Published papers

Novel protic ionic liquids (PILs) were synthesized by neutralization of primary alkylamines with bis(trifluoromethanesulfonyl)amide acid. An extensive hydrogen bonding network in these PILs was observed via lower thermal stability, temperature dependent inversion from non-Newtonian to Newtonian fluidic behavior, and lower ionicity compared to their secondary and tertiary analogues.

In this study, the effect of hydrophilic silica nanoparticle (AEROSIL 200) addition on the rheological and transport properties of several protic ionic liquids (PILs) consisting of protonated 1,8-diazabicyclo[5.4.0]undec-7-ene cation (DBU) was studied. Interactions between the surface silanol groups of the silica nanoparticles and the ions of these PILs affected the nature of particle aggregation and the hydrogen bonding environment, which was reflected in the nonlinear rheological behaviors and transport properties of their colloidal suspensions. In contrast to shear-thinning gels formed by colloidal suspensions of the silica nanoparticles in [DBU][TFSA] ([TFSA] = [N(SO₂CF₃)₂]), [DBU][TfO] ([TfO] = [CF₃SO₃]), and [DBU][TFA] ([TFA] = [CF₃CO₂]), a shear-thickening stable suspension was formed in the [DBU][MSA] ([MSA] = [CH₃SO₃]) system. A relatively strong interaction between the silanol groups and the ions of [DBU] [MSA] and the ability of this PIL to form a thicker solvation layer through hydrogen bonding were assumed to be responsible for this unique behavior. Moreover, the [DBU][MSA]-silica system showed a large enhancement in the conductivity at a certain silica concentration. This enhancement was not observed in the other PIL-silica composites that exhibited shear-thinning behavior. Even though diffusion of ions was found to be restricted in the presence of silica, a preferentially stronger interaction between [MSA] anions and the silica surface resulted in an increase in the number of charge carriers.

The development of suitable separation technologies for the separation of carbon dioxide is a pressing technological requirement. The application of ion gel membranes for this purpose continues to stimulate a great deal of research, and in this study we focus on the chemical structure of the ionic liquid component in the ion gel, and its interactions with the sulfonated polyimide polymer. Whilst such membranes are known to give promising carbon dioxide separation properties together with mechanical strength and thin-film-processability, we further elaborate on how changing the cation of the ionic liquid from a typical imidazolium cation to a protic variant effects the physicochemical, thermal, and structural properties of the membranes, and how these changes further influence the carbon dioxide separation properties. We compare and contrast our findings with our earlier study on protic and aprotic ammonium-based ionic liquids, and highlight that for CO₂ absorption behavior in the imidazolium systems, the importance of directionality of interactions (ion pairs exhibit a large energy stabilization only for a specific geometrical arrangement of cation and anion, e.g., hydrogen bonding rather than Coulombic interaction) between cation and anion applies not only to the protic system, but also to the nominally aprotic cation. Finally, we demonstrate that the phase separation behavior in the ion gels is an important factor in determining the carbon dioxide separation behavior.

An extensive and systematic study has been carried out on the catalytic effect of more than 20 elements on the aerobic oxidation of p-xylene to terephthalic acid in super-and subcritical water. Reactions have been performed in a continuous reactor under catalyst unsaturated conditions. Reaction product, by-products and intermediates have been quantified as well as the burn (the amount of CO2 originating from total oxidation of p-xylene). CuBr2 has been found to be a superior catalyst to MnBr2, which has been widely used in the literature for this reaction in water at high temperatures. At catalyst unsaturated conditions (i.e. with low concentrations of catalyst), MnBr2 gives a terephthalic acid yield of 36.1% whereas CuBr2 enhances this value to 55.6%. A strong synergistic effect has been found between CuBr2 and other metals and sources of bromide. Indeed, we show that Cu/Co/Br, Cu/Co/NH4/Br and other mixtures give better results than CuBr2 reaching a terephthalic acid yield of 70.5% for the four component catalyst. The compositions of the catalyst as well as the reactor temperature have been optimized and their effects on the analyzed compounds are discussed. A substantial amount of additional data is included in the electronic supplementary information.

In this paper we report a strong dependence of the observed performance of the catalyst on the geometry and the configuration of laboratory scale reactors in the continuous aerobic oxidation of p-xylene in supercritical water. Small differences, such as the length of the feed pipes protruding into the reactor, have a very large effect on the observed yields and selectivities as well as on the reproducibility of the results. Different reactor designs also exert an influence on the perceived catalyst performance. We demonstrate that these effects are consistent with the relative efficiency of mixing of the reactant streams in the different reactors. The overall conclusion is that caution is required when comparing sets of data derived from studying such reactions even in apparently similar experimental arrangements.

The major bottleneck for widespread realization of fuel cells has been the usage of precious-metal-based electrocatalysts, such as Pt/C or Pt-alloy/C, at the cathode. Owing to the high cost and limited natural resources of platinum, nonprecious metal catalysts, such as iron-doped carbons, have emerged as promising substitute catalyst materials. Protic salts and protic ionic liquids can provide a simple, quick, and cost-effective approach for fabricating iron-doped carbons without any additives or high-surface-area carbon supports. We demonstrate here the fabrication of an efficient electrocatalyst based on a protic salt, 1,10-phenanthrolinium dihydrogen sulfate ([Phen][2HSO4]), in combination with iron(iii) chloride, FeCl3, via nanocasting. A predominantly mesoporous architecture with a narrow pore size distribution was achieved owing to the suitability of the precursors and silica template. The material also exhibited in situ formation of Fe-N bonds in the nitrogen and sulfur co-doped carbons. We found that maximizing the content of this motif was beneficial towards efficient conversion of oxygen into water in alkaline media. The prototype catalyst after post treatment (acid leaching and 2nd carbonization) also exhibited efficient reduction of oxygen in acidic media. The contribution of Fe-N bonds to the observed activity in acidic solution was less than in alkaline solution. The simplicity of the synthesis of the protic salt and the versatility of the ionic liquid platform make this molecular-level carbon precursor a unique candidate for future development of iron doped catalysts for fuel cells.

A solvate ionic liquid (SIL) was compared with a conventional organic solvent for the electrolyte of the Li-O-2 battery. An equimolar mixture of triglyme (G3) and lithium bis(trifluoromethanesulfonyl)amide (Li[TFSA]), and a G3/Li[TFSA] mixture containing excess glyme were chosen as the SIL and the conventional electrolyte, respectively. Charge behavior and accompanying gas evolution of the two electrolytes was investigated by electrochemical mass spectrometry (ECMS). From the linear sweep voltammetry performed on an as-prepared cell, we demonstrate that the SIL has a higher oxidative stability than the conventional electrolyte and, furthermore, offers the advantage of lower volatility, which would benefit an open-type lithium-O-2 cell design. Moreover, CO2 evolution during galvanostatic charge was less in the SIL, which implies less side reaction. However, O-2 evolution during charge did not reach the theoretical value in either of the two electrolytes. Several mass spectral fragments were generated during the charge process, which provided evidence for side reactions of glyme-based electrolytes. We further relate the difference in observed discharge product morphology for these electrolytes to the solubility of the superoxide intermediate, determined by rotating ring disk electrode (RRDE) measurements.

Following our recent study demonstrating predominant Li-ion hopping conduction in sulfolane (SL)-based highly concentrated electrolytes with LiBF4, LiClO4, and lithium bis(fluorosulfonyl)amide, herein a systematic study on transport properties and Li-ion coordination of SL-based electrolytes with lithium bis(trifluoromethanesulfonyl)amide was performed. In the highly concentrated region, Li ions clearly diffuse faster than SL and TFSA anions. The two oxygen atoms of the SL sulfonyl group tend to coordinate to two different neighboring Li ions and TFSA anions form ionic clusters with Li ions, verifying the previous observation of the unusual Li-ion conduction and its relevance to the SL-and anion-bridged, chainlike Li-ion coordination structure for the SL-based concentrated systems with other Li salts. Moreover, addition of hydrofluoroether (HFE) to the SL-based concentrated electrolytes greatly enhances diffusion coefficients but fragments the chainlike Li-ion coordination to smaller clusters, leading to a reduced contribution of Li-ion hopping to the overall Li-ion conduction. The SL-based concentrated electrolyte and its mixtures with HFE showed lower lithium polysulfide solubility and higher rate capability for lithium-sulfur (Li-S) cells compared with previously reported tetraglyme-based electrolytes. The SL-based electrolytes were found to manifest a significant improvement in Li-ion mass transfer as a sparingly solvating electrolyte, enabling the solid-state sulfur redox reactions in high-performance Li-S batteries.

Shuttling of soluble polysulfide species within electrodes is one of the most challenging issues in lithium-sulfur (Li-S) batteries. The resulting deposition of polysulfide species reduces the conductivity of the metallic Li electrode and the quantity of active material. Here, we demonstrate pronounced suppression of polysulfide shuttle using a sulfide-impermeable glass-ceramic membrane, which is employed as separator between the positive and negative electrodes. As a result, highly stable Li-S electrochemistry occurs in the sulfur-dissolving tetrahydrofuran catholyte solution, which provides good capacity retention and Coulombic efficiency for cycling. This demonstration holds promise for practical next-generation batteries with marked reversibility and the possibility to increase the energy density when equipped with a catholyte flow-through mode.

In this study, the effect of water on the oxygen reduction reaction is initially investigated in aprotic ionic liquids by cyclic voltammetry, revealing that the presence of water significantly deteriorates the reversibility of the oxygen reduction reaction and oxygen evolution reaction, which will be detrimental to performance of a practical lithium-air battery. In order to prevent moisture intrusion from ambient air, a hydrophobic electrolyte is then designed and the moisture content in the electrolyte exposed to ambient air is greatly suppressed, to less than 1 wt% at 30 degrees C and 90% RH (relative humidity). Charge and discharge tests using the hydrophobic electrolyte are reversible for several cycles even in O-2 with a RH of 28%. This approach for enhancing the hydrophobicity of the electrolyte, and thus the inherent equilibrium moisture content, for the Li-air battery demonstrates the possibility for improved stability to ambient moisture.

Organic ionic plastic crystals (OIPCs) have attracted attention as novel organic solid electrolyte materials, but their insufficient mechanical strength and ionic conductivity have prevented their application. In this study, a lithium salt, lithium bis(fluorosulfonyl)amide (LiFSA), and an inorganic solid electrolyte, Li₇La₃Zr₂O₁₂ (LLZO), were added to an OIPC, N,N-diethylpyrrolidinium bis(fluorosulfonyl)amide ([C₂epyr][FSA]). The fabricated organic-inorganic hybrid solid electrolytes were evaluated thermally, mechanically, and electrochemically to reveal which factors affect the properties of the electrolytes. All samples showed excellent thermal stability regardless of LiFSA or LLZO concentration, and they were found to be highly plastic and ion-conductive solids at a wide range of temperatures. It was also revealed that the addition of LLZO raised the nanoindentation stiffness (H-IT) of the [C₂epyr][FSA]/LiFSA composites. The ionic conductivity of the hybrid electrolytes was higher than that of the pristine OIPC, reaching a value of 2.1 × 10⁻⁴ S cm⁻¹ at 25 degrees C upon addition of appropriate amounts of LiFSA and LLZO. Overall, samples with higher LiFSA concentration and moderate LLZO concentration exhibited higher ionic conductivity. Cyclic voltammetry results showed that the [C₂epyr][FSA]/LiFSA/LLZO composites were lithium-ion conductors. These findings indicate that by optimizing the concentrations of lithium salt and LLZO, it would be possible to realize their applications as solid electrolytes.

In lithium-oxygen (Li-O2) batteries, nanocatalysts have been widely employed as a means to suppress the large recharge overpotential and to possibly improve cyclability. However, these studies have consistently been mired with ambiguity relating to the possible exacerbation of side reactions, which in turn has brought into question the role of such catalysts in Li-O2 cells. Here, we shed light on the viability of nanocatalysts by examining the use of Ru, Pt, Pd, Co3O4, and Au nanoparticles supported on carbon nanotubes in Li-O2 cells. We show that while there can be noticeable reduction in overpotential with catalysts, the facile decomposition of Li2O2 is not accompanied by a decrease in side reactions, and as a consequence, there is no notable improvement in rechargeability or cyclability. Instead, highly active catalysts can exhibit nonselectivity for all oxidation reactions including Li2O2 and the electrolyte. This work underscores the importance of metrics beyond simple consideration of the recharge overpotential and the necessity of pursuing approaches that can promote reversible Li-O2 electrochemistry.

We demonstrate that Li+ hopping conduction, which cannot be explained by conventional models i.e., Onsager's theory and Stokes' law, emerges in highly concentrated liquid electrolytes composed of LiBF4 and sulfolane (SL). Self-diffusion coefficients of Li+ (D-Li), BF4- (D-BF4), and SL (D-SL) were measured with pulsed-field gradient NMR. In the concentrated electrolytes with molar ratios of SL/LiBF4 <= 3, the ratios D-SL/D-Li and D-BF4/D-Li become lower than 1, suggesting faster diffusion of Li+ than SL and BF4-, and thus the evolution of Li+ hopping conduction. X-ray crystallographic analysis of the LiBF4/SL (1:1) solvate revealed that the two oxygen atoms of the sulfone group are involved in the bridging coordination of two different Li+ ions. In addition, the BF4- anion also participates in the bridging coordination of Li+. The Raman spectra of the highly concentrated LiBF4-SL solution suggested that Li+ ions are bridged by SL and BF4- even in the liquid state. Moreover, detailed investigation along with molecular dynamics simulations suggests that Li+ exchanges ligands (SL and BF4-) dynamically in the highly concentrated electrolytes, and Li+ hops from one coordination site to another. The spatial proximity of coordination sites, along with the possible domain structure, is assumed to enable Li+ hopping conduction. Finally, we demonstrate that Li+ hopping suppresses concentration polarization in Li batteries, leading to increased limiting current density and improved rate capability compared to the conventional concentration electrolyte. Identification and rationalization of Li+ ion hopping in concentrated SL electrolytes is expected to trigger a new paradigm of understanding for such unconventional electrolyte systems.

This study demonstrates that the amount of discharge product (Li2O2) precipitated on the separator in a lithium oxygen cell using glyme-based electrolytes depends on the anion. The stability of the discharge intermediate (LiO2) in the electrolyte has been shown to depend on the anionic species, which is related to Li2O2 precipitation on the separator. The implications for producing an efficient and long-life Li-O-2 cell are elaborated.

© 2018 American Chemical Society. The use of LiI as redox mediator for the charge reaction in nonaqueous Li/O2 cells has been widely studied recently, as a possible means to fulfill the great promise of the Li/O2 system as a high energy density "beyond Li-ion" battery. In this work, we highlight the importance of considering the redox potential for both the I-/I3- and I3-/I2 redox couples and how the electrolyte solvent (here tetraglyme (G4) and dimethyl sulfoxide (DMSO)) and concentration (here 1.0 and 2.8 M) have a profound influence on these potentials. Through a combination of galvanostatic cycling, electrochemical mass spectrometry, and cyclic voltammetry, we thus consider the influence of solvent and electrolyte concentration on both the redox mediation and redox shuttle processes and suggest that this important aspect must be considered for further studies with mediators in Li/O2 and related systems. We demonstrate that, in our system, 100 mM LiI in 1.0 M Li[TFSA]/DMSO provides the most effective redox mediation among the electrolytes we have studied but conversely exhibits the highest degree of redox shuttling (in the absence of O2). The balance between effective limitation of redox shuttle and ease of mediator diffusion to discharge products is of great importance and should be considered in any future cell design utilizing a mediator.

Water can be an attractive solvent for Li-ion battery electrolytes owing to numerous advantages such as high polarity, nonflammability, environmental benignity, and abundance, provided that its narrow electrochemical potential window can be enhanced to a similar level to that of typical nonaqueous electrolytes. In recent years, significant improvements in the electrochemical stability of aqueous electrolytes have been achieved with molten salt hydrate electrolytes containing extremely high concentrations of Li salt. In this study, we investigated the effect of divalent salt additives (magnesium and calcium bis(trifluoromethanesulfonyl)amides) in a molten salt hydrate electrolyte (21 mol kg(-1) lithium bis(trifluoromethanesulfonyl)amide) on the electrochemical stability and aqueous lithium secondary battery performance. We found that the electrochemical stability was further enhanced by the addition of the divalent salt. In particular, the reductive stability was increased by more than 1 V on the Al electrode in the presence of either of the divalent cations. Surface characterization with X-ray photoelectron spectroscopy suggests that a passivation layer formed on the Al electrode consists of inorganic salts (most notably fluorides) of the divalent cations and the less-soluble solid electrolyte interphase mitigated the reductive decomposition of water effectively. The enhanced electrochemical stability in the presence of the divalent salts resulted in a more-stable charge-discharge cycling of LiCoO2 and Li4Ti5O12 electrodes.

An ongoing major outbreak of mountain pine beetle in Western Canada has provided a clear opportunity to utilize waste pinewood as a source of renewable energy. Therefore hydrothermal processing of waste pinewood as a feedstock for bio-oil and biochar production using subcritical and supercritical water technology was carried out in semi-batch mode to investigate the effect of pressure (200–400 bar) and temperature (300–400 °C) on the yield and composition of bio-oil. The pinewood samples have very high cellulose and hemicellulose content but low ash content and are thus a formidable feedstock for bioenergy production. The optimum conditions for the hydrothermal processing of the pinewood in a tubular reactor were found to be 400 °C and 250 bars with respect to biochar and bio-oil yield based on the highest calorific value analysis. Detailed characterization of bio-oil and biochar was performed using GCMS, NMR, SEM, calorific value, and elemental analysis, respectively. The critical components of bio-oil were found to be phenols, methoxyphenols, hydroxymethyl furfural (HMF), and vanillin, whereas as compared to the raw pine wood, the biochar was considerably lower H:C and O:C ratios than those of the unprocessed pinewood. The analyses of bio-oil by means of GCMS and ¹H NMR showed that it was mainly composed of heterocyclic compounds, phenols, aldehydes and acids.

We present here the application of Raman microscopy in providing simultaneous visual and spectroscopic characterisation of the physical and chemical changes occurring in organometallic materials while undergoing hydrothermal treatment. The effect of water at elevated pressures and temperatures on three prototype manganese carbonyls, Mn-2(CO)(10), (eta(5)-C5H5)Mn(CO)(3) and Mn(CO)(5)Br, was investigated. A Bassett-type hydrothermal diamond-anvil cell (HDAC) was used to subject each compound to conditions of at least 22.1 MPa and 374 degrees C (i.e., beyond the critical point of water), while Raman microscopy was used to monitor the structural changes occurring during the heating and cooling cycles of the cell. The hydrothermal studies showed that Mn-2(CO)(10), (eta(5)-C5H5)Mn(CO)(3) and Mn(CO)(5)Br dissolved in subcritical water at 150, 125 and 225 degrees C. respectively. Moreover, Mn(CO)(5)Br is also believed to have dimerized to Mn-2(CO)(8)Br-2 when the cell temperature was increased to 425 degrees C. (C) 2011 Elsevier B.V. All rights reserved.

The applications of synchrotron X-ray powder diffraction (XRPD) and laser micro-Raman techniques in an examination of the dissolution, transformation, and gasification of pure cellulose and models for biomass residue under hydrothermal conditions in a diamond-anvil cell are reported. The results contribute to the measurement of in situ time-resolved profiles of biomass reactions, catalyst stability, and residue formation that occur in aqueous fluids at near-and supercritical conditions.