Amphoteric Nature Research Articles

Recent Advances in Zinc Oxide Nanoparticles: Synthesis Methods, Characterization Techniques, and Emerging Applications

Abstract: Zinc oxide (ZnO) is an inorganic compound with unique physicochemical characteris-tics that make it versatile and suitable for various applications, especially in the form of nanoparti-cles (NPs). ZnO nanoparticles (ZnO NPs) exhibit distinct properties and are produced through diverse techniques, making them valuable for applications ranging from consumer goods to medi-cal and catalytic uses. The increasing popularity of ZnO NPs is driven by novel synthesis methods that allow for modification of chemical composition and control over size and shape, thereby en-hancing their properties and expanding their applications. The catalytic activity of ZnO NPs is influenced by parameters such as oxophilicity, large surface area, amphoteric nature, and the zinc cation's ability to approach activated starting material supports, making them viable heterogeneous catalysts for a variety of applications. Various analytical techniques, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) analysis, atomic force microscopy (AFM), and many more, are used to characterize the nanoparticles. This article explores various synthesis methods and characterization techniques and focuses on the catalytic activities of ZnO NPs

Amino Acid–Based Block Copolymer Templates‐Dependent Enhancement of Physicochemical and Electrochemical Characteristics of Mesoporous Carbons

ABSTRACTAmino acid–based block copolymers (BCPs) have distinct features such as secondary structure formation, chirality, amphoteric nature, non‐toxicity, and biodegradability, setting them apart from other BCPs. This suggests that amino acid–based BCPs may exhibit unique self‐assembly behaviors. Despite these advantages, they have not yet been utilized as templates for mesoporous carbons (MCs) synthesis. Here, we investigate, for the first time, the effect of hydrophobicity of two different poly(ethylene glycol) (PEG) conjugated amino acid–based BCP templates (PEG‐poly(β‐benzyl‐l‐aspartate) (PEG‐PBLA) and PEG‐poly(γ‐benzyl‐l‐glutamate) (PEG‐PBLG)) on the construction of MC materials and also their physicochemical and electrochemical characteristics. MCs produced using PEG‐PBLA and PEG‐PBLG as templates are labeled CPBLA and CPBLG, respectively. Utilizing amino acid–based BCP systems enabled achieving MC materials with nearly 1 at% nitrogen doping without external nitrogen dopants. Physicochemical analysis showed CPBLA had a smaller particle size, higher specific surface area, pore size, and hydrophilicity due to increased oxygen and nitrogen contents, as well as a higher defective structure than CPBLG. The higher hydrophilicity of PEG‐PBLA led to the formation of CPBLA MC particles with smaller size and higher specific surface area of 602 m2g−1 and pore size of 7.8 nm. Cyclic voltammetry demonstrated that CPBLA had superior charge‐storing capacity (specific capacitance of 147 F g−1 at 1 mv s−1) than CPBLG, attributed to its better physicochemical properties. These promising findings suggest that amino acid–based BCP systems can serve not only as templates but also as carbon and nitrogen sources, offering potential for high‐performance electrochemical energy storage devices.

Elucidation of amphoteric nature of Pr2O3 using XPS and conductivity measurement in lead-free NKBT host lattice

The study of the piezoelectric response in praseodymium-doped (Na0.41K0.09Bi0.5)TiO3 (NKBT) revealed an unusual behaviour at doping level near 0.5 and 1.0 at%. Although there is a marginal increment in the piezoelectric charge coefficients for samples with praseodymium doping of 0.5–1.0 at% compared to undoped NKBT, importantly, the response drastically diminishes for doping concentrations exceeding 1.0 at%. To comprehend the observed anomaly, X-ray photoelectron spectroscopy (XPS) and temperature dependent conductivity measurement was carried out. These investigations provided critical insights into the role of oxygen vacancy and the behaviour of praseodymium ions in the NKBT matrix. The XPS analysis revealed the presence of core level peak corresponding to O-1s with asymmetric broadening at higher energy side implying the presence of oxygen bound to the perovskite lattice (binding energy: 529.2±0.3 eV) along with oxygen vacancy (binding energy: 531.5±0.4 eV). The XPS study further revealed that the concentration of the oxygen vacancy is lowest around 0.5 at% of praseodymium doping and beyond this the oxygen vacancy increases. The high temperature conductivity measurement supported these findings by showing similar trends in the electrical conductivity. Both the XPS and conductivity measurements further corroborate the conjecture that praseodymium behaves as amphoteric ion. The praseodymium occupies the A-site of perovskite (Na0.41K0.09Bi0.5)TiO3 for lower praseodymium concentration (<1.0 at%), whereas for higher doping concentration (>1.0 at%) it occupies the B-site exhibiting acceptor like behavior that deteriorates the piezoelectric response.

Sealing of cerium oxide coating primers on anodized AA2024-T3 alloy by boiling in Lourier buffers

Although their exceptional re-passivation ability, Al-alloys are susceptible to corrosion due to the amphoteric nature of the alumina passivation films. This issue is exacerbated by the disruption of these films by intermetallics on the surfaces of highly doped ones, like AA2024-T3 aircraft alloy. The combination of anodized aluminium oxide (AAO) and cerium conversion coatings (CeCC) shows promise as a coating primer. However, the defective structures of CeO2 and Al2O3 require additional sealing. This research proposes sealing the CeCC/AAO layer by boiling it for 10 minutes in two relatively neutral Lourier buffers, adjusted to pH 7.75, and in a mixture of them. The samples underwent a series of analyses to compare the impact of the sealing procedure on surface topology, properties (e.g., colour and wettability on two samples from each set), and corrosion protective ability. It was assessed after 24 hours of exposure to 3.5 % NaCl model corrosive medium on six samples from each set. The assessments included electrochemical impedance spectroscopy (EIS) and potentiodynamic scanning (PDS) techniques. The results indicate that the borate buffer improves the corrosion protection of the coating primers more effectively than the phosphate and mixed ones.

Enhanced hydrotreating performance of hierarchical NiMo-S/Al2O3 catalysts through ZrO2 incorporation and template-driven structural modulation

A dual template-assisted approach for optimizing support structures to enhance catalytic efficiency in hydrotreating reactions is presented. Catalysts synthesized using activated carbon (AC) templates exhibited significantly higher activity in both hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) compared to those prepared with starch (ST) templates. The unique porous architecture, characterized by well-distributed meso- and macropores, facilitated efficient access of bulky molecules to the active sites. On the other hand, while the reactivity in the selective opening of the naphthenic ring (SONR), which is indicative of hydrocracking functionality, was similar across all catalysts, those modified with Zr exhibited a slight improvement. The catalysts displayed bifunctional characteristics, and their performance was influenced by the amphoteric nature of the support and the specific ratios of active species on the surface. A clear correlation between catalytic activity, selectivity, and the distribution of active sites was established.

Development and characterization of novel CS-ZnO-Alg polyelectrolyte complex for enhanced removal of Cd(II), Cu(II), and Ni(II) from simulated paint industrial wastewater

In this study, we developed and characterized a novel chitosan-alginate-based polyelectrolyte complex impregnated with zinc oxide nanoparticles (CS-ZnO-Alg PEC) for the enhanced removal of Cd(II), Cu(II), and Ni(II) from simulated paint industrial wastewater. The prepared PEC was characterized by X-ray Diffraction (XRD), Fourier-Transform Infrared (FTIR) Spectroscopy, Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS), X-ray Photoelectron Spectroscopy (XPS), Brunauer-Emmett-Teller (BET), and Thermogravimetric analysis/Differential Thermal Analysis (TGA/DTA). The equilibrium data for said metal ions was best appropriated by Freundlich isotherm with maximum adsorption capacity of 217.72 mg/g for Cd(II), 130.41 mg/g Cu(II), and 159.06 mg/g for Ni(II), illustrating the multilayer adsorption of metal ions on the heterogeneous surface sites of the adsorbent. The kinetics of all three metal ions adsorption process onto discussed PEC was consistent with pseudo-second-order model. The thermodynamics results illustrate exothermic and spontaneous processes for Cd(II) (ΔH° = −3.57 KJ/mol, ΔS° = 0.009 KJ/mol*K, ΔG° = −6.42 to −6.61 KJ/mol) and Cu(II) (ΔH° = −3.32 KJ/mol, ΔS° = 0.006 KJ/mol*K, ΔG° = −5.25 to −5.37 KJ/mol), and spontaneous but less favorable adsorption for Ni(II) (ΔH° = −0.82 KJ/mol, ΔS° = −0.001 KJ/mol*K, ΔG° = −0.39 to −0.36 KJ/mol). Notably, the PEC could be easily recycled and regenerated, maintaining adsorption efficiency after five cycles. Overall, the CS-ZnO-Alg PEC, due to its amphoteric nature, high adsorption efficiency, cost-effectiveness, excellent recyclability, and biodegradability, could be a promising adsorbent for paint industrial wastewater.

Impact of the Amphoteric Nature of a Chelating Surfactant on its Interaction with an Anionic Surfactant: A Surface Tension and Neutron Reflectivity Study of Binary Mixed Solutions.

2-Dodecyldiethylenetriaminepentaacetic acid (C12-DTPA) is a chelating, amphoteric surfactant with a bulky headgroup containing eight pH-responsive groups. The hypothesis was that the amphoteric nature of the chelating surfactant would affect the interaction with another surfactant and, consequently, also the composition of mixed surface layers. Binary mixed monolayers of C12-DTPA and the anionic surfactant sodium dodecyl sulfate (SDS) were examined using neutron reflection and surface tension measurements. The experiments were conducted at pH 5, where the C12-DTPA monomers carried a net negative charge. Surface excess calculations at low total surfactant concentration revealed that the chelating surfactant dominated the surface composition. However, as the concentration was raised, the surface composition shifted toward an SDS-dominant state. This phenomenon was attributed to the increased ionic strength at increased concentrations, which altered the balance between competing entropic forces in the system. Interaction parameters for mixed monolayer formation were calculated, following a framework based on regular solution theory. In accordance with the hypothesis, the chelating surfactant's ability to modulate its charge and mitigate repulsive interactions in the surface layer resulted in favorable interactions between the anionic SDS and negatively charged C12-DTPA monomers. These interactions were found to be concentration-dependent, which was consistent with the observed shift in the surface layer composition.

Exploring Unconventional σ-Hole Interactions: Computational Insights into the Interaction of XeO3 with Non-Aromatic Coordinating Solvents.

In order to control the explosiveness and shock sensitivity of XeO3 , we have investigated its plausible interaction with various non-aromatic coordinating solvents, serving as potential Lewis base donors, through density functional theory (DFT) calculations. Out of twenty six such solvents, the top ten were thus identified and then thoroughly examined by employing various computational tools such as the mapping of the electrostatic potential surface (MESP), Wiberg bond indices (WBIs), non-covalent interaction (NCI) plots, Bader's theory of atoms-in-molecules (AIM), natural bond orbital (NBO) analysis, and the energy decomposition analysis (EDA). The amphoteric nature of XeO3 was also explored by investigating the extent of back donation from the lone pair of Xe to the antibonding orbital of the donating atom/group of the solvent molecules. The C-H…O interactions were also found to be a contributing factor in the stabilization of these adducts. Although these aerogen-bonding interactions were found to be predominantly electrostatic, significant contributions from the orbital contributions, as well as dispersion interactions, were observed. The top three non-aromatic solvents (among the twenty six studied) which form the strongest adducts with XeO3 are proposed to be hexamethylphosphoramide (HMPA), N,N'-dimethylpropyleneurea (DMPU) and tetramethylethylenediamine (TMEDA).

Carboiodanation of Arynes: Organoiodine(III) Compounds as Nucleophilic Organometalloids.

Organic iodine(III) compounds represent the most widely used hypervalent halogen compounds in organic synthesis, where they typically perform the role of an electrophile or oxidant to functionalize electron-rich or -nucleophilic organic compounds. In contrast to this convention, we discovered their unique reactivity as organometallic-like nucleophiles toward arynes. Equipped with diverse transferable ligands and supported by a tethered spectator ligand, the organoiodine(III) compounds undergo addition across the electrophilic C-C triple bond of arynes while retaining the trivalency of the iodine center. This carboiodanation reaction can forge a variety of aryl-alkynyl, aryl-alkenyl, and aryl-(hetero)aryl bonds along with the concurrent formation of an aryl-iodine(III) bond under mild conditions. The newly formed aryl-iodine(III) bond serves as a versatile linchpin for downstream transformations, particularly as an electrophilic reaction site. The amphoteric nature of the iodine(III) group as a metalloid and a leaving group in this sequence enables the flexible and expedient synthesis of extended π-conjugated molecules and privileged biarylphosphine ligands, where all of the iodine(III)-containing compounds can be handled as air- and thermally stable materials.

Oxygenated bio-fuel synthesis in reactive distillation: A technological reform under process intensification

Chemical Engineering processes demands separation of reaction products to obtain them in purest form. Reactive Distillation facilitates this feature by incorporating a reactive zone for reaction between conventional rectifying and stripping zone for distillation. It also aid for solid catalyst incorporation of amphoteric nature to avoid repetitive addition of catalyst for different experimental run and will also improve the product yield. The other beneficial features of Reactive Distillation include reduced synthesis cost, reduced utility space required and higher selectivity. This technique is introduced in this paper for synthesis of oxygenated bio-fuel. For this, fuel additive of ether family namely Tert Amyl Ethyl Ether (TAEE) is synthesized using ethanol. Similarly, Biodiesel synthesis is done using transesterification of waste cooking oil with methanol. Both fuel-oxygenate (TAEE) and biodiesel are then blended in varying proportion to improve ignition quality of biodiesel fuel. The study is done experimentally and analyzed under object oriented modeling mode in simulation. Optimization of synthesis process is done using revamping in experimental mode corresponding to sensitivity analysis in simulation. The congruence results show that purity of 95 % and 65 % for biodiesel and TAEE respectively is obtained in reactive distillation corresponding to reboiler duty of 2 kW and reflux ratio 4.

Facile preparation of re-dispersible/amphoteric nanochitin powder via choline chloride/propanedioic composite for stabilizing Pickering emulsions

Choline chloride (ChCl)/propanedioic acid (PA) based hydrated composites are synthesized for producing nanochitins from crab shell in this work. The yield of nanochitin remains higher than 75 %, even if the water content reaches 80 %. ChCl is found necessary for the successful nano-fibrillation of chitin. However, PA contributes more to the yield improvement of nanochitin. ChCl mediated PA hydrolysis leads to the successful grafting of carboxyl groups in nanochitins, contributing to its amphoteric dispersed nature. After salt-induced separation and freeze-drying treatment, dried nanochitin powder can be prepared and found to disperse well either in acidic or alkaline suspension, exhibiting efficient drying/redispersion performance. The well amphoteric and drying/redispersion nature both benefit the facile preparation of nanochitin-based Pickering emulsions. For Pickering emulsion prepared under different pH, creaming only appears under acidic conditions (pH 3) for which the creaming index reaches 10.56 % after 30 days of storage. No obvious de-emulsification can be observed under pH 7 and 10. The efficient amphoteric and drying/redispersion nature together with the simplified preparation process of nanochitins are believed to facilitate the processing and practical applications of nanochitin.

The Field of Main Group Lewis Acids and Lewis Superacids: Important Basics and Recent Developments.

New developments in the field of Lewis acidity are highlighted, with the focus of novel Lewis acids and Lewis superacids of group 2, 13, 14, and 15 elements. Several important basics, illustrated by modern examples (classification of Donor-Acceptor (DA) complexes, amphoteric nature of any compound in terms of DA interactions, reorganization energies of main group Lewis acids and the role of the energies of frontier orbitals) are presented and discussed. It is emphasized that the Lewis acidity phenomena are general and play vital role in different areas of chemistry: from weak "atomophilic" interactions to the complexes of Lewis superacids.

An Electrochemically Prepared Mixed Phase of Cobalt Hydroxide/Oxyhydroxide as a Cathode for Aqueous Zinc Ion Batteries

Cobalt hydroxide is a widely studied electrode material for supercapacitor and alkaline zinc ion batteries. The large interlayer spacing of Co(OH)2 is also attractive to store Zn ions. However, Co(OH)2 is quite unstable in the acidic ZnSO4 electrolyte due to its amphoteric nature. Herein, we synthesized a mixed phase of Co(OH)2/CoOOH via a two-step electrochemical preparation. As the cathode material for an aqueous zinc ion battery (AZIB), Co(OH)2/CoOOH delivered a maximum capacity of 164 mAh g−1 at 0.05 A g−1 and a high energy density of 275 Wh kg−1. Benefiting from the low charge-transfer resistance, a capacity of 87 mAh g−1 was maintained at 1.6 A g−1, showing a good rate performance of the mixed phase. Various spectroscopy analyses and simulations based on the density functional theory (DFT) suggested a higher thermal stability of the mixed phase than pure Co(OH)2, due to its less local structural disorder. The reduced Co-Co and Co-O shells increased the mechanical strength of the mixed phase to accommodate Zn2+ ions and endure the electrostatic repulsion, resulting in an enhanced cycling stability. The mixed phased also delivered a good stability at the current density of 0.05 A g−1. After 200 cycles, a capacity retention of 78% was retained, with high Coulombic efficiencies. These results provide a new route to synthesize high-performance LDH for aqueous zinc ion batteries.

Recent developments and challenges in uranium extraction from seawater through amidoxime-functionalized adsorbents.

As per statistical estimations, we have only around 100 years of uranium life in terrestrial ores. In contrast, seawater has viable uranium resources that can secure the future of energy. However, to achieve this, environmental challenges need to be overcome, such as low uranium concentration (3.3 ppb), fouling of adsorbents, uranium speciation, oceanic temperature, and competition between elements for the active site of adsorbent (such as vanadium which has a significant influence on uranium adsorption). Furthermore, the deployability of adsorbent under seawater conditions is a gigantic challenge; hence, leaching-resistant stable adsorbents with good reusability and high elution rates are extremely needed. Powdered (nanostructured) adsorbents available today have limitations in fulfilling these requirements. An increase in the grafting density of functional ligands keeping in view economic sustainability is also a major obstacle but a necessity for high uranium uptake. To cope with these challenges, researchers reported hundreds of adsorbents of different kinds, but amidoxime-based polymeric adsorbents have shown some remarkable advantages and are considered the benchmark in uranium extraction history; they have a high affinity for uranium because of electron donors in their structure, and their amphoteric nature is responsible for effective uranium chelation under a wide range of pH. In this review, we have mainly focused on recent developments in uranium extraction from seawater through amidoxime-based adsorbents, their comparative analysis, and problematic factors that are needed to be considered for future research.

Preparation of a robust and degradable nanocapsule by polymer deposition over the liposome for loading and release of cargos

We prepared biobased nanocapsules by the polymer deposition over the ceramide-containing liposomes to render abilities to load versatile substances and to release them in response to enzymatic degradation of the capsule wall. First, we carried out phosphorylation of chitosan (CHI) to make it amphoteric. Then, we prepared a liposome containing glucosylceramide (GlcCer) and carried out deposition of phosphorylated chitosan (PCHI). The obtained capsule showed high structural stability against solubilization by surfactants and organic solvents, where it maintained its size even in 90 vol% DMSO. Next, we attempted to load various substances into the capsule. A lipophilic Nile red dissolved in 50 vol% DMSO could be loaded into the capsule without rupturing. The loading capacity of PCHI-deposited liposomes was almost three times higher than that of bare liposomes. Its release was suppressed to less than 10 % in an aqueous solution, whereas it could be released to more than 40 % when a small amount of surfactant was added to mimic a lipophilic environment. Also, an amphoteric nature of the capsule derived from PCHI allowed for loading of both cationic and anionic substances. Furthermore, lysozyme (Lyso) was deposited onto the capsule to provide the capsule wall with the enzymatic degradability. Although the release of substances from the capsule was suppressed to less than 10 % without Lyso, it was increased to approximately 50 % by enzymatic degradation of the PCHI layer.

ALD deposited bipolar HfOx films for silicon surface passivation

Hafnium oxide thin films consist of trap states which can degrade or enhance the device performance depending upon the application. These trap states play a crucial role in silicon surface passivation when using HfOx films. This paper investigates the dependence of crucial surface passivation parameters on different film growth components of thermal ALD process. Our study is focused on understanding different oxide charges present at the HfOx/Si interface using capacitance-voltage and constant voltage stress studies; particularly trap states introduced during thermal atomic layer deposition process. This study is performed for different film growth conditions to understand the origin of traps states. We show that the interfacial layer (IL) grows during the film deposition and therefore two interfaces are formed, i.e., HfOx/SiOx and SiOx/Si. Acting as the tunnelling oxide, this interlayer consists of trap states which are intrinsic in origin. The investigation on MOS structures fabricated using n and p type silicon substrates gives an understanding towards amphoteric nature of the trap states. Their nature (acceptor/donor) depends on the substrate doping type (n-Si/p-Si) giving it bipolar characteristic. However, the interaction of such trap states with the majority carrier band edge of the substrate strongly depends on the IL thickness. Additionally, the trap charge density increases with metal pulsing duration, suggesting that the metal precursor may be the source of these trap charges rather than the oxidant. By shedding light on the nature and behaviour of trap states in HfOx films, our study contributes to a deeper understanding of their impact on device performance. This knowledge can aid in optimizing surface passivation strategies and improving the overall performance of HfOx-based devices in various applications.

Design of amphoteric MOFs-cellulose based composite for wastewater remediation: Adsorption and catalysis

Water pollution remains a serious problem for aquatic organism and human beings. Developing an efficient material which can simultaneously remove and convert pollutants into low or no harmful compounds is an essential issue. Targeting at this goal, a multifunctional and amphoteric wastewater treatment material of Co-MOF and functionalized cellulose-based composite (CMC/SA/PEI/ZIF-67) was designed and prepared. Carboxymethyl cellulose (CMC) and sodium alginate (SA) were selected as support to construct an interpenetrating network structure and made it crosslinked with polyethyleneimine (PEI) for further in situ growth of ZIF-67 with good dispersion. The material was characterized using an appropriate set of spectroscopic and analytical techniques. When applied in the adsorption of heavy metal oxyanions with no adjustment of pH, the adsorbent could completely decontaminate Cr(VI) at both low and high initial concentrations with good reduction rates. The adsorbent maintained good reusability after five cycles. Meanwhile, the cobalt species of CMC/SA/PEI/ZIF-67 can activate peroxymonosulfate to generate high oxidizing substances (such as SO4ˉ· and ·OHˉ radicals) to degrade cationic rhodamine B dye within 120 min, thus indicating the amphoteric and catalytic nature of our CMC/SA/PEI/ZIF-67 adsorbent. The mechanism of the adsorption and catalytic process was also discussed based with the assistance of different characterization analysis.

Electronic structure and imaginary dielectric function for 2D GaAs doped with Si amphoteric impurities: A DFT study

Without a doubt, the impact of the discovery of 2D systems such as graphene has led to both theoretical and experimental investigations of a large number of materials such as Silicene, Borene, Arsenene, Phosphorene, just to mention some of the most emblematic ones, but other materials and its heterostructures are also of interest. From this point of view, in this work we present the band structure, density of states as well as the imaginary part of the dielectric function of a 2D GaAs system, by means of a density functional theory implementation. The aim of this study is to investigate the basic physical properties for a freestanding 2D GaAs sheet, as well as the effect of Si substitutional atoms, since it has an amphoteric nature in the GaAs, which means that depending on which atom is substituted, this can be an n- or p-type impurity atom. We report, as expected, that the levels do indeed appear near the conduction band (or valence) if the impurity is n-type (or p-type), respectively. Also the density of states due to the impurity is modified as well as the imaginary part of the dielectric function

Guanidine-Based Covalent Organic Frameworks: Cooperation between Cores and Linkers for Chromic Sensing and Efficient CO2 Conversion.

C(sp)-H carboxylation with CO2 is an attractive route of CO2 utilization and is traditionally promoted by transition metal catalysts, and organocatalysis for the conversion remains rarely explored and challenging. In this article, triaminoguanidine-derived covalent organic frameworks (COFs) were used as platforms to develop heterogeneous organocatalysts for the reaction. We demonstrated that the COFs with guanidine cores and pyrazine linkers show high catalytic performance as a result of the cooperation between cores and linkers. The core is vitally important, which is deprotonated to the guanidinato group that binds and activates CO2. The pyrazine linker collaborates with the core to activate the C(sp)-H bond through hydrogen bonding. In addition, the COFs show acid- and base-responsive chromic behaviors thanks to the amphoteric nature of the core and the auxochromic effect of the pyrazine linker. The work opens up new avenues to organocatalysts for C-H carboxylation and chromic materials for sensing and switching applications.

Ab initio molecular dynamics study of proton transport in imidazolium-based ionic liquids with added imidazole.

Development of efficient anhydrous proton-conducting materials would expand the operational temperature ranges of hydrogen fuels cells (HFCs) and eliminate their dependence on maintaining sufficient hydration levels to function efficiently. Protic ionic liquids (PILs), which have high ionic densities and low vapor pressures, have emerged as a potential material for proton conducting layers in HFCs. In this work, we investigate proton transport via the Grotthuss mechanism in 1-ethylimidazolium bis-(trifluoromethanesulfonyl)imide ([C2HIm][TFSI]) protic ionic liquids with added imidazole (Im0) using ab initio molecular dynamics. In particular, we vary the composition of the systems studied from pure [C2HIm][TFSI] to those where the mole fraction of Im0 is 0.67. Given the large difference in pKa between C2HIm+ and HTFSI, TFSI- does not accept acidic protons from C2HIm+; conversely, imidazolium (HIm+) and C2HIm+ have very similar pKa values, and thus Im0 can readily accept protons. We find that the unprotonated nitrogen on Im0 dominates solvation of the labile protons on C2HIm+ and other Im0 species, resulting in formation of robust imidazole wires. Given the amphoteric nature of Im0, i.e. its ability to accept and donate protons, these wires provide conduits along which protons can rapidly traverse via the Grotthuss mechanism, thereby greatly increasing the proton coefficient of self-diffusion. We find that the average length of the wires increases with added Im0, and thus as the mole fraction of Im0 increases so too does the proton diffusion constant. Lastly, we analyze our trajectories to determine the energy and time scales associated with proton transfer.