High Oxidation Potential Research Articles

Enhanced NIR Electrochromic Properties of Corannulene-(triphenylamine)5 and EDOT-Derived Polymers via Electrochemical Layer-by-Layer Polymerization Compared to Copolymerization.

This study explores the electrochemical and electrochromic properties of polymers derived from corannulene-(triphenylamine)5 (CT) and 3,4-ethylenedioxythiophene (EDOT) through electrochemical copolymerization and layer-by-layer polymerization techniques. To address the high oxidation potential of EDOT, an EDOT dimer (BiEDOT) was synthesized, which facilitated successful copolymerization with CT. The resulting copolymer films, P10 and P8, exhibit enhanced near-infrared (NIR) electrochromic properties, with P8 showing better performance in NIR absorption. Comparative analysis with layer-by-layer films (PLs) reveals distinct electrochemical behaviors with PLs demonstrating higher NIR and lower visible absorbance with improved optical properties. Among PLs, PL6 exhibits the best NIR absorbance at 0.6 V, while the absorbance of the others does not show a significant increase until 0.7 V. Additionally, it also demonstrates excellent switching properties, with only a 3% loss of optical contrast at 1400 nm after 500 switching cycles. The study concluded that layer-by-layer polymerization offers an effective method for constructing PCT-PEDOT electrochromic films, providing better performance and higher NIR absorption than copolymerized films.

N-Protonated Acridinium Catalyst Enables Anti-Markovnikov Hydration of Unconjugated Tri- and Disubstituted Olefins.

The preparation of alcohols with anti-Markovnikov selectivity directly from olefins and water is a sought-after reaction due to its atom-economy and potential cost-effectiveness. Herein, we present the first general method for direct, catalytic anti-Markovnikov hydration of unconjugated tri- and disubstituted olefins. The key advancement is made possible by an oxidative (E*red = 2.15 V) N-H acridinium catalyst, which allowed for the functionalization of alkenes that were previously unreactive in such transformations due to their high oxidation potential. The developed protocol is not limited to hydration but also enables other hydrofunctionalizations, such as hydroetherifications, following the same mechanistic pathway.

High-Rate 4.2 V Solid-State Potassium Batteries by In Situ Polymerized Epoxide Ether Electrolyte.

Solid-state metallic potassium batteries (SSMPBs) afresh have attracted incremental attention because of their potential to supplement solid-state metallic lithium batteries. However, SSMPBs suffer poor electrochemical performances due to the low ionic conductivity of solid electrolytes and huge electrode/electrolyte interfacial resistance. Herein, high-rate SSMPBs are achieved by in situ ring-opening polymerization of 1,3-dioxolane with succinonitrile as a plasticizer and Al(OTf)3 as the catalyst, where the succinonitrile enables short-chain polyether electrolytes. The in situ polymerized electrolytes deliver a high ionic conductivity of 4.5 × 10-5 S cm-1 at room temperature and excellent stabilities at high oxidation potentials (4.2 V vs K+/K) and against metallic K anodes. All these result in SSMPBs with a discharge capacity of 69 mAh g-1 under a high rate of 100 mA g-1 and a retention of 88.8% after 100 cycles, and the rate and capacity retention are higher than those in previous work on SSMPBs.

Nickel/Photoredox Catalyzed Aryl-Alkyl Cross-Coupling with Alkyl Boronic Esters as Radical Precursors.

Nickel/photoredox dual catalyzed cross-coupling of aryl halides with alkylboron compounds is one of the effective methodologies for the construction of C(sp2)-C(sp3) bonds. Although elegant results have been achieved by using alkyl trifluoroborates as alkyl radical precursors, the generation of alkyl radicals from readily available alkyl boronic esters is still limited due to their high oxidation potential. We disclosed here that activation of alkyl boronic esters by MeOLi is highly efficient for the generation of alkyl radicals under photocatalysis conditions. The reaction featured with a wide substrate scope, high functional group tolerance, and late-stage modification of bioactive substances. In addition, the method was also successfully extended to alkyl boronic acids. Experimental and computational mechanistic studies indicated that the cross-coupling likely proceeds via a Ni(I)-catalyzed pathway.

Activating Oxygen via the 3‐Electron Pathway to Hydroxyl Radical by La−O4 Single‐atom on WO3 for Water Purification

AbstractShifting photocatalytic oxygen activation towards 3‐electron (e−) pathway to hydroxyl radicals, instead of the normal 1 e− to superoxide radicals, becomes increasingly important for pollution degradation since hydroxyl radicals possess a high oxidation potential (2.80 V). Here, we demonstrate a selective oxygen activation to hydroxyl radicals via 3 e− pathway using single atomically dispersed La based on WO3 fabricated with oxygen vacancies to weaken La−O coordination strength (denoted as LaO4−WOv). Unsaturated‐state La overcomes the rate‐limited step of 2 e− oxygen reduction reaction towards to hydrogen peroxide via tuning binding free energy of key reaction intermediate *OOH, stepped by easy generation of hydroxyl radicals via 1 e−. This strategy alters the activation of oxygen process from 1 e− to 3 e−. Hydrogen peroxide and hydroxyl radicals over LaO4−WOv produces 3.8 and 3.3 mmol L−1 h−1, 35 and 8 times that of detected over WO3, respectively. Rapid and complete removal of tetracycline realizes over LaO4−WOv with 0.077 min−1 of rate constant, 38 times that of WO3. Degradation efficiencies keep greater than 98 % following five repeats, revealing a practical‐utilization‐level robust stability. This work builds an unsaturated‐state transition metal site for manipulating oxygen activation towards an effective water purification as a representative application.

(Invited) Carbon/Metal Hybrid Materials for Robust Biosensors Development

Carbon nanotubes (CNTs) are well known for their flexibility, electrical conductivity and chemical inertness, however their use as biorecognition elements is limited due to multiple fabrication and interface aspects. Among them those related to their uniformity and stability of the CNT assemblies employed as microelectrodes. Although CNTs have shown improved detection capabilities when employed as sensors, their lack of reliable connectivity to metal surfaces has compromised their long-term performance. This talk will report fundamental calculations and experimental studies for a robust chemical bond formation of open-ended vertically oriented CNTs to copper metal surfaces. Theoretically, the nature of the bonding and the electrical resistance at the interface were determined. Experimentally, CNT bonding to metal surfaces was accomplished by grafting linker molecules to copper and gold surfaces using diazonium chemistry, for subsequent cross-linking to the proper functional groups on CNTs. These linkers were bonded to the open-ended CNTs while maintained their vertical orientation. The technique has also been applied for bonding functionalized sidewalls of CNTs to gold and other metal substrates. The application of these chemically bonded CNTs to nanostructured gold substrates as electrochemical sensors displayed high stability of the signal when exposed to oxidative conditions. Even after 540 h of exposure to a high oxidative potential, the current response remained stable, having negligible deviations between runs. Hydrogen peroxide detection using these hybrid materials involves an indirect enzyme-free oxidation mechanism, enabling their quantification at low potentials. The use of CNT/gold hybrid electrode materials allows for classifying the system as a fourth generation H2O2 sensor. Because of the low working potential, a 20-fold excess of fructose, creatinine, dopamine, uric acid, citric acid, and ascorbic acid did not interfere with hydrogen peroxide detection. Moreover, these carbon nanotube-based hybrid materials provide a large number of functionalization possibilities to employ them as electrode platforms for sensor development.

Activating Oxygen via the 3-Electron Pathway to Hydroxyl Radical by La-O4 Single-atom on WO3 for Water Purification.

Shifting photocatalytic oxygen activation towards 3-electron (e-) pathway to hydroxyl radicals, instead of the normal 1 e- to superoxide radicals, becomes increasingly important for pollution degradation since hydroxyl radicals possess a high oxidation potential (2.80 V). Here, we demonstrate a selective oxygen activation to hydroxyl radicals via 3 e- pathway using single atomically dispersed La based on WO3 fabricated with oxygen vacancies to weaken La-O coordination strength (denoted as LaO4-WOv). Unsaturated-state La overcomes the rate-limited step of 2 e- oxygen reduction reaction towards to hydrogen peroxide via tuning binding free energy of key reaction intermediate *OOH, stepped by easy generation of hydroxyl radicals via 1 e-. This strategy alters the activation of oxygen process from 1 e- to 3 e-. Hydrogen peroxide and hydroxyl radicals over LaO4-WOv produces 3.8 and 3.3 mmol L-1 h-1, 35 and 8 times that of detected over WO3, respectively. Rapid and complete removal of tetracycline realizes over LaO4-WOv with 0.077 min-1 of rate constant, 38 times that of WO3. Degradation efficiencies keep greater than 98 % following five repeats, revealing a practical-utilization-level robust stability. This work builds an unsaturated-state transition metal site for manipulating oxygen activation towards an effective water purification as a representative application.

Peracetic acid treatment for removing steroid hormones in a pilot-scale wastewater installation

The global water scarcity challenge urges sustainable solutions such as wastewater reuse, which is crucial to alleviate pressure on dwindling freshwater sources. However, this approach must address the presence of emerging pollutants (EPs), demanding specific treatment processes to ensure water safety and environmental protection. Peracetic acid (PAA) has garnered global interest due to its high oxidation potential and production of low-toxicity byproducts, making it a promising alternative for wastewater decontamination. This study aimed to assess PAA efficacy in removing three EPs: estrone (E1), 17β-estradiol (E2), and 17α-ethinylestradiol (EE2). Conducted in a pilot-scale wastewater treatment facility using real wastewater, the study explored six operational conditions, with varying PAA concentrations (5 mg/L to 15 mg/L) and hydraulic retention times (HRT) of 5, 10, and 15 min. Control parameters were monitored throughout the study. The condition with 15 mg/L PAA and 15 min HRT was the most efficient achieving over 85 % removal efficiency for all three compounds. The condition with 15 mg/L PAA and 10 min HRT was less efficient, achieving 70 % removal for E1 and 60 % and 44 % for E2 and EE2, respectively. A Spearman correlation matrix identified temperature and E. coli as strongly correlated with EPs removal, potentially influencing PAA decay. Overall, PAA demonstrated effective removal of target EPs under real wastewater conditions, underscoring its viability as a sustainable alternative for enhancing wastewater treatment processes, contributing to environmental protection and public health. Future studies could explore the long-term efficiency of PAA application and its scalability.

High time resolution quantification of PM2.5 oxidative potential at a Central London roadside supersite

The oxidative potential (OP) of airborne particulate matter (PM) is gaining increasing attention as a health-relevant metric to describe the capacity of PM to promote oxidative stress and cause adverse health effects. To date, most OP studies use filter-based approaches to sample PM and quantify OP, which have relatively poor time resolution (∼24 h) and underestimate the contribution of reactive components to OP due to the time delay between sample collection and analysis. To address this important limitation, we have developed a novel instrument which uses a direct-to-reagent sampling approach, providing robust, continuous, high time resolution (5 min) OP quantification, hence overcoming analytical limitations of filter-based techniques. In this study, we deployed this instrument in the Marylebone Road Air Quality Monitoring Station in London, UK, alongside a broad suite of high time resolution PM2.5 composition measurements for three months continuous measurement during Summer 2023. High time resolution OP quantification reveals dynamic changes in volume-normalised (OPv) and mass normalised (OPm) OP evolving over ∼hourly timescales, observed at an average PM2.5 mass concentration of 7.1 ± 4.2 µg m−3, below the WHO interim 4 target of 10 µg m−3. In addition, high time resolution data facilitates directional analysis, allowing us to determine the influence of wind speed and wind direction on OP, and the identification of PM2.5 chemical components and sources which drive dynamic changes in OP; this includes traffic emissions, as well as emissions from the London Underground into the ambient airshed. These results demonstrate the capacity of high time resolution measurements to provide new insights into the temporal evolution of OP, as well as the composition and emission sources which drive OP, developing our understanding of the characteristics of PM2.5 which may promote adverse health impacts.

The application of ozone within the food industry, mode of action, current and future applications, and regulatory compliance.

The food industry faces numerous challenges today, with the prevention and reduction of microbial contamination being a critical focus. While traditional chemical-based methods are effective and widely used, rising energy costs, the development of microbial tolerances, and growing awareness of the ecological impact of chemical biocides have renewed interest in novel biocides. Ozone, in both its gaseous and aqueous forms, is recognized as a potent disinfectant against bacteria, viruses, and fungi due to its high oxidation potential. Our review highlights several studies on the applications of ozone within the food industry, including its use for surface and aerosol disinfection and its capacity to reduce viable Listeria monocytogenes, a pertinent foodborne pathogen harbouring environmental and biocide stress tolerances and biofilm former. We also explore the use of ozone in food treatment and preservation, specifically on blueberries, apples, carrots, cabbage, and cherry tomatoes. While ozone is an effective disinfectant, it is important to consider material incompatibility, and the risks associated with prolonged human exposure to high concentrations. Nevertheless, for certain applications, ozone proves to be an efficacious and valuable alternative or complementary method for microbial control. Compliance with the biocide products regulation will require ozone device manufacturers to produce proven efficacy and safety data in line with British standards based on European standards (BS EN), and researchers to propose adaptations to account for ozone's unique properties.

Multisite Crosslinked Poly(ether-urethane)-Based Polymer Electrolytes for High-Voltage Solid-State Lithium Metal Batteries.

Utilizing solid-state polymer electrolytes (SPEs) in high-voltage Li-metal batteries is a promising strategy for achieving high energy density and safety. However, the SPEs face the challenges such as undesirable mechanical strength, low ionic conductivity and incompatible high-voltage interface. Here, a novel crosslinked poly(ether-urethane)-based SPE with a molecular cross-linked structure is fabricated to create high-throughput Li+ transport pathway. The amino-modified Zr-porphyrin-based metal-organic frameworks (ZrMOF) are introduced as multisite cross-linking nodes and polymer chain extenders. The abundant ether/ketonic-oxygen and Lewis acid sites in the SPE achieve high Li+ conductivity (5.7 × 10-4 S cm-1 at 30°C) and Li+ transference number (0.84). The interpenetrating cross-linked structure of SPE with robust mechanical strength results in a record cycle life of 8000h in Li||Li symmetric cell. The high structural stability of ZrMOF and abundant electron-withdrawing urethane/ureido groups in the SPE with high oxidation potential (5.1V) enables a discharge capacity of 182 mAh g-1 at 0.3 C over 500 cycles in a LiNi0.8Co0.1Mn0.1O2||Li cell. Remarkably, a high energy density of 446Wh kg-1 in a 1.5-Ah pouch cell is obtained with high loading cathode (≈4 mAh cm-2), demonstrating a great prospect of the current SPE for practical application in solid-state, high-voltage Li-metal batteries.

Constructing high performance dry-processing oxide composite electrolyte via interfacial interactions for durable solid-state lithium batteries

Composite solid electrolytes (CSEs) have considerable combination properties, which have been considered as the most promising choice for realizing advanced solid-state lithium batteries. Yet the ionic conductivity of CSEs fails to meet the practical requirements. Herein, we develop a dry-processing CSEs based on Li1.5Al0.5Ge1.5(PO4)3 (LAGP) and succinonitrile (SN) through polytetrafluoroethylene fibrillation. On the one hand, SN can enable fast ion transport in ceramic network and serve as high-speed conducive path. On the other hand, the strong affinities of LAGP towards SN and anions can significantly improve the conductive behavior and restrict side reactions at electrolyte/Li interface. Under such regulations, the composite electrolyte exhibits high ionic conductivity (0.64 mS cm−1 at 30 °C), high transference number (0.50), and high oxidation potential (>5.0V vs. Li+/Li). The assembled lithium metal batteries demonstrate excellent stability over 300 cycles at 1.0C. This work demonstrates the ion migration mechanism and the interactions at the heterogeneous interface for SN enhanced CSEs, contributing to the development of durable solid lithium metal batteries with extended lifespan.

High-efficiency treatment of oily wastewater by photocatalytic in-situ Fenton oxidation under visible light

Oily wastewater poses a significant threat to environmental safety, and complex water environments have caused numerous disturbances in oil pollution treatment. Therefore, constructing composite systems is expected to improve oil pollution treatment efficiency. This study developed an efficient photocatalytic in-situ Fenton oxidation system, HTCC@ZnFe2O4/Ag3PO4 (HZFA), loaded onto polypropylene spheres (PP) for treating oily wastewater (diesel oil) in complex environments. The built-in electric field of HZFA promotes photogenerated carrier separation, enhancing photocatalytic effect. At a diesel concentration of 3.2 g/L, performance of HZFA degraded diesel in deionized water and artificial seawater (ASW) were 60.80 % and 52.62 %, respectively, much higher than a pure photocatalytic system (13.84 %). The dual system compensated for single system defects like instability and narrow application range, achieving 8 effective cycles in ASW. Experimental and computational results showed that high oxidation and reduction potentials in the dual system promoted hydrocarbon oxidative degradation and H2O2 production/activation. The amount of OH, O2−, and h+ produced in different environments is fundamental for the stabilization of catalytic degradation by HZFA. GC–MS, and DFT analysis revealed potential oxidative chain-breaking processes for diesel components like alkanes, aromatics, alcohols, acids, aldehydes, and esters. This study offers a new method for green and efficient oily wastewater treatment, overcoming inherent defects of traditional Fenton, with broad application prospects.

Electrochemical Gold Redox Catalysis

AbstractThe high oxidation potential of Au(I)/Au(III) redox couple renders the development of gold‐catalyzed cross‐coupling reactions highly challenging. In the pursuit of Au(I)/Au(III) redox catalysis, various strategies, such as the use of stoichiometric oxidants, merged gold/photoredox systems, or ligand‐enabled approaches, have been adopted to achieve the oxidation of Au(I) to Au(III) complexes. Recently, electrochemical anodic oxidation‐based gold redox catalysis has emerged as a new technique to facilitate gold‐catalyzed cross‐coupling reactions. This concept article provides a succinct overview of electrochemical gold redox catalysis, highlighting the challenges and potential future developments.

Piezoelectric field accelerating charge transfer in Z-scheme heterojunction 2D-KNbO3/1D-CdS for efficient piezo-photocatalytic H2 evolution and TCH degradation

The piezo-phototronic effect utilizes the piezoelectric polarization field to tune the photogenerated carrier separation and transport performance in heterojunctions, which portrays a promising strategy for addressing energy shortage and environmental pollutants. Herein, a novel Z-scheme piezoelectric semiconductor heterojunction, 2D-KNbO3/1D-CdS-x (KNCS-x), was fabricated using hydrothermal and solvothermal methods, resulting in enhanced redox capacity. Under the simultaneous light and strain, KNCS-15 exhibits the highest piezo-photocatalytic activity, with degradation rates of tetracycline hydrochloride degradation rate constant, H2O2 as well as H2 production rates being 1.806 × 10−2s−1, 45.56 mM·h−1·g−1 and 8.87 mmol·h−1·g−1, respectively, which are 1.4, 2.4 and 1.9 times of photocatalysis alone, and 9.8, 9.2 and 9.8 times of piezocatalysis alone. DFT calculations, EPR and PALS indicate that the Z-scheme structure realizes effective separation of electron-hole pairs with strong redox ability and a higher carrier concentration. The enhanced catalytic activity is attributed to the introduction of piezoelectric potential, which facilitates improved spatial separation of electrons with high reduction and holes with high oxidation potential.

Cu-EDTA decomplexation by UV/peracetic acid oxidation and coupled Cu recovery by alkaline precipitation: Efficiency and mechanism

The high degree of complexation between metal ions and organic ligands presents a significant challenge to their removal via conventional chemical precipitation methods. Currently, oxidative decomplexation followed by alkali precipitation of Cu2+ represents an efficacious strategy for addressing Cu-ethylenediaminetetraacetic acid (Cu-EDTA). The efficacy of activated peracetic acid (PAA) processes in degrading contaminants has demonstrated excellent performance due to their higher oxidation potential. In this study, the UV/PAA process was initially employed for Cu-EDTA decomplexation, resulting in complete removal within 30 min. The 92.41 % released Cu2+ was successfully recovered by alkaline precipitation within 90 min. The mechanism of decomplexation is comprised of two principal stages. Firstly, the UV/PAA process gradually generates reactive oxygen species (ROS), including R-C•, •OH, and 1O2. These ROS facilitate the decomplexation of Cu-EDTA, resulting in the release of Cu2+. Additionally, Cu2+ can participate in the activated PAA, further promoting the production of ROS, which in turn enhances the removal of organic ligands. Furthermore, the transformation process of Cu-EDTA was subjected to analysis, along with the decomplexation products. Meanwhile, except for HCO3−, H2PO4−, and humic acid, which exerted a relatively minor impact on Cu2+ recovery, Cl− and NO3− demonstrated a negligible influence. Moreover, the reaction exhibits enhanced efficacy under acidic conditions and demonstrates robust performance in electroplating wastewater samples. In summary, this study provided a promising method for the decomplexation of Cu-EDTA efficiently and Cu recovery.

Glass fiber-based metal organic gel composite electrolytes for solid-state lithium batteries

Abstract Quasi-solid-state electrolytes encounter great obstacles in structural stability due to their inherent heterogeneity. Here, we introduce a new composite structure of glass-fiber-based metal-organic gel as a solid-state electrolyte and explore its electrochemical properties in lithium-metal batteries. We use a straightforward in-situ sol-gel method to synthesize this composite electrolyte, where glass fiber acts as matrices, ferric nitrate reacts with trimeric acid to form interconnected channels with abundant unsaturated metal sites, while ionic liquid electrolyte is in-situ confined into interconnected channels. The as-prepared composite electrolyte membrane has a uniform structure and composition, exhibiting a high room-temperature ionic conductivity of 1.79×10−3 S cm−1 and a high electrochemical oxidation potential of 4.76 V vs Li/Li+. This composite has excellent cycling performance in LiFePO4//Li (99.5% after 100 cycles) and NCM811//Li (86.6% after 200 cycles) batteries.

Kinetics of regeneration of oxidative Cu(II) and Fe(III) species in aerated acid chloride leaching solutions at 75 °C

In the leaching of copper sulfide ores or refractory gold ores in chloride solutions, the regeneration of oxidative agents such as Cu (II) and Fe (III) is a key aspect for a sustainable process over time. This regeneration is carried out from the oxidation of Cu (I) and Fe (II) with O2, which helps to maintain a conveniently high oxidative potential in solution and a high leaching efficiency. In this context, Cu (I) and Fe (II) oxidation are affected by the accumulation of Cu or Fe species resulting from sulfide dissolution during the process. Therefore, a good understanding of the interaction mechanism of O2 with Cu (I), Cu (II), Fe (II), and Fe (III) species is necessary to describe the oxidation kinetics in this complex environment. The present work reports a study of the Cu (I) and Fe (II) oxidation at 75 °C in solutions containing 4.0 M NaCl and 0.1 M HCl. The solutions used in the experiments contained different initial concentrations of Cu (I), Cu (II), Fe (II), and Fe (III) with values in the range of 0.0001 – 0.1 M. Experiments were conducted in a thermostatized reactor containing 0.5 L solution agitated with a magnetic stirrer at 450 rpm, while oxygenated by air bubbling at 3.5 L/min. The evolution of the concentration of Cu (I), Cu (II), Fe (II), and Fe (III) during oxidation was determined by an electrochemical method, which was mainly based on Eh measurements of solution over time. A reaction mechanism was proposed for the oxidation of Cu (I) and Fe (II) with O2 in the presence of Cu and Fe species, which described very well the results obtained in the oxidation experiments under various conditions. Based on the proposed mechanism, a kinetic model was developed that could predict the concentration of Fe (II), Fe (III), Cu (I), Cu (II), O2, HO2–, H2O2, OH– and H+ in acid aerated chloride solutions satisfactorily. These proved to be a valuable tool to approach the modeling of chloride-leaching reactors.

Deep learning-assisted research on high-performance electrolyte for zinc-ion capacitors

Zinc-ion capacitors (ZICs) have garnered significant attention due to their ability to balance energy density and power density. The properties of electrolytes greatly influence the electrochemical performance of ZICs, and the oxidation potential (OP) of electrolytes can be used to determine the most suitable electrolyte for ZICs. However, traditional methods for exploring OP are time-consuming and inefficient, making it difficult to effectively determine the most suitable electrolyte for ZICs. Herein, we propose a machine learning-assisted method that combines deep learning with the traditional machine learning algorithm Gradient Boosting Regression (GBR), which we refer to as DeepGBR. This method can accurately predict the OP of electrolytes even when dealing with complex features and small datasets. Furthermore, with the assistance of deep learning, the accuracy of the predictions improves as the dataset size increases. We further validated the model with four common electrolyte molecules, finding that the predicted results are highly consistent with the theoretical values. The results show that acetonitrile has a high OP, which can achieve high energy density and long-cycle stability when used as an electrolyte solvent for ZICs. This work provides a certain reference for the database modeling strategy of electrolytes for electrochemical energy storage devices.

Redox Behaviour and Redox Potentials of Dyes in Aqueous Buffers and Protic Ionic Liquids.

Organic dyes hold promise as inexpensive electrochemically-active building blocks for new renewable energy technologies such as redox-flow batteries and dye-sensitised solar cells, especially if they display high oxidation and/or low reduction potentials in cheap, non-flammable solvents such as water or protic ionic liquids. Systematic computational and experimental characterisation of a representative selection of acidic and basic dyes in buffered aqueous solutions and propylammonium formate confirm that quinoid-type mechanisms impart electrochemical reversibility for the majority of systems investigated, including quinones, fused tricyclic heteroaromatics, indigo carmine and some aromatic nitrogenous species. Conversely, systems that generate longlived radical intermediates - arylmethanes, hydroquinones at high pH, azocyclic systems - tend to display irreversible electrochemistry, likely undergoing ring-opening, dimerisation and/or disproportionation reactions.