Aryl Ether Bonds Research Articles

Covalent/ionic co-crosslinking constructing ultra-densely functionalized ether-free poly(biphenylene piperidinium) amphoteric membranes for vanadium redox flow batteries

A novel covalently/ionically co-crosslinked poly(biphenylene piperidinium) amphoteric membrane was designed for improved stability and efficiencies in vanadium redox flow batteries (VRFB). The amphoteric-side-chain structure provides an ultrahigh functionalization degree (4.93 mmol·g − 1) and unobstructed ion channels, which endowed the membrane with an excellent ion conduction capacity comparable to Nafion 212 (area resistance: 0.23–0.29 Ω·cm2). Surpassing traditional sulfonated membranes and single ionic crosslinked membranes, even at high level functionalization, the covalently/ionically co-crosslinking structures guaranteed the membrane a low swelling ratio (10.1%) and VO2+ permeability of 0.79 × 10−8 cm2·s − 1. Moreover, due to the lack of sensitive aryl ether bonds, these membranes showed very good chemical stability, with a slight mass loss of 3.43% (nearly 5.5 times lower than SPEEK) after soaking in vanadium oxygen species for 30 days. On this basis, the membrane exhibited excellent battery performance. The Coulombic, voltage, and energy efficiencies of a battery using the above membrane reached 98.12, 87.27, and 85.98% at 120 mA·cm−2 current density and no obvious decline occurred after 400 cycles. The self-discharge time of battery up to 136 h. These observations indicated that this membrane appeared very promising for use in VRFB applications.

Acid-catalysed \u03b1-O-4 aryl-ether bond cleavage in methanol/(aqueous) ethanol: understanding depolymerisation of a lignin model compound during organosolv pretreatment

The selective lignin conversion into bio-based organic mono-aromatics is a major general challenge due to complex structure itself/additional macromolecule modifications, caused by the cleavage of the ether chemical bonds during the lignocellulosic biomass organosolv pulping in acidified aqueous ethanol. Herein, the acido-lysis of connected benzyl phenyl (BPE), being a representative model compound with α-O-4 linkage, was investigated in methanol, EtOH and 75 vol% EtOH/water mixture solutions, progressing each time with protonating sulfuric acid. The effect of the physical solvent properties, acidity of the reaction process media and temperature on rate was determined. Experiments suggested BPE following SN1 mechanism due to the formation of a stable primary carbocation/polarity. The product species distribution in non-aqueous functional alcohols was strongly affected. The addition of H2O was advantageous, especially for alkoxylation. Yield was reduced by a factor of 3, consequently preserving reactive hydroxyl group. Quantitative experimental results indicated key performance parameters to achieve optimum. Organosolv lignins were further isolated under significantly moderate conditions. Consecutive structural differences observed supported findings, obtained when using BPE. H2O presence was again found to grant a higher measured –OH content. Mechanistic pathway analysis thus represents the first step when continuing to kinetics, structure–activity relationships or bio-refining industrial resources.

Hydrogenolysis of Aryl Ether Bond over Heterogeneous Cobalt-Based Catalyst

The development of efficient non-noble metal catalysts is of critical importance for conversion of lignin toward value-added chemicals. The trans-metal Co catalysts and the counterparts promoted wi...

Lignin valorization and cleavage of arylether bonds in chemical processing of wood: a mini-review

Lignin valorization is strongly dependent on a right strategy for converting lignin into value-added products. Conversion of lignin into monomeric degradation products is one of the important avenues. In this study, chemical mechanisms and monomeric product compositions in hydrolysis (acidic and alkaline), hydrogenolysis, catalytic oxidation, electrochemical oxidation and reduction, photochemical and enzymatic degradation of native and technical lignins, and lignin model compounds are comparatively analyzed. The effect of the structure of a phenylpropane unit in lignin on the chemical reactivity of α-O-4 and β-O-4 bonds in cleavage reactions is also described. Published experimental data suggest some form of activation to be a necessary prerequisite for the splitting of a β-O-4 bond in all chemical reactions under consideration, the nature of which is dependent on the reagents and reaction conditions. Thus, in catalytic oxidation processes, a benzyl hydroxyl group is converted into carbonyl group at the first stage. Chemical transformation involving the α-position in a phenylpropane unit is a usual trigger of further lignin depolymerization. The yield of monomeric products of hydrogenolysis of native lignin is close to the theoretical one, reaching 23% in softwood and 51% in hardwood; in alkaline hydrolysis as well as oxygen and nitrobenzene oxidation of native lignin, the trend is the same that is explained in this study. On the other hand, the yield of monomeric products from isolated samples and technical lignins is much lower. A loss of arylether bonds in the process of lignin separation from wood and in wood pulping explains this difference.

The application of DFRC method for the analysis of carbohydrates in a peat bog: Validation and comparison with conventional chemical and thermochemical degradation techniques

Traditional acid hydrolysis is the main method used for carbohydrates characterization in soils and sediments. It has been used to cleave the glycosidic bond, yielding monomers that compose polysaccharides of the non-cellulosic pool (free, ligno-cellulosic and hemicellulosic carbohydrates). In this study, the widely used chemical and thermochemical degradation procedures have been compared with the derivatisation followed by reductive cleavage (DFRC) method. This method presented efficiency in specifically cleaving the aryl ether bonds, yielding for sugar moieties linked to aromatic structures (ligno-cellulosic fraction). Once applied for peat samples, some discrepancies were observed. DFRC method revealed some information about the origin of carbohydrates that was hidden from the traditional chemical and thermochemical degradation methods. Several patterns of carbohydrates have been obtained with DFRC indicating difference in the origin and/or degradation rates between monosaccharides. For xylose, it showed an increase in the catotelm (deepest layer of the peatland), indicating an angiosperm vegetation input at the early stage of the peatland formation. Ribose, commonly known as a microbial indicator, showed the same profile as for hexoses and deoxyhexoses, with acid hydrolysis. The difference in the profile yielded in the case of DFRC method, revealed its microbial input. These information were hindered from acid hydrolysis and thermochemolysis, as the first showed nearly the same profile for all monosaccharides and the second one didn't have the capacity to analyze arabinose and ribose.Generally, higher similarity was obtained between DFRC and acid hydrolysis than between DFRC and thermochemolysis. This is due to the difference of mechanisms involved in chemolytic and thermochemolytic methods. For the first group, both methods shared acid conditions and milder temperature conditions if compared to the second group. In addition thermochemolysis is performed under alkaline conditions.

Selective hydrogenolysis of aryl ether bond over Ru-Fe bimetallic catalyst

RuFe/CeO2 catalysts were studied in the hydrodeoxygenation (HDO) of diphenyl ether (DPE). We find that the hydrogenation reactivity is favored over 2Ru/CeO2, leading to the formation of dicyclohexyl ether and cyclohexyl phenyl ether as main products. Addition of oxophilic Fe inhibits the hydrogenation of aromatic rings but enhances the hydrogenolysis of CO bonds to produce benzene and phenol as well as cyclohexane and cyclohexanol formed from subsequent hydrogenation of phenol. ∼92 % selectivity to CO bond ruptured products were achieved with ∼21 % yield toward aromatics (benzene and phenol) on 0.5Ru1.5Fe/CeO2 catalyst. Characterization using X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR) reveals that the adsorption of aromatic ring is weakened on the RuFe alloy surface compared to Ru which leads to reduced hydrogenation of arenes, while oxophilic nature of Fe facilitates the adsorption of the aryl-ether bond that enhances the hydrogenolysis of CO bonds in DPE.

Photo-cross-linked poly(N-allylisatin biphenyl)-co-poly(alkylene biphenyl)s with pendant N-cyclic quaternary ammonium as anion exchange membranes for direct borohydride/hydrogen peroxide fuel cells

The slightly crosslinked poly(N-allylisatin biphenyl)-co-poly(alkylene biphenyl)s (PIB-co-PAB) based anion exchange membranes are prepared by super-acid catalyst polycondensation and thiol-ene click chemistry in situ. The hydrophilic crosslinked structure improves the hydroxide conductivity due to enhanced the water uptake and well-developed microphase separation. Furthermore, the introduction of N-spirocyclic quaternization ammonium groups promotes the chemical stability of the prepared membranes. Among them, the crosslinked PIB-co-PAB membrane with high ion exchange capacity exhibit high ion conductivity of 24.7 and 39.1 mS·cm−1 at 30 °C for chloride and hydroxide ionic conduction, respectively. Moreover, it possesses an acceptable alkaline stability, which remains the 65.19% of original hydroxide conductivity after storage in 1 M NaOH solution at 80 °C for 1000 h. Meanwhile, the crosslinked membranes exhibit lower permeability for borohydride anion than un-crosslinked membranes. Additionally, the peak power density of direct borohydride/hydrogen peroxide fuel cells using the crosslinked membrane as separator is 76.1 mW·cm−2 at 149.2 mA·cm−2, which is higher than un-crosslinked membranes (17.3 mW·cm−2 at 48.2 mA·cm−2) Therefore, all the results reveal that the prepared free aryl-ether bonds linkage membranes with hydrophilic crosslinked structure provide potential application in fuel cells.

Structural insights into the alkali lignins involving the formation and transformation of arylglycerols and enol ethers

Soda process is one of the most important pulping processes in paper industry producing large quantities of alkali lignins that can afford plenty of biofuels, aromatic chemicals and materials. However, the structural and size-related heterogeneities and complexities hinder the development in these directions. Herein, we report new insights into the structure of alkali lignin, through investigating the formation and transformation of enol ether and arylglycerol structures that are significant responsible for the structural transformation from native lignin to alkali lignin. Four-type enol ethers composed of G/S units in hardwood alkali lignin were identified by 2D HSQC NMR. A series of alkali lignins prepared by alkali treatment of eucalyptus cellulolytic enzyme lignin under various temperatures were analyzed by 2D HSQC NMR, 31P NMR and gel permeation chromatography (GPC). Upon these analyses and related model compound studies, it was found that the arylglycerols formed from native β-O-4 linkages tends to be oxidized with the further degradation of aryl ether bonds, and that the enol ether linkages are facile to be hydrolyzed or oxidized in the air. These insights improve the mechanistic understanding for the structural evolution and the diversity of alkali lignins and will aid the development of further lignin valorization strategies.

Laccase-catalyzed oxidative modification of lignosulfonates from acidic sulfite pulping of eucalyptus wood

Abstract Lignosulfonates (LS) from acidic magnesium-based sulfite cooking of Eucalyptus globulus wood were modified via laccase-catalyzed oxidative treatment with the aim to improve their performance as plasticizing additives in concrete formulations. The target parameters were the increment of molecular weight (Mw) and the amount of oxidized groups. The laccase-assisted oxidation under optimized conditions (40°C, pH 4.5, enzyme loads of 83–500 U g−1 for 90 min) allowed Mw increment up to 11-fold and almost doubled the amount of carbonyl and carboxyl groups without using any mediators. Modified LS maintained their solubility in water and possessed a zeta- potential close to that of initial LS. The characterization of modified LS has been carried out by ultraviolet-visible (UV-Vis), Fourier transform infrared-attenuated total reflectance (FTIR-ATR) and quantitative 13C nuclear magnetic resonance (NMR) spectroscopy, and the sulfonic and phenolic groups were assessed by conductometric titration. It was concluded that LS polymerization occurred mostly via the formation of new aryl ether bonds (two thirds of the modification) and biphenyl bonds (the remaining third). However, part of the newly formed bonds of unknown origin are temperature labile and cleaved during the concentration of LS at pH 4 and 80°C under vacuum, which led to the reduction of the Mw of the modified lignin to almost one third.

Behaviors of hydrogen bonds formed by lignite and aromatic solvents in direct coal liquefaction: Combination analysis of density functional theory and experimental methods

Hydrogen bonds play a crucial role in thermal conversion of low rank coal, especially direct coal liquefaction (DCL) because of their wealthy abundance and great influence on generation of light products. Relative distribution of hydrogen bonds was evaluated with in-situ diffuse reflectance infrared Fourier transformation (DRIFT), while visualization analysis of hydrogen bonds (OH-π in particular) between coal and solvents were performed using density functional theory (DFT) and reduced density gradient (RDG) analysis. In terms of their effects, DCL experiments of demineralized Yunnan lignite (DeYN) with/without addition of benzene at 200, 250 and 300 °C were carried out, and oxygen-containing functional groups were investigated by solid-state 13C NMR and in-situ DRIFT. Relative content of OH-π hydrogen bonds increased with temperature rising. Benzene is the stronger hydrogen bonds acceptor compared to tetralin (THN). Conclusions drawn from DCL experiments are consistent with DFT calculations. To be specific, benzene with mass concentration of 2% promotes cleavage of O–H bonds, carboxyl groups and the generation of aryl ether bonds, and the differences caused by benzene are intensified when DCL temperature rises.

Database Mining for Novel Bacterial β-Etherases, Glutathione-Dependent Lignin-Degrading Enzymes.

Lignin is the most abundant aromatic polymer in nature and a promising renewable source for the provision of aromatic platform chemicals and biofuels. β-Etherases are enzymes with a promising potential for application in lignin depolymerization due to their selectivity in the cleavage of β-O-4 aryl ether bonds. However, only a very limited number of these enzymes have been described and characterized so far. Using peptide pattern recognition (PPR) as well as phylogenetic analyses, 96 putatively novel β-etherases have been identified, some even originating from bacteria outside the order Sphingomonadales A set of 13 diverse enzymes was selected for biochemical characterization, and β-etherase activity was confirmed for all of them. Some enzymes displayed up to 3-fold higher activity than previously known β-etherases. Moreover, conserved sequence motifs specific for either LigE- or LigF-type enzymes were deduced from multiple-sequence alignments and the PPR-derived peptides. In combination with structural information available for the β-etherases LigE and LigF, insight into the potential structural and/or functional role of conserved residues within these sequence motifs is provided. Phylogenetic analyses further suggest the presence of additional bacterial enzymes with potential β-etherase activity outside the classical LigE- and LigF-type enzymes as well as the recently described heterodimeric β-etherases.IMPORTANCE The use of biomass as a renewable source and replacement for crude oil for the provision of chemicals and fuels is of major importance for current and future societies. Lignin, the most abundant aromatic polymer in nature, holds promise as a renewable starting material for the generation of required aromatic structures. However, a controlled and selective lignin depolymerization to yield desired aromatic structures is a very challenging task. In this regard, bacterial β-etherases are especially interesting, as they are able to cleave the most abundant bond type in lignin with high selectivity. With this study, we significantly expanded the toolbox of available β-etherases for application in lignin depolymerization and discovered more active as well as diverse enzymes than previously known. Moreover, the identification of further β-etherases by sequence database mining in the future will be facilitated considerably through our deduced etherase-specific sequence motifs.

Efficient and controllable ultrasound-assisted depolymerization of organosolv lignin catalyzed to liquid fuels by MCM-41 supported phosphotungstic acid.

In this study, effects of catalyst types, reaction temperatures, reaction times, reaction solvents and ultrasound frequencies were carefully investigated to improve the yields and characteristics of various depolymerization products of organosolv lignin. Generally, both catalyst types and ultrasound frequencies played important roles in promoting lignin depolymerization and reducing char yield. In particular, the yield and distribution of phenolic monomer (PM) products were greatly influenced by pore structure and acidity of the catalyst. The optimal reaction condition was got in isopropanol at 310 °C for 6 h with 30% ultrasound frequency and 50% phosphotungstic acid (PTA)/MCM-41 catalyst. The highest yields of PM, bio-oil, liquid fuels and lignin conversion were reached as 8.63 wt%, 86.89 wt%, 95.52 wt% and 98.54 wt%, respectively. The results showed that ultrasound acoustic cavitation could enhance the depolymerization of lignin, thus greatly enhancing production of liquid fuels. Simultaneously, the hydrogen composition and high heating value of various lignin depolymerization products improved, and the oxygen content decreased, indicating that hydrogenation and/or hydrodeoxygenation happened during the depolymerization process. Finally, we also found that the 50% PTA/MCM-41 catalyst had high stability; it could be reused for up to five cycles without loss of catalytic activity.

Cleavage of aryl-ether bonds in lignin model compounds using a Co-Zn-beta catalyst.

Efficient cleavage of aryl–ether linkages is a key strategy for generating aromatic chemicals and fuels from lignin. Currently, a popular method to depolymerize native/technical lignin employs a combination of Lewis acid and hydrogenation metal. However, a clear mechanistic understanding of the process is lacking. Thus, a more thorough understanding of the mechanism of lignin depolymerization in this system is essential. Herein, we propose a detailed mechanistic study conducted with lignin model compounds (LMC) via a synergistic Co–Zn/Off-Al H-beta catalyst that mirrors the hydrogenolysis process of lignin. The results suggest that the main reaction paths for the phenolic dimers exhibiting α-O-4 and β-O-4 ether linkages are the cleavage of aryl–ether linkages. Particularly, the conversion was readily completed using a Co–Zn/Off-Al H-beta catalyst, but 40% of α-O-4 was converted and β-O-4 did not react in the absence of a catalyst under the same conditions. In addition, it was found that the presence of hydroxyl groups on the side chain, commonly found in native lignin, greatly promotes the cleavage of aryl–ether linkages activated by Zn Lewis acid, which was attributed to the adsorption between Zn and the hydroxyl group. Followed by the cobalt catalyzed hydrogenation reaction, the phenolic dimers are degraded into monomers that maintain aromaticity.

Ni–Mg–Al Catalysts Effectively Promote Depolymerization of Rice Husk Lignin to Bio-Oil

Catalytic depolymerization of lignin to produce bio-oil, liquid fuels, and aromatic chemicals in high yields is important for a biorefinery to remain competitive. In this study, undoped and Ni-doped catalysts for depolymerization of rice husk lignin (RHL) were developed and analyzed. The results showed that the catalysts had hydrotalcite-like structures with lamellar morphology. With suitable Ni-doping amount, the catalysts had high activity, thus better promoted the depolymerization of RHL. Among all catalysts, the Ni1/4MgAl catalyst could best promote the cleavage of the β-O-4 aryl ether bond in RHL molecule and thus could substantially increase the yields of bio-oil. The depolymerization catalyzed by this catalyst was also found to be temperature-, time-, and solvent-dependent. This study provides information that can be beneficial to the biorefinery industries and may help promote the valorization of lignin.

Catalytic Mechanism of Aryl-Ether Bond Cleavage in Lignin by LigF and LigG.

Given the abundance of lignin in nature, multiple enzyme systems have been discovered to cleave the β-O-4 bonds, the most prevalent intermonomer linkage. In particular, stereospecific cleavage of lignin oligomers by glutathione S-transferases (GSTs) has been reported in several sphingomonads. Here, we apply quantum mechanics/molecular mechanics simulations to study the mechanism of two glutathione-dependent enzymes in the β-aryl ether catabolic pathway of Sphingomonas sp. SYK-6, namely, LigF, a β-etherase, and LigG, a lyase. For LigF, the free-energy landscape supports a SN2 reaction mechanism, with the monoaromatic leaving group being promptly neutralized upon release. Specific interactions with conserved residues are responsible for stereoselectivity and for activation of the cofactor as a nucleophile. A glutathione conjugate is also released by LigF and serves the substrate of LigG, undergoing a SN2-like reaction, in which Cys15 acts as the nucleophile, to yield the second monoaromatic product. The simulations suggest that the electron-donating substituent at the para-position found in lignin-derived aromatics and the interaction with Tyr217 are essential for reactivity in LigG. Overall, this work deepens the understanding of the stereospecific enzymatic mechanisms in the β-aryl ether cleavage pathway and reveals key structural features underpinning the ligninolytic activity detected in several sphingomonad GSTs.

From lignin-derived bio-oil to lignin-g-polyacrylonitrile nanofiber: High lignin substitution ratio and maintaining good nanofiber morphology

In this work, lignin-based nanofibers were produced from corn stalk lignin (CSL)/lignin-derived bio-oil (LBO) and polyacrylonitrile (PAN) co-polymers via electrospinning. During depolymerization, the addition of phosphotungstic acid (PTA) promoted the CSL catalytic conversion to some extent, the decrease of β-O-4 aryl ether bond, molecular weight (Mw) and polydispersity (PDI) was obvious. Compared with CSL, LBO can promotes the formation of uniform and smooth lignin-based nanofibers under high replacement rates condition and maintaining good morphology. Subsequent reactions between LBO and PAN fragments formed a better-integrated co-polymers structure containing linear PAN backbone. The Td of LBO-g-PAN was improved to 153 °C and the Tg was decreased to 96.5 °C. Rheological conclusions displayed that the viscosity of PAN/LBO/DMF was 0.082 Pa s, illustrating the polymer substance could be continuously spun into filament without causing degradation of the polymer substance. LBO-g-PAN also had high thermal stability, yielding of residual mass was 56.32 wt% at 700 °C.

Biomimetic Reductive Cleavage of Keto Aryl Ether Bonds by Small-Molecule Thiols.

The nucleophilic and reductive properties of thiolates and thiols make them ideal candidates as redox mediators via the thiol/disulfide couple. One mechanism for biological lignin depolymerization entails reduction of keto aryl ether bonds by an SN 2 mechanism with the thiol redox mediator glutathione. In this study, mimicking this chemistry in a simple protein- and metal-free process, several small organic thiols are surveyed for their ability to cleave aryl keto ethers that model the β-O-4 linkages found in partially oxidized lignin. In polar aprotic solvents, β-mercaptoethanol and dithiothreitol yielded up to 100 % formation of phenol and acetophenone products from 2-phenoxyacetophenone, but not from its reduced alcohol congener. The effects of reaction conditions and of substituents on the aryl rings and the keto ether linkage are assessed. These results, together with activation barriers computed by quantum chemical simulations and direct observation of the expected intermediate thioether, point to an SN 2 mechanism. This study confirms that small organic thiols can reductively break down lignin-relevant keto aryl ether linkages.

Development of Highly Durable Anion Conductive Membrane with All-Aromatic Backbone for Alkaline Fuel Cell Application

Introduction: Solid alkaline fuel cell using anion conductive membrane (ACM) attracts increasing attention since non-noble metal electrode catalyst and high density liquid fuel can be used in this system. However, development of chemically durable membrane is critical for practical device application. Currently, benzyl trimethylammonium modified polyarylene ethers (i.e. polyethersulfone, polyphenyleneoxide, polyetherketon) are used as typical aromatic ACMs for alkaline fuel cell application. However, aryl ether bond in the backbone is not stable and suffered from chain scission under alkaline environment [1], leading to a loss of mechanical strength and conductivity of the membrane For this sense, ACM consisting of only aromatic backbone such as polyphenylene ACM is potential candidate for highly durable membranes [2-4]. However, these membranes are usually suffered from low solubility because of the rigid linear backbone and strong intermolecular π-π interaction. This drawback results in the difficultly for processing membranes To overcome these problems, in this work, we have synthesized a novel ACM with all-aromatic backbone for alkaline fuel cell application. The designed polymer backbone is composed of alternative m-phenylene and p-phenylene unit, changing the polymer structure to 2D zigzag conformation to suppress strong intermolecular π-πstacking. (Fig 1). Also, branched alkyl side chain was introduced for further enhancing solubility. We expected that AEM with both high durability and solubility can be obtained by using this membrane. Method: The precursor polymer for target membrane was synthesized by Pd-catalyzed Suzuki-Miyaura polymerization between m-phenylene and p-phenylene derivatives [5]. Structure and molecular weight of this precursor polymer were evaluated by 1H-NMR and gel permeation chromatography (GPC). Bromide groups at the polymer side chain were reacted with trimethylamine to afford the target membrane. Ion exchange capacity (IEC) of the membrane was evaluated by both 1H-NMR and titration. Ion conductivity of the membrane was calculated by alternative current impedance measurement. Alkaline stability of this membrane was evaluated by comparing 1H-NMR spectra before and after soaking into 8M NaOH aq, at 80 oC. Results and Discussion: The number average molecular weight (Mn) and polydistersity (PDI) of the precursor polymer were Mn=18000 and PDI=1.6, respectively. Quaternization of the precursor polymer proceeded almost quantitatively from 1H-NMR spectra. IEC of target polymer was 2.6 meq from NMR analysis and similar value (2.4) was obtained in titration. The synthesized membrane can be dissolved well into methanol, dimethylsulfoxide.and also 1-propanol/water (1:1 vol) mixture, which is typically used as suitable solvent for membrane electrode assembly (MEA) preparation. This indicates that the developed polymer is also promising candidate for an ionomer of fuel cells. Bormide and bicarbonate conductivity of the membrane were 52 mS/cm and 41 mS/cm (70 oC, RH100%), respectively. The conductivity value is high enough for fuel cell application. Chemical stability of the developed membrane was evaluated in harsh alkaline condition (8M NaOH, 80 oC). Even after one week, no detectable change was observed in the membrane. In fact, 1H-NMR spectra of the membrane after the alkaline stability test shows that both the anion exchange group and the backbone are stable in this condition. These results indicate that the developed all-aromatic ACM is promising candidate for a membrane and an ionomer of alkaline fuel cell. Reference [1] S. Miyanishi, T. Yamaguchi, Phys. Chem. Chem. Phys., 2016,18, 12009-12023 [2] E. J. Park and Y. S. Kim, J. Mater. Chem. A, 2018, 6, 15456-15477 [3] S. Miyanishi, T. Yamaguchi, J. Mater. Chem. A, 2019,7, 2219-2224 [4] H. P. R. Graha, S. Ando, S. Miyanishi and T. Yamaguchi, Chem. Commun., 2018, 54, 10820–10823. [5] B. Deffner and A.D. Schluter, Poly. Chem. 2015, 6, 7833-7840 Figure 1

Molecular Engineering of Hydroxide Conducting Polymers for Anion Exchange Membranes in Electrochemical Energy Conversion Technology.

Anion exchange membranes (AEMs) based on hydroxide-conducting polymers (HCPs) are a key component for anion-based electrochemical energy technology such as fuel cells, electrolyzers, and advanced batteries. Although these alkaline electrochemical applications offer a promising alternative to acidic proton exchange membrane electrochemical devices, access to alkaline-stable and high-performing polymer electrolyte materials has remained elusive until now. Despite vigorous research of AEM polymer design, literature examples of high-performance polymers with good alkaline stability at an elevated temperature are uncommon. Traditional aromatic polymers used in AEM applications contain a heteroatomic backbone linkage, such as an aryl ether bond, which is prone to degradation via nucleophilic attack by hydroxide ion. In this Account, we highlight some of the progress our group has made in the development of advanced HCPs for applications in AEMs and electrode ionomers. We propose that a synthetic polymer design with an all C-C bond backbone and a flexible chain-tethered quaternary ammonium group provides an effective solution to the problem of alkaline stability. Because of the critical demand for such a polymer system, we have established new synthetic strategies for polymer functionalization and polycondensation using an acid catalyst. The first approach is to graft a cationic tethered alkyl group to pre-existing, commercially available styrene-based block copolymers. The second approach is to synthesize high-molecular-weight aromatic backbone polymers using acid-catalyzed polycondensation of arene monomers and a functionalized trifluoromethyl ketone substrate. Both strategies involve a simple two-step reaction process and avoid the use of expensive metal-based catalysts and toxic chemicals, thereby making the synthetic processes easily scalable to large industrial quantities. Both polymer systems were found to have excellent alkaline stability, confirmed by the preservation of ion exchange capacity and ion conductivity of the membrane after an alkaline test under conditions of 1 M NaOH at 80-95 °C. In addition, the advantage of good solvent processability and convenient scalability of the reaction process generates considerable interest in these polymers as commercial standard AEM candidates. AEM fuel cell and electrolyzer tests of some of the developed polymer membranes showed excellent performance, suggesting that this new class of HCPs opens a new avenue to electrochemical devices with real-world applications.

Photocatalytic Cleavage of Aryl Ether in Modified Lignin to Non-phenolic Aromatics

Depolymerization of lignin meets the difficulty in cleaving the robust aryl ether bond. Herein, through installing an internal nucleophile in the β-O-4′ linkage, the selective cleavage of aryl ethe...