Mesh‐Shaped Nanopatterning of Pt Counter Electrodes for Dye‐Sensitized Solar Cells with Enhanced Light Harvesting

A facile process to produce large‐area platinum (Pt) counter electrode platforms with well‐arrayed, mesh‐shaped nanopatterns using commercially available TiO₂ paste and poly(dimethyl siloxane) (PDMS) nanostamps is presented. The process involves mesh‐shaped (200 nm × 200 nm) nanopatterning of a TiO₂ scaffold onto a fluorine‐doped tin oxide (FTO) substrate, followed by Pt sputtering. The structure and morphology of the counter electrodes are characterized by a field emission scanning electron microscope (FE‐SEM) and an atomic force microscope (AFM). Solid‐state dye‐sensitized solar cells (ssDSSCs) fabricated with these mesh‐shaped Pt counter electrodes showed an efficiency of 7.0%. This is one of the highest efficiencies observed for N719 dye and is much higher than that of devices with non‐patterned, thermally deposited electrodes (5.4%) or non‐patterned, sputtering deposited electrodes (5.7%). This improvement is attributed to enhanced light harvesting and a greater surface area and has been confirmed by incident photon‐to current efficiency (IPCE), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) measurements.     

The non-specific inhibition of enzymes by environmental pollutants: a study of a model system towards the development of electrochemical biosensor arrays

Previous research has shown that lactate dehydrogenase (LDH) was competitively inhibited by pentachlorophenol (PCP) and a modified assay produced a detection limit of 1 μM (270 μg l⁻¹). This work used spectrophotometric rate-determination but in order to move towards biosensor development the selected detection method was electrochemical. The linkage of LDH to lactate oxidase (LOD) provided the electroactive species, hydrogen peroxide. This could be monitored using a screen-printed carbon electrode (SPCE) incorporating the mediator, cobalt phthalocyanine, at a potential of +300 mV (vs. Ag/AgCl). A linked LDH/LOD system was optimised with respect to inhibition by PCP. It was found that the SPCE support material, PVC, acted to reduce inhibition, possibly by combining with PCP. A cellulose acetate membrane removed this effect. Inhibition of the system was greatest at enzyme activities of 5 U ml⁻¹ LDH and 0.8 U ml⁻¹ LOD in reactions containing 246 μM pyruvate and 7.5 μM NADPH. PCP detection limits were an EC₁₀ of 800 nM (213 μg l⁻¹) and a minimum inhibition detectable (MID) limit of 650 nM (173 μg l⁻¹). The inclusion of a third enzyme, glucose dehydrogenase (GDH), provided cofactor recycling to enable low concentrations of NADPH to be incorporated within the assay. NADPH was reduced from 7.5 to 2 μM. PCP detection limits were obtained for an assay containing 5 U ml⁻¹ LDH, 0.8 U ml⁻¹ LOD and 0.1 U ml⁻¹ GDH with 246 μM pyruvate, 400 mM glucose and 2 μM NADPH. The EC₁₀ limit was 150 nM (39.9 μg l⁻¹) and the MID was 100 nM (26.6 μg l⁻¹). The design of the inhibition assays discussed has significance as a model for other enzymes and moves forward the possibility of an electrochemical biosensor array for pollution monitoring.     

Ion fluxes in giant excised cardiac membrane patches detected and quantified with ion-selective microelectrodes

We have used ion-selective electrodes (ISEs) to quantify ion fluxes across giant membrane patches by measuring and simulating ion gradients on both membrane sides. Experimental conditions are selected with low concentrations of the ions detected on the membrane side being monitored. For detection from the cytoplasmic (bath) side, the patch pipette is oscillated laterally in front of an ISE. For detection on the extracellular (pipette) side, ISEs are fabricated from flexible quartz capillary tubing (tip diameters, 2-3 microns), and an ISE is positioned carefully within the patch pipette with the tip at a controlled distance from the mouth of the patch pipette. Transport activity is then manipulated by solution changes on the cytoplasmic side. Ion fluxes can be quantified by simulating the ion gradients with appropriate diffusion models. For extracellular (intrapatch pipette) recordings, ion diffusion coefficients can be determined from the time courses of concentration changes. The sensitivity and utility of the methods are demonstrated with cardiac membrane patches by measuring (a) potassium fluxes via ion channels, valinomycin, and Na/K pumps; (b) calcium fluxes mediated by Na/Ca exchangers; (c) sodium fluxes mediated by gramicidin and Na/K pumps; and (d) proton fluxes mediated by an unknown electrogenic mechanism. The potassium flux-to-current ratio for the Na/K pump is approximately twice that determined for potassium channels and valinomycin, as expected for a 3Na/2K pump stoichiometery (i.e., 2K/charge moved). For valinomycin-mediated potassium currents and gramicidin-mediated sodium currents, the ion fluxes calculated from diffusion models are typically 10-15% smaller than expected from the membrane currents. As presently implemented, the ISE methods allow reliable detection of calcium and proton fluxes equivalent to monovalent cation currents <1 pA in magnitude, and they allow detection of sodium and potassium fluxes equivalent to <5 pA currents. The capability to monitor ion fluxes, independent of membrane currents, should facilitate studies of both electrogenic and electroneutral ion-coupled transporters in giant patches.     

Visibly‐Transparent Organic Solar Cells on Flexible Substrates with All‐Graphene Electrodes

Portable electronic devices have become increasingly widespread. Because these devices cannot always be tethered to a central grid, powering them will require low‐cost energy harvesting technologies. As a response to this anticipated demand, this study demonstrates transparent organic solar cells fabricated on flexible substrates, including plastic and paper, using graphene as both the anode and cathode. Optical transmittance of up to 69% at 550 nm is achieved by combining the highly transparent graphene electrodes with organic polymers that primarily absorb in the near‐IR and near‐UV regimes. To address the challenge of transferring graphene onto organic layers as the top electrode, this study develops a room temperature dry‐transfer technique using ethylene‐vinyl‐acetate as an adhesion‐promoting interlayer. The power conversion efficiency achieved for flexible devices with graphene anode and cathode devices is 2.8%–3.8% at for optical transmittance of 54%–61% across the visible regime. These results demonstrate the versatility of graphene in optoelectronic applications and it is important step toward developing a practical power source for distributed wireless electrical systems.     

Paramelaconite‐Enriched Copper‐Based Material as an Efficient and Robust Catalyst for Electrochemical Carbon Dioxide Reduction

A copper‐oxide‐based catalyst enriched with paramelaconite (Cu₄O₃) is presented and investigated as an electrocatalyst for facilitating electroreduction of CO₂ to ethylene and other hydrocarbons. Cu₄O₃ is a member of the copper‐oxide family and possesses an intriguing mixed‐valance nature, incorporating an equal number of Cu⁺ and Cu²⁺ ions in its crystal structure. The material is synthesized using a solvothermal synthesis route and its structure is confirmed via powder X‐ray diffraction, transmission electron microscope based selected area electron diffraction, and X‐ray photoelectron spectroscopy. A flow reactor equipped with a gas diffusion electrode is utilized to test a copper‐based catalyst enriched with the Cu₄O₃ phase under CO₂ reduction conditions. The Cu₄O₃‐rich catalyst (PrC) shows a Faradaic efficiency for ethylene over 40% at 400 mA cm^?2. At ?0.64 versus reversible hydrogen electrode, the highest C₂₊/C₁ product ratio of 4.8 is achieved, with C₂₊ Faradaic efficiency over 61%. Additionally, the catalyst exhibits a stable performance for 24 h at a constant current density of 200 mA cm^?2.     

Graphitic Petal Electrodes for All‐Solid‐State Flexible Supercapacitors

The charge storage characteristics of a composite nanoarchitecture with a highly functional 3D morphology are reported. The electrodes are formed by the electropolymerization of aniline monomers into a nanometer‐thick polyaniline (PANI) film that conformally coats graphitic petals (GPs) grown by microwave plasma chemical vapor deposition (MPCVD) on conductive carbon cloth (CC). The hybrid CC/GPs/PANI electrodes yield results near the theoretical maximum capacitance for PANI of 2000 F g^?1 (based on PANI mass) and a large area‐normalized specific capacitance of ≈2.6 F cm^?2 (equivalent to a volumetric capacitance of ≈230 F cm^?3) at a low current density of 1 A g^?1 (based on PANI mass). The specific capacitances remain above 1200 F g^?1 (based on PANI mass) for currents up to 100 A g^?1 with correspondingly high area‐normalized values. The hybrid electrodes also exhibit a high rate capability with an energy density of 110 Wh kg^?1 and a maximum power density of 265 kW kg^?1 at a current density of 100 A g^?1. Long‐term cyclic stability is good (≈7% loss of initial capacitance after 2000 cycles), with coulombic efficiencies >99%. Moreover, prototype all‐solid‐state flexible supercapacitors fabricated from these hybrid electrodes exhibit excellent energy storage performance.     

Integrating ZnO Microwires with Nanoscale Electrodes Using a Suspended PMMA Ribbon for Studying Reliable Electrical and Electromechanical Properties

A simple method for making electrical connections to ZnO microwires is reported. By using a suspended poly(methyl methacrylate) (PMMA) ribbon, it is shown that it is possible to electrically contact 1–2 μm diameter ZnO microwires with metal electrodes that are only 90 nm thick. The contact resistances of ZnO microwire‐based electronic devices fabricated by this method are lower than those of devices fabricated by standard electron‐beam lithography and evaporation processes. As one of the possible device applications from this fabrication method, suspended ZnO microwire‐based electromechanical devices are produced and their piezoelectric properties are investigated. Piezoelectric‐induced current is detected when the suspended microwires are induced to vibrate at their resonant frequency. This fabrication method can be readily and generally applied to prepare nanoscale electrodes on micrometer‐sized materials and provides a convenient means for studying their electrical and electromechanical phenomena in a reliable manner.     

High‐Performance Suspended Particle Devices Based on Copper‐Reduced Graphene Oxide Core–Shell Nanowire Electrodes

Smart windows are one of the key components of so‐called “green” buildings. These windows are based on an actively switchable electro‐optic material that is sandwiched between two transparent electrodes. Although great progress has been made in identifying the optimal materials for such active windows, there is still a great need to improve their key elements, especially the performance of the transparent electrodes. Here, a new suspended particle device (SPD), holding a great potential for smart window applications, which is built upon copper‐reduced graphene oxide (Cu‐rGO) core–shell nanowire (NW) films as a transparent conductive electrode is reported. With the wrapping of rGO, the Cu NW electrodes demonstrate both high optical transparency and electrical conductivity, as well as significantly improved stability under various testing conditions. The novel sandwich‐structured SPDs, based on these electrodes, show a large change in their optical transmittance (42%) between “on” and “off” states, impressively fast switching time and superior stability. These high performances are comparable to those of the SPDs based on indium tin oxide electrodes. These promising results pave the way for the electrodes to be an integral part of a variety of optoelectronic devices, including energy‐friendly and flexible electronics.     

Minimizing the Electrolyte Volume in Li–S Batteries: A Step Forward to High Gravimetric Energy Density

Sulfur electrodes confined in an inert carbon matrix show practical limitations and concerns related to low cathode density. As a result, these electrodes require a large amount of electrolyte, normally three times more than the volume used in commercial Li‐ion batteries. Herein, a high‐energy and high‐performance lithium–sulfur battery concept, designed to achieve high practical capacity with minimum volume of electrolyte is proposed. It is based on deposition of polysulfide species on a self‐standing and highly conductive carbon nanofiber network, thus eliminating the need for a binder and current collector, resulting in high active material loading. The fiber network has a functionalized surface with the presence of polar oxygen groups, with the aim to prevent polysulfide migration to the lithium anode during the electrochemical process, by the formation of S–O species. Owing to the high sulfur loading (6 mg cm^?2) and a reduced free volume of the sulfide/fiber electrode, the Li–S cell is designed to work with as little as 10 µL cm^?2 of electrolyte. With this design the cell has a high energy density of 450 Wh kg^?1, a lifetime of more than 400 cycles, and the possibility of low cost, by use of abundant and eco‐friendly materials.     

All‐Manganese‐Based Binder‐Free Stretchable Lithium‐Ion Batteries

Advanced electrode materials with bendability and stretchability are critical for the rapid development of fully flexible/stretchable lithium‐ion batteries. However, the sufficiently stretchable lithium‐ion battery is still underdeveloped that is one of the biggest challenges preventing from realizing fully deformable power sources. Here, a low‐temperature hydrothermal synthesis of a cathode material for stretchable lithium‐ion battery is reported by the in situ growth of LiMn₂O₄ (LMO) nanocrystals inside 3D carbon nanotube (CNT) film networks. The LMO/CNT film composite has demonstrated the chemical bonding between the LMO active materials and CNT scaffolds, which is the most important characteristic of the stretchable electrodes. When coupled with a wrinkled MnO_x /CNT film anode, a binder‐free, all‐manganese‐based stretchable full battery cell is assembled which delivers a high average specific capacity of ≈97 mA h g^?1 and stabilizes after over 300 cycles with an enormous strain of 100%. Furthermore, combining with other merits such as low cost, natural abundance, and environmentally friendly, the all‐manganese design is expected to accelerate the practical applications of stretchable lithium‐ion batteries for fully flexible and biomedical electronics.