Proton Hopping Research Articles

Performance and Durability of HT-PEMFC Enhanced By One-Step Electrochemical Exfoliated Phosphonated Graphene Oxide

The high-temperature proton exchange membrane fuel cell (HT-PEMFC) conducts protons through the hydrogen bond network established by the polymer and phosphoric acid (PA), which reduces the dependence on humidity and allows its operating temperature to be higher than 100°C [1]. A higher operating temperature is conducive to improve catalyst activity, reducing carbon dioxide adsorption on the catalyst thus reducing the requirement for hydrogen purity, and convenient water management [2]. As the most widely commercialized HT-PEMFC proton exchange membrane material, the performance and durability of Polybenzimidazole (PBI) still need to be improved. In particular, it has insufficient proton conductivity, insufficient mechanical properties, and phosphoric acid leaching issues under high acid doping level [3] [4] [5].The doping of functionalized graphene oxide in the PBI membrane can build additional proton transfer channels, promote proton hopping and act as a trap for PA to reduce its leaching by virtue of abundant functional groups of functionalized GO [6] [7] [8]. Among the groups that can be used for functionalization, the phosphoric acid group has become one of the most promising due to its strong hydrogen bonding and water retention ability [9] [10] [11]. Phosphonated graphene oxide (PGO) is usually synthesized by further phosphonation of GO obtained by chemical exfoliation [6] [7]. Chemical exfoliation methods usually require the long-term action of strong acids and strong oxidants [12]. The safety and environmental issues caused by those methods can not be underestimated. And the two-step synthesis method of PGO has a long reaction period.This work achieved the rapid, safe, and large-yield production of electrochemically exfoliated PGO by using a 3D printed reactor, ammonium dihydrogen phosphate as the electrolyte and natural graphite flakes as the raw material. The two-step electrochemical exfoliation method of producing GIC with concentrated sulfuric acid as the first electrolyte is also used to synthesize electrochemical exfoliated (E)GO. 1.5wt% EGO or PGO was doped in the PBI membrane to explore the effect of different GO on the performance and durability of the PBI- membrane-based HT-PEMFC. Compared with pure PBI, the doping of EGO and PGO increases the peak power density of HT-PEMFC by 17.4% and 35.4%, respectively.[1] Y.-L. Ma, J.S. Wainright, M.H. Litt, R.F. Savinell, Journal of The Electrochemical Society 2004, 151, A8.[2] H. Su, S. Pasupathi, B. Bladergroen, V. Linkov, B.G. Pollet, International Journal of Hydrogen Energy 2013, 38, 11370.[3] S. Galbiati, A. Baricci, A. Casalegno, R. Marchesi, International Journal of Hydrogen Energy 2013, 38, 6469.[4] S.H. Eberhardt, F. Marone, M. Stampanoni, F.N. Büchi, T.J. Schmidt, Journal of Synchrotron Radiation 2014, 21, 1319.[5] Q. He, X. Yang, W. Chen, S. Mukerjee, B. Koel, S. Chen, Physical Chemistry Chemical Physics 2010, 12, 12544.[6] J. Yang, C. Liu, L. Gao, J. Wang, Y. Xu, R. He, RSC Advances 2015, 5, 101049.[7] C. Xu, Y. Cao, R. Kumar, X. Wu, X. Wang, K. Scott, Journal of Materials Chemistry 2011, 21, 11359.[8] Y. Cai, Z. Yue, S.X.-J. of A.P. Science, undefined 2017, Wiley Online Library 2017, 134, 44986.[9] E. Abouzari-Lotf, H. Ghassemi, A. Shockravi, T. Zawodzinski, D. Schiraldi, Polymer 2011, 52, 4709.[10] E. Abouzari-Lotf, M. Zakeri, M.M. Nasef, M. Miyake, P. Mozarmnia, N.A. Bazilah, N.F. Emelin, A. Ahmad, Journal of Power Sources 2019, 412, 238.[11] S. Some, I. Shackery, S.J. Kim, S.C. Jun, Chemistry - A European Journal 2015, 21, 15480.[12] C. Xu, Y. Cao, R. Kumar, X. Wu, X. Wang, K. Scott, Journal of Materials Chemistry 2011, 21, 11359.

Ultralow-concentration electrolyte boosting K0.486V2O5 for high-performance proton storage

High-concentration electrolytes are considered a promising tool for widening stable electrochemical windows and enhancing the electrochemical performance of aqueous batteries. However, their high cost, high viscosity, and low conductivity remain thorny issues. Because of the special Grotthuss mechanism of protons in water, proton batteries can use a low-concentration electrolyte to obtain sufficient kinetic performance. Herein, we present an unusual, ultralow-concentration sulfuric acid (0.01 mol L−1) electrolyte to boost the electrochemical stability of K-ion pre-intercalated V2O5 (K0.486V2O5, KVO). The KVO electrode exhibits a high reversible capacity of approximately 129 mA h g−1 at a low current density of 50 mA g−1 and impressive capacity retention of 78% over 20,000 cycles at 1 A g−1. Ultralow-concentration electrolyte chemistry will open a novel route to exploit durable and low-cost aqueous energy storage systems.

Mechanochemical Synthesis of Phosphonate-Based Proton Conducting Metal-Organic Frameworks.

Water-stable metal-organic frameworks (MOFs) with proton-conducting behavior have attracted great attention as promising materials for proton-exchange membrane fuel cells. Herein, we report the mechanochemical gram-scale synthesis of three new mixed-ligand phosphonate-based MOFs, {Co(H2PhDPA)(4,4'-bipy)(H2O)·2H2O}n (BAM-1), {Fe(H2PhDPA)(4,4'-bipy) (H2O)·2H2O}n (BAM-2), and {Cu(H2PhDPA)(dpe)2(H2O)2·2H2O}n (BAM-3) [where H2PhDPA = phenylene diphosphonate, 4,4'-bipy = 4,4'-bipyridine, and dpe = 1,2-di(4-pyridyl)ethylene]. Single-crystal X-ray diffraction measurements revealed that BAM-1 and BAM-2 are isostructural and possess a three-dimensional (3D) network structure comprising one-dimensional (1D) channels filled with guest water molecules. Instead, BAM-3 displays a 1D network structure extended into a 3D supramolecular structure through hydrogen-bonding and π-π interactions. In all three structures, guest water molecules are interconnected with the uncoordinated acidic hydroxyl groups of the phosphonate moieties and coordinated water molecules by means of extended hydrogen-bonding interactions. BAM-1 and BAM-2 showed a gradual increase in proton conductivity with increasing temperature and reached 4.9 × 10-5 and 4.4 × 10-5 S cm-1 at 90 °C and 98% relative humidity (RH). The highest proton conductivity recorded for BAM-3 was 1.4 × 10-5 S cm-1 at 50 °C and 98% RH. Upon further heating, BAM-3 undergoes dehydration followed by a phase transition to another crystalline form which largely affects its performance. All compounds exhibited a proton hopping (Grotthuss model) mechanism, as suggested by their low activation energy.

Improving the performance of protonic ceramic fuel cells and electrolyzers: The role of acceptor impurities in oxide membranes

Protonic ceramic electrochemical cells (PCECs) are promising energy conversion devices offering an efficient and environmentally friendly way to produce electricity and pure hydrogen. An important challenge in the development of PCECs is the enhancement of their performance through selection of optimal dopants for acceptor-doped oxide perovskites, commonly used as electrolyte membranes. In this work, we elucidate the implications of the interaction of protons and oxygen vacancies with acceptor impurities in oxide membranes for the performance of PCECs operating in the fuel cell and electrolysis modes. The analysis relies on our recent theoretical developments on fuel cell operation and oxide hydration, as well as on the proposed statistical theory of proton hopping conduction in acceptor-doped oxides. It is shown that the interaction between ionic defects and impurities can substantially affect the characteristics of proton-conducting membranes. General relationships between the output characteristics of PCECs based on membranes with proton and hole conductivity and the energies of acceptor-bound states of ionic defects are determined. It is established that trapping of protons and oxygen vacancies reduces both proton and hole currents and effective conductivities, thereby altering the dependences of the voltage and power density on current density. We demonstrate the possibility of tuning the power density and faradaic efficiency of PCECs by doping oxide membranes using acceptor impurities with varying defect trapping energies. The presented results contribute to understanding the functioning mechanisms of protonic ceramic fuel cells and electrolyzers, and provide new fundamental criteria for the selection of acceptor impurities for oxide membranes to develop high-efficient devices.

Ab initio investigation of H-bond disordering in δ-AlOOH

\ensuremath{\delta}-AlOOH (\ensuremath{\delta}) is a high-pressure hydrous phase that participates in the deep geological water cycle. At 0 GPa, \ensuremath{\delta} has asymmetric hydrogen bonds (H bonds). Under pressure, it exhibits H-bond disordering, tunneling, and finally, H-bond symmetrization at \ensuremath{\sim}18 GPa. This study investigates these 300 K pressure-induced state changes in \ensuremath{\delta} with ab initio calculations. H-bond disordering in \ensuremath{\delta} was modeled using supercell multiconfiguration quasiharmonic calculations. We examine (a) energy barriers for proton jumps, (b) the pressure dependence of phonon frequencies, (c) 300 K compressibility, (d) neutron diffraction pattern anomalies, and (e) compare ab initio bond lengths with measured ones. Such thorough and systematic comparisons indicate that (a) proton ``disorder'' has a restricted meaning when applied to \ensuremath{\delta}. Nevertheless, H bonds are disordered between 0 and 8 GPa, and a gradual change in H-bond configuration results in enhanced compressibility. (b) Several structural and vibrational anomalies at \ensuremath{\sim}8 GPa are consistent with the disappearance of a particular (HOC-12) H-bond configuration and its change into another one (HOC-11*). (c) Between 8 and 11 GPa, H-bond configuration (HOC-11*) is generally ordered, at least in short- to midrange scale. (d) Between 11.5 and 18 GPa, H-bond lengths approach a critical value that impedes compression, resulting in decreased compressibility. In this pressure range, especially approaching H-bond symmetrization at \ensuremath{\sim}18 GPa, anharmonicity and tunneling should play an essential role in the proton dynamics. Further simulations accounting for these effects are desirable to clarify the protons' state in this pressure range.

Rotational Mechanism of FO Motor in the F-Type ATP Synthase Driven by the Proton Motive Force.

In FOF1 ATP synthase, driven by the proton motive force across the membrane, the FO motor rotates the central rotor and induces conformational changes in the F1 motor, resulting in ATP synthesis. Recently, many near-atomic resolution structural models have been obtained using cryo-electron microscopy. Despite high resolution, however, static information alone cannot elucidate how and where the protons pass through the FO and how proton passage is coupled to FO rotation. Here, we review theoretical and computational studies based on FO structure models. All-atom molecular dynamics (MD) simulations elucidated changes in the protonation/deprotonation of glutamate—the protein-carrier residue—during rotation and revealed the protonation states that form the “water wire” required for long-range proton hopping. Coarse-grained MD simulations unveiled a free energy surface based on the protonation state and rotational angle of the rotor. Hybrid Monte Carlo and MD simulations showed how proton transfer is coupled to rotation.

Molecular dynamics simulation analysis of sulfonated polybenzimidazole/[formula omitted]: A potential polymer electrolyte membrane for high-temperature fuel cells

In this research work, the ionic conductivity performance of a prospective candidate polymer electrolyte membrane, sulfonated polybenzimidazole/[DEMA+][NTf2-], was investigated using the molecular dynamics simulation technique. At first, a unit cell consisting of three chains (each one consisting 30 monomers) of polybenzimidazole polymer was determined as the optimum amorphous unit cell by comparing the simulated solubility parameter and glass transition temperature with available experimental data. Furthermore, the behavior of the ionic self-diffusion coefficients was investigated using the mean square displacement curves. It was found that the diffusion of [DEMA+] and [NTf2-] depends on the degrees of sulfonation (DS) values: with increasing DS, the ionic self-diffusion coefficients enhance, which could be attributed to a reduction in [DEMA+][NTf2-]- polymer chains interactions. The results revealed that the simulated ionic conductivities of this ionic liquid-based membrane is comparable with other electrolyte membranes and would be suitable for high-temperature applications. In addition, the investigation was complemented with analysis of plausible proton conduction pathways by evaluating the radial/angular distribution function and cationic/anionic clusters. The results suggest that proton hopping through very short ionic bridges is possible but could not be dominated. This work would pave the way for further research into the new protic ionic liquid -doped sulfonated polybenzimidazole membranes for proton exchange membrane fuel cells.

Dual Proton Conducting Channels Constructed by Acid‐Base Double‐Shell Carbon Nanotubes to Boost the Proton Conductivity of SPEEK

AbstractSulfonated poly(ether ether ketone) (SPEEK) has been widely investigated as a substitution of commercial Nafion as proton exchange membranes (PEMs). However, the disadvantages such as shrinkage of proton transfer channels at high temperature and low humidity conditions cannot be neglected. In this manuscript, the carboxyl and imidazole double‐shelled carbon nanotubes(CNTs−C@N) was incorporated into the SPEEK matrix to fabricate composite PEM (denoted as SPEEK/CNTs−C@N−Y, Y is the percentage composition of CNTs−C@N), serving as one‐dimensional fillers. SPEEK/CNTs−C@N‐1.0 composite membrane performed a higher horizontal proton conductivity (0.302 S/cm) under 80 °C and 100 % relative humidity (RH) compared with original SPEEK membrane 0.181 S/cm. The high proton conductivity could be mainly attributed to the dual proton conducting channel formed by two types of acid‐base pairs, which immensely promote the Grotthuss mechanism. Therefore, SPEEK/CNTs−C@N composite membranes are expected to develop PEMs with high proton conductivity at high temperature and low humidity.

Mechanisms of the antiferro-electric ordering in superprotonic conductors Cs3H(SeO4)2 and Cs3D(SeO4)2.

Wide ranges of absorbance spectra were measured to elucidate a difference in the antiferro-electric (AF) ordering mechanisms below 50 and 168K in Cs3H(SeO4)2 and Cs3D(SeO4)2, respectively. Collective excitations due to deuterons successfully observed at 610 cm-1 exhibit a remarkable isotope effect. This indicates that the transfer state in the dimer of Cs3D(SeO4)2 is dominated by a deuteron hopping in contrast to Cs3H(SeO4)2, where a proton hopping makes a tiny contribution compared to a phonon-assisted proton tunneling (PAPT) associated with 440-cm-1 defbend . The fluctuation relevant to the AF ordering in Cs3D(SeO4)2 is not driven by the conventional deuteron hopping but by the phonon-assisted deuteron hopping associated with 310-cm-1 defbend . Consequently, Cs3D(SeO4)2 has a distinct ordering mechanism from Cs3H(SeO4)2, in which quantum fluctuations toward the AF ordering are enhanced through the PAPT associated with the in-phase libration.

Hybrid Pyridine-Pyridone Foldamer Channels as M2-Like Artificial Proton Channels.

Currently, completely abiotic channel systems that concurrently reproduce the high selectivity and high permeation rate of natural protein channels are rare. Here, we provide one such biomimetic channel system, i.e., a novel family of helically folded hybrid amide foldamers that can serve as powerful artificial proton channels to mimic key transport features of the exceptionally selective Matrix-2 (M2) proton channels. Possessing an angstrom-scale tubular pore 3 Å in diameter, these low water permeability artificial channels transport protons at a rate 1.22 and 11 times as fast as gramicidin A and M2 channels, respectively, with exceptionally high selectivity factors of 167.6, 122.7, and 81.5 over Cl- , Na+ , and K+ ions. Based on the experimental and computational findings, we propose a novel proton transport mechanism where a proton may create a channel-spanning water chain from two or more short water chains to facilitate its own transmembrane flux via the Grotthuss mechanism.

Hybrid Pyridine–Pyridone Foldamer Channels as M2‐Like Artificial Proton Channels

AbstractCurrently, completely abiotic channel systems that concurrently reproduce the high selectivity and high permeation rate of natural protein channels are rare. Here, we provide one such biomimetic channel system, i.e., a novel family of helically folded hybrid amide foldamers that can serve as powerful artificial proton channels to mimic key transport features of the exceptionally selective Matrix‐2 (M2) proton channels. Possessing an angstrom‐scale tubular pore 3 Å in diameter, these low water permeability artificial channels transport protons at a rate 1.22 and 11 times as fast as gramicidin A and M2 channels, respectively, with exceptionally high selectivity factors of 167.6, 122.7, and 81.5 over Cl−, Na+, and K+ ions. Based on the experimental and computational findings, we propose a novel proton transport mechanism where a proton may create a channel‐spanning water chain from two or more short water chains to facilitate its own transmembrane flux via the Grotthuss mechanism.

Grotthuss Molecular Dynamics Simulations for Modeling Proton Hopping in Electrosprayed Water Droplets.

Excess protons in water exhibit unique transport properties because they can rapidly hop along H-bonded water wires. Considerable progress has been made in unraveling this Grotthuss diffusion mechanism using quantum mechanical-based computational techniques. Unfortunately, high computational cost tends to restrict those techniques to small systems and short times. Molecular dynamics (MD) simulations can be applied to much larger systems and longer time windows. However, standard MD methods do not permit the dissociation/formation of covalent bonds, such that Grotthuss diffusion cannot be captured. Here, we bridge this gap by combining atomistic MD simulations (using Gromacs and TIP4P/2005 water) with proton hopping. Excess protons are modeled as hydronium ions that undergo H3O+ + H2O → H2O + H3O+ transitions. In accordance with ab initio MD data, these Grotthuss hopping events are executed in "bursts" with quasi-instantaneous hopping across one or more waters. The bursts are separated by regular MD periods during which H3O+ ions undergo Brownian diffusion. The resulting proton diffusion coefficient agrees with the literature value. We apply this Grotthuss MD technique to highly charged water droplets that are in a size regime encountered during electrospray ionization (5 nm radius, ∼17,000 H2O). The droplets undergo rapid solvent evaporation and occasional H3O+ ejection, keeping them at ca. 81% of the Rayleigh limit. The simulated behavior is consistent with phase Doppler anemometry data. The Grotthuss MD technique developed here should be useful for modeling the behavior of various proton-containing systems that are too large for high-level computational approaches. In particular, we envision future applications related to electrospray processes, where earlier simulations used metal cations while in reality excess protons dominate.

A cobalt(II) complex based on imidazole dicarboxylate ligand with high proton conductivity

In order to search for new crystalline proton conductive materials, a highly stable Co(II) complex, namely, [Co(HPhIDC)(4,4′-bipy)] (1) (H3PhIDC = 2-phenyl-4,5-imidazole dicarboxylic acid, 4,4′-bipy = 4,4′-bipyridine) has been successfully synthesized under hydrothermal conditions and structurally characterized. 1 exhibits high thermal, water and chemical stabilities, which promoted us to investigate its proton conductivity in water vapor. The results showed that proton conductivity of 1 was dependent on temperature and relative humidity (RH). The optimal proton conductivity of 1 reaches up to a highest value of 1.35 × 10−4 S·cm−1 at 373 K under 98% RH. According to the Ea value, the proton conduction mechanism of 1 maybe a combination of Grotthuss and Vehicle mechanisms at 98% RH and major Vehicle mechanism at 75% RH.

Cost-effective Prussian blue analogue composite proton exchange membranes for low humidity fuel cell operation

Proton exchange membranes (PEMs) exhibit reduced proton conductivity caused by severe dehydration under low relative humidity (RH), which is a pivotal bottleneck toward widespread commercialization of PEM fuel cells (PEMFCs). Previous PEM optimizing strategies have predominantly pursued increasing water uptake or enlarging hydrophilic domains, for which there is less focus on the mode of proton transport (Grotthuss or vehicular mechanisms) as the underlying reason. Here, a counterintuitive route is proposed by incorporating CuII[FeIII(CN)6]2/3 Prussian blue analogue (CuFe-PBA) additive, which possesses a hydrophobic framework. However, due to the ideal lattice length of CuFe-PBA, the lattice water molecules contained within this framework form well-connected hydrogen bond networks, which promote Grotthuss-type proton transport that is less dependent on RH conditions. Consequently, CuFe-PBA doped in sulfonated polysulfone (SPSf) matrix yields SPSf/CuFe-PBA composite PEMs showing better performance over unfilled PEM in both ex situ and in situ evaluations, especially under low RH conditions, which are competitive with Nafion 212. Preliminary trials of scale-up for CuFe-PBA and composite PEMs with cost estimation, and feasibility of incorporating polytetrafluoroethylene reinforcement, suggest economic and practical potential. Thus, CuFe-PBA composite PEMs may be of particular interest to PEMFC and related materials communities.

Phosphinate MOFs Formed from Tetratopic Ligands as Proton-Conductive Materials.

Metal-organic frameworks (MOFs) are attracting attention as potential proton conductors. There are two main advantages of MOFs in this application: the possibility of rational design and tuning of the properties and clear conduction pathways given by their crystalline structure. We hereby present two new MOF structures, ICR-10 and ICR-11, based on tetratopic phosphinate ligands. The structures of both MOFs were determined by 3D electron diffraction. They both crystallize in the P3̅ space group and contain arrays of parallel linear pores lined with hydrophilic noncoordinated phosphinate groups. This, together with the adsorbed water molecules, facilitates proton transfer via the Grotthuss mechanism, leading to a proton conductivity of up to 4.26 × 10-4 S cm-1 for ICR-11. The presented study demonstrates the high potential of phosphinate MOFs for the fabrication of proton conductors.

The role of sulfonate groups and hydrogen bonding in the proton conductivity of two coordination networks.

The proton conductivity of two coordination networks, [Mg(H2O)2(H3L)]·H2O and [Pb2(HL)]·H2O (H5L = (H2O3PCH2)2-NCH2-C6H4-SO3H), is investigated by AC impedance spectroscopy. Both materials contain the same phosphonato-sulfonate linker molecule, but have clearly different crystal structures, which has a strong effect on proton conductivity. In the Mg-based coordination network, dangling sulfonate groups are part of an extended hydrogen bonding network, facilitating a “proton hopping” with low activation energy; the material shows a moderate proton conductivity. In the Pb-based metal-organic framework, in contrast, no extended hydrogen bonding occurs, as the sulfonate groups coordinate to Pb2+, without forming hydrogen bonds; the proton conductivity is much lower in this material.

Electro-osmotic Drag and Thermodynamic Properties of Water in Hydrated Nafion Membranes from Molecular Dynamics.

One of the important parameters in water management of proton exchange membranes is the electro-osmotic drag (EOD) coefficient of water. The value of the EOD coefficient is difficult to justify, and available literature data on this for Nafion membranes show scattering from in experiments and simulations. Here, we use a classical all-atom model to compute the EOD coefficient and thermodynamic properties of water from molecular dynamics simulations for temperatures between 330 and 420 K, and for different water contents between λ = 5 and λ = 20. λ is the ratio between the moles of water molecules to the moles of sulfonic acid sites. This classical model does not capture the Grotthuss mechanism; however, it is shown that it can predict the EOD coefficient within the range of experimental values for λ = 5 where the vehicular mechanism dominates proton transfer. For λ > 5, the Grotthuss mechanism becomes dominant. To obtain the EOD coefficient, average velocities of water and ions are computed by imposing different electric fields to the system. Our results show that the velocities of water and hydronium scale linearly with the electric field, resulting in a constant ratio of ca. 0.4 within the error bars. We find that the EOD coefficient of water linearly increases from 2 at λ = 5 to 8 at λ = 20 and the results are not sensitive to temperature. The EOD coefficient at λ = 5 is within the range of experimental values, confirming that the model can capture the vehicular transport of protons well. At λ = 20, due to the absence of proton hopping in the model, the EOD coefficient is overestimated by a factor of 3 compared to experimental values. To analyze the interactions between water and Nafion, the partial molar enthalpies and partial molar volumes of water are computed from molecular dynamics simulations. At different water uptakes, multiple linear regression is used on raw simulation data within a narrow composition range of water inside the Nafion membrane. The partial molar volumes and partial molar excess enthalpies of water asymptotically approach the molar volumes and molar excess enthalpies of pure water for water uptakes above 5. This confirms the model can capture the bulklike behavior of water in the Nafion at high water uptakes.

Ionic conductivity and ion transport mechanisms of solid‐state lithium‐ion battery electrolytes: A review

AbstractThis review article deals with the ionic conductivity of solid‐state electrolytes for lithium batteries. It has discussed the mechanisms of ion conduction in ceramics, polymers, and ceramic‐polymer composite electrolytes. In ceramic electrolytes, ion transport is accomplished with mobile point defects in a crystal. Li+ ions migrate mainly via the vacancy mechanism, interstitial mechanism, or interstitial‐substitutional exchange mechanism. In solid polymer electrolytes, Li+ ions are transported mainly via the segment motion, ion hopping (Grotthuss mechanism), or vehicle mechanism (mass diffusion). This study has also introduced various electrolyte materials including perovskite oxides, garnet oxides, sodium superionic conductors, phosphates, sulfides, halides, cross‐linked polymers, block‐copolymers, metal‐organic frameworks, covalent organic frameworks, as well as ceramic‐polymer composites. In addition, it has highlighted some strategies to improve the ionic conductivity of solid‐state electrolytes, such as doping, defect engineering, microstructure tuning, and interface modification.

Revealing the Anticorrelation Behavior Mechanism between the Grotthuss and Vehicular Diffusions for Proton Transport in Concentrated Acid Solutions.

In this study, we performed reactive molecular dynamics simulations to characterize proton solvation and transport in concentrated hydrochloric acid solutions. The correlation contribution to the total proton mean square displacement is found to be negative for all acid concentrations, indicating the anticorrelation between the Grotthuss and vehicular diffusions. For the vehicular diffusion, the hydronium ions tend to move freely toward the lone pair side independent of acid concentrations, whereas for the Grotthuss diffusion, the proton hopping direction is limited to one of the hydrogen-bonded water molecules on the opposite side of the lone pair region, which are specifically oriented with respect to the neighboring hydronium ion at higher acid concentrations. This result is justified by our findings of the higher fraction of proton rattling with the single hopping event and longer hydrogen bond lifetimes at higher acid concentrations. However, the angular distribution for both the vehicular and Grotthuss diffusions is found to be rather broad and comparable for all acid concentrations, and thus, the anticorrelation shows a minimal dependence on the acid concentration. Our results reveal that the anticorrelation behavior between the vehicle and Grotthuss diffusions is attributed to the amphiphilic nature of hydronium ions and thus is independent of the acid concentrations in solutions.

Surface proton conduction below 100 °C of Ce0.80Sm0.20O2−δ thin film with oxygen vacancies

Ce0.80Sm0.20O2−δ thin films with (111) orientation were prepared on (0001) Al2O3 substrates by RF magnetron sputtering. The Ce3+ valence ratios, which are closely related to the oxygen vacancies’ concentration, of the as-deposited and wet-annealed thin films were 37.8% and 29.3%, respectively. These thin films exhibited oxygen ion related conduction in the medium-temperature region of 800 to 200 °C. Below 100 °C, the conductivity (σ) of the wet-annealed thin film increased as the temperature (T) decreased and the σT value was ∼1.0 S cm−1 K at 25 °C. The O 1s photoemission spectrum exhibited H2O and OH− peaks on the surface. The above results indicate that the protons on the surface of the wet-annealed thin film actively migrated through the physisorbed water layer by the Grotthuss mechanism.