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This study demonstrates the charge additivity of core valence metal ions with fixed ionic pendant groups can significantly boost the thermoelectrochemical valorisation of waste heat into electricity, but is solvent-specific.

Thermogalvanic devices can harvest wasted thermal energy; a waste product that is generated by humanity in staggering abundance. However, the incorporation of thermogalvanic devices in applications from hot, industrial environments through to waste body heat harvesting necessitates safe chemicals. In particular, since the redox active ions are the charge carriers the chemistry of these is crucial; the bigger and more powerful the device, the greater the abundance of these chemicals. The anionic ferricyanide/ferrocyanide ([Fe(CN)6]3−/4−) redox couple is arguably the most widely utilised and investigated thermogalvanic electrolyte, but has inherent (in)stability issues, and therefore safety issues. This study has investigated a wide range of anionic polycarboxylate and polyaminocarboxylate ligands in conjunction with iron(II/III) chloride (FeCl2/3) in an effort to develop a safer [Fe(CN)6]3−/4−-replacement. Detailed electrochemical and spectroscopic characterisation was used across the wide range of ligands investigated, and several were found to be viable for use in thermogalvanic cells. In particular, optimised nitriloacetic acid was found to yield a redox-active complex, [Fe(NTA)2]3−/4−, with a good Seebeck coefficient (−1.35 mV K−1) on par with [Fe(CN)6]3−/4−. However, diethylenetriaminepentaacetic acid (to form [Fe(DEPTA)]2−/3−) demonstrated the optimum compromise between thermodynamic and kinetic properties; this was used to prepare an in-series thermogalvanic device with the parent Fe2+/3+ species. Benchmarking against relative costs, and the principles of green chemistry and green chemical engineering was used to identify the relative merits of the different systems.

The analysis of 'cutting' or additive agents in cocaine, like benzocaine (BZC), allows police analysts to identify each component of the sample, thus obtaining information like the drugs' provenience. This kind of drug profiling is of great value in tackling drug trafficking. Electropolymerized molecularly imprinted polymers (e-MIPs) on portable screen-printed carbon electrodes (SPCEs) were developed in this study for BZC determination. The MIPs' electropolymerization was performed on a carbon surface using the anaesthetic BZC as the template molecule and 3-amino-4-hydroxybenzoic acid (3,4-AHBA) as the functional monomer. The build-up of this biomimetic sensor was carefully characterized by cyclic voltammetry (CV) and optimized. Cyclic voltammetric investigation demonstrated that BZC oxidation had a complex and pH-dependent mechanism, but at pH 7.4 a single, well-defined oxidation feature was observed. The BZC-MIP interactions were studied by computer-aided theoretical modeling by means of density functional theory (DFT) calculations. The electroanalytical methodology was effectively applied to artificial urine samples; BZC molecular recognition was achieved with a low limit of detection (LOD) of 2.9 nmol L-1 employing square-wave voltammetry (SWV). The e-MIPs were then used to 'fingerprint' genuine cocaine samples, assisted by principal component analysis (PCA), at the central forensic laboratory of the Brazilian Federal Police (BFP) with a portable potentiostat. This electroanalysis provided proof-of-concept that the drugs could be voltammetrically 'fingerprinted' using e-MIPs supported by chemometric analysis.

Thermogalvanic cells typically utilise equimolar concentrations of the oxidised and reduced states of a redox couple in solution, sandwiched between two electrodes at dissimilar temperatures; entropy drives redox processes to occur at these electrodes, generating a potential difference and a current. However, significant gaps still exist in fundamental data and understanding of these ‘thermocells’. In this study, thermocells based upon potassium ferricyanide, K3[Fe(CN)6], and potassium ferrocyanide, K4[Fe(CN)6], were investigated. The ratio of the oxidised and reduced states were systematically varied, and this had a significant effect upon the power produced; notably maximum power did not correspond to the equimolar ratio. A concentration study using equimolar ratios was also performed. Trends in the potential generated as a function of temperature (or ‘Seebeck coefficient’) were rationalised by the Nernst equation and Debye–Huckel theory. The trends in the current and the electrical power produced were successfully modelled using the Butler–Volmer equation. The effects of heterogeneous electrocatalysis were also explored (using platinum and two types of graphite) as well as homogeneous electrocatalysis, by the direct addition of alkali metal salts (as lithium, sodium, potassium, rubidium and caesium chlorides and sulphates). Clear trends were observed, and homogeneous and heterogeneous electrocatalysis had an additive effect when combined. Addition of CsCl was able to boost the maximum power output by upto ca. 80%, via both an increased Seebeck coefficient (through altered solvation) and through increased current (via homogeneous electrocatalysis of electron transfer). Finally, a limited economic comparison was performed, which highlights how the use of non-stoichiometric ratios of the redox couple could improve the cost-per-power value of the systems.

Two methods are reported for the one-pot preparation of high concentrations of gold nanoparticles (AuNPs) embedded throughout sodium polyacrylate hydrogels; this stabilises the AuNP in even extremely high ionic strength environments, and enables them to act as effective catalysts for the hydride-reduction of nitrophenols and of dyes, with zero order kinetics.

Thermogalvanic cells can act like ‘liquid thermoelectrics’ to convert a thermal energy gradient to electrical energy. Such cells are typically combined electrically in-series in devices to boost the output voltage (as thermocells). However, the typical system involves a potentially fatal combination of inherently acidic or acidified Fe2+/3+ and [Fe(CN)6]3−/4− electrolytes; mixing and heating is expected to trigger extremely toxic HCN gas release. Here we demonstrate that benign aqueous iron(II/III) sulphate can be combined with equally benign sodium sulphate and sodium hydrogen sulphate; the first leads to an [Fe(SO4)2]−/2− thermocell (Seebeck coefficient, Se = −0.4 mV K−1), and the second to a thermocell with intermediate [FeSO4]0/+ and [Fe(HSO4)]+/2+ character (Se = +0.57 mV K−1). Their fundamental thermoelectrochemistry was explored, and their speciation elucidated. It was demonstrated that these can be utilised electrically in-parallel and in-series in thermogalvanic devices. When connected electrically in-series the thermocells presented here displayed temperature-dependent open circuit potentials only ca. one-third that typically reported for the ‘conventional’ combination of Fe2+/3+- and [Fe(CN)6]3−/4−-based thermocells (0.8 mV K−1vs. ca. 3 mV K−1, respectively). However, whereas the latter thermocells cannot be safely mixed, when the iron-sulphate cells were ‘accidently’ mixed they safely form a mixed thermocell electrolyte (Se = +0.19 mV K−1), enabling a ‘second life’ of both the electrolyte and thermocell devices. This novel ‘all-iron sulphate’ thermocell was compared against the typically employed Fe2+/3+ and [Fe(CN)6]3−/4− combination using the 12 principles of green chemistry and of green engineering, further demonstrating the inherent sustainability, safety and ‘green’ credentials of this system (but not yet efficiency). This work demonstrates how functionality and complexity can be introduced in a safe manner, while also preventing potential accidents and enabling new ‘end-of-life’ opportunities.

Harvesting wasted thermal energy could make important contributions to global energy sustainability. Thermogalvanic devices are simple, chemistry-based devices which can convert heat to electricity, through facile redox chemistry. The efficiency of this process is the ratio of electrical energy generated by the cell (in Watts) to the quantity of thermal energy that passes through the cell (also in Watts). Prior work estimated the quantity of thermal energy passed through a thermocell by applying a conductive heat transfer model to the electrolyte. Here, we employ a heat flux sensor to unambiguously quantify both heat flux and electrical power. By evaluating the effect of electrode separation, temperature difference and gelation of the electrolyte, we found significant discrepancy between the estimated model and the quantified reality. For electrode separation, the trend between estimated and measured efficiency went in opposite directions; as a function of temperature difference, they demonstrated the same trend, but estimated values were significantly higher. This was due to significant additional convection and radiation contributions to the heat flux. Conversely, gelled electrolytes were able to suppress heat flux mechanisms and achieve experimentally determined efficiency values in excess of the estimated values (at small electrode separations), with partially gelled systems being particularly effective. This study provides the ability to unambiguously benchmark and assess the absolute efficiency and Carnot efficiency of thermogalvanic electrolytes and even the whole thermocell device, allowing 'total device efficiency' to be quantified. The deviation between the routinely applied estimation methodology and actual measurement will support the rational development of novel thermal energy harvesting chemistries, materials and devices.

Wastewater was sourced directly from an industrial anaerobic biodigestion system to assess its potential to serve as a growth medium and improve the digestibility of microalgae in a closed-loop bioenergy system. Cyanobacteria (Oscillatoria sp.) were cultured in the wastewater and further explored as a feedstock for biomethane production via methanogenesis. Promisingly high levels of nitrate (1180 mg L−1) and phosphate (61.5 mg L−1) were found in the nitrification-treated, NO3-rich wastewater stream. While cyanobacteria were not observed to grow directly in this NO3-rich wastewater stream, a modest dilution of the wastewater by a factor of two produced denser cultures than could be grown in standard f/2 media, which was made by enriching seawater. Growth in wastewater to improve the digestibility of the cyanobacteria resulted in significantly more methane from cultures in both the NO3-rich and the untreated, NH4-rich wastewater streams.

Solvate ionic liquids are a relatively new class of liquids produced by combining a coordinating solvent with a salt. They have a variety of uses and their suitability for such depends upon the ratio of salt to coordinating solvent. This work investigates the Kamlet-Taft solvent parameters of, NMR chemical shifts of nuclei in, and thermoelectrochemistry of a selected set of solvate ionic liquids produced from glymes (methyl terminated oligomers of ethylene glycol) and lithium bis(trifluoromethylsulfonyl)imide at two different compositions. The aim is to improve the understanding of the interactions occurring in these ionic liquids to help select suitable solvate ionic liquids for future applications.

Thermogalvanic conversion of temperature gradients into electricity via a redox couple represents a potential method of waste energy harvesting, but inexpensive, effective and sustainable redox couples are required. In this study four aqueous Fe(II)/Fe(III) salt systems are considered, based upon ammonium iron sulphate, iron sulphate, iron trifluoromethanesulfonate and iron nitrate. A range of Seebeck coefficients were observed, from +0.18 ± 0.04 mV K−1 for ammonium iron(II/III) sulphate to +1.46 ± 0.02 mV K−1 for acidified iron(II/III) trifluoromethanesulfonate, both at a temperature difference of 20 K; notably these apparent Seebeck coefficients vary with temperature difference due to significant chemical equilibria. The iron(II/III) nitrate system generated the highest thermogalvanic power output. The systems were probed by cyclic voltammetry, pH, UV-Vis spectroscopy and electrochemical impedance spectroscopy, and two competing mechanisms noted, which strongly affect both the current output and Seebeck coefficient (i.e. potential output) of their thermoelectrochemical cells (or thermocells). Green and economic consideration are important aspects if these systems are to be employed in harvesting low-grade heat energy at a larger scale; iron nitrate and acidified iron sulphate were the most highly competitive systems.

Summary The majority of usable energy generated by humanity is lost as waste heat, but thermogalvanic systems (or thermocells) can address this problem by converting low-grade waste heat directly into electricity using redox chemistry. The concentration of the redox couple is a critical parameter; almost invariably, higher concentrations result in more power. This study exploits the simple synergy between Na+ and K+ counter ions to achieve—to the best of our knowledge—the most concentrated stable aqueous ferricyanide/ferrocyanide thermocell to date, at 1.6 m [Fe(CN)6]3−/4−. Despite increasing the concentration by 400% relative to the standard K3/K4[Fe(CN)6] electrolyte (0.4 m), electrical power production increased only 166%. Pushing the system from conventional salt-in-water electrolytes into the quasi-stable water-in-salt region (up to 2.4 m) resulted in a decrease in power. Detailed characterization highlighted the various physicochemical hurdles introduced by these extremely concentrated electrolytes; the identified issues have direct relevance to other energy systems also seeking to use the highest possible concentration.

Biomass pretreatment is a key first step in converting recalcitrant lignocellulosic biomass into value-added products. Aqueous hydroxide solutions can be effective biomass pretreatment media, and the cation of the hydroxide salt can have an extremely significant effect upon the physicochemical behavior of the hydroxide solution. However, the cation effect has not been comprehensively investigated with respect to biomass pretreatment. Here, we investigated pretreatment of rice husks (from Oryza sativa) and show that the cation indeed has a significant effect upon downstream enzymatic hydrolysis of the cellulose (with cellulase). In particular, the ability of the solution to dissolve cellulose was negatively correlated with pretreatment effectiveness, as judged by the downstream glucose yield. This was observed by investigating aqueous solutions of lithium, potassium, cesium, tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, and tetrahexylammonium hydroxide. Silica solubility was almost cation-independent, lignin solubility was moderately cation-dependent, while cellulose solubility was strongly cation-dependent. The rate of lignin extraction was inversely correlated with the size of the cation. As cellulose dissolution is a demanding chemical process, it initially limited the ability of the solution to disrupt the whole biomass, necessitated extensive washing of the pretreated rice husk, and still resulted in significant cation contamination downstream. Overall, lithium hydroxide was found to be the most effective hydroxide.

Imidazolium-based ionic liquids (ILs) with acetate, formate, and chloride anions have been investigated for lignocellulosic biomass pretreatment in both their (conventional) aprotic and (largely unexplored) protic forms. Notably, the protic IL 1-ethylimidazolium chloride has been demonstrated to reversibly dissolve whole wood (Pinus radiata) and significantly enhance enzymatic hydrolysability of the pretreated biomass. The acetate-based and formate-based protic IL could only extract lignin. Solid-state 13C NMR and thermogravimetric analysis demonstrate that the protic IL physically pretreats the biomass in a different manner to the aprotic ILs; however, the extent of lignin side-reactions such as methoxy group loss was dominated by the nature of the anion. The protic IL 1-ethylimidazolium chloride could be recycled by vacuum distillation and undergo several rounds of wood pretreatment followed by distillation recycle without a decrease in effectiveness.

Copper(II) coordination complexes, 1 and 2, containing nonsteroidal anti-inflammatory drugs (NSAIDs) potently kill breast cancer stem cells (CSCs) and bulk breast cancer cells. Although detailed biological studies have been conducted to shed light on their mechanism of cytotoxicity, little is known about their molecular level mechanism of action. This biophysical study, aided by the preparation of a fluorophore-containing analogue, 3, reveals that the complexes operate by undergoing reduction to a copper(I) form and releasing the associated NSAIDs.

The low potentials generated by individual thermoelectric and thermogalvanic ‘heat to electricity’ elements necessitate that numerous cells be placed electrically in series to generate useful voltages. The thermoelectrochemistry of two redox couples with opposite signs for their Seebeck coefficients have therefore been evaluated and combined, in order to generate the first thermoelectrochemical (or thermocell) assembly that is electrically in series without a hot-to-cold thermal short-circuit. This was achieved using potassium ferrocyanide(II)/ferricyanide(III) and iron(II)/iron(III) sulphate (plus sulphuric acid) thermocells. Quantitative evaluation of thermocells electrically parallel and/or in series demonstrated relatively simple additive behaviour for current and potential (and thus power density) over a very wide range of concentrations of the redox species. Keywords: Thermoelectrochemistry, Thermogalvanic, Thermocell, Waste heat harvesting, Seebeck coefficient

The electrochemical oxidation of phenols typically passivates electrodes, due to the reactive one-electron oxidation intermediate, a phenoxyl radical cation. Here, we show that the addition of polyoxometalates to the electrolyte can prevent electrode passivation via an EC`E mechanism; the initial oxidation is unchanged, but oxidation of the phenoxyl radical intermediate is mediated. As such the electrochemistry assumes an ideal EE process, as confirmed by cyclic voltammetric simulation, with no electrode fouling on the voltammetric timescale. Bulk electrolysis of phenolic molecules can even be performed to isolate solution-phase products. This is exemplified by the scenario of vanillin (phenolic compound) and phosphotungstic acid (H3[PW12O40], a polyoxometalate). Keywords: Phenols, Vanillin, Polyoxometalates, Mediators, Passivation, Electrode fouling

The exposed surface facets play an important role in determining the gas-sensing performance of nanostructured materials. This study reports the facile hydrothermal synthesis of zinc oxide nanoflakes with exposed {1 0 1¯ 0} facets, as confirmed by the high resolution transmission electron microscopy (HRTEM) and the corresponding selected area electron diffraction (SAED) analysis. The gas-sensing properties of the ZnO nanoflake sensor were investigated toward toxic n-butylamine, an important marker compound in food and medical industries. The pure ZnO nanoflake sensor exhibits a response of 23.9–50 ppm of n-butylamine at an optimum operating temperature of 300 °C. Density Functional Theory (DFT) simulations were used to study the adsorption behavior of n-butylamine on the ZnO(1 0 1¯ 0) surface. The results show that n-butylamine chemically adsorb on the ZnO(1 0 1¯ 0) surface through the formation of a bond between the nitrogen atom of the n-butylamine (C4H11N) and the surface Zn atom of ZnO. To further improve the gas-sensing properties, the as-prepared ZnO nanoflakes were subsequently loaded with three different quantities of Au (1.37, 2.82, and 5.41 wt% Au). The gas-sensing measurements indicate that the Au nanoparticle-decorated ZnO nanoflakes display superior sensing performance to non-modified ZnO nanoflakes by exhibiting 4–6 times higher response and an improved selectivity toward n-butylamine gas, along a decreased optimum operating temperature of 240 °C. Moreover, the response and recovery properties of the ZnO nanoflake sensor are improved by a factor of 1.5–2.5 depending on the Au loading. The enhanced sensing performance of the Au nanoparticle-decorated ZnO nanoflakes to n-butylamine gas can be attributed to the excellent catalytic activity of Au nanoparticles (NPs) which promotes a greater adsorption of oxygen molecules on the surface of ZnO and the presence of multiple electron depletion layers, specifically at the surface of ZnO and at the ZnO/Au interface, which greatly increases their conductivity upon exposure to the gas.

The electroreduction of corannulene (C20H10) has been investigated in a room temperature ionic liquid (RTIL) for the first time. In the RTIL 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([Bmpyrr][NTf2]) the resultant voltammetry shows a peak-to-peak separation of 100 mV, and this separation does not vary with scan rate (as predicted by a simple E mechanism). We propose a square scheme that is capable of accurately describing this behavior. Specifically, the use of a square scheme takes into account the effect of ion pairing between the ionic liquid cation and the corannulene anion on the overall reaction mechanism. Importantly, investigation in acetonitrile with a range of conventional electrolytes does not display the trends observed in the RTIL. This result likely provides a general insight into all RTILs as a class of electrolyte, because of the high concentration of ions and the proclivity of RTILs to ion-pair.

Combining ferrocene and iodine results in enhanced thermoelectrochemical (or thermogalvanic) waste heat harvesting abilities, for both the Seebeck coefficient and the overall power output. All systems displayed a mixture of ferrocene, ferrocenium, iodine and triiodide. The observed enhancement correlates with lower electron-density on the ferrocene; the synergistic improvement observed for mixtures of substituted ferrocenes and iodine is attributed to the formation of charge-transfer complexes. Combining dibutanoylferrocene and iodine resulted in the highest Seebeck coefficient of 1.67 mV K-1

Thermoelectrochemistry offers a simple, scalable technique for direct conversion of waste heat into useful electricity. Here the thermoelectrochemical properties of lithium-glyme solvate ionic liquids, as well as their dilute electrolyte analogues, have been investigated using mixtures of tetraglyme (G4, tetraethylene glycol dimethyl ether) and lithium bis(trifluoromethylsulfonyl)imide (Li[NTf2]). The thermoelectrochemical process is entropically-driven by release of the glyme from the lithium-glyme complex cation, due to electrodeposition of lithium metal at the hotter lithium electrode with concomitant electrodissolution at the cooler lithium electrode. The optimum ratio for thermochemical electricity generation is not the solvate ionic liquid (equimolar mixture of Li[NTf2] and glyme), but rather one Li[NTf2] to four G4, due to the mixtures relatively high ionic conductivity and good apparent Seebeck coefficient (+1.4 mV K(-1)). Determination of the lithium-glyme mixture thermal conductivity enabled full assessment of the Figure of Merit (ZT), and the efficiency relative to the Carnot efficiency to be determined. As the lithium electrodeposits are porous, alternating the temperature gradient results in a system that actually improves with repeated use.

Aqueous solutions of tetrabutylphosphonium hydroxide have been evaluated as pretreatment media for rice husks, prior to sulphuric acid hydrolysis or cellulase enzymatic hydrolysis. Varying the water:tetrabutylphosphonium hydroxide ratio varied the rate of delignification, as well as silica, lignin and cellulose solubility. Pre-treatment with 60wt% hydroxide dissolved the rice husk and the regenerated material was thus heavily disrupted. Sulphuric acid hydrolysis of 60wt%-treated samples yielded the highest amount of glucose per gram of rice husk. Solutions with good lignin and silica solubility but only moderate to negligible cellulose solubility (10-40wt% hydroxide) were equally effective as pre-treatment media for both acid and enzymatic hydrolysis. However, pre-treatment with 60wt% hydroxide solutions was incompatible with downstream enzymatic hydrolysis. This was due to significant incorporation of phosphonium species in the regenerated biomass, which significantly inhibited the activity of the cellulase enzymes.

Thermoelectrochemical cells (thermocells) designed for harvesting human body heat can provide constant power output for wearable electronics, supplementing state‐of‐the‐art flexible power storage and conversion solutions. However, a systematic investigation into the optimization of wearable thermocells is lacking, especially with regard to device design, n‐type electrolytes, and electrode/electrolyte integration. Here, a n‐type gel electrolyte: polyvinyl alcohol‐FeCl2/3 with outstanding flexibility and elasticity and exceptional electrolyte/electrode integration into a 3D porous poly(3,4‐ethylenedioxythiophene)/polystyrenesulfonate (PEDOT/PSS) electrode, is produced via an in situ chemical crosslinking method. The integrated n‐type cell shows excellent seebeck coefficients (0.85 mV K−1) and output current density (1.74 A m−2 K−1) that are comparable with an optimized p‐type cell consisting of a carboxymethylcellulose‐K3/4Fe(CN)6 electrolyte with a 3D PEDOT/PSS‐edge functionalized graphene/carbon nanotube electrode (−1.22 mV K−1 and 1.85 A m−2 K−1). The equivalent performance of the n‐type and p‐type cells enables the effective series connection of up to 18 pairs of p–n cells that combines to give an output voltage of 0.34 V (∆T = 10 K). This in‐series device is fabricated into a proof‐of‐concept watch strap, which can harvest body heat, charge supercapacitor (up to 470 mF) as well as illuminate a green light emitting diode, demonstrating the practical applications.

Thermogalvanic cells (or thermocells) are being increasingly investigated due to their ability to directly convert modest temperature gradients into electricity, using redox chemistry. However, this has resulted in a diverse range of cells, electrolytes, temperature gradients, etc. being reported. Recently, so-called temperature-difference ‘normalised’ power outputs have been reported; the power output is divided by the square of the temperature difference to yield temperature-insensitive power output values. The validity of this procedure is quantitatively assessed here, and found to be far from accurate. Additionally, numerous different experimental procedures for measuring the current and power output from thermocells can be found in the literature, covering different approaches, vastly different time scales, and employing a diverse range of measuring instruments. A range of experimental methodologies covering a sequence of constant resistances (or resistive loads), a sequence of constant currents, a sequence of constant potentials (or voltage), chronoamperometry and linear sweep voltammetry (LSV) were evaluated in this study, using source measure units, potentiostats and voltammeters/multimeters. While most methodologies were consistent, the measurement time and number of electrodes were found to be highly influential, with LSV and 3-electrode assemblies especially overestimating the current and power output from thermocells.

Methylone (also known as bk-MDMA) is a substituted cathinone developed to elicit similar psychotropic effects as 4-methylenedioxymethamphetamine (MDMA, also known as ecstasy). Although methylone is a scheduled substance, its specific structural features means it generally cannot be detected and quantified using the same conditions commonly employed for ecstasy. This work therefore describes the development of an electroanalytical method for the selective quantification of methylone. This method uses an electropolymerized molecularly imprinted polymer (MIP) on the surface of screen-printed gold electrodes (SPAuEs), using 2-mercaptobenzimidazole (2-MBI) as the building monomer and methylone as the analyte template. The construction and optimization of the SPAuE-MIP sensor was studied, step-by-step, using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Additionally, the direct electrooxidation of methylone was investigated, and methylone-MIP interactions probed computationally. Ultimately, square-wave voltammetry (SWV) quantification of methylone using the SPAuE-MIP sensor was demonstrated to be both sensitive and selective. The electroanalytical determination showed suitable analytical parameters as: intra-day repeatability of 1.5%, a limit of detection (LOD) of 1.1 μmol L−1 (0.23 mg L−1) and a linear range up to 50 μmol L−1 (ca. 10 mg dL−1) with an r2 of 0.996, as well as much higher currents towards the analyte than similar compounds and commonly present interferents.

For the third time, a Faraday Discussion addressed ionic liquids. Encompassing the wealth of research in this field, the contributions ranged from fundamental insights to the diverse applications of ionic liquids. Lively discussions initiated in the lecture hall and during poster sessions then seamlessly continued during the social program.

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The evaluation of batteries under thermal gradients is essential for safety and longevity reasons, and to investigate power generation via the thermogalvanic effect. The thermogalvanic Seebeck coefficient of lithium metal (+1.0mV·K−1) and solid lithium ferri/ferrocyanide intercalation electrodes (−0.6mV·K−1) were determined. The measured Seebeck coefficients of identical asymmetric cells containing both electrodes deviated from the expected values, having Seebeck coefficients which also varied as a function of thermal conditions (+0.7 to +4.3mV·K−1). This work demonstrates that the thermal responses of asymmetric battery assemblies are more complex than predicted based upon their individual half-cell performances in symmetric cells. Keywords: Seebeck coefficient, Thermal energy, Temperature effect on battery, Thermocell, Thermogalvanic

International audience

Thermogalvanic (or thermoelectrochemical) systems can convert a temperature difference into an electrical current by exploiting the entropy change associated with a redox process. This work investigates coupling thermogalvanic redox processes with thermogalvanic corrosion. Ferri/ferrocyanide and iodide/triiodide redox couples were investigated at platinum and stainless steel electrodes. Dilute iodine displays a Seebeck coefficient of +0.26 mV K−1 at platinum electrodes and +2.1 mV K−1 at stainless steel electrodes. An apparent Seebeck coefficient of +13.6 mV K−1 could be achieved under optimal conditions. This is demonstrated to be due to a combination of the iodide/triiodide thermogalvanic redox couple and thermogalvanic iodine-induced corrosion of the stainless steel. Keywords: Thermocell, Waste heat, Sustainable energy, Thermal energy

The effect of ionic liquids upon the mechanical and (bio)chemical integrity of macadamia nut shells (from Macadamia integrifolia) has been investigated. Whole macadamia nuts-in-shell are notoriously difficult to crack, and the Australian macadamia nut shells used in this study required 2240 ± 430 N of force to crack. Ionic liquids were screened for their solubility values, with 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) able to dissolve 5.5 ± 0.5 wt % macadamia nut shell. Treatment with small quantities of [Emim][OAc] resulted in weakened whole nut-in-shells that could be cracked with only ca. 46% of the displacement (0.67 ± 0.16 mm), ca. 34% of the force (760 ± 240 N) and ca. 15% of the energy (0.25 ± 0.10 J per shell) relative to no treatment. Further treatment by dissolution and precipitation of macadamia nut shell, followed by enzymatic hydrolysis with cellulase, resulted in the release of 80 ± 15% of the expected glucose content, relative to 1.3 ± 1.0% before any pretreatment.

Ionic liquids can be used as non-volatile, tunable solvents, extractants and electrolytes. This work investigates their ability to extract an organic analyte, capsaicin, from fresh Capsicum annuum Bird's eye chilli peppers (also known as Thai chillies), followed by the electroanalytical quantification of the extracted analyte. Ascorbic acid (vitamin C) was also extracted and quantified. Two ionic liquids were identified to extract capsaicin from fresh chilli more effectively than the conventional ethanol-based process; the inherently basic 1-ethyl-3-methylimidazolium acetate, [Emim][OAc], and the inherently acidic 1-ethyl-3-methylimidazolium hydrogen sulfate, [Emim][HSO4]. The ionic liquid extracts could be electrochemically quantified using a bare glassy carbon electrode either in the pure ionic liquid (one pot extraction and quantification) or after dilution with water/ethanol to assist resolution of the capsaicin (flavour indicator) and ascorbic acid (freshness indicator) features.

A facile technique for the quantification of lignin solubility in ionic liquids has been established. This was used to examine the effect of the anionic and cationic components of ionic liquids on lignin solubility. Changing the cation was shown to have a significant effect on lignin solubility. Interaction of aromatic cations with the solute was significant in most, but not all, ionic liquids. The anion was required to have a minimum hydrogen bonding basicity value for lignin to dissolve, but after this point the anion effect on the overall lignin solubility was negligible relative to the cation.

A range of lignin model compounds were examined for their reactivity with hydrogen bromide in the ionic liquid N-butylpyridinium triflate. It was found that the ionic liquid enabled rapid reaction at both the hydroxy and methyl ether sites of the model compounds at room temperature. Reactions at the phenyl ether moieties were more complex; rather than facilitating cleavage at these sites, alternate breakdown products that had not been seen in previous studies were observed; these products are consistent with functionalisation of the aromatic components of the model compounds.

The cleavage of a series of ethers was examined in an ionic liquid containing hydrogen bromide. Reactions that did not proceed in either water or DMSO were found to proceed readily in this system, with notable selectivity between the cleavage of the different ether types examined herein. Increasing the proportion of water in the reaction mixture dramatically decreased the rate constant of ether cleavage; this could, in part, be attributed to a decrease in the solvent stabilisation of the transition state. Through analysis of the electronic requirements of the reaction (using substrates containing substituents with different Hammett parameters) and observation of rate enhancements for an ortho substituted system, the importance of the extent of protonation of the ether prior to nucleophilic attack was demonstrated.

Thermoelectrochemistry involves the study or application of temperature-dependant parameters in an electrochemical system. Thermoelectrochemistry can be exploited in non-isothermal cells to form thermogalvanic cells (or thermocells) to convert a temperature gradient into a useful electrical current. However, heat can also transfer and reduce the temperature gradient, while spillage is a potential issue for liquid electrolytes. For this reason, we have investigated aqueous thermocells containing potassium ferricyanide and potassium ferrocyanide (0.1 M K3[Fe(CN)6]/0.1 M K4[Fe(CN)6]) as a gelled electrolyte. Fumed silica and gelatine were not found to be sufficient gelling agents, whereas agar agar (agarose) and beads of poly(sodium acrylate) were found to form effective gelled electrolytes; the latter gel was also self-healing. Thermocells were prepared using commercial CR2032 battery casings, and surface treatments and preparations of the stainless steel electrodes evaluated for their electrocatalytic effects and influence on long-term current output. Emphasis was placed upon body heat harvesting, and preliminary heat transfer modelling through the CR2032 systems also performed. Ultimately, the gelled electrolytes were found to result in more stable power output and effectively frustrate heat transfer through the cells, relative to the un-gelled (liquid) electrolytes. These results will inform the development of both more efficient electrolytes and housings for thermocells.

Many pharmaceutically relevant molecules are still extracted directly from lignocellulosic biomass sources. As this can be a bottleneck in supply, total quantification followed by total extraction are desirable processes to ensure as much as possible is obtained, at the optimal time in the growth cycle. Herein we report the application of solid-state 13C nuclear magnetic resonance (NMR) spectroscopy to quantify shikimic acid present inside Chinese star anise (or star aniseed, llicium verum). Subsequently, methanol soxhlet extraction is compared with conventional aqueous hydroxides (i.e. sodium hydroxide) and cellulose-dissolving aqueous hydroxides (i.e. tetraethylammonium and tetrabutylammonium hydroxide) for shikimic acid isolation. Methanol extraction isolated ca. 6.6±0.1wt% (wt%) shikimic acid (post-purification), and solid-state NMR confirmed extraction was incomplete even after 72h. Conversely, dissolution of the star anise at room temperature in tetrabutylammonium hydroxide ([N4444]OH) allowed isolation of ca. 14.0±0.6wt% shikimic acid (post-purification). Solid state NMR confirmed the star anise initially contained 19±3wt% shikimic acid, which was quantitatively extracted after dissolution in the aqueous hydroxide solution. The solubility of the star anise and the kinetics of the shikimic acid extraction were also briefly evaluated.

In this study, a “membrane-less and spill-less” gas-sensing device has been evaluated for the electrochemical detection of oxygen. Iron oxide magnetic nanoparticles were prepared by chemical co-precipitation and used to prepare an aqueous ferrofluid. The iron oxide nanoparticles were subsequently stabilised and passivated with a cationic polymer, namely, poly(diallyldimethyl ammonium chloride). The resulting ferrofluid was evaluated as an electrolyte for the analytical quantification of oxygen on screen-printed carbon electrodes. An applied magnetic field immobilised the ferrofluid electrolyte in place to result in a “membrane-less and spill-less” ferrofluid-based gas sensor. The polymer poly(diallyldimethyl ammonium chloride) was found to result in an apparent enhancement in the electrocatalysis of the system towards the oxygen reduction reaction. Furthermore, as the strength of the applied magnetic field was increased, the oxygen reduction current also increased owing to the response of the polymer-coated nanoparticles. The oxygen reduction current was linear from 0 to 100 % oxygen content.

The electrochemistry of chloride in water-containing hydrophobic ([Emim][NTf2] and [BmPyrr][NTf2]) and hydrophilic ([Emim][OAc]) ionic liquids (ILs) has been described in detail for the first time. Cyclic voltammetric studies at a glassy carbon electrode note the significant effect of ambient water on the electrochemistry of chloride, with different outcomes based upon the hydrophilicity (c.f. water content) of the hygroscopic ILs. Added hydroxide highlighted this as a reactive species. Evaluation of chloride, hypochlorite, chlorite, chlorate and perchlorate electrochemistry (chlorine oxidation states −1, +1, +3, +5 and +7) was performed. Ultimately, the electrochemically formed chlorine (Cl2) was determined to react with water or hydroxide to yield higher oxidation state species via oxychloride intermediates (e.g. hypochlorite) through multiple EC steps, likely resulting in chlorate as the final product. Keywords: Cyclic voltammetry, Chloride, Oxychloride, Water content, 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, Acetate

The oxygen reduction reaction (ORR) has been studied at platinum, gold, and glassy carbon electrodes using cyclic voltammetry and potential-step chronoamperometry in 11 room temperature protic ioni...

The electrochemistry of HgCl(2) and [Hg(NTf(2))(2)] ([NTf(2)](-)=bis-{(trifluoromethyl)sulfonyl}imide) has been studied in room temperature ionic liquids. It has been found that the cyclic voltammetry of Hg(II) is strongly dependent on a number of factors (e.g., concentration, anions present in the mixture, and nature of the working electrode) and differs from that found in other media. Depending on conditions, the cyclic voltammetry of Hg(II) can give rise to one, two, or four reduction peaks, whereas the reverse oxidative scans show two to four peaks. Diffuse reflectance UV-vis spectroscopy and X-ray powder diffraction have been used to aid the assignment of the voltammetric waves.