No abstract

Gold nanoparticle (Au NP) mirrors, which exhibit both high reflectance and electrical conductance, were self-assembled at a [heptane + 1,2-dichloroethane]/water liquid/liquid interface. The highest reflectance, as observed experimentally and confirmed by finite difference time domain calculations, occurred for Au NP films consisting of 60 nm diameter NPs and approximate monolayer surface coverage. Scanning electrochemical microscopy approach curves over the interfacial metallic NP films revealed a transition from an insulating to a conducting electrical material on reaching a surface coverage at least equivalent to the formation of a single monolayer. Reflectance and conductance transitions were interpreted as critical junctures corresponding to a surface coverage that exceeded the percolation threshold of the Au NP films at the [heptane + 1,2-dichloroethane]/water interface.

Redox flow batteries (RFBs) are particularly well suited for storing the intermittent excess supply of renewable electricity, so-called "junk" electricity. Conventional RFBs are charged and discharged electrochemically, with electricity stored as chemical energy in the electrolytes. In the RFB system reported here, the electrolytes are conventionally charged but are then chemically discharged over catalytic beds in separate external circuits. The catalytic reaction of particular interest generates hydrogen gas as secondary energy storage. For demonstration, indirect water electrolysis was performed generating hydrogen and oxygen in separate catalytic reactions. The electrolyte containing V(II) was chemically discharged through proton reduction to hydrogen on a molybdenum carbide catalyst, whereas the electrolyte comprising Ce(IV) was similarly discharged in the oxidation of water to oxygen on a ruthenium dioxide catalyst. This approach is designed to complement electrochemical energy storage and may circumvent the low energy density of RFBs especially as hydrogen can be produced continuously whilst the RFB is charging. Broader contextRenewable energy technologies have evolved to deliver hundreds of terawatt hours of electricity, yet without its direct utilization in the grid part of that energy could be lost. In order to establish a thriving renewable energy economy it is of paramount importance that intermediate energy storage systems be developed. Mediating electricity production and usage will overcome the issues relating to intermittency, which presently limits widespread dependence on wind and photovoltaic power. Various approaches are under development, but no single approach is liable to address the issue as a whole. Combining technologies and hybridizing storage systems to adapt to a multifaceted energy future is the more viable option. This paper discusses one such hybrid system, in which electrochemical energy storage is combined with renewable hydrogen production, delivering a dual platform for energy storage as an electrochemical and chemical medium. † Electronic supplementary information (ESI) available: Charging and discharging curves, cyclic voltammetry, UV-vis spectra of V(II) and V(III), a picture of the cell, and details on the kinetics measurement and calculations. See

Keywords:redox flow battery redox targeting redox mediator solid charge storage materials polyaniline A B S T R A C TIn this work, the viability of polyaniline as a solid charge storage material in an aqueous redox-mediated flow battery is investigated. Fe(III/II) and V(IV/III) were identified as potential redox mediators to target the emeraldine-pernigraniline and leucoemeraldine-emeraldine redox transitions of the polymer. An indirect chemical cycling method was developed and used to investigate the charging/discharging of the polymer by the selected redox mediators. With Fe(III/II) as a redox mediator, respectable specific capacity and cycling stability were demonstrated over 25 cycles. V(IV/III) was deemed unsuitable as a redox mediator, due to rather poor kinetics. When added to the electrolyte tanks of a complete flow battery, a conductive composite of polyaniline and carbon black provided a significant improvement in capacity, exhibiting a specific capacity of 64.8 mA h g À1 at a current density of 38.5 mA cm À2. This represents a three-fold improvement in volumetric capacity, compared with the electrolyte alone. Moreover, the addition of the polyaniline composite was observed to lower the average potential at the positive electrode, providing a considerable improvement in voltage efficiency. This work demonstrates the potential of utilizing redox mediators to enable bulk solid-phase charge storage in the tanks of aqueous redox flow batteries.

Graphene oxide (GO) in water was reduced heterogeneously by decamethylferrocene (DMFc) or ferrocene (Fc) in 1,2-dichloroethane (DCE), which could then act as a catalyst for an interfacial oxygen reduction reaction (ORR) and production of hydrogen peroxide (H 2 O 2 ). The reduced graphene oxide (RGO) produced at the liquid/liquid interface was characterized by using electron microscopy, spectroscopy (Raman, infrared, and electron energy loss), and electrochemical techniques.The oxygenated functional groups at the edge/defects of the RGO surface activate O 2 adsorption, forming superoxidelike adducts that can be protonated at the liquid/liquid interface and reduced by DMFc or Fc. This process is facilitated by the higher electrical conductivity of the RGO sheets. The key feature of this catalytic reaction is the in situ partial-reduction of GO at the liquid/liquid interface, forming an efficient and inexpensive catalyst for the production of H 2 O 2 .Electrochemistry at polarized interfaces between two immiscible electrolyte solutions (ITIES) has developed over the past 30 years, in which charge-transfer (electron-and ion-transfer) reactions have found applications in areas such as phase-transfer catalysis, solvent-extraction processes, chemical sensing, solar-energy-conversion systems, drug release and delivery, and in mimicking the function of biological membranes. [1] Liquid/liquid interfaces provide a unique platform at which to study ORRs, at which aqueous protons react with organic solubilized electron donors in the absence or presence of adsorbed catalysts, usually through a proton-coupled electron-transfer (PCET) reaction. [2] The molecular catalysts studied include cobalt, [3] free-base porphyrins, [4] and in situ-deposited platinum particles. [5] The ORR proceeds either by a 4 e À /4 H + pathway to produce water or a 2 e À /2 H + route to yield H 2 O 2 , which is considered a green oxidant.H 2 O 2 is widely used in many industrial areas, particularly in the chemical industry or for environmental protection, and is currently produced on an industrial scale through the biphasic anthrahydroquinone oxidation (AO) process (representing ca. 95 % of the world's H 2 O 2 production). [6] Generally, anthrahydroquinone is oxidized by O 2 to produce H 2 O 2 and anthraquinone and, subsequently, the formed anthraquinone is reduced back to the anthrahydroquinone by using H 2 in the presence of a metal catalyst. Both reactions occur in the organic phase, and H 2 O 2 is recovered by extraction to the aqueous phase. [6] The advantage of the AO process is the very high yield of H 2 O 2 generated per cycle. Conversely, side reactions generating organic byproducts need to be dealt with by regenerating the solution and by using separation techniques to eliminate such impurities. Conceptually, following the AO process, the reduction of O 2 was investigated at quinone-modified carbon surfaces. O 2 reduction to H 2 O 2 was mediated by surface-bound quinone groups via superoxide anion intermediates, [7] and such modified elec...

Recent studies have shown that electrolysis can be an efficient process for nitrogen removal from urine. These studies have been conducted with urea solutions or fresh urine, but urine collected in NoMix toilets and urinals has a substantially different composition, because bacteria hydrolyse urea quickly to ammonia and carbonate. In this study, we compared electrochemical removal of nitrogen from synthetic solutions of fresh and stored urine using IrO 2 anodes. We could show that in fresh urine both ammonia and urea are efficiently eliminated, mainly through chlorine-mediated oxidation. However, in stored urine the presence of carbonate, arising from urea hydrolysis, leads to an inhibition of ammonia oxidation. We suggest two parallel mechanisms to explain this effect: the competition between chloride and carbonate oxidation at the anode and the competition between chlorate formation, enhanced by the buffering effect of carbonate, and ammonia oxidation for the consumption of active chlorine in the bulk. However, further experiments are needed to support the latter mechanism. In conclusion, this study highlights the negative consequences of the presence of carbonate in urine solutions, but also in other wastewaters, when subjected to an electrolytic treatment on IrO 2 in alkaline media.

A low-cost, reliable and sensitive electrochemical method for free chlorine analysis in water using inkjet printed silver electrodes is presented. Free chlorine detection was based on linear sweep voltammetry (LSV) analysis of AgCl/Ag 2 O films formed over an inkjet printed silver electrode by the spontaneous reaction between silver and free chlorine species (i.e. HClO and ClO − ) present in solution. The formation of AgCl/Ag 2 O films was studied and characterized by high resolution scanning electron microscopy (HR SEM) and X-ray photoelectron spectroscopy (XPS) techniques. LSV characterization demonstrated a quantitative linear relationship between the amount of AgCl/Ag 2 O formed and the concentration of free chlorine in water within a range from 1 to 100 ppm. After optimization of several parameters (e.g. scan rate, reaction time, starting potential), lowest detectable free chlorine concentration was 0.4 ppm (by standard addition method), while the limit of detection (S/N = 3) was equal to 2 ppm, with a sensitivity of 30 μC/ppm. The validation of the proposed methodology was performed by comparison with the standard N,N-diethylparaphenylenediamine (DPD) method for analyzing swimming pool water samples. Finally, it was demonstrated that reproducible and disposable silver electrodes could be easily prepared by inkjet printing in a large scale and in any required geometry to fit on-line and onsite free chlorine analyses requirements.

Micro-domains of water molecules surrounded by organic solvent exhibit enhanced reactivity towards oxidation compared to highly hydrogen-bonded bulk water molecules.