A multiswitchable poly(terthiophene) bearing a spiropyran functionality: understanding photo and electrochemical control

An electroactive nitrospiropyran-substituted polyterthiophene, 2-(3,3′′-dimethylindoline-6′-nitrobenzospiropyranyl)ethyl 4,4′′-didecyloxy-2,2′:5′,2′′-terthiophene-3′-acetate, has been synthesized for the first time. The spiropyran, incorporated into the polymer backbone by covalent attachment to the alkoxyterthiophene monomer units, leads to multiple coloured states as a result of both electrochemical isomerization of the spiropyran moiety to merocyanine forms as well as electrochemical oxidation of the polyterthiophene backbone and the merocyanine substituents. While electrochemical polymerization of the terthiophene monomer could occurs without the apparent oxidation of the spiropyran, the subsequent electrochemistry is complex and clearly involves this substituent. In order to understand this complex behaviour, the first detailed electrochemical study of the oxidation of the precursor spiropyran, 1-(2-hydroxyethyl)-3,3-dimethylindoline-6’-nitrobenzospiropyran, was undertaken, showing that, in solution, an irreversible electrochemical oxidation of the spiropyran occurs leading to reversible redox behaviour of at least two merocyanine isomers. With these insights, an extensive electrochemical and spectroelectrochemical study of the nitrospiropyran-substituted polyterthiophene films reveals an initial irreversible electrochemical oxidative ring opening of the spiropyran to oxidized merocyanine. Subsequent reduction and cyclic voltammetry of the resulting nitromerocyanine-substituted polyterthiophene film gives rise to the formation of both merocyanine π-dimers or oligomers and π-radical cation dimers, between polymer chains. Although merocyanine formation is not electrochemically reversible, the spiropyran can be photochemically regenerated, at least in part, through irradiation with visible light. SEM and AFM images support the conclusion that the bulky spiropyran substituent is electrochemically isomerizes to the planar merocyanine moiety affording a smoother polymer film. The conductivity of the freestanding polymer film was found to be 0.4 S cm-1

Photo-chemopropulsion – light-stimulated movement of microdroplets

The controlled movement of a chemical container by the light-activated expulsion of a chemical fuel, named here photo-chemopropulsion , is an exciting new development in the array of mechanisms employed for controlling the movement of microvehicles, herein represented by lipid-based microdroplets. This chemopropulsion effect can be switched on and off, and is fully reversible

Negative phototaxis behaviour of organic droplets in channels

Along the evolutionary path from single cells to multicellular organisms with a central nervous system, there are species of intermediate complexity that possess many autonomous cells programmed to respond to environmental stimuli. One of the more striking responses is phototaxis[1], in which motile organisms adjust their locomotory path according to the incident light in a finely controlled manner, either towards or against the light source (positive or negative phototaxis). Inspired by them we developed an inanimate/chemical system in which an organic droplet is self-propelled in response to a photo-stimulus. The centimetre-scale directional movement of the organic droplet on the aqueous solution is powered by the combination of photo-induced pH change and surface tension effects

Alkaline Fuel Cells with Novel Gortex-Based Electrodes are Powered Remarkably Efficiently by Methane Containing 5% Hydrogen

Numerous electric and gas utilities are actively pursuing power-to-gas technology, which involves using unwanted, excess renewable energy to manufacture hydrogen gas (H 2 ) that is then injected into the existing natural gas pipeline network in 5-10% by volume. This work reports an alkaline fuel cell that has the potential to harness such gas mixtures for downstream generation of electric power. The fuel cell, which employs novel Gortex-based electrodes layered with Pd/Pt catalysts, generates electricity remarkably efficiently when fuelled with methane (CH 4 ) containing 5% hydrogen. Methane constitutes the major component of natural gas. The fuel cell has been studied over a range of hydrogen to methane ratios using Tafel plots and electrochemical impedance spectroscopy. These show that, in terms of fundamental operation, there is, astonishingly, almost no difference between using pure hydrogen and 5% hydrogen in methane, as the fuel. The Gortex electrodes and alkaline electrolyte are clearly able to utilize the dilute hydrogen as a fuel with remarkable efficiency. The methane acts as an inert carrier gas and is not consumed

A study of TiO2 binder-free paste prepared for low temperature dye-sensitized solar cells

A binder-free titania paste was prepared by chemical modification of an acidic TiO2 sol with ammonia. By varying the ammonia concentration, the viscosity of the acidic TiO2 suspension increased, thereby allowing uniform films to be cast. The photoelectrochemical performance of TiO2 electrodes, cast as single layers, was dependent on the thermal treatment cycle. Fourier transform infrared spectroscopy was used to characterize the extent of residual organics and found that acetates from the TiO2 precursor preparation were retained within the electrode structure after thermal treatment at 150 °C. Electrodes of nominal thickness 4 lm produced an energy conversion efficiency as high as 5.4% using this simple thermal treatment

An electrochemical cell with Gortex-based electrodes capable of extracting pure hydrogen from highly dilute hydrogen-methane mixtures

In this work we report a novel liquid-acid electrochemical cell containing Gortex-based gas diffusion electrodes, layered with suitable catalysts and current collectors, that is capable of sustainably extractin g pure hydrogen from methane mixtures containing as little as 5% hydrogen. The origin of its efficiency appears to derive from the solid-liquid interface between the solid Gortex electrodes and the liquid electrolyte, as well as the high proton conductivity of the electrolyte. This interface and electrolyte exhibit an efficiency for reaction that greatly exceeds that achieved by the comparable solid-solid interface and proton conductor in Proton Exchange Membrane Fuel Cell (PEMFC) technology. We report hydrogen yields and recovery by the cell from a range of methane-hydrogen mixtures. Electrochemical impedance spectroscopy has been used to characterise the cell and to illuminate the system limitations

Electrotactic ionic liquid droplets

To our knowledge, this work describes the first example of electro-guided, self-propelled droplets composed solely of an ionic liquid (IL), namely trihexyl(tetradecyl)phosphonium chloride ([P6,6,6,14][Cl]). These self-propelled droplets travel along an aqueous-air boundary to desired destinations within the fluidic network. Electrotactic movement of the droplets is due to asymmetric electro-stimulated release of a constituent of the IL droplet, the [P6,6,6,14]+ ion, which is a very efficient cationic surfactant, through electrochemically generated Cl- gradients. The direction and speed of movement can be controlled by switching the impressed voltage (typically 5 - 9V) ON or OFF, and by changing the polarity of the electrodes in contact with the electrolyte solution. The Cl- gradients required for droplet movement are electrochemically generated using 3D printed electrodes which are embedded within the fluidic channels. On demand creation of these Cl- gradients electrochemically allows reversible droplet movement over expended periods of time, and provides a means for precise control over the droplet trajectory

Electro-tactic ionic liquid droplets

Here we report for the first time electro-guided, self-propelled droplets, which are composed solely of an ionic liquid (IL), namely trihexyl(tetradecyl)phosphonium chloride ([P6,6,6,14][Cl]). These self-propelled droplets travel along an aqueous-air boundary and are guided to specific destinations within the fluidic network through the use of electro-chemically generated Cl- gradients. The direction of movement can be controlled by switching the impressed voltage (9V, ON or OFF) and polarity of the electrodes in contact with the electrolyte solution. Controlled release of surfactants has been investigated previously as a method of controlling surface tension in aqueous systems in order to achieve spontaneous movement of droplets at the air-liquid interface [1,2]. When a surfactant is released into an aqueous solution, the surface tension is lowered. Liquid flows from areas of low surface tension to areas of high surface tension, a phenomenon known as the Marangoni effect. Using stimuli-responsive surfactants, smart droplets have been designed which can solve complex mazes [1] or can be attracted or repelled by light [2], in a contactless manner. Electro-tactic movement of the droplets is due to the controlled release of the [P6,6,6,14]+, a very efficient cationic surfactant, which is a constituent of the IL droplet (Fig. 1). The asymmetric release of the cationic surfactant is controlled through modulation of the IL counter anion (Cl-) solubility, as this controls the rate of release of the cationic surfactant in order to maintain electroneutrality within the droplet. The solubility of the [P6,6,6,14]+ is limited in aqueous solutions and is dependent on the local ionic strength of the solution (Fig. 2). Therefore in ionic strength gradients there is a differential release of the surfactant from droplet boundary into the solution, which in turn results in an asymmetrical surface tension gradient around the droplet. This leads to Marangoni like flows, which propel the droplet from areas of low surface tension to areas of high surface tension. The chip used in this work was 3D printed (Objet350 Connex printer) as were the titanium mesh electrodes (Realizer SLM-50) embedded in the chip. By applying an external electric field to the solution, a [P6,6,6,14][Cl] droplet can be moved from the cathode (-) to the anode (+) (Fig. 3). The external electric field causes migration of ions, which results in concentration enrichment of ions in the proximity of the electrodes [3], Na+ at the cathode (starting position) and Cl- at the anode (destination). The resulting ion migration towards the electrodes creates an ionic strength gradient within the channel which controls the movement of the droplet. Additionally, the applied electric field causes Faradic arrangement of the charged ions within the IL droplet [3]. This also creates concentration gradients of the ions within the droplet, reinforcing the droplet movement mechanism. The electro-generation of gradients therefore provides a simple means to control the speed and direction of movement of droplets within fluidic channels in a very flexible manner