Suchergebnisse

The dynamics of ion intercalation into solid matrices influences the performance of key components in most energy storage devices (Li-ion batteries, supercapacitors, fuel cells, etc.). Electrochemical methods provide key information on the thermodynamics and kinetics of these ion transfer processes but are restricted to matrices supported on electronically conductive substrates. In this article, the electrified liquid|liquid interface is introduced as an ideal platform to probe the thermodynamics and kinetics of reversible ion intercalation with non-electronically active matrices. Zinc(II) meso-tetrakis(4-carboxyphenyl)porphyrins were self-assembled into floating films of ordered nanostructures at the water|trifluorotoluene interface. Electrochemically polarising the aqueous phase negatively with respect to the organic phase lead to organic ammonium cations intercalating into the zinc porphyrin nanostructures by binding to anionic carboxyl sites and displacing protons through ion exchange at neutral carboxyl sites. The cyclic voltammograms suggested a positive cooperativity mechanism for ion intercalation linked with structural rearrangements of the porphyrins within the nanostructures, and were modelled using a Frumkin isotherm. The model also provided a robust understanding of the dependence of the voltammetry on the pH and organic electrolyte concentration. Kinetic analysis was performed using potential step chronoamperometry, with the current transients composed of "adsorption" and nucleation components. The latter were associated with domains within the nanostructures where, due to structural rearrangements, ion binding and exchange took place faster. This work opens opportunities to study the thermodynamics and kinetics of purely ionic ion intercalation reactions (not induced by redox reactions) in floating solid matrices using any desired electrochemical method. ; A. G.-Q. acknowledges funding received from an Irish Research Council Government of Ireland Postdoctoral Fellowship Award (grant number ...

Programmed cell death via apoptosis is a natural defence against excessive cell division, crucial for foetal development to maintenance of homeostasis and elimination of precancerous and senescent cells. Here we demonstrate an electrified liquid bio-interface that replicates the molecular machinery of the inner mitochondrial membrane at the onset of apoptosis. By mimicking in vivo cytochrome c (Cyt c) interactions with cell membranes, our platform allows us to modulate the conformational plasticity of the protein by simply varying the electrochemical environment at an aqueous|organic interface. Remarkably, we observe interfacial electron transfer between an organic electron donor decamethylferrocene and O2, electrocatalysed by Cyt c. This interfacial reaction requires partial Cyt c unfolding, mimicking Cyt c in vivo peroxidase activity. As proof-of-concept, we use our electrified liquid bio-interface to identify drug molecules, such as bifonazole, that can potentially downregulate Cyt c and protect against uncontrolled neuronal cell death in neurodegenerative disorders. ; D.T. thanks Science Foundation Ireland (SFI) for computing resources at the SFI/Higher Education Authority Irish Center for High-End Computing (ICHEC). A.G.-Q. acknowledges funding received from an Irish Research Council (IRC) Government of Ireland Postdoctoral Fellowship Award (Grant Number GOIPD/2018/252). G.H. and M.D. are grateful to the French Programme Investissement d'Avenir (PIA) "Lorraine Université d'Excellence" (Reference no. ANR-15-IDEX-04-LUE). M.D.S. and G.H. are grateful to the support of the IRC and Campus France for travel support between the French and Irish groups through their joint ULYSSES programme. DT thanks Science Foundation Ireland (SFI) for support (awards Grant Numbers 15/CDA/3491 and 12/RC/2275_P2).

Soft molecular assemblies that respond reversibly to external stimuli are attractive materials as on/off switches, in optoelectronic, memory and sensor technologies. In this article, we present the reversible structural rearrangement of a soft porphyrin membrane under an electrical potential stimulus in the absence of solid-state architectures. The free-floating porphyrin membrane lies at the interface between immiscible aqueous and organic electrolyte solutions and is formed through interfacial self-assembly of zinc(II) meso-tetrakis(4-carboxyphenyl)porphyrins (ZnPor). A potential difference between the two immiscible electrolyte solutions induces the intercalation of bis(triphenylphosphoranylidene)ammonium cations from the organic electrolyte that exchange with protons in the porphyrin membrane. In situ UV/vis absorbance spectroscopy shows that this ionic intercalation and exchange induces a structural interconversion of the individual porphyrin molecules in the membrane from an H- to a J-type molecular configuration. These structural rearrangements are reversible over 30 potential cycles. In situ polarisation-modulation fluorescence spectroscopy further provides clear evidence of structural interconversion of the porphyrin membrane, as intercalation of the organic electrolyte cations significantly affects the latter's emissive properties. By adjusting the pH of the aqueous phase, additional control of the electrochemically reversible structural interconversion can be achieved, with total suppression at pH 3. ; A.G.-Q. acknowledges funding received from an Irish Research Council Government of Ireland Postdoctoral Fellowship Award (Grant Number GOIPD/2018/252). H.N. acknowledges a Grant-in-Aid for Scientific Research (C) (No.19K05541) from Japan Society for the Promotion of Science (JSPS). S. Y. thanks the JSPS Research Fellowship for Young Scientists (No.17J02009).

Miniaturization of electrochemical detection methods for point-of-care-devices is ideal for their integration and use within healthcare environments. Simultaneously, the prolific pathogenic bacteria Pseudomonas aeruginosa poses a serious health risk to patients with compromised immune systems. Recognizing these two factors, a proof-of-concept electrochemical method employing a micro-interface between water and oil (w/o) held at the tip of a pulled borosilicate glass capillary is presented. This method targets small molecules produced by P. aeruginosa colonies as signalling factors that control colony growth in a pseudo-multicellular process known as quorum sensing (QS). The QS molecules of interest are 4‐hydroxy‐2‐heptylquinoline (HHQ) and 2‐heptyl‐3,4‐dihydroxyquinoline (PQS, Pseudomonas quinolone signal). Hydrophobic HHQ and PQS molecules, dissolved in the oil phase, were observed electrochemically to facilitate proton transfer across the w/o interface. This interfacial complexation can be exploited as a facile electrochemical detection method for P. aeruginosa and is advantageous as it does not depend on the redox activity of HHQ/PQS. Interestingly, the limit-of-linearity is reached as [H+]≈[ligand]. Density functional theory calculations were performed to determine the proton affinities and gas-phase basicities of HHQ/PQS, as well as elucidate the likely site of stepwise protonation within each molecule. ; E.D.B. acknowledges funding received from an Irish Research Council Government of Ireland Postgraduate Scholarship Award (grant number GOIPG/2016/1217). This publication has emanated from research by M.D.S. and A.F.M.-O. supported by the European Research Council through a Starting Grant (agreement no. 716792) and in part by a research grant from Science Foundation Ireland (SFI) (grant number 13/SIRG/2137). G.M.G. and R.S. thank the Irish Research Council for funding. T.J.S is grateful to NSERC for funding with an NSERC Discovery Grant.

Breakthrough alternative technologies are urgently required to alleviate the critical need to decarbonise our energy supply. We showcase non-conventional approaches to battery and solar energy conversion and storage (ECS) system design that harness key attributes of immiscible electrolyte solutions, especially the membraneless separation of redox active species and ability to electrify certain liquid-liquid interfaces. We critically evaluate the recent development of membraneless redox flow batteries based on biphasic systems, where one redox couple is confined to an immiscible ionic liquid or organic solvent phase, and the other couple to an aqueous phase. Common to all solar ECS devices are the abilities to harvest light, leading to photo-induced charge carrier separation, and separate the products of the photo-reaction, minimising recombination. We summarise recent progress towards achieving this accepted solar ECS design using immiscible electrolyte solutions in photo-ionic cells, to generate redox fuels, and biphasic "batch" water splitting, to generate solar fuels. ; This publication has emanated from research by M.D.S. and A.F.M.-O. supported by the European Research Council through a Starting Grant (agreement no.716792) and in part by a research grant from Science Foundation Ireland (SFI) (grant number 13/SIRG/2137). A.G.-Q. acknowledges funding received from an Irish Research Council Government of Ireland Postdoctoral Fellowship Award (grant number GOIPD/2018/252). P.P. gratefully acknowledges the Academy Research Fellow funding from the Academy of Finland (grant number 315739).

We present a mathematical model to study the steady-state performance of a membrane-less reversible redox flow battery formed by two immiscible electrolytes that spontaneously form a liquid-liquid system separated by a well defined interface. The model assumes a two-dimensional battery with two coflowing electrolytes and flat electrodes at the channel walls. In this configuration, the analysis of the far downstream solution indicates that the interface remains stable in all the parameter range covered by this study. To simplify the description of the problem, we use the dilute solution theory to decouple the calculation of the velocity and species concentration fields. Once the velocity field is known, we obtain the distribution of the mobile ionic species along with the current and the electric potential field of the flowing electrolyte solution. The numerical integration of the problem provides the variation of the battery current density Iapp with the State of Charge (SoC) for different applied cell voltages Vcell. A detailed analysis of the concentration density plots indicates that the normal operation of the battery is interrupted when reactant depletion is achieved near the negative electrode both during charge and discharge. The effect of the electrolyte flow on the performance of the system is studied by varying the Reynolds, Re and Péclet, Pe, numbers. As expected, the flow velocity only affects the polarization curve in the concentration polarization region, when is well below the equilibrium potential, resulting in limiting current densities that grow with Re. ; This work has been partially funded by the Spanish Agencia Estatal de Investigación under projects (PID2019-106740RB- I00 and PID2019-108592RB-C41/AEI/10.13039/50110 0 011033), by Grant IND2019/AMB-17273 of the Comunidad de Madrid and by project MFreeB which have received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant Agreement No. 726217). D. Ruiz-Martín acknowledges the support of an FPI predoctoral fellowship (BES-2016-078629) under project ENE2015-68703-C2-1-R (MINECO/FEDER, UE) and the insigh- ful conversations with professor Mark Blyth during her research visit at the University of East Anglia (UK).

Redox Flow Batteries (RFB) stand out as a promising energy storage technology to mitigate the irregular energy generation from renewable sources. However, some hurdles limit their massive implementation including high cost of vanadium and the poor-performance of ion-selective membranes. Recently, we presented a revolutionary Membrane-Free Battery based on organic aqueous/nonaqueous immiscible electrolytes that eludes both separators and vanadium compounds. Here, we demonstrate the feasible application of this archetype in Aqueous Biphasic Systems (ABS) acting as an unprecedented Total Aqueous Membrane-Free Battery. After evaluating several organic molecules, methylviologen (MV) and 2,2,6,6-Tetramethyl-1-piperidinyloxy (TEMPO) were selected as active species due to their optimum electrochemical behavior and selective partitioning between the phases. When connected electrically, this redox-active ABS becomes a Membrane-Free Battery with an open circuit voltage (OCV) of 1.23 V, high peak power density (23 mWcm-2) and excellent long-cycling performance (99.99% capacity retention over 550 cycles). Moreover, essential aspects of this technology such as the crossover, controlled here by partition coefficients, and the inherent self-discharge phenomena were addressed for the first time. These results point out the potential of this pioneering Total Aqueous Membrane-Free Battery as a new energy storage technology. ; This work was partly developed within the scope of the project CICECO-Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT ref. UID/CTM/50011/2013). C.M.S.S.N. also acknowledges FCT for the postdoctoral grant SFRH/BPD/109057/2015. MFreeB project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 726217). The results reflect only the authors' view and the Agency is not responsible for any use that may be made of the information they contain. We also gratefully acknowledge financial support from ...

Flexible and scalable energy storage solutions are necessary for mitigating fluctuations of renewable energy sources. The main advantage of redox flow batteries is their ability to decouple power and energy. However, they present some limitations including poor performance, short-lifetimes, and expensive ion-selective membranes as well as high price, toxicity, and scarcity of vanadium compounds. We report a membrane-free battery that relies on the immiscibility of redox electrolytes and where vanadium is replaced by organic molecules. We show that the biphasic system formed by one acidic solution and one ionic liquid, both containing quinoyl species, behaves as a reversible battery without any membrane. This proof-of-concept of a membrane-free battery has an open circuit voltage of 1.4 V with a high theoretical energy density of 22.5 WhL-1, and is able to deliver 90% of its theoretical capacity while showing excellent long-term performance (coulombic efficiency of 100% and energy efficiency of 70%). ; We also gratefully acknowledge financial support from the Spanish Government through projects ENE2012-31516 and MAT2015-64167-C2-1- R (MINECO/FEDER, UE). P.N. acknowledges the Spanish Government for the personnel grant through the "FPI" program.

Lately, the field of redox flow batteries is flourishing because of the emergence of new redox chemistries, including organic compounds, new electrolytes, and innovative designs. Recently, we reported an original membrane-free battery concept based on the mutual immiscibility of an aqueous catholyte containing hydroquinone and an ionic liquid anolyte containing para-benzoquinone as redox species. Here, we investigate the versatility of this concept exploring the electrochemical performance of 10 redox electrolytes based on different solvents, such as propylene carbonate, 2-butanone, or neutral-pH media, and containing different redox organic molecules, such as 2,2,6,6-tetramethylpiperidine-1-oxyl, 4-hydroxy- 2,2,6,6-tetramethylpiperidine1-oxyl (OH-TEMPO), or substituted anthraquinones. The most representative electrolytes were paired and used as immiscible anolyte−catholyte in 5 different membrane-free batteries. Those batteries with substituted anthraquinones in the anolyte exhibited up to 50% improved open-circuit voltage (2.1 V), an operating voltage of 1.75 V, and 62% higher power density compared with our previous work. On the other hand, the partition coefficient of redox molecules between the two immiscible phases and the inherent self-discharge occurring at the interphase are revealed as intrinsic features affecting the performance of this type of membrane-free battery. It was successfully demonstrated that the functionalization of redox molecules is an interesting strategy to tune the partition coefficients mitigating the crossover that provokes low battery efficiency. As a result, the cycling life of a battery having OH-TEMPO as active species in the catholyte and containing propylene carbonate-based anolyte was evaluated over 300 cycles, achieving 85% capacity retention. These results demonstrated the huge versatility and countless possibilities of this new membrane-free battery concept. ; Authors gratefully acknowledge financial support from the Spanish government through projects ENE2012-31516 and ...

Dip coating is a common technique used to cover a solid surface with a thin liquid film, the thickness of which was successfully predicted by the theory developed in the 1940s by Landau & Levich (Acta Physicochem. URSS, vol. 17, 1942, pp. 141–153) and Derjaguin (Acta Physicochem. URSS, vol. 20, 1943, pp. 349–352). In this work, we present an extension of their theory to the case where the dipping bath contains two immiscible liquids, one lighter than the other, resulting in the entrainment of two thin films on the substrate. We report how the thicknesses of the coated films depend on the capillary number, on the ratios of the properties of the two liquids and on the relative thickness of the upper fluid layer in the bath. We also show that the liquid/liquid and liquid/gas interfaces evolve independently from each other as if only one liquid were coated, except for a very small region where their separation falls quickly to its asymptotic value and the shear stresses at the two interfaces peak. Interestingly, we find that the final coated thicknesses are determined by the values of these maximum shear stresses. ; L.C. acknowledges funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 882429. B.S. thanks the F.R.S-FNRS for financial support. A.A.K. thanks Universidad Carlos III de Madrid and Banco Santander for the financial support of his Chair of Excellence. J.R.-R. acknowledges the support of the Spanish Ministry of Economy and Competitiveness through grants DPI2017-88201-C3-3-R and DPI2018-102829-REDT, partly funded with European funds

Electrochemistry is an old but still flourishing field of research due to the importance of the efficiency and kinetics of electrochemical reactions in industrial processes and (bio-)electrochemical devices. The heterogeneous electron transfer from an electrode to a reactant in the solution has been well studied for metal, semiconductor, metal oxide, and carbon electrodes. For those electrode materials, there is little correlation between the electronic transport within the electrode material and the electron transfer occurring at the interface between the electrode and the solution. Here, we investigate the heterogeneous electron transfer between a conducting polymer electrode and a redox couple in an electrolyte. As a benchmark system, we use poly(3,4-ethylenedioxythiophene) (PEDOT) and the Ferro/ferricyanide redox couple in an aqueous electrolyte. We discovered a strong correlation between the electronic transport within the PEDOT electrode and the rate of electron transfer to the organometallic molecules in solution. We attribute this to a percolation-based charge transport within the polymer electrode directly involved in the electron transfer. We show the impact of this finding by optimizing an electrochemical thermogalvanic cell that transforms a heat flux into electrical power. The power generated by the cell increased by four orders of magnitude on changing the morphology and conductivity of the polymer electrode. As all conducting polymers are recognized to have percolation transport, we believe that this is a general phenomenon for this family of conductors. ; Funding agencies: Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University Faculty Grant [SFO-Mat-LiU 2009-00971]

The reversible oxidation and reduction of Cytochrome c (Cyt c) is demonstrated with a closed bipolar electrochemical cell (CBPEC). Herein, a 4-electrode configuration was studied with the opposite poles of the bipolar electrode resting in separate aqueous and organic electrolyte solutions, respectively. Using biocompatible indium tin oxide (ITO) slides as the bipolar electrode poles, we investigated the influence of the redox potential of the reductant (decamethyferrocene or dimethylferrocene) in a trifluorotoluene organic phase on the observed voltammetry. Reversible electron transfer was only observed between Cyt c and decamethylferrocene. Use of the weaker dimethylferrocene as the reductant required a larger external bias of the driving electrodes to initiate the electron transfer reaction between the two poles of the bipolar electrode. Consequently, the surface of the ITO slide at the aqueous pole experienced a significant negative cathodic potential and underwent irreversible reduction. The biphasic setup using the 4-electrode CBPEC provides insights into electron transfer processes at an interface between two immiscible electrolyte solutions (ITIES), highlighting the strong probability of observing interfacial electron transfer between decamethylferrocene (but not dimethylferrocene) and Cyt c within the short ~ 1 V polarisable potential window available at an ITIES. ; A. G.-Q. acknowledges funding received from an Irish Research Council Government of Ireland Postdoctoral Fellowship Award (grant number GOIPD/2018/252). G. H. is grateful to the French Programme Investissement d'Avenir (PIA) "Lorraine Université d'Excellence" (Reference No. ANR-15-IDEX-04-LUE). for the partial financial support of this work. The authors are grateful to the support of the Irish Research Council and Campus France for travel support between the French and Irish groups through their joint ULYSSES programme.