Detrimental Side Reactions Research Articles

Bioinspired PDA@TiO2 modification on high-voltage LiNi0.5Mn1.5O4 toward enhancing electrochemical performance

Improving the cycling performance without sacrificing its capacity is challenging for high-voltage LiNi0.5Mn1.5O4 cathode due to the trade-off nature among the key properties. A self-polymerization process of dopamine was utilized to grow polydopamine (PDA)-nano titanium dioxide assembly. PDA@TiO2 composite was demonstrated to be integrated with the particles of high-voltage spinel LiNi0.5Mn1.5O4 cathodes via wet chemical method. PDA@TiO2 decorated LNMO improved the long-term cycling performance and rate capability by suppressing detrimental side reactions in balancing the interfacial stability and Li+ diffusion kinetics of LNMO and consequently providing efficient conductive pathways. As a result, 2% PDA@TiO2 modified LNMO cathode exhibited the high reversible capacity of 117mAhg−1 after 1000 cycles with good capacity retention of 90.7% at 1 C, and superior rate capability (78.5mAhg−1 at 5 C) at room temperature. Remarkably, a significant improvement in cycling stability at an elevated temperature (50°C) was obtained for the PDA@TiO2-LNMO composite, giving a capacity retention of 93% after 100 cycles at 1 C. The mechanism of performance improvement could be attributed to the maintenance of the structural stability of LNMO cathode materials and the enhanced kinetics of the remarkable lithium-ion diffusion through the protective effect of PDA@TiO2 decorating.

Operando diffuse reflectance infrared detection of cyanide intermediate species during the reaction of formaldehyde with ammonia over V2O5/WO3-TiO2

Hydrogen cyanide (HCN) is a highly poisonous gas that can form through the reaction between formaldehyde and ammonia (NH3) in the exhaust. While this detrimental side reaction has been the subject of recent catalytic studies under selective catalytic reduction conditions, the molecular mechanism leading to the release of HCN remains far from elucidated. Here, we report the detection of the cyanide intermediate species by operando diffuse reflectance infrared spectroscopy, thereby providing unambiguous evidence that the HCN-forming reaction occurs on the catalyst surface. Formaldehyde likely reacts from the gas phase with pre-adsorbed NH3 to form HCN. Although formate species were formed abundantly upon formaldehyde introduction, they were not responsible for the high level of HCN emissions observed. TiO2 alone is sufficient to catalyze the side reaction, but VOx and/or WOx sites increase HCN production by preventing the formation of inactive polyamide species. These mechanistic insights should serve as a basis for understanding the chemistry responsible for the side reaction so that mitigation measures can be put forward.

Lithium Phosphonate Functionalized Polymer Coating for High‐Energy Li[Ni0.8Co0.1Mn0.1]O2 with Superior Performance at Ambient and Elevated Temperatures

AbstractHigh‐energy Ni‐rich lithium transition metal oxides such as Li[Ni0.8Co0.1Mn0.1]O2 (NCM811) are appealing positive electrode materials for next‐generation lithium batteries. However, the high sensitivity toward moist air during storage and the high reactivity with common organic electrolytes, especially at elevated temperatures, are hindering their commercial use. Herein, an effective strategy is reported to overcome these issues by coating the NCM811 particles with a lithium phosphonate functionalized poly(aryl ether sulfone). The application of this coating allows for a substantial reduction of lithium‐based surface impurities (e.g., LiOH, Li2CO3) and, generally, the suppression of detrimental side reactions upon both storage and cycling. As a result, the coated NCM811‐based cathodes reveal superior Coulombic efficiency and cycling stability at ambient and, particularly, at elevated temperatures up to 60 °C (a temperature at which the non‐coated NCM811 electrodes rapidly fail) owing to the formation of a stable cathode electrolyte interphase with enhanced Li+ transport kinetics and the well‐retained layered crystal structure. These results render the herein presented coating strategy generally applicable for high‐performance lithium battery cathodes.

Elucidating the Solubility and Diffusivity of Atmospheric Gases in a Wide Variation of Liquid Electrolytes for Lithium-Air Batteries

Due to their high theoretical energy density, Li–O2 and Li–air batteries are considered as a promising alternative to Li-ion batteries, especially for mobile applications. However, dissolved gases in the liquid electrolyte, in particular O2, can be involved in detrimental side reactions at the lithium anode. Moreover, CO2 that can form from side reactions with the electrolyte or the cathode material, and N2 from the ambient air might be dissolved in the electrolyte.In order to evaluate the impact of these dissolved gases on the stability of the anode and to know their concentrations in possible side reactions, the solubility and the diffusion coefficient for each gas in the electrolyte are crucial parameters to know.In this work, we utilize gas uptake measurements to systematically determine the diffusion coefficients and Henry’s law solubility constants of O2, N2 and CO2 in different ether- and DMSO-based electrolytes and pure solvents. Additionally, we calculate the diffusion coefficient with molecular dynamics simulations and show good qualitative agreement between simulations and experimental results. We discuss the influence of solvent parameters, such as surface tension and viscosity, on the solubility and the diffusivity as well as the impact of different conducting salts. All investigated conducting salts reduce the diffusivity of the gases; however, we observe the solubility can both decrease or increase, depending on the solvent, the gas and the molecular structure of the salt. Therefore, we emphasize that both components, solvent and conducting salt, have to be considered for optimizing the gas transport properties of the electrolyte for Li–O2 and Li–air batteries.

Tackling the Interfacial Issues of Spinel LiNi0.5Mn1.5O4 by Room-Temperature Spontaneous Dediazonation Reaction.

The detrimental interfacial side reactions, inducing electrolyte decomposition and transition-metal dissolution, are regarded as "arch-criminal" for the utilization of spinel LiNi0.5Mn1.5O4 (LNMO) in high-power Li-ion batteries (LIBs). To conquer this issue, herein, we construct a thin polyphenyl film onto the surface of LNMO via the spontaneous dediazonation of C6H5N2+BF4- at room temperature. This conductive film facilitates the Li+ transport within cathode and at LNMO|electrolyte interface while reinforcing the compatibility of LNMO against electrolyte by efficiently suppressing the electrolyte decomposition catalyzed by LNMO and even the transition-metal dissolution. Consequently, polyphenyl-grafted LNMO exhibits improved electrochemical performances, e.g., the considerable discharge capacity of 136.7 mAh g-1 at low current density (0.1C), excellent rate capability, and long-term cyclability with a reversible capacity of 107.4 mAh g-1 along with high capacity retention of ∼85% after cycling 500 times, that are superior to those of the pristine LNMO counterpart. All these results demonstrate that our strategy is instrumental in solving the interface issues with respect to the spinel LNMO cathode, impelling the development of LNMO-based batteries with high energy density.

Improved Cycling Performance of High‐Nickel NMC by Dry Powder Coating with Nanostructured Fumed Al2O3, TiO2, and ZrO2: A Comparison

AbstractSurface coating is an effective concept to protect layered cathode active materials (CAMs) in lithium ion batteries from detrimental side reactions. Dry powder coating is a fast and cost‐effective coating process, and here we transfer this coating approach from Al2O3 to nanostructured fumed TiO2 and ZrO2 coatings on the same NMC (Li[Ni,Mn,Co]O2) material. Using similar processing, this allows a direct comparison of the characteristics of the achieved coating layers and their influence on the cycling performance of high‐nickel NMC. The nanostructured small oxide aggregates result in a quite homogeneous coating layer with a certain porosity around each CAM particle. Significantly enhanced long‐term cycling stability is observed, with a trend of increasing stability in the series ZrO2<TiO2<Al2O3. Fumed Al2O3 and TiO2 coating layers prevent cathode particle cracking and disintegration successfully, while fumed ZrO2 only shows a moderate protection effect. Each coating material enhances the rate performance compared to uncoated NMC in the row TiO2<ZrO2<Al2O3. XPS measurements of cycled electrodes indicate a partial incorporation of lithium ions in the crystalline TiO2 and ZrO2 coating layers, contributing to the enhanced lithium‐ion transport across the CAM surface layer, as observed before for fumed γ‐Al2O3 coatings. Summarizing the results, the best overall cycling performance was achieved by coating high‐nickel NMC with fumed Al2O3, providing the highest rate capability and the best long‐term cycling stability.

A reaction engineering approach to non-aqueous battery lifetime

<h2>Summary</h2> Complex side reactions drive capacity fade in modern Li-ion batteries and are a key factor in achieving extended battery lifetimes. Unfortunately, the interconnected nature of the reaction pathways means that optimizing one aspect of performance can result in a shift between benign and detrimental side reactions, and that simple Coulombic efficiency is unable to capture these differences. Because batteries are ultimately chemical reactors, reaction engineering principles can provide a suitable framework for understanding. The electrocatalytic systems of Li-O₂ batteries and electrochemical CO₂ reduction demonstrate both the importance of quantifying reaction selectivity and the key role that reactor geometry plays in this process. Recent findings from these fields suggest that battery side reactions should also be studied in reactors that have been optimized for analytics. In this reaction engineering context, we discuss the advantages and disadvantages of existing analytical tools and present pathways for designing new reactors that can directly evaluate Li-ion battery reaction selectivity. Quantification of selectivity and reaction parameters can direct materials design and improve lifetime prediction.

An effective strategy for shielding polysulfides and regulating lithium deposition in lithium–sulfur batteries

The lithium–sulfur (Li–S) battery is an appealing choice for the next-generation high-energy-density energy storage systems. However, side reactions between lithium polysulfides (LiPSs) and Li metal anode cause the growth of Li dendrites, loss of active materials, and safety issues, which severely hinders the practical application of Li–S batteries. Constructing a protection layer on the surface of Li anode is an effective strategy to shield LiPSs and regulate lithium uniform deposition in Li–S batteries. Herein, we design and fabricate a lithiated Nafion protective layer to alleviate the side reactions between LiPSs and the Li anode and guide uniform deposition of Li, in which, their mechanism is investigated. The optimal protective layer effectively protects the Li anode from the detrimental side reactions, which boosts the stability of the Li anode. Li–Li and Li-stainless steel cells with 4 M [S] Li2S8 electrolyte can last for more than 400 cycles and 100 cycles at current density of 1 mA cm−2. A Li–S full cell also exhibits a high reversible capacity of 791.5 mA h g−1 after 250 cycles at 0.5 C. This work reveals the vital role of the artificial protective layer in enhancing the stability of the Li anode in Li–S batteries.

A superb 3D composite lithium metal anode prepared by in-situ lithiation of sulfurized polyacrylonitrile

Lithium metal has been regarded as the most promising anode for the next generation high energy- density batteries. However, detrimental side reactions with electrolyte, uncontrollable lithium dendrite growth, distinct volume expansion and fragile solid electrolyte interface (SEI) layer lead to low coulombic efficiency (CE), rapid battery failure and even safety hazards, which hinders its practical application. Herein, we propose a novel composite anode which embeds Li metal particles into a Li+/electron hybrid conductive framework and is reinforced by CNTs. Sulfurized pyrolyzed poly(acrylonitrile) (S@pPAN), which is extensively studied as superior cathode materials, is creatively adopted to render abundant Li3N and Li2S on the surface of the Li particles and in the free-space. The in-situ formed hybrid framework not only provides a rapid Li+ transfer channel throughout the electrode, but also suppresses the Li dendrite growth and inhibits the volume expansion. With further assistance of lithiophilic nano-MgO, the composite anode achieved dense and reversible Li plating/striping. As a result, a long cycle life of more than 800 hours with 10 mAh cm−2 and excellent electrode kinetics are obtained for symmetric cells. Moreover, the full cells coupled with S@pPAN and LiFePO4 cathodes deliver a long and stable cycle life. The rational 3D composite anode design provides a feasible strategy to build high performance Li metal batteries.

Constructing a Low-Impedance Interface on a High-Voltage LiNi0.8Co0.1Mn0.1O2 Cathode with 2,4,6-Triphenyl Boroxine as a Film-Forming Electrolyte Additive for Li-Ion Batteries.

Compared with other commercial cathode materials, the LiNi0.8Co0.1Mn0.1O2 cathode (NCM811) has high specific capacity and a relatively low cost. Nevertheless, the higher nickel content in NCM811 leads to an extremely unstable interface between the electrode and the electrolyte, resulting in inferior cyclic stability of the corresponding cell. Use of film-forming additives is regarded as the most feasible and economic approach to construct a stable interface on the NCM811 cathode. However, less effective electrolyte additives have been reported to date. Herein, we propose a valid film-forming electrolyte additive, 2,4,6-triphenyl boroxine (TPBX), for application in a high-voltage NCM811 cathode. Experimental and computational results reveal that the TPBX additive can be preferentially oxidized to generate a highly stable and conductive cathode electrolyte interface (CEI) layer on the NCM811 cathode, which efficiently suppresses the detrimental side reaction and improves the electrochemical performance eventually. In detail, the cyclic stability of the Li/NCM811 half-cell is enhanced from 57% (without additive) to 78% (with 5% TPBX) after 200 cycles at 1C between 3.0 and 4.35 V. At a high current rate of 15C, the TPBX-containing electrode delivers a capacity of about 135 mAh g-1, which is much higher than that of the electrode without the additive (80 mAh g-1). Interestingly, the TPBX is also reduced earlier than the ethylene carbonate (EC) solvent to form an ionically conductive solid electrolyte interface (SEI) film on the graphite anode. Due to the CEI layer on the cathode and the SEI film on the anode simultaneously formed by the TPBX additive, the cyclic performance of the graphite/LiNi0.8Co0.1Mn0.1O2 full cell is enhanced. Therefore, the incorporation of the TPBX additive into the electrolyte provides a convenient method for the commercial application of the high-energy-density NCM811 cathode in high-voltage lithium-ion batteries.

High-Efficiency Lithium Metal Anode Enabled by a Concentrated/Fluorinated Ester Electrolyte.

Lithium (Li) metal anode (LMA) has received growing attention due to its highest theoretical capacity (3860 mA h g-1) and lowest redox potential (-3.04 V versus standard hydrogen electrode). However, practical application of LMA is obstructed by the detrimental side reactions between Li metal and organic electrolytes, especially when cycled in traditional carbonate ester electrolytes. Herein, we propose a novel fluorinated carbonate ester-based electrolyte by combining diethyl fluorocarbonate (ETFEC) solvent and 5 M LiFSI concentration (M = mol L-1). Using this electrolyte, an ultrahigh Li plating/stripping Coulombic efficiency (CE) of 99.1% can be obtained in Li||Cu cells and a stable cycle performance of Li||LiFePO4 is achieved under the conditions of limited Li metal (5 mA h cm-2), moderate loading LiFePO4 (7-8 mg cm-2), and lean electrolyte (40 uL). The fundamental functioning mechanism of this novel electrolyte has been carefully investigated by scanning electronic microscopy (SEM), operando optical microscopy (OM), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and solid state nuclear magnetic resonance (SS-NMR). The results demonstrate that this optimized electrolyte facilitates formation of a high Li+ conductive SEI layer enriched with LiF and inorganic sulfur-containing species, which can effectively suppress the side reactions between electrolyte and Li metal and prevent formation of dead Li.

Thiol-ene addition of mercaptoalcohols to poly(vinylsiloxanes) under visible light photocatalysis – An approach towards cross-linkable hydrophilic silicones

Addition of thiol compounds bearing electron-withdrawing substituents linked to sulphur atom to vinyl-group containing organosiloxane polymers may be achieved without any catalyst or initiator, only on exposure to visible light. This approach allows for preparation of silicone copolymers with desired amount of unsaturated residues and hydrophilic groups. No detrimental side reactions involving vinyl substituents were observed. The copolymers can be easily cross-linked, as it was shown in model experiments carried out with tetrafunctional pentaerythritol tetrakis(3-mercaptopropionate). Specific surface energy of the obtained cross-linked films and their linear precursors is relatively low despite the presence of –OH groups, irrespectively of their amount and the nature of the support. It makes the prepared copolymers interesting materials to be used as silicone inks for stretchable and wearable electronic devices as well as in microfluidics.

Tailoring Dihydroxyphthalazines to Enable Their Stable and Efficient Use in the Catholyte of Aqueous Redox Flow Batteries

To enable cost-efficient stationary energy storage, organic active materials are the subject of current investigations with regard to their application in aqueous redox flow batteries. Especially quinones with their beneficial electrochemical properties and natural abundance pose a promising class of compounds for this challenging endeavor. Yet, there are not many active materials available for the catholyte side to realize solely quinone-based systems. Herein we introduce the novel hydroquinone 5,8-dihydroxy-2,3-phthalazine together with two of its derivatives and propose it as a promising active material for the catholyte side of aqueous redox flow batteries. We systematically investigate the electrochemical properties as well as the structure–property relationship of this class of compounds. The unmodified dihydroxyphthalazine exhibits a favorably high redox potential of 796 mV vs SHE in acidic solution that is competitive with benzoquinone compounds. Moreover, the introduced dihydroxyphthalazines feature a high electron transfer rate surpassing benzoquinone species by almost one order of magnitude. With regard to stable cycling performance, we further achieved a high resilience against detrimental side reactions such as Michael addition by adding methyl substituents to the base structure. Our experimental findings are supported and extended by theoretical considerations in terms of density functional theory calculations. With this combined approach we outline further promising dihydroxyphthalazine-based materials with regard to performance-relevant quantities like redox potential, cycling stability, and water solubility. This study aims to propel further research in the field of quinone-based active materials for the catholyte of future aqueous redox flow batteries.

Improved electrochemical property of Ni-rich LiNi0.6Co0.2Mn0.2O2 cathode via in-situ ZrO2 coating for high energy density lithium ion batteries

Surface coating is an effective routine to improve the cycling stability and reversible capacity of nickel-rich LiNi0.6Co0.2Mn0.2O2 (NCM622) cathode in lithium ion batteries (LIBs), especially at high voltage. Herein, an amorphous Zirconium dioxide (ZrO2) coating modified NCM622 cathode materials are successfully prepared by in-situ method based on UiO-66. As the cathode material for LIBs, the in-situ ZrO2 coated NCM622 retains 82.5% capacity retentions over 2.8–4.5 V after 100 cycles, higher than those for the pristine NCM622, which are only 52.4%. Such significant improvements are mainly attributed that the homogeneous ZrO2 coating effectively stabilized the cathode/electrolyte interface. It is confirmed that the uniform ZrO2 coating layer suppressed the structural degradation induced by detrimental side reactions with electrolyte. Meanwhile, the unique porous framework of UiO-66 also provides massive active sites on the NCM622 surface, keeping the lithium diffusion even at a high level upon cycling. The in-situ synthesized method provides an available and simple modifying strategy for high performance ZrO2-coated cathode materials at high voltage.

Selective Catalytic Reduction of NO with NH3 on Cu−SSZ‐13: Deciphering the Low and High‐temperature Rate‐limiting Steps by Transient XAS Experiments

AbstractCu‐exchanged small‐pore SSZ‐13 catalysts have found wide use for the selective catalytic reduction (SCR) of nitrogen oxides from automotive exhaust gases. The transient working environment of the Cu−SSZ‐13 catalyst during NH3‐SCR requires studying the rate limiting steps under the different operation conditions this catalyst is exposed to. By exploiting time‐resolved operando X‐ray absorption spectroscopy in combination with multivariate analysis we followed the transient speciation of Cu during unsteady state conditions. The results reveal that depending on operating temperature two different rate limiting behaviours inhibit the reduction of NO. At temperatures below 283 °C, ammonia hinders reoxidation of solvated CuI species thereby inhibiting reduction of NO. Whilst at temperatures of 283 °C and above, the reduction of zeolite bound CuII(OH−) is the rate limiting step in the SCR reaction. The results also reveal the presence of two detrimental side reactions occurring, the direct oxidation of zeolite bound CuI at low temperatures and the oxidation of ammonia over Cu at temperatures in excess of 283 °C. Between 250 °C and 350 °C, both side reactions may be present and could explain the dip in the SCR activity typically denoted by the seagull shape.

Ultrathin LiV2O4 Layers Modified LiNi0.5Co0.2Mn0.3O2 Single‐Crystal Cathodes with Enhanced Activity and Stability

AbstractNickel–cobalt–manganese ternary cathode materials for lithium‐ion batteries are prone to detrimental side reactions and deterioration performance at deep charge. Coating is one of the effective methods to boost electrochemical performance of materials. This work conducts an ultrathin LiV2O4 layer on the single‐crystal LiNi0.5Co0.2Mn0.3O2 (NCM523) particles and scrutinizes the optimal coating amount. It turns out that 0.3 wt% LiV2O4‐modified NCM523 cathode achieves a reversible discharging capacity of 131.2 mAh g−1 after 100 cycles (3.0–4.5 V vs Li/Li+), with a capacity retention of 80% (which is 50% higher than that of the pristine sample). The experimental data suggest that this lithium vanadate coating technique provides an innovative strategy to boost the performance of NCM cathodes.

Online Electrochemical Mass Spectrometry for Rechargeable Batteries

Operando analytical techniques for lithium ion batteries (LIBs) have proven to be valuable tools to gain insight into the processes ongoing during battery cycling. Among these techniques, operando (or online) electrochemical mass spectrometry (OEMS) is a very versatile tool for tracking reactivity of cell components during its operation. Mass spectrometry made a first appearance as analytical technique for LIBs about two decades ago in the course of studies about the mechanisms of electrolyte reduction on graphitic surfaces (1). However, the then-used experimental cells required large amounts of electrolyte and had rather moderate detection limits. In recent years the cell design and overall experimental setup underwent significant overhaul, thus allowing the identification and quantification of various gases down to ppm level. This, in turn, allowed the more extensive application of OEMS to investigate a broad variety of LIB-related processes and it has been used by us and other groups to study: cell-component reactivity and electrolyte decomposition (2), SEI formation on graphite/silicon composite anodes (3), gas release from cathode active materials due to irreversible anionic oxygen redox (4), surface reconstruction (5) and surface impurities (6). In this contribution we present the current OEMS setup at PSI, which can be used for measurements down to the ppm level, and highlights from our recent research. One example is the application of the electrolyte additive TMSPa as chemical probe: it allows to monitor the formation of inorganic fluorides such as HF and LiF during cell operation, which in turn made it possible to gain insight into detrimental side-reactions taking place during cell operation (7). Another example is the application of OEMS to study the mechanisms in beyond Li-ion technologies, such as sodium batteries. The study covers the surface reactivity of the graphite anode which acts as a ternary intercalation compounds in the investigated system.(8) The gas release here showed significant differences compared to the Li system stemming from the (electro)chemical reactivity of the conduction salts as well as the sodium anode. The obtained data allowed to draw conclusions for the further optimization of the Na-ion batteries as well as for future OEMS studies in the field of sodium ion batteries. ___________________________________________________________________________________ (1) R. Imhof, P. Novák, J. Electrochem. Soc. 145,1081-1087 (1998). (2) A. Guéguen, D. Streich, M. He, M. Mendez, F. F. Chesneau, P. Novák, E. J. Berg, J. Electrochem. Soc. 163 A1095-A1100 (2016); M. Metzger, B. Strehle, S. Solchenbach, H. A. Gasteiger, J. Electrochem. Soc. 163 A1219-A1225 (2016). (3) R. Jung, M. Metzger, D. Haering, S. Solchenbach, C. Marino, N. Tsiouvaras, C. Stinner, H. A. Gasteiger, J. Electrochem. Soc. 163 A1705-A1716 (2016). (4) E. Castel, E. J. Berg, M. El Kazzi, P. Novák, C. Villevieille, Chem. Mater. 26, 5051-5057 (2014); K. Luo, M. R. Roberts, R. Hao, N. Guerrini, D. M. Pickup, Y. S. Liu, K. Edstrom, J. Guo, A. V. Chadwick, L. C. Duda, P. G. Bruce, Nat. Chem. 8, 684-691 (2015). (5) D. Streich, C. Erk, A. Guéguen, P. Müller, F. Chesneau, E. J. Berg, J. Phys. Chem. C 121, 13481-13486 (2017); R. Jung, M. Metzger, F. Maglia, C. Stinner, H. A. Gasteiger, J. Electrochem. Soc. 164 A1361-A1377 (2017). (6) S. E. Renfrew, B. D. McCloskey, J. Amer. Chem. Soc. 139, 17853-17860 (2017). (7) C. Bolli, A. Guéguen, M. Mendez, E. J. Berg, Chem. Mater. submitted. (8) G. Mustafa, C. Bolli, E. J. Berg, P. Novák, K. Pollok, F. Langenhorst, M. v. Roeder, O. Lenchuk, D. Mollenhauer, P. Adelhelm, Adv. Energy Mater. 8, 1702724 (2017).

Cleavage of lignin model compounds and ligninox using aqueous oxalic acid.

Aqueous oxalic acid cleaves oxidised β-O-4 lignin model compounds by two distinct mechanisms that are dependent on the presence of the hydroxymethyl substituent. Various β-O-4 phenoxyacetophenones that do not contain the hydroxymethyl substituent undergo oxidative cleavage upon exposure to aqueous oxalic acid in the presence of air, likely through concerted ring opening of a dioxetane intermediate to give the corresponding benzoic acid and phenyl formate. Importantly, detrimental side reactions arising from singlet oxygen and hydroperoxy radicals (from both O2 and oxalic acid) are minimal when the cleavage is run under air compared to neat oxygen. When oxidised β-O-4 lignin model compounds bearing the hydroxymethyl group are cleaved by aqueous oxalic acid, the resulting diketone and phenol products arise from a redox neutral cleavage that is analogous to the formic acid-sodium formate mediated lignin cleavage process reported by Stahl. Aqueous oxalic acid also cleaves lignin itself, with oxidised milled wood lignin (MWLox) from Pinus radiata giving a 14% yield of ethyl acetate soluble aromatics with good selectivity for vanillin. Aqueous oxalic acid appears to be a promising lignin cleavage system given the benign, bio-based reagents, absence of metals and organic solvents and a simple extraction procedure that enables oxalic acid recycling.

Scalable porous zinc anode to improve the cycling performance of aqueous lithium energy storage systems

Abstract A porous zinc anode is successfully fabricated using a simple, scalable method for use in Rechargeable Hybrid Aqueous Battery (ReHAB) systems. The porous anode provides a higher surface area (2X), roughness, and wettability than the planar one. These properties allow for better contact between the anode surface and the electrolyte, increasing the cycling performance when used in the ReHAB system. ReHABs with the porous anode show an improvement in initial discharge capacity (34%) at 1C, capacity retention after 300 cycles at 1C, rate performance at various C-rates, and float charge current (a 94% decrease). This decrease in float charge current corresponds to the lower levels of gas generated from detrimental side reactions during battery operation. The enhancements in the rate performance as well as minimized gas evolution in both small (1.13 cm2 in 1.15 mAh coin-cell) and large (9 cm2 in 7 mAh big battery) show the promising potential of the porous anode for use in large-scale battery applications. Based on the findings from various characterization techniques, suppression in dendrite growth and side reactions on the porous anode surface during battery operations have been the main reason for the improvement in ReHAB cycling performance.

Biphasic Voltammetry and Spectroelectrochemistry in Polymer of Intrinsic Microporosity\u20144-(3-Phenylpropyl)-Pyridine Organogel/Aqueous Electrolyte Systems: Reactivity of MnPc Versus MnTPP

A hydrophobic polymer of intrinsic microporosity (PIM-EA-TB) is employed to stabilize an organogel/aqueous electrolyte phase boundary based on an organic water-insoluble 4-(3-phenylpropyl)-pyridine phase. The organogel with electrocatalytic metal complexes embedded is immobilized on glassy carbon or on transparent mesoporous tin-doped indium oxide (ITO) electrodes. Liquid/liquid ion transfer voltammetry is investigated for a 4-(3-phenylpropyl)-pyridine organogel/aqueous electrolyte interface for two types of redox systems: tetraphenylporphyrinato-Mn(III/II) (MnTPP) and phthalocyanato-Mn(III/II) (MnPc). Electron transfer is shown to be coupled to reversible liquid/liquid anion transfer processes for PF6−, ClO4−, SCN−, and NO3−, with a change in mechanism for the more hydrophilic anions Cl−, F−, and SO42−. In situ UV-Vis spectroelectrochemistry reveals reversible Mn(III/II) redox processes coupled to ion transfer for MnTPP. But further complexity and a detrimental side reaction are observed for MnPc causing gradual loss of the electrochemical response in the presence of dioxygen.Graphical ᅟ