Protonic Acid Research Articles

Polymeric ionic liquids and piperidinium synergistically improve proton conductivity and acid retention of polybenzimidazole-based proton exchange membranes

Amino-type polybenzimidazole is prepared, then ionic liquid with three nitrogen positive sites ([CTDTr]Br3) is polymerized into polymeric ionic liquids (PILs) by in-situ radical polymerization, and AmPBI-CTDTr-Px membranes were prepared by piperidinium (PPd) and [CTDTr]Br3 combination to cross-linked with AmPBI. Following treatment with KOH and phosphoric acid (PA), the ion pairs (N+ - H2PO4-) generated in the composite membrane system can enhance proton conductivity and facilitate proton transport. The AmPBI-CTDTr-Px membranes shown exceptional PA retention as a result of the alkaline properties of both [CTDTr]Br3 and PPd, which can engage in acid-base interactions with phosphoric acid. Specifically, the proton conductivity of AmPBI-CTDTr-P5 at 180 °C is 129.7 mS cm-1, which is 2.52 times that of pure membranes. Acid retention of AmPBI-CTDTr-P5 at 80 °C/40% RH and 160 °C are 64.4% and 84%.

Acid‐doped polyaniline‐based asymmetric supercapacitors with high energy density by electrochemical polymerization

AbstractIn this article, conductive polyaniline (PANI) was prepared by electrochemical polymerization on the FTO surface doping different protonic acids (H2SO4, HCl and H3PO4), named the rod‐like PANI‐S, dogtail‐like PANI‐Cl and burr‐like PANI‐P, respectively. The three‐type PANIs possess stable structure, novel morphology and low charge transfer resistance after careful investigation. Among them, the obtained rod‐like PANI‐S has the best specific capacitance of 542.8 F g−1. Also, biomass activated carbon AC with good specific capacitance was successfully prepared by chemical activation of green tea. Interestingly, the asymmetric supercapacitor (ASC) device was assembled with PANI‐S in PVA‐H2SO4 as the positive electrode and AC3:1 in PVA‐KOH as the negative electrode and the obtained ASC device has voltage window of 1.6 V and energy density of 29 Wh kg−1. Electrochemical evaluation in the PANI‐based ASC devices improves the potential applications in energy storage fields.

Oxide Acidity Modulates Structural Transformations in Hydrogen Titanates during Electrochemical Li-Ion Insertion.

Hydrogen titanates (HTOs) form a diverse group of metastable, layered titanium oxides with an interlayer containing both water molecules and structural protons. We investigated how the chemistry of this interlayer environment influenced electrochemical Li+-insertion in a series of HTOs, H2TiyO2y+1·nH2O (y = 3, 4, and 5). We correlated the electrochemical response with the physical and chemical properties of HTOs using operando X-ray diffraction, in situ differential electrochemical mass spectroscopy, solid-state proton nuclear magnetic resonance, and quasi-elastic neutron scattering. We found that the potential for the first reduction reaction trended with the relative acidity of the structural protons. This mechanism was supported with first-principles density functional theory (DFT) calculations. We propose that the electrochemical reaction involves reduction of the structural protons to yield hydrogen gas and formation of a lithiated hydrogen titanate (H2-xLixTiyO2y+1). The hydrogen gas is confined within the HTO lattice until the titanate structure expands upon subsequent oxidation. Our work has implications for the electrochemical behavior of insertion hosts containing hydrogen and structural water molecules, where hydrogen evolution is expected at potentials below the hydrogen reduction potential and in the absence of electrolyte proton donors. This behavior is an example of electrochemical electron transfer to a nonmetal element in a metal oxide host, in analogy to anion redox.

Effect of the carbon surface chemistry on the metal speciation in Ru/C catalysts. Impact on the transformation of levulinic acid to γ-valerolactone

A set of Ru/C catalysts prepared using a commercial active carbon and a series of carbon materials derived from it (treatment in N2 flow, at 300, 600 or 900 °C that selectively removes surface oxygen complexes), of similar textural properties and different surface chemistry, were used, without reduction treatment, in the aqueous phase transformation of levulinic acid (LA) to γ-valerolactone (GVL) at 70 °C. The prepared Ru/C catalysts were active, being activity and selectivity strongly dependent on the support surface chemistry. It was confirmed that the supported Ru species became reduced under reaction conditions, and this process was more efficient in catalysts prepared with the heat treated supports, due to the different interactions created between Ru species and the support surface. In a cleaner carbon surface, the anchorage of the Ru species on carbon oxygen groups was limited, and they were more prone to be reduced and to move, forming more defined metallic structures. The carbon surface chemistry determined the Ru speciation (reduced and oxidized species), and the proportion of reduced Ru drived the H spill over process, which was related to the creation of protonic acid sites, proposed to be key point to explain the trend in selectivity to GVL.

Tunable Emission and Structural Insights of 6-Arylvinyl-2,4-bis(2'-hydroxyphenyl)pyrimidines and Their O∧N∧O-Chelated Boron Complexes.

In this study, we present the synthesis and photophysical characteristics of a novel series of 6-arylvinyl-2,4-bis(2'-hydroxyphenyl)pyrimidines. These compounds exhibit nonemissive properties attributed to the potential occurrence of a excited-state intramolecular proton transfer process from the OH groups to the nitrogen atoms of the pyrimidine ring. The introduction of an acid for protonation of the pyrimidine ring results in a significant enhancement of the fluorescence response, easily perceptible to the naked eye. Notably, these molecules serve as intriguing rigid O∧N∧O ligands for boron chelation. The incorporation of boron atoms promotes structural planarity, increases rigidity, and successfully restores fluorescence in both solution and the solid state. Moreover, the photoluminescence was found to be strongly influenced by the nature of the end groups on the arylvinylene fragment, allowing for the modulation of the emission color and covering the optical spectrum from blue to red. Strong emission solvatochromism was observed in various solvents, a finding that supports the formation of intramolecular charge-separated emitting states, particularly when terminal electron-donating groups are present in the structure. X-ray diffraction analysis enables the determination of inter- and intramolecular interactions, as well as molecular packing structures, aiding in the rationalization of distinct luminescent behaviors in the solid state. All experimental findings are elucidated through extensive density functional theory (DFT) and time-dependent DFT calculations.

Waxberry-like Mo2C@N doped carbon hierarchical structures for broadband electromagnetic absorptions

Broadband electromagnetic absorption materials showcase advantages for coping the increasingly complicated electromagnetic pollution and interferences. Among them, carbon-based materials, with light weight and high stability, are potential ideal electromagnetic absorption materials. The broadband design strategy for carbon-based electromagnetic absorption materials usually involves with hierarchical structure and interface engineering, which is often costly or complex. In this paper, the phosphomolybdic acid is designed to simultaneously serve as the doping protonic acid, as well as the doping Mo source. Waxberry-like Mo2C@N doped carbon hierarchical structures are synthesized through the carbonization of low-cost polyaniline precursors. The hierarchical structures exhibit significantly enhanced electromagnetic absorptions. The optimal RL reaches −50.4 dB, and the effective bandwidth can reach 5.1 GHz at a thickness of 2.0 mm. The enhanced electromagnetic absorptions are mainly attributed to the microscale waxberry-like hierarchical structure, the Mo2C and N doped carbon polarization structures, as well as the asymmetric Mo–N interfacial hybridizations. This work provides a reference path for the design of broadband carbon-based electromagnetic absorption materials.

Highly active nitrogen-phosphorus co-doped carbon fiber@graphite felt electrode for high-performance vanadium redox flow battery

Heteroatom-doped electrodes offer promising applications for enhancing the longevity and efficiency of vanadium redox flow battery (VRFB). Herein, we controllably synthesized N, P co-doped graphite fiber electrodes with conductive network structure by introducing protonic acid and combining electrodeposition and high temperature carbonization. H2SO4 and H3PO4 act as auxiliary and dopant, respectively. The synergistic effect between N and P introduces additional defect structures and active sites on the electrodes, thereby enhancing the reaction rate, as confirmed by density functional theory calculations. Furthermore, the conductive network structure of carbon fibers improves electrode-to-electrode connectivity and reduces internal battery resistance. The optimized integration of these strategies enhances VRFB performance significantly. Consequently, the N, P co-doped carbon fiber modified graphite felt electrodes demonstrate remarkably high energy efficiency at 200 mA cm−2, surpassing that of the blank battery by 7.9 %. This integrated approach to in-situ controllable synthesis provides innovative insights for developing high-performance, stable electrodes, thereby contributing to advancements in the field of energy storage.

Compound catalyst of ReMoSx@HSSZ-39 and SAPO-34 zeolites for high performance conversion of CO2 to C2-4 hydrocarbons

We report here a high-performance catalyst ReMoSx@HSSZ-39 compounded with SAPO-34 for conversion of CO2 to C2-4 hydrocarbons, in which the ReMoSx clusters are responsible for highly efficient hydrogenation of CO2 to methanol as the intermediate and then the surrounding zeolitic acid sites for further conversion of methanol to hydrocarbons. The investigation finds that uniform ReMoSx clusters can be reliably fabricated in zeolitic cages by co-introduction of rhenium and molybdenum species into the HSSZ-39 zeolite and followed by sulfidation, which constitutes an intimate bifunction catalyst through better cooperation of ReMoSx clusters and the zeolitic acid sites. Compared with MoSx@HSSZ-39, the introduction of rhenium significantly suppresses CO generation. By mixing some SAPO-34 zeolite, with increased density of protonic acid, more than 86 % C2-4 hydrocarbons in organic products and only 21 % CO at 32.5 % of CO2 conversion are obtained and the composite catalyst shows excellent stability with more than 95 % C2-4 hydrocarbons in organic products, less than 30 % CO and above 26.6 % of CO2 conversion after 1000 h on stream.

Accelerated proton dissociation in an excited state induces superacidic microenvironments around graphene quantum dots

Investigating proton transport at the interface in an excited state facilitates the mechanistic investigation and utilization of nanomaterials. However, there is a lack of suitable tools for in-situ and interfacial analysis. Here we addresses this gap by in-situ observing the proton transport of graphene quantum dots (GQDs) in an excited state through reduction of magnetic resonance relaxation time. Experimental results, utilizing 0.1 mT ultra-low-field nuclear magnetic resonance relaxometry compatible with a light source, reveal the light-induced proton dissociation and acidity of GQDs’ microenvironment in the excited state (Hammett acidity function: –13.40). Theoretical calculations demonstrate significant acidity enhancement in –OH functionalized GQDs with light induction (pKa*\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\\mathrm{p}}}{K}_{{\ ext{a}}}^{*}$$\\end{document} = –4.62, stronger than that of H2SO4). Simulations highlight the contributions of edge and phenolic –OH groups to proton dissociation. The light-induced superacidic microenvironment of GQDs benefits functionalization and improves the catalytic performances of GQDs. Importantly, this work advances the understanding of interfacial properties of light-induced sp2–sp3 carbon nanostructure and provides a valuable tool for exploring catalyst interfaces in photocatalysis.

Development of High Performance Thermoelectric Polymers via Doping or Dedoping Engineering.

It is of great significance to develop high-performance thermoelectric (TE) materials, because they can be used to harvest waste heat into electricity and there is abundant waste heat on earth. The conventional TE materials are inorganic semimetals or semiconductors like Bi2Te3 and its derivatives. However, they have problems of high cost, scarce/toxic elements, high thermal conductivity, and poor mechanical flexibility. Organic TE materials emerged as the next-generation TE materials because of their merits including solution processability, low cost, abundant element, low intrinsic thermal conductivity, and high mechanical flexibility. Organic TE materials are mainly conducting polymers because of their high conductivity. Both the conductivity and Seebeck coefficient depend on the doping level, and they are interdependent. Hence, the TE properties of polymers can be improved through doping/dedoping engineering. There are three types of doping forms, oxidative (or reductive) doping, protonic acid doping, and charge transfer doping. Accordingly, they can be dedoped by different approaches. In this article, we review the methods to dope and dedope p-type and n-type TE polymers and the combination of doping and dedoping to optimize their TE properties. Secondary doping is also covered, since it can significantly enhance the conductivity of some TE polymers.

Mechanism of high sensitivity proton acids doped polypyrrole molecularly imprinted electrochemical sensor and its application in urea detection

Molecularly imprinted electrochemical sensor is a kind of convenient, fast, and stable analyzer, but the conductivity of electrode materials and their affinity with the analyte affect its performance. A proton acid (PSS, SA, SSA) doping method was proposed to improve the electrochemical performance of the polypyrrole molecularly imprinted polymer (PPy-MIP), which promoted the electropolymerization of pyrrole, reduced the charge transfer resistance, and increased the electrochemical surface area. In terms of both improving conductivity and affinity, the response of the proton acids doped the polypyrrole molecularly imprinted electrochemical sensors (PPy-MIECS) to urea was improved by 25-fold (PSS), 5-fold (SA), and 3-fold (SSA) over that of PPy-MIECS. In addition, the PSS-PPy-MIECS was validated for the practical application with a linear detection range from 0.1 mM to 100 mM, high selectivity (α = 39.73), reusability (RSD% = 4.54 %), reproducibility (RSD% = 0.93 %), and stability (11 days). The advantage of proton acid doping method in PSS-PEDOT-MIECS to urea and PSS-PPy-MIECS to glucose extended its application in the performance enhancement of MIECS design.

The effect of nitrogen positive sites on the proton conductivity and acid stability of polybenzimidazole-based proton exchange membranes

High-temperature proton exchange membranes (HT-PEMs) based on amino-type polybenzimidazole (AmPBI) and double-bonded ionic liquids (ILs) are prepared. To prevent leakage of ILs, three kinds of polymeric ionic liquids (PILs) with different nitrogen positive sites are synthesized through in-situ free radical polymerization, and then the AmPBI-PIL membranes are prepared. The ion pairs (N+ - H2PO4−) formed after treatment with KOH and PA have a good effect on both proton conductivity and PA retention. After acid doping, the nitrogen positive sites in the PILs form ion pairs with PA, which serves as a jumping site for protons and promotes proton transport. The excellent proton conductivity and PA remaining of the AmPBI-PIL membranes are noteworthy. In particular, the proton conductivity of AmPBI-CTDTr is as high as 184.9 mS cm−1 at 180 °C, and the acid reservation is 83 % at 160 °C after 240 h. AmPBI-CTDTr has a 550.9 mW cm−2 peak power density when it is anhydrous at 160 °C.

Abnormal Michael Reaction: Condition-Dependent Product Distributions in the Michael Reaction of Monoalkyl-Substituted Malonates.

The abnormal Michael reaction reported by Thorpe and Michael in 1900, which involves the transfer of an activating group from a nucleophilic species to an α-carbon of the Michael acceptor in reaction with monosubstituted malonates, was revisited using prototypical substrates for both intramolecular and intermolecular reactions. In both reactions, condition-dependent product distributions were observed. Thus, under the conditions using NaHMDS or NaH in THF or Et2O, no formation of the abnormal Michael product was observed, and the major product was an apparent retrograde Michael reaction in the abnormal Michael product resulting from an elimination of a malonate anion with the migrated acyl group as a part of it. The use of a base capable of generating a proton source such as NaOEt resulted in formation of the abnormal Michael product in the intermolecular reaction, although the retrograde Michael product was still a major product. On the other hand, in the intramolecular reaction, the abnormal product was not detected under any conditions used. A plausible reaction mechanism in which the lower kinetic acidity of the malonate proton compared to the thermodynamic acidity plays a significant role has been proposed.

Microbial mechanisms in nitrogen fertilization: Modulating the re-mobilization of clay mineral-bound cadmium in agricultural soils

Soil cadmium (Cd) can affect crop growth and food safety, and through the enrichment in the food chain, it ultimately poses a risk to human health. Reducing the re-mobilization of Cd caused by the release of protons and acids by crops and microorganisms after stabilization is one of the significant technical challenges in agricultural activities. This study aimed to investigate the re-mobilization of stabilized Cd within the clay mineral-bound fraction of soil and its subsequent accumulation in crops utilizing nitrogen ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3−-N), at 60 and 120 mg kg−1. Furthermore, the study harvested root exudates at various growth stages to assess their direct influence on the re-mobilization of stabilized Cd and to evaluate the indirect effects mediated by soil microorganisms. The results revealed that, in contrast to the NO3−-N treatment, the NH4+-N treatment significantly enhanced the conversion of clay mineral-bound Cd in the soil to NH4NO3-extractable Cd. It also amplified the accumulation of Cd in edible amaranth, with concentrations in roots and shoots rising from 1.7–6.0 mg kg−1 to 4.3–9.8 mg kg−1. The introduction of NH4+-N caused a decrease in the pH value of the rhizosphere soil and stimulated the production and secretion organic and amino acids, such as oxalic acid, lactic acid, stearic acid, succinic acid, and l-serine, from the crop roots. Furthermore, compared to NO3−-N, the combined interaction of root exudates with NH4+-N has a more pronounced impact on the abundance of microbial genes associated with glycolysis pathway and tricarboxylic acid cycle, such as pkfA, pfkB, sucB, sucC, and sucD. The effects of NH4+-N on crops and microorganisms ultimately result in a significant increase in the re-mobilization of stabilized Cd. However, the simulated experiments showed that microorganisms only contribute to 3.8–6.6 % of the re-mobilization of clay mineral-bound Cd in soil. Therefore, the fundamental strategy to inhibit the re-mobilization of stabilized Cd in vegetable cultivation involves the regulation of proton and organic acid secretion by crops.

Synthesis of photo- and ionochromic N-acylated 2-(aminomethylene)benzo[b]thiophene-3(2Н)-ones with a terminal phenanthroline group.

A series of novel photo- and ionochromic N-acylated 2-(aminomethylene)benzo[b]thiophene-3(2Н)-ones with a terminal phenanthroline receptor substituent was synthesized. Upon irradiation in acetonitrile or DMSO with light of 436 nm, they underwent Z-E isomerization of the C=C bond, followed by very fast N→O migration of the acyl group and the formation of nonemissive O-acylated isomers. These isomers were isolated preparatively and fully characterized by IR, 1H, and 13C NMR spectroscopy as well as HRMS and XRD methods. The reverse thermal reaction was catalyzed by protonic acids. N-Acylated compounds exclusively with Fe2+ formed nonfluorescent complexes with a contrast naked-eye effect: a color change of the solutions from yellow to dark orange. Subsequent selective interaction with AcO- led to the restoration of the initial absorption and emission properties. Thus, the obtained compounds represent dual-mode "on-off-on" switches of optical and fluorescent properties under sequential exposure to light and H+ or sequential addition of Fe2+ and AcO- ions.

Complex chemistry of carbon nanotubes toward efficient and stable p-type doping

Developing efficient and stable carbon nanotube (CNT) doping techniques and elucidating their chemistry is essential for their further implementation in electronic and energy devices. Here, protonic acids and lithium salts are employed as p-type inducers and stabilizers of the doped state, respectively. Leveraging the electron-withdrawing capability of protons, protonic acids can easily induce heavily p-doped states in CNTs. Anionic species from the acids attach to the positively charged CNTs to achieve charge compensation. Introducing lithium salts with bulky, charge-delocalized anions to the p-doped CNTs results in an anion replacement driven by the free energy gain. The newly formed complexes demonstrate outstanding thermal stability in air, enduring a temperature of 100 °C for over a year. The chemical hardness of the applied anion effectively explains the difference in stability of the doped CNTs, indicating that the doping process and its stabilization can be understood and controlled through complex chemistry.

Divergent Electrochemical Synthesis of Indoles through pKa Regulation of Amides: Synthetic and Mechanistic Insights.

A divergent synthetic approach to access highly substituted indole scaffolds is illustrated. By virtue of a tunable electrochemical strategy, distinct control over the C-3 substitution pattern was achieved by employing two analogous 2-styrylaniline precursors. The chemoselectivity is governed by the fine-tuning of the acidity of the amide proton, relying on the appropriate selection of N-protecting groups, and assisted by the reactivity of the electrogenerated intermediates. Detailed mechanistic investigations based on cyclic voltametric experiments and computational studies revealed the crucial role of water additive, which assists the proton-coupled electron transfer event for highly acidic amide precursors, followed by an energetically favorable intramolecular C-N coupling, causing exclusive fabrication of the C-3 unsubstituted indoles. Alternatively, the implementation of an electrogenerated cationic olefin activator delivers the C-3 substituted indoles through the preferential nucleophilic nature of the N-acyl amides. This electrochemical approach of judicious selection of N-protecting groups to regulate pKa/E° provides an expansion in the domain of switchable generation of heterocyclic derivatives in a sustainable fashion, with high regio- and chemoselectivity.

Assessment of polybenzimidazole/MOF composite membranes for the improvement of high-temperature PEM fuel cell performance

This study aims to determine the most effective utilization of ZIF-8 type metal-organic framework (MOF) doped polybenzimidazole (PBI) composite membrane in high-temperature polymer electrolyte membrane fuel cells (HT-PEMFC) and investigate how ZIF-8 filler affects performance. ZIF-8 particles were prepared by solvothermal method and added to the PBI polymer using a weight percentage varying from 1 to 5 %. XRD, BET, and TEM examined the prepared ZIF-8. Composite membrane properties were investigated by XRD, SEM analysis, proton conductivity measurements, acid doping, and acid stripping tests. The HT-PEMFC performances of the membranes were carried out using Hydrogen and dry air at 150–180. The highest performance was acquired with the composite ZIF8/PBI-2 membrane as 0.432 W/cm2 at 170 °C. The obtained result is explained by easier proton transfer over ZIF-8's enlarged tunnel network. This study proposes a promising strategy to use ZIF-8 to prepare a PBI composite membrane with excellent proton conductivity, acid doping, and low acid leaching for HT-PEMFC application. The current study's findings can support future research on PBI/MOF-based composite membranes for HT-PEMFC applications.

Pyridinium trifluoroacetate ionic liquids as proficient catalysts for synthesis of 3,5,5‐trimethyl‐2‐pyrazoline

AbstractIn this work, pyridinium trifluoroacetate ionic liquids, as a protonic acid catalyst, were used to catalyze intramolecular cyclization of ketazine to synthesize 2‐pyrazoline. The investigation encompassed the impact of temperature, solvent, dosage of ionic liquid catalyst, and the structure‐activity relationship in the cyclization reaction of 2‐propyl ketazine. The optimal catalytic performance was achieved at 100 °C with 8 mol % of 3,5‐dimethylpyridinium trifluoroacetate in a solvent‐free environment. Moreover, thermodynamic and kinetic data were determined through density functional theory calculations and calorimetric experiments. These protonic acid ionic liquids address the issue of excessive traditional protonic acid dosage in the intramolecular cyclization of ketazine, while also presenting a viable pathway for the catalytic synthesis of 2‐pyrazolines.

In-situ swelling of pH-responsive microgel particles during photopolymerization to mitigate shrinkage stress of UV-cured materials

This paper utilizes a soap-free emulsion polymerization process to prepare microgel particles that can swell in response to in-situ generated acid in photocurable resin. By controlling the type and concentration of end-capping agents and the content of cross-linking agents, pH-responsive microgel particles with significantly increased particle size in acidic environments are synthesized. The strong protonic acid generated by the photoacid upon exposure to ultraviolet light can reduce the pH of the UV-curable resin, leading to an enlargement of the particle size. This can compensate for the volume shrinkage of the resin, ultimately reducing shrinkage stress. The research findings indicate that the addition of 5 wt% of pH-responsive particless and 2 wt% of photoacid to the UV-curable resin results in a reduction of approximately 40% in shrinkage stress and shrinkage rate.