquid electrolytes (LEs) (6.77%). The high PCE was a result of an enhance in the current density in the presence of the 5 wt.% MMT nanofillers. The DSSC efficiency was found to maintain 99.9% of its initial value after 194 h of testing at 60℃ under dark environments. The stability of the DSSC using PGEs with the optimal amount of MMT nanofillers was higher than that for the cells using liquid electrolyte and pure PGE.

Improvement in Cobalt Phosphate Electrocatalyst Activity toward Oxygen Evolution from Water by Glycine Molecule Addition and Functional Details.

Electrochemical water splitting using renewable energy shows promise for the development of sustainable hydrogen production methods. The process requires a highly active electrocatalyst for oxygen evolution to improve the overall water splitting efficiency. The present study showed that oxygen evolution improved dramatically upon the addition of glycine to cobalt phosphate, when the glycine was added to the electrolyte solution during electrodeposition. The functionality of the organic molecules was investigated using in situ UV-vis absorption, in situ X-ray absorption fine structure, and in situ infrared (IR) absorption spectroscopy in the attenuated total reflection mode. The results demonstrated that the glycine molecules assembled cobalt oxide clusters composed of CoO6 (CoOOH) octahedrons a few nanometers in diameter upon the electrodeposition of cobalt catalysts. This suggests that the cobalt-glycine catalyst can decompose water to oxygen gas efficiently, because the number of cobalt oxide clusters increased as active reaction sites upon the addition of glycine molecules.

Ultra-thin phospholipid layers physically adsorbed upon glass characterized by nano-indentation at the surface contact level.

Dipalmitoylphosphatic acid was chosen as a model to interpret how molecules physically adsorbed upon glass responded to an infinitesimal oscillation force at the surface contact level. Oscillation of a nano-indentation tip toward the phospholipid layers was driven by a dynamic contact module at a constant harmonic frequency; the phase angle of the oscillation frequency was exponentially relaxed along the nano-scale displacement. The tip-on-molecule contact was thereafter identified and influenced by the characteristic of the physically adsorbed phospholipids. By applying the harmonic displacement of the nano-indentation tip and making a distinction between full contact displacements, the thickness of the phospholipid layers was thereafter estimated. Moreover, the additional force required to penetrate through the physically adsorbed molecules was minor compared to the analogous process for the chemically adsorbed ones. The importance of recognizing the physically adsorbed molecules is relevant to applications of contact mechanics for the distinction of various phospholipids. Furthermore it is very promising to interpret the mechanism by which cells convert mechanical stimuli into biochemical responses on the channels of phospholipids.

High-Efficiency Bifacial Dye-Sensitized Solar Cells for Application under Indoor Light Conditions.

High-efficiency, stable bifacial dye-sensitized solar cells (DSSCs) are prepared for application under indoor light conditions. A 3-methoxypropionitrile solvent and cobalt redox couples are utilized to prepare the electrolytes. To obtain the best cell performance, the components of the DSSCs, including electrolytes, photoanodes, and counter electrodes (CEs), are regulated. The experimental results indicate that an electrolyte comprising a Co (II/III) ratio of 0.11/0.025 M, 1.2 M 4-tert-butylpyridine, Y123 dye, a CE with the platinum (Pt) layer thickness of 0.16 nm, and a photoanode with titanium dioxide (TiO2) layer thickness of 10 µm (6 µm main layer and 4 µm scattering layer) are the best conditions under which to achieve a high power conversion efficiency. It is also found that the best cells have high recombination resistance at the photoelectrode/electrolyte interface and low charge transfer resistance at the counter electrode/electrolyte interface, which contributes to, respectively, the high current density and open-circuit voltage of the corresponding cells. This DSSC can achieve efficiencies of 22.66%, 23.48%, and 24.52%, respectively, under T5 light illumination of 201.8, 607.8, and 999.6 lx. For fabrication of bifacial DSSCs with a semitransparent property, photoanodes without the TiO2 scattering layer, as well as an ultrathin Pt film, are utilized. The thicknesses of the TiO2 main layer and Pt film are reregulated. This shows that a Pt film with 0.55 nm thickness has both high transmittance (76.01%) and catalytic activity. By using an 8 µm TiO2 main layer, optimal cell efficiencies of 20.65% and 17.31% can be achieved, respectively, for the front-side and back-side illuminations of 200 lx T5 light. The cells are highly stable during a long-term performance test at both 35 and 50 °C.

Graphene Oxide Sponge as Nanofillers in Printable Electrolytes in High-Performance Quasi-Solid-State Dye-Sensitized Solar Cells.

A graphene oxide sponge (GOS) is utilized for the first time as a nanofiller (NF) in printable electrolytes (PEs) based on poly(ethylene oxide) and poly(vinylidene fluoride) for quasi-solid-state dye-sensitized solar cells (QS-DSSCs). The effects of the various concentrations of GOS NFs on the ion diffusivity and conductivity of electrolytes and the performance of the QS-DSSCs are studied. The results show that the presence of GOS NFs significantly increases the diffusivity and conductivity of the PEs. The introduction of 1.5 wt % of GOS NFs decreases the charge-transfer resistance at the Pt-counter electrode/electrolyte interface ( Rpt) and increases the recombination resistance at the photoelectrode/electrolyte interface ( Rct). QS-DSSC utilizing 1.5 wt % GOS NFs can achieve an energy conversion efficiency (8.78%) higher than that found for their liquid counterpart and other reported polymer gel electrolytes/GO NFs based DSSCs. The high energy conversion efficiency is a consequence of the increase in both the open-circuit potential ( Voc) and fill factor with a slight decrease in current density ( Jsc). The cell efficiency can retain 86% of its initial value after a 500 h stability test at 60 °C under dark conditions. The long-term stability of the QS-DSSC with GOS NFs is higher than that without NFs. This result indicates that the GOS NFs do not cause dye-desorption from the photoanode in a long-term stability test, which infers a superior performance of GOS NFs as compared to TiO2 NFs in terms of increasing the efficiency and long-term stability of QS-DSSCs.

Importance of Compact Blocking Layers to the Performance of Dye-Sensitized Solar Cells under Ambient Light Conditions.

Power generation in indoor environments is the next step in dye-sensitized solar cell (DSSC) evolution. To achieve this goal, a critical recombination route which is usually inhibited by the TiCl4-derived blocking layers (BLs), that is, charge transfer at the fluorine-doped tin oxide substrate/electrolyte interface, is of concern. In this study, we demonstrate that because of low surface coverage, the conventional TiCl4 BLs are unable to suppress such electron leakage, thus limiting the photovoltaic performance of Co(bpy)32+/3+-mediated DSSCs (bpy = 2,2'-bipyridine) under ambient lighting. On the other hand, by introducing compact BLs prepared by spray pyrolysis, the DSSCs show lower dark current and operate efficiently not only under high-intensity sunlight but also under ambient light conditions. The better blocking function of the compact BL is verified by the cyclic voltammetry; other thin-film preparation methods, except for the common TiCl4 treatment, are anticipated to realize a similar blocking effect. This study illustrates that dense thin film with a predominant blocking function is highly required as the BL for DSSCs under low-light conditions, and this concept will pave the way for more development of indoor DSSCs.

Adsorption Behavior of TBPS in the Process of Cu Electrodeposition on an Au Film.

The adsorption behavior of an Cu electroplating additive, 3,3 thiobis-(1-propanesulfonic acid sodium salt) (TBPS) in a process of Cu deposition onto a single crystalline Au(111) surface is studied by an in-situ Surface-Enhanced Infrared Absorption Spectroscopy (SEIRAS). The SEIRAS spectra of the TBPS adlayer on a Cu film is investigated first and compared to that on an Au film. These results are utilized to evaluate the characteristics of TBPS adlayer on the electrode surface during the Cu deposition and stripping processes. The results show that the SEIRAS spectra of TBPS adsorbed on the Cu film resembles closely to that on the Au film, and the most pronounced peaks are symmetric S-O (ss-SO) and asymmetric S-O (as-SO) stretching modes. However, the as-SO band is sharper with a higher intensity on the Cu film. Since the ss-SO and as-SO peaks correspond to the molecular with upright and lie-down orientations, respectively, it implies that the TBPS molecules have higher ratio of lie-down orientation on the Cu film. In the Cu electrodeposition process, the cyclic voltammetry (CV) result shows that the presence of the TBPS in the HClO4 solution can decrease the inhibition effect of HClO4 to the Cu deposition. For the spectra measured at various potential during cathodic and anodic sweeping, an obvious change of the spectra occurs at ca. 0.6 V, the initiation of Cu underpotential deposition (Cu-UPD). For potentials higher and lower than 0.6 V, the spectra are similar, respectively, to those measured for the Au and Cu films. This result indicates that the TBPS molecules originally adsorbing on the Au film transfer to the surface of deposited Cu layer. This inference is also confirmed by the variation in wavenumber and peak intensity of ss-SO and as-SO peaks during the potential sweeping.

Extensibility effect of poly(3-hexylthiophene) on the glucose sensing performance of mixed poly(3-hexylthiophene)/octadecylamine/glucose oxidase Langmuir-Blodgett films.

Poly(3-hexylthiophene) (P3HT) is utilized as a material to enhance the glucose sensing performance of glucose oxidase (GOx) Langmuir-Blodgett (LB) films. To enhance the extensibility and homogeneity of the P3HT in the LB films, octadecylamine (ODA) is introduced. The characteristics of the mixed P3HT/ODA Langmuir monolayers are investigated first and then, utilized as template layers to adsorb GOx from the subphase, preparing P3HT/ODA/GOx Langmuir-Blodgett films for glucose sensing. The results show that P3HT molecules tend to aggregate at the air/liquid interface and, furthermore, the P3HT monolayer has a weak ability to adsorb GOx from the subphase. By using mixed P3HT/ODA monolayer, the presence of ODA not only inhibits the aggregation of P3HT, but also increases the adsorption ability of the monolayer to GOx. The extensibility of P3HT and the homogeneity of the P3HT/ODA monolayers are closely related to the concentration of P3HT/ODA stock solutions. On the glucose sensing experiments, the performance of the P3HT/ODA/GOx LB film is greatly improved due to the presence of P3HT and, furthermore, the sensibility increases with increasing extensibility of P3HT molecules. The best sensitivity achieved for the P3HT/ODA/GOx film is 5.4µAmM-1cm-2 which is over two times the value obtained by the ODA/GOx film (2.3µAmM-1cm-2).

Roles of nitrogen functionalities in enhancing the excitation-independent green-color photoluminescence of graphene oxide dots.

Fluorescent graphene oxide dots (GODs) are environmentally friendly and biocompatible materials for photoluminescence (PL) applications. In this study, we employed annealing and hydrothermal ammonia treatments at 500 and 140 °C, respectively, to introduce nitrogen functionalities into GODs for enhancing their green-color PL emissions. The hydrothermal treatment preferentially produces pyridinic and amino groups, whereas the annealing treatment produces pyrrolic and amide groups. The hydrothermally treated GODs (A-GODs) present a high conjugation of the nonbonding electrons of nitrogen in pyridinic and amino groups with the aromatic π orbital. This conjugation introduces a nitrogen nonbonding (nN 2p) state 0.3 eV above the oxygen nonbonding state (nO 2p state; the valence band maximum of the GODs). The GODs exhibit excitation-independent green-PL emissions at 530 nm with a maximum quantum yield (QY) of 12% at 470 nm excitation, whereas the A-GODs exhibit a maximum QY of 63%. The transformation of the solvent relaxation-governed π* → nO 2p transition in the GODs to the direct π* → nN 2p transition in the A-GODs possibly accounts for the substantial QY enhancement in the PL emissions. This study elucidates the role of nitrogen functionalities in the PL emissions of graphitic materials and proposes a strategy for designing the electronic structure to promote the PL performance.

Performance Characterization of Dye-Sensitized Photovoltaics under Indoor Lighting.

Indoor utilization of emerging photovoltaics is promising; however, efficiency characterization under room lighting is challenging. We report the first round-robin interlaboratory study of performance measurement for dye-sensitized photovoltaics (cells and mini-modules) and one silicon solar cell under a fluorescent dim light. Among 15 research groups, the relative deviation in power conversion efficiency (PCE) of the samples reaches an unprecedented 152%. On the basis of the comprehensive results, the gap between photometry and radiometry measurements and the response of devices to the dim illumination are identified as critical obstacles to the correct PCE. Therefore, we use an illuminometer as a prime standard with a spectroradiometer to quantify the intensity of indoor lighting and adopt the reverse-biased current-voltage (I-V) characteristics as an indicator to qualify the I-V sampling time for dye-sensitized photovoltaics. The recommendations can brighten the prospects of emerging photovoltaics for indoor applications.