Development of an alkaline redox flow battery : from fundamentals to benchtop prototype

textThis work presents the first alkaline redox flow battery (a-RFB) based on the coordination chemistry of cobalt(III/II) and iron(III/II) with amino-alcohol ligands in concentrated NaOH([subscript aq]). The a-RFB was developed by carrying out systematic structural and electrochemical characterizations of various redox-active coordination compounds to find the most suitable candidates for electrochemical energy storage. In the characterization studies, particular attention was given to the redox couple Fe(III/II)- TEA, where TEA = triethanolamine, because of its importance in the fields of supramolecular chemistry, magnetic memory films, and electrochemical energy storage. The structures of Fe(III)-TEA in the solid state and in alkaline solution are reported for the first time. Moreover, experimental evidence is presented for the existence of an EC reaction in the heterogeneous reduction of Fe(III/II)-TEA in concentrated base. Furthermore, experiments were carried out to study the reactivity of Fe(II)-TEA with O2. This is important because O2 reacts spontaneously with Fe(II)-TEA to produce hydrogen peroxide, decreasing the charging-discharging capacity of the a-RFB. The reduction of oxygen by Fe(II)-TEA in concentrated base was studied by UV-Vis spectroscopy and coulometric titrations. Additionally, a new method for the quick identification of redox couples with slow EC reactions, k[subscript f] < 0.1 s-1, is presented. The new method is based on scanning electrochemical microscopy (SECM) and consists of creating a thin-layer cell between the tip and substrate electrode. During analysis of a redox couple, the tip reports a current transient proportional to the decaying concentration of the product of the E reaction, from which an apparent forward rate constant for the C reaction can be determined. This method was designed for the field of RFB research, where the identification of redox couples with no EC reactions is necessary to ensure that a battery can run for thousands of cycles. Lastly, surface oxidation of polycrystalline Ir ultramicroelectrodes was studied by the surface interrogation mode of SECM (SI-SECM), using Fe(II)-TEA as the titrant. This was done to demonstrate the existence of hydrous oxides of Ir(IV) and Ir(V) prior to the onset of oxygen evolution in concentrated base. Numerical simulations were carried out using commercial software and were used to validate the experimental results reported in this work.Chemistr

Carbon leakage in a fragmented climate regime: The dynamic response of global energy markets

As a global climate agreement has not yet been achieved, a variety of national climate policy agendas are being pursued in different parts of the world. Regionally fragmented climate policy regimes are prone to carbon leakage between regions, which has given rise to concerns about the environmental effectiveness of this approach. This study investigates carbon leakage through energy markets and the resulting macro-economic effects by exploring the sensitivity of leakage to the size and composition of pioneering regions that adopt ambitious climate action early on. The study uses the multi-regional energy–economy–climate model REMIND 1.5 to analyze the implications of Europe, China and the United States taking unilateral or joint early action. We find that carbon leakage is the combined effect of fossil fuel and capital market re-allocation. Leakage is limited to 15% of the emission reductions in the pioneering regions, and depends on the size and composition of the pioneering coalition and the decarbonization strategy in the energy sector. There is an incentive to delay action to avoid near-term costs, but the immediate GDP losses after acceding to a global climate regime can be higher in the case of delayed action compared to early action. We conclude that carbon leakage is not a strong counter-argument against early action by pioneers to induce other regions to adopt more stringent mitigation

Substituent Inductive Effects on the Electrochemical Oxidation of Flavonoids Studied by Square Wave Voltammetry and Ab Initio Calculations

Flavonoids are natural products commonly found in the human diet that show antioxidant, anti-inflammatory and anti-hepatotoxic activities. These nutraceutical properties may relate to the electrochemical activity of flavonoids. To increase the understanding of structure–electrochemical activity relations and the inductive effects that OH substituents have on the redox potential of flavonoids, we carried out square-wave voltammetry experiments and ab initio calculations of eight flavonoids selected following a systematic variation in the number of hydroxyl substituents and their location on the flavan backbone: three flavonols, three anthocyanidins, one anthocyanin and the flavonoid backbone flavone. We compared the effect that the number of –OH groups in the ring B of flavan has on the oxidation potential of the flavonoids considered, finding linear correlations for both flavonols and anthocyanidins ( R 2 = 0.98 ). We analyzed the effects that position and number of –OH substituents have on electron density distributions via ab initio quantum chemical calculations. We present direct correlations between structural features and oxidation potentials that provide a deeper insight into the redox chemistry of these molecules

Expanding the Monolayer Scope for Nucleic Acid-Based Electrochemical Sensors Beyond Thiols on Gold: Alkylphosphonic Acids on ITO

Electrochemical biosensors are a powerful and rapidly evolving molecular monitoring technology. Evidenced by the success of the continuous glucose monitor in managing Type 1 Diabetes, these sensors are capable of precise, accurate measurements in unprocessed biological environments. Nucleic acid-based electrochemical sensors (NBEs) are a specific type of biosensor that employs the target binding and conformational dynamics of nucleic acids for signal transduction. Currently, the vast majority of NBEs are fabricated via self-assembly of alkylthiols on Au electrodes. However, this architecture is limited in scope, as Au electrodes are not universally deployable for all potential NBE applications. Here, to expand the repertoire of materials on which NBEs can be made, we describe the multistep procedure for creating sensing monolayers of alkylphosphonic acids on a conductive oxide surface. Using such monolayers on indium tin oxide (ITO)-coated glass slides, we couple redox reporter-modified nucleic acids and demonstrate signaling of procaine-binding NBE sensors in buffer and human serum. We investigate the operational stability of these NBE sensors to reveal faster signal loss relative to benchmark thiol-on-gold sensing layers, a result that arises due to poor stability of the underlying ITO. Finally, we discuss future directions to continue expansion of NBE sensor materials and applications

Substituent Inductive Effects on the Electrochemical Oxidation of Flavonoids Studied by Square Wave Voltammetry and Ab Initio Calculations

Flavonoids are natural products commonly found in the human diet that show antioxidant, anti-inflammatory and anti-hepatotoxic activities. These nutraceutical properties may relate to the electrochemical activity of flavonoids. To increase the understanding of structure–electrochemical activity relations and the inductive effects that OH substituents have on the redox potential of flavonoids, we carried out square-wave voltammetry experiments and ab initio calculations of eight flavonoids selected following a systematic variation in the number of hydroxyl substituents and their location on the flavan backbone: three flavonols, three anthocyanidins, one anthocyanin and the flavonoid backbone flavone. We compared the effect that the number of –OH groups in the ring B of flavan has on the oxidation potential of the flavonoids considered, finding linear correlations for both flavonols and anthocyanidins ( R 2 = 0.98 ). We analyzed the effects that position and number of –OH substituents have on electron density distributions via ab initio quantum chemical calculations. We present direct correlations between structural features and oxidation potentials that provide a deeper insight into the redox chemistry of these molecules