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Protonic ceramic cells (PCCs) have gained significant attention as a promising electrochemical device for hydrogen production and power generation at intermediate temperatures. However, the lack of high‐performance air electrodes, specifically in terms of proton conduction ability, has severely hindered the improvement of electrochemical performances for PCCs. In this study, a high‐efficiency air electrode La0.8Ba0.2CoO3 (LBC) is rationally designed and researched by a machine‐learning model and density functional theory (DFT) calculation, which boosts the performances of PCCs. Specifically, an elements‐property map for designing high‐efficiency oxides is created by predicting and studying the proton uptake ability of La1–xA′xBO3 (A′ = Na, K, Ca, Mg, Ba, Cu, etc.) by an eXtreme Gradient Boosting model. PCC with LBC air electrode yields high current destiny in electrolysis mode (1.72 A cm−2 at 600 °C) and power density in fuel cell mode (1.00 W cm−2 at 600 °C). In addition, an ultra‐low air electrode reaction resistance (0.03 Ω cm2 at 600 °C) is achieved, because LBC can significantly facilitate the formation of O2*. This work not only reports an effective air electrode but also presents a new avenue for the rational design of air electrodes for PCCs. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Rapid dynamics and remarkable proton conduction induced by confined water in nanospaces have attracted much attentions from researchers, which is crucial for advancing the development of innovative proton conductors and deepening comprehension of proton and water transport mechanisms within biological systems. In this aspect, carbon nanotubes (CNTs) are frequently employed as a research platform. However, they possess certain limitations, such as their inherent electronic conductivity and extreme hydrophobicity, which can impede the accurate assessment and precise regulation of proton conduction. We herein prepared two 2D COFs with different hydrophilic fragment, and obtained maximum acid‐free proton conductivity of 3.04 × 10–4 S·cm–1 at 70 °C and 100% RH with Grotthuss type activation energy of 0.14 eV. This is mainly due to that the water molecules in the center of channel form strong hydrogen bonds, enhancing proton dissociation and guiding fast directional diffusion. [ABSTRACT FROM AUTHOR]

Since specifying the structure during operation tends to be challenging for intrinsically proton‐conducting polymers, it becomes increasingly essential to establish a well‐defined migration path in order to predict the proton conductivity. Zwitterion covalent organic frameworks (ziCOFs) provide a platform in crystal frameworks to investigate the proton transfer mechanism, considering their specific charged channel walls, deprotonation surface, and host–guest interactions. Here, a zwitterion nanoconfined proton‐sieves (ziNPS) with "charged casing" channel of charged pathways is proposed to demonstrate theoretically the effectiveness of proton conduction. Density functional theory and molecular dynamic simulation results show that the ziNPS with different anion groups all achieve a shorter hydrogen bond to increase the dense "hydronium‐water" domain, creating a channel of hydrogen bond networks to provide a long‐range pathway for the proton to migrate. As expected, the proton conductivity test by electrochemical impedance spectroscopy demonstrates the aforementioned concept as well. This research presents a fresh view of the ion conduction mechanism originating from localized zwitterionic units, which can apply to the fabrication of COF‐based proton conductors. [ABSTRACT FROM AUTHOR]

Hydrogen‐bonded organic frameworks (HOFs) are crystalline materials assembled by intermolecular hydrogen‐bonding interactions, and their hydrogen‐bonding structures are effective pathways for proton transport. Herein, we synthesize iHOF‐45 using 4,4'‐diaminodiphenylmethane and 1,3,6,8‐pyrenetetrasulfonicacid sodium salt with 2D hydrogen‐bonding networks. The stability of ionic HOFs (iHOFs) can be enhanced by introducing ionic bonds in addition to hydrogen‐bonding forces. Thermal analyses demonstrated that iHOF‐45 exhibited excellent thermal stability up to 332 °C. The proton conductivity of iHOF‐45 was evaluated, demonstrating a notable increase with rising temperature and RH. At 100 °C and 98 % RH, the conductivity reached 5.25×10−3 S cm−1. The activation energy (Ea) of iHOF‐45 was calculated to be 0.281 eV for 98 % RH, and the proton conduction was attributed to the Grotthuss mechanism, whereby the protons were transported in 2D hydrogen‐bonding networks. Moreover, iHOF‐45 was doped into SPEEK to prepare composite membranes, the proton conductivity of the 15 % iHOF‐45/SPEEK membrane reached 9.52×10−2 S cm−1 at 80 °C and 98 % RH, representing a 45.1 % increase over that of the SPEEK. This suggests that doping enhances the proton conductivity of SPEEK and providing a reference for the development of high proton conductivity materials. [ABSTRACT FROM AUTHOR]

Highlights: The effects of the size structure and stability of metal–organic frameworks (MOFs) on proton conduction are comprehensively summarized. Advanced strategies for constructing proton conduction MOFs are critically discussed. Challenges and opportunities for the development of novel proton-conducting MOFs are further outlined. Proton-conducting materials have attracted considerable interest because of their extensive application in energy storage and conversion devices. Among them, metal–organic frameworks (MOFs) present tremendous development potential and possibilities for constructing novel advanced proton conductors due to their special advantages in crystallinity, designability, and porosity. In particular, several special design strategies for the structure of MOFs have opened new doors for the advancement of MOF proton conductors, such as charged network construction, ligand functionalization, metal-center manipulation, defective engineering, guest molecule incorporation, and pore-space manipulation. With the implementation of these strategies, proton-conducting MOFs have developed significantly and profoundly within the last decade. Therefore, in this review, we critically discuss and analyze the fundamental principles, design strategies, and implementation methods targeted at improving the proton conductivity of MOFs through representative examples. Besides, the structural features, the proton conduction mechanism and the behavior of MOFs are discussed thoroughly and meticulously. Future endeavors are also proposed to address the challenges of proton-conducting MOFs in practical research. We sincerely expect that this review will bring guidance and inspiration for the design of proton-conducting MOFs and further motivate the research enthusiasm for novel proton-conducting materials. [ABSTRACT FROM AUTHOR]

To develop proton exchange membranes (PEMs) with robust structure stability and remarkable proton conductivity and explore their application in PEMs fuel cells have significant implications for realizing reduced carbon emission and environmental pollution. Covalent organic frameworks (COFs), as crystalline porous polymer material composed of organic monomers and connected by covalent bond, possess specific framework, inherent porosity, adjustable functional group and eminent thermal/chemical structure stability. Therefore, COFs display prominent superiorities in constructing rigid ordered proton transfer channels and improving fuel cell performance long‐term durability. In this review, the proton conduction properties of extrinsic proton‐conductive COFs (incorporating carriers into the pore), intrinsic proton‐conductive COFs (introducing conductive groups on the backbone) and combined extrinsic/intrinsic proton‐conductive COFs in the form of pressed pellets are discussed in detail. Meanwhile, proton‐conductive COFs related PEMs, including COFs‐related polymer‐based composite membranes, COFs‐based composite membranes and self‐supporting COFs membranes are also systematically summarized. In addition, the existing challenges are analyzed and future outlooks are addressed. [ABSTRACT FROM AUTHOR]

Although metal‐organic frameworks (MOFs) and metalo hydrogen‐bonded organic frameworks (MHOFs) are designed as promising solid‐state proton conductors by incorporating various protonic species intrinsically or extrinsically, design and development of such materials by employing the concept of proton conduction through coordinated polar protic solvent is largely unexplored. Herein, we have constructed two proton‐conducting materials having different solvent coordinated metal cationic species: In‐H2O‐MOF, ({[In(H2O)6][In3(Pzdc)6] ⋅ 15H2O}n; H2Pzdc: pyrazine‐2,3‐dicarboxylic acid) with coordinated water molecules from hexaaquaindium cationic species, and MHOF‐4, ([{Co(NH3)6}2(2,6‐NDS)2(H2O)2]n; 2,6‐H2NDS: 2,6‐naphthalenedisulfonic acid) with coordinated ammonia from hexaammoniacobalt cationic species. Interestingly, higher proton conductivity was achieved for In‐H2O‐MOF (1.5×10−5 S cm−1) than MHOF‐4 (6.3×10−6 S cm−1) under the extreme conditions (80 °C and 95 % RH), which could be attributed to enhanced acidity of coordinated water molecules having much lower pKa value than that of coordinated ammonia. Greater charge polarization on hydrogen atoms of In3+‐coordinated water molecules than that of Co2+‐coordinated ammonia led to the high conductivity of In‐H2O‐MOF, as evident by quantum chemical studies. Such a comparative study on metal‐coordinated protic polar solvents in achieving proton conduction in crystalline solids is yet to be made. [ABSTRACT FROM AUTHOR]

2D architectures and superior physiochemical properties of MXene offer an exciting opportunity to develop a new class of polymer electrolyte membranes by controlling the stacking behavior of MXene nanosheets. However, assembling MXene nanosheets into macroscopic stable and high‐performance proton conductors is challenging. Here, a general strategy is reported for achieving stable and high‐performance MXene‐based heterogeneous proton conductors via crosslinked cellulose nanofiber/sodium alginate (CNF/SA). Through the coordination of calcium ions with 1D CNF/SA, MXene nanosheets with abundant hydrogen‐bonding networks are firmly locked into the heterogeneous polymer network, and meanwhile, the heterogeneous polymer chains are transformed from a randomly arranged state to a long‐range ordered arrangement, and such arranged polymer molecular channels collaborate with the tightly‐stacked MXene nanosheets jointly guide the stable and efficient proton conduction. Thus, the as‐built CNF/SA/MXene (CSM) composite membrane exhibits superior mechanical properties (164.7 MPa), proton conductivity (45.4 mS cm−1), power density (49.5 mW cm−2), and low open circuit voltage (OCV) decay rate (0.4 mV h−1). The design principle of 2D material anchoring through ionic‐cross‐linking and mixed‐dimensional assembly can inspire the synthesis of various ion exchange membranes for ion filtration, ion transport, ion sieving, and more. [ABSTRACT FROM AUTHOR]

A CO 2 -stable, easily sintered proton-conducting oxide electrolytes based on solid solution Ba 7 In 6 Al 2– x Zn x O 19-0.5 x with hexagonal structure has been synthesized for the first time. Within the homogeneity region (0 ≤ x ≤ 0.10), there is an increase in unit cell parameters, cell volumes and free cell volumes. The addition of Zn2+ markedly improved the sinterability of the material. The relative density of the ceramics of the doped samples reached 95 % at lower sintering temperatures than the parent phase. The electrical conductivity was studied using electrochemical impedance spectroscopy. Upon doping the oxygen-ion conductivity increased by 0.25 orders of magnitude at 800 °C. Proton transport was predominant below 500 °C for a wet atmosphere (pH 2 O = 1.92·10−2 atm). The investigated phases Ba 7 In 6 Al 2– x Zn x O 19-0.5 x are capable of hydration and incorporate up to 1.45 mol H 2 O vs 0.41 mol H 2 O for the parent phase. The studied phases exhibit chemical resistance to CO 2 under heat treatment at 600 °C. It was shown that solid solution Ba 7 In 6 Al 2– x Zn x O 19-0.5 x is a promising electrolyte material for intermediate-temperature fuel cells. [Display omitted] • The Zn-doping in solid solution Ba 7 In 6 Al 2– x Zn x O 19-0.5 x markedly improved the sinterability of the material and well-sintered ceramics were obtained with relative density 95 %. • The water uptake increased with increasing Zn-concentration. • Ba 7 In 6 Al 2– x Zn x O 19-0.5 x phases were protonic conductors at T < 500 °C in wet air. • Ba 7 In 6 Al 2– x Zn x O 19-0.5 x phases exhibited chemical resistance to pure CO 2. [ABSTRACT FROM AUTHOR]

[Display omitted] • Four functionalized terephthalic acid-based HOFs were prepared. • Their ultrahigh proton conductivities were explored and compared. • The conducting mechanisms were highlighted. Recently, the utilization of hydrogen-bonded organic frameworks (HOFs) with high crystallinity and inherent well-defined H-bonding networks in the field of proton conduction has received increasing attention, but obtaining HOFs with excellent water stability and prominent proton conductivity (σ) remains challenging. Herein, by employing functionalized terephthalic acids, 2,5-dihydroxyterephthalic acid, 2-hydroxyterephthalic acid, 2-nitro terephthalic acid, and terephthalic acid, respectively, four highly water-stable ionic HOFs (iHOFs), [(C 8 H 5 O 6)(Me 2 NH 2)]∙2H 2 O (iHOF 1), [(C 8 H 5 O 5)(Me 2 NH 2)] (iHOF 2), [(C 8 H 4 NO 6)(Me 2 NH 2)] (iHOF 3) and [(C 8 H 5 O 4)(Me 2 NH 2)] (iHOF 4) were efficiently prepared by a straightforward synthesis approach in DMF and H 2 O solutions. The alternating-current (AC) impedance testing in humid conditions revealed that all four iHOFs were temperature- and humidity-dependent σ, with the greatest value reaching 10-2 S·cm−1. As expected, the high density of free carboxylic acid groups, crystallization water, and protonated [Me 2 NH 2 ]+ units offer adequate protons and hydrophilic environments for effective proton transport. Furthermore, the σ values of these iHOFs with different functional groups were compared. It was discovered that it dropped in the following order under 100 °C and 98 % relative humidity (RH): σ iHOF 1 (1.72 × 10−2 S·cm−1) > σ iHOF 2 (4.03 × 10−3 S·cm−1) > σ iHOF 3 (1.46 × 10−3 S·cm−1) > σ iHOF 4 (4.86 × 10−4 S·cm−1). Finally, we investigated the causes of the above differences and the proton transport mechanism inside the framework using crystal structure data, water contact angle tests, and activation energy values. This study provides new motivation to develop highly proton-conductive materials. [ABSTRACT FROM AUTHOR]

Elusive ion behaviors in aqueous electrolyte remain a challenge to break through the practicality of aqueous zinc‐manganese batteries (AZMBs), a promising candidate for safe grid‐scale energy storage systems. The proposed electrolyte strategies for this issue most ignore the prominent role of proton conduction, which greatly affects the operation stability of AZMBs. Here we report a water‐poor quasi‐solid electrolyte with efficient proton transfer pathways based on the large‐space interlayer of montmorillonite and strong‐hydration Pr3+ additive in AZMBs. Proton conduction is deeply understood in this quasi‐solid electrolyte. Pr3+ additive not only dominates the proton conduction kinetics, but also regulates the reversible manganese interfacial deposition. As a result, the Cu@Zn||α‐MnO2 cell could achieve a high specific capacity of 433 mAh g−1 at 0.4 mA cm−2 and an excellent stability up to 800 cycles with a capacity retention of 92.2 % at 0.8 mA cm−2 in such water‐poor quasi‐solid electrolyte for the first time. Ah‐scale pouch cell with mass loading of 15.19 mg cm−2 sustains 100 cycles after initial activation, which is much better than its counterparts. Our work provides a new path for the development of zinc metal batteries with good sustainability and practicality. [ABSTRACT FROM AUTHOR]

Surface proton hopping conduction (SPHC) mechanisms is an important proton conduction mechanism in conventional polymer electrolytes, along with the Grotthuss and vehicle mechanisms. Due to the small diffusion coefficient of protons in the SPHC mechanism, few studies have focused on the SPHC mechanism. Recently, it has been found that a dense alignment of SO3− groups significantly lowers the activation energy in the SPHC mechanism, enabling fast proton conduction. In this study, a series of polymerizable amphiphilic‐zwitterions is prepared, forming bicontinuous cubic liquid‐crystalline assemblies with gyroid symmetry in the presence of suitable amounts of bis(trifluoromethanesulfonyl) imide (HTf2N) and water. In situ polymerization of these compounds yields gyroid‐nanostructured polymer films, as confirmed by synchrotron small‐angle X‐ray scattering experiments. The high proton conductivity of the films on the order of 10−2 S cm−1 at 40 °C and relative humidity of 90% is based solely on the SPHC mechanism. [ABSTRACT FROM AUTHOR]

Highlights The effects of the size structure and stability of metal–organic frameworks (MOFs) on proton conduction are comprehensively summarized. Advanced strategies for constructing proton conduction MOFs are critically discussed. Challenges and opportunities for the development of novel proton-conducting MOFs are further outlined.

The solid solution Ba 5 In 2– x Y x Al 2 ZrO 13 (0 ≤ х ≤0.50) with hexagonal structure (space group P 6 3 / mmc) was prepared by the solid-state reaction method. The effects of isovalent Y3+-substitution on the structure, hydration, bandgap and transport properties have been investigated. The introduction of yttrium was accompanied by lattice expansion, which led to an increase in the concentration of protons during hydration. The doping did not lead to a significant increase in oxygen-ion conductivity since there was no change in oxygen stoichiometry. At the same time, doping led to an increase in ionic transport numbers due to a decrease in hole conductivity. Proton conductivity contribution and the values of proton conductivity increase with the increase in yttrium concentration. The phases with yttrium content x > 0.2 were predominant proton conductors at the temperature below 600°С under wet air. [ABSTRACT FROM AUTHOR]

[Display omitted] Proton exchange membranes (PEMs) applied in fuel cell technology suffer from the trade-off between fast proton conduction and durable operation involving dimensional stability, mechanical strength, and oxidative resistance. To address this issue, a novel branched polybenzimidazole (brPBI) was synthesized, covalently cross-linked with (3-chloropropyl)triethoxysilane (CTS), and doped with a novel proton conductor FeATMP to prepare brPBI-CTS/FeATMP membranes. The branching degree of brPBI was optimized to achieve high molecular weight while the branching structure offered high free volume, abundant end-groups, and self-cross-linking moiety that enhanced proton conduction and dimensional/mechanical/oxidative stability. Covalent cross-linking with CTS enhanced the dimensional, mechanical, and oxidative stability while improving the water-assisted proton conduction owing to the hydrophilic nature of siloxane structure formed. At 180 ℃, the proton conductivity of the brPBI3-CTS/FeATMP composite membrane reached 0.136, 0.073, and 0.041 S cm−1 at 100 % RH, 50 % RH, and 0 % RH, respectively, while its swelling ratio after immersion in water at 90 ℃ for 24 h was 4.69 %. The performance of the membranes demonstrated that construction of hydrophilic structure by covalent cross-linking was a successful strategy to break the trade-off effect for PEMs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cu2+-chelated SPEEK membrane with high IEC is prepared. • High mechanical and dimensional stability are observed for SPEEK-Cu membrane. • Proton conductivity of SPEEK-based membranes reaches 0.074 S/cm at −25 °C. • Water states of samples at subzero temperatures are quantified via DSC analysis. • SPEEK-Cu membrane possesses a stronger anti-freezing property. Improving the proton conductivity (σ) of proton exchange membranes at low temperatures is very important for expanding their application areas. Here, sulfonated poly ether ether ketone (SPEEK) membranes were prepared with different sulfonation degrees, and its maximum ion exchange capacity is 3.15 mmol/g for 10 h at 60 °C. Highly sulfonated SPEEK membrane exhibits ultra-high water uptake and excellent proton conductivity of 0.074 S/cm at −25 °C due to its abundant −SO 3 H. Nevertheless, its high swelling ratio and low mechanical strength are not conducive to the practical application of the membrane. Luckily, by employing the chelation of Cu2+ with −SO 3 − on the SPEEK chain, Cu2+-coordinated SPEEK membranes were prepared, and they not only retain high −SO 3 H content but also possess robust mechanical properties and good dimensional stability compared to pristine SPEEK membrane. Meanwhile, the σ of the SPEEK-Cu membrane reaches 0.054 S/cm at −25 °C, and its fuel cell maximum power (W max) reaches 0.42 W/cm2 at −10 °C, demonstrating superior low-temperature performance in comparison to other reported materials. Particularly, water states in the prepared membranes are quantified by low-temperature differential scanning calorimetry. Because much more water bound to the plentiful −SO 3 H and Cu2+ inside the membrane endows it with anti-freezing performance, the decay of the σ and the W max for the SPEEK-Cu membrane is retarded at sub-zero temperatures. It is envisioned that composite membranes comprising metal ions such as Cu2+-SPEEK have a high potential for sub-zero fuel cell applications. [ABSTRACT FROM AUTHOR]

Systematically orchestrating fundamental building blocks into intricate high‐dimensional molecular assemblies at molecular level is imperative for multifunctionality integration. However, this remains a formidable task in crystal engineering due to the dynamic nature of inorganic building blocks. Herein, we develop a multi‐template‐guided strategy to control building blocks. The coordination modes of ligands and the spatial hindrance of anionic templates are pivotal in dictating the overall structures. Flexible multi‐dentate linkers selectively promote the formation of oligomeric assembly ([TeO3(Mo2O2S2)3O2(OH)(C5O2H7)3]4− {TeMo6}) into tetrahedral cages ([(TeO3)4(Mo2O2S2)12(OH)12(C9H9O4P)6]8− {Te4Mo24} and [(AsO4)4(Mo2O2S2)12(OH)12(C9H9O6)4]12− {As4Mo24}), while steric hindrance from anionic templates further assists in assembling cages into an open quadruply twisted Möbius nanobelt ([(C6H5O3P)8(Mo2O2S2)24(OH)24(C8H10O4)12]16− {P8Mo48}). Among these structures, the hydrophilic‐hydrophobic hybrid cage {Te4Mo24} emerges as an exemplary molecular model for proton conduction and serves as a prototype for humidity gradient‐based power generators (HGPGs). The Te4Mo24‐PVDF‐based HGPG (PVDF=Poly(vinylidene fluoride)) exhibits notable stability and power generation, yielding an open‐circuit voltage of 0.51 V and a current density of 77.8 nA cm−2 at room temperature and 90 % relative humidity (RH). Further insights into the interactions between water molecules and microscale molecules within the generator are achieved through molecular dynamics simulations. This endeavor unveils a universal strategy for synthesizing multifunctional integration molecules. [ABSTRACT FROM AUTHOR]

Solid‐state proton conductors with high conductivity at intermediate temperatures (100–300 °C) have recently gained attention due to their potential for a wide range of new electrochemical applications. The proton conductivity of cesium hydroxide hydrate (CsOH.H2O) is reported on, a superprotonic conductor whose ionic conductivity is hitherto unreported. Via a thermal treatment, the hexagonal and tetragonal CsOH.H2O phases are prepared and the effect of the degree of hydration (H2O content) on the structure and proton conductivity is investigated. It is shown that the temperature in the thermal treatment has an enormous influence on the structure and water content, and consequently, the proton transport. The conductivity of the hexagonal and tetragonal phases exceeds 3 × 103 S cm−1 at 30 °C and 10−2 S cm−1 at 120 °C, making them potentially suitable for both low‐ and intermediate‐temperature electrochemical applications. 1H NMR spin‐lattice relaxation rate measurements reveal fast dynamic processes with rates reaching the GHz regime, resulting in diffusion coefficients as high as 1.3 × 10−11 m2 s−1 at 60 °C, in good agreement with the proton conductivity results derived from impedance spectroscopy. These findings will inspire the development of novel inorganic solid proton conductors based on hydroxide hydrates. [ABSTRACT FROM AUTHOR]

Designing efficient proton-conductive materials is crucial in fuel cells. Yet, it remains a substantial challenge because of the issues in proton mobility, proton-carrier amount, and orientation of proton host materials. Herein, we report an in-situ protonation strategy to produce a locally flexible porous coordination polymer (PCP) to enhance the proton-carrier loading and proton conductivity. The local dipole flipping of the ligand allows effective proton exchange with low activation energy, promoting interpore proton transport through the pore apertures and pore walls. The protonation induces substantial charges to the frameworks and enhances the interaction with proton carriers, thereby increasing the loading of the proton carriers. By this design strategy, the resulting PCP exhibits enhanced phosphoric acid loading and extraordinary proton conductivities under both aqueous and anhydrous conditions compared to its isoreticular analog that features rigidity without proton-exchange capability. Our work provides a new avenue for designing proton-conductive materials that combine structural dynamics with performance merits. [ABSTRACT FROM AUTHOR]

Flexible ion-conductive materials exhibit intriguing advantages for applications in flexible electronic devices. Currently, the further enhancement of their conductivity within environmental limitations is an urgent demand for the development of flexible electronic devices, yet remains as a great challenge. Herein, we report a "dual-acid" strategy, via the encapsulation of two acids, H3PW12O40 (HPW) and NH2SO3H (SA), with synergistic interaction into poly(vinyl alcohol)-glycerol (PVA-Gly) hydrogel, to achieve polyoxometalate(POM)-based flexible materials with superionic conductivity under various environmental conditions. As a representative example, the prepared PVA-Gly/HPW-SA-20% hydrogel presents an ultrahigh proton conductivity ranging from −30 °C (3.33×10−2 S cm−1) to room temperature (2.78×10−1 S cm−1) under ambient humidity. Moreover, the PVA-Gly/HPW-SA-20% hydrogel exhibits remarkable advantages in anti-freezing, mechanical flexibility and self-adhesiveness, making it a promising multifunctional electrolyte for flexible electronic devices. Both experimental results and molecular dynamics (MD) simulations jointly demonstrate that SA bridges HPW clusters to form a dense proton transport pathway induced by multiple electrostatic and hydrogen bonding interactions between SA and HPW counterparts, which contributes to the high-level proton conductivity of the PVA-Gly/HPW-SA-20% hydrogel. This work provides new insights into the design of POM-based flexible materials with superionic conductivity. [ABSTRACT FROM AUTHOR]

A challenging task in solid oxide fuel cells (SOFCs) is seeking for an alternative electrolyte, enabling high ionic conduction at relatively low operating temperatures, i.e., 300–600 °C. Proton‐conducting candidates, in particular, hold a significant promise due to their low transport activation energy to deliver protons. Here, a unique hierarchical TiO2‐SrTiO3@TiO2 structure is developed inside an intercalated TiO2‐SrTiO3 core as "yolk" decorating densely packed flake TiO2 as shell, creating plentiful nano‐heterointerfaces with a continuous TiO2 and SrTiO3 "in‐house" interfaces, as well the interfaces between TiO2‐SrTiO3 yolk and TiO2 shell. It exhibits a reduced activation energy, down to 0.225 eV, and an unexpectedly high proton conductivity at low temperature, e.g., 0.084 S cm−1 at 550 °C, confirmed by experimentally H/D isotope method and proton‐filtrating membrane measurement. Raman mapping technique identifies the presence of hydrogenated HO─Sr bonds, providing further evidence for proton conduction. And its interfacial conduction is comparatively analyzed with a directly‐mixing TiO2‐SrTiO3 composite electrolyte. Consequently, a single fuel cell based on the TiO2‐SrTiO3@TiO2 heterogeneous electrolyte delivers a good peak power density of 799.7 mW cm−2 at 550 °C. These findings highlight a dexterous nano‐heterointerface design strategy of highly proton‐conductive electrolytes at reduced operating temperatures for SOFC technology. [ABSTRACT FROM AUTHOR]

Water in hydrophobic nanospaces shows specific dynamic properties different from bulk water. The investigation of these properties is important in various research fields, including materials science, chemistry, and biology. The elucidation of the correlation between properties of water and hydrophobic nanospaces requires nanospaces covered only with simple hydrophobic group (e.g. fluorine) without impurities such as metals. This work successfully fabricated all‐organic diamondoid porous organic salts (d‐POSs) with highly fluorinated nanospaces, wherein hydrophobic fluorine atoms are densely exposed on the void surfaces, by combining fluorine substituted triphenylmethylamine (TPMA) derivatives with tetrahedral tetrasulfonic acid. This d‐POSs with a highly fluorinated nanospace significantly improved their water stability, retaining their crystal structure even when immersed in water over one week. Moreover, this highly hydrophobic and fluorinated nanospace adsorbs 160 mL(STP)/g of water vapor at Pe/P0=0.90; this is the first hydrophobic nanospace, which water molecules can enter, in an all‐organic porous material. Furthermore, this highly fluorinated nanospace exhibits very high proton conductivity (1.34×10−2 S/cm) at 90 °C and 95 % RH. POSs with tailorable nanospaces may significantly advance the elucidation of the properties of specific "water" in pure hydrophobic environments. [ABSTRACT FROM AUTHOR]

Post Synthetic Modification (PSM) of Metal‐Organic Frameworks (MOFs) is a crucial strategy for developing new MOFs with enhanced functional properties compared to their parent one. PSM can be accomplished through various methods:1) modification of organic linkers; 2) exchange of metal ions or nodes; and 3) inclusion or exchange of solvent/guest molecules. Herein, PSM of bimetallic and monometallic MOFs containing biphenyl dinitro‐tetra‐carboxylates (NCA) are demonstrated. The tetra carboxylate NCA, produces monometallic Cd‐MOF‐1 and Cu‐MOF‐1 and bimetallic CoZn‐MOF in solvothermal reactions with the corresponding metal salts. The CoZn‐MOF undergoes post‐synthetic transmetallation with Cd(NO3)2 and Cu(NO3)2 in aqueous solution to yield Cd‐MOF‐2 and Cu‐MOF‐2, respectively. Additionally, green crystals of Cu‐MOF‐1 found to undergo a single‐crystal‐to‐single‐crystal (SCSC) transformation to blue crystals of Cu‐MOF‐3 upon dipped into water at room temperature. These MOFs demonstrate notable proton conductivities ranging from 10−3 to 10−4 S cm−1 under variable temperatures and humidity levels. Among them, Cu‐MOF‐3 achieves the highest proton conductivity of 1.36×10−3 S cm−1 at 90 °C and 98 % relative humidity, attributed to its continuous and extensive hydrogen bonding network, which provides effective proton conduction pathways within the MOF. This work highlights a convenient strategy for designing proton‐conducting MOFs via post‐synthetic modification. [ABSTRACT FROM AUTHOR]

Dimensional regulation in polyoxometalates is an effective strategy during the design and synthesis of polyoxometalates-based high proton conductors, but it is not available to date. Herein, the precise regulation of dimensionality has been realized in an unprecedented gigantic molybdenum blue wheel family featuring pentagonal {(W)Mo5} motifs through optimizing the molar ratio of Mo/W, including [Gd2Mo124W14O422(H2O)62]38− (0D-{Mo124W14}, 1), [Mo126W14O441(H2O)51]70− (1D-{Mo126W14}n, 2), and [Mo124W14O430(H2O)50]60− (2D-{Mo124W14}n, 3). Such important {(W)Mo5} structural motif brings new reactivity into gigantic Mo blue wheels. There are different numbers and sites of {Mo2} defects in each wheel-shaped monomer in 1–3, which leads to the monomers of 2 and 3 to form 1D and 2D architectures via Mo–O–Mo covalent bonds driven by {Mo2}-mediated H2O ligands substitution process, respectively, thus achieving the controllable dimensional regulation. As expected, the proton conductivity of 3 is 10 times higher than that of 1 and 1.7 times higher than that of 2. The continuous proton hopping sites in 2D network are responsible for the enhanced proton conductivity with lower activation energy. This study highlights that this dimensional regulation approach remains great potential in preparing polyoxometalates-based high proton conductive materials. [ABSTRACT FROM AUTHOR]

Proton conduction is important in both fundamental research and technological development. Here we report designed synthesis of crystalline porous covalent organic frameworks as a new platform for high‐rate anhydrous proton conduction. By developing nanochannels with different topologies as proton pathways and loading neat phosphoric acid to construct robust proton carrier networks in the pores, we found that pore topology is crucial for proton conduction. Its effect on increasing proton conductivity is in an exponential mode other than linear fashion, endowing the materials with exceptional proton conductivities exceeding 10−2 S cm−1 over a broad range of temperature and a low activation energy barrier down to 0.24 eV. Remarkably, the pore size controls conduction mechanism, where mesopores promote proton conduction via a fast‐hopping mechanism, while micropores follow a sluggish vehicle process. Notably, decreasing phosphoric acid loading content drastically reduces proton conductivity and greatly increases activation energy barrier, emphasizing the pivotal role of well‐developed proton carrier network in proton transport. These findings and insights unveil a new general and transformative guidance for designing porous framework materials and systems for high‐rate ion conduction, energy storage, and energy conversion. [ABSTRACT FROM AUTHOR]

Nafion membranes are widely used as proton exchange membranes, but their proton conductivity deteriorates in high-temperature environments due to the loss of water molecules. To address this challenge, we propose the utilization of porous aromatic frameworks (PAFs) as a potential solution. PAFs exhibit remarkable characteristics, such as a high specific surface area and porosity, and their porous channels can be post-synthesized. Here, a novel approach was employed to synthesize a PAF material, designated as PAF-45D, which exhibits a specific surface area of 1571.9 m2·g−1 and possesses the added benefits of facile synthesis and a low cost. Subsequently, sulfonation treatment was applied to PAF-45D in order to introduce sulfonic acid groups into its pores, resulting in the formation of PAF-45DS. The successful incorporation of sulfonic groups was confirmed through TG, IR, and EDS analyses. Furthermore, a novel Nafion composite membrane was prepared by incorporating PAF-45DS. The Nyquist plot of the composite membranes demonstrates that the sulfonated PAF-45DS material can enhance the proton conductivity of Nafion membranes at high temperatures. Specifically, under identical film formation conditions, doping with a 4% mass fraction of PAF-45DS, the conductivity of the Nafion composite membrane increased remarkably from 2.25 × 10−3 S·cm−1 to 5.67 × 10−3 S·cm−1, nearly 2.5 times higher. Such promising and cost-effective materials could be envisioned for application in the field of Nafion composite membranes. [ABSTRACT FROM AUTHOR]

Proton-conducting solid oxide fuel cell is an emerging technology to deliver sustainable energy conversion with the benefit of fuel flexibility. A low proton conduction energy barrier in the perovskite-type electrolytes facilitates the fuel cells to operate at lower temperatures. The design of electrolytes heavily relies on a better understanding of the proton conduction mechanism in the lattice. However, the manifestation of multiple cations, vacancies, and structural distortion in the electrolyte materials raises complexities in the proton conduction mechanism. This article briefly reviews the proton conduction mechanism to explain the roles of electronegativity, dopants, and sintering aids on the hydration behavior. The impact of acceptor dopants on protonic defect formation and mobility is discussed with particular emphasis on the proton trapping effect. • Protonic defects formation and migration in proton conducting solid oxide fuel cells. • Grotthuss mechanism to transport protons in perovskites. • Dopants ionic radius, electronic structure, and compatibility with the parent lattice affect proton conduction. • Proton trapping at higher concentrations of acceptor dopants. [ABSTRACT FROM AUTHOR]

Alkaline earth (AE) metal complexes have garnered significant interest in various functional fields due to their nontoxicity, low density, and low cost. However, there is a lack of systematic investigation into the structural characteristics and physical properties of AE‐metal‐organic frameworks (MOFs). In this research, we synthesized isostructural MOFs consisting of AE4(μ4‐Cl) clusters bridged by benzo‐(1,2;3,4;5,6)‐tris(thiophene‐2′‐carboxylic acid) (BTTC3−) ligands. The resulting structure forms a truncated octahedral cage denoted as [AE4(m4‐Cl)]6(BTTC)8, which further linked to a porous three‐dimensional framework. Among the investigated AE ions (Ca, Sr, and Ba), the Ca4‐MOF demonstrated good chemical stability in water compared to Sr4‐MOF and Ba4‐MOF. The N2 adsorption and solid‐state UV‐vis‐NIR absorption behaviors were evaluated for all AE4‐MOFs, showing similar trends among the different metal ions. Additionally, the proton conduction study revealed that the Ca4‐MOF exhibited ultra‐high proton conductivity, reaching 3.52×10−2 S cm−1 at 343 K and 98 % RH. Notably, the introduction of LiCl via guest exchange resulted in an improved proton conduction of up to 6.36×10−2 S cm−1 under similar conditions in the modified LiCl@Ca4‐MOF. The findings shed light on the regulation of physical properties and proton conductivity of AE‐MOFs, providing valuable insights for their potential applications in various fields. [ABSTRACT FROM AUTHOR]

Solid electrolyte materials with high structural stability and excellent proton conductivity (σ) have long been a popular and challenging research topic in the fuel cell field. This problem can be addressed because of the crystalline metal–organic frameworks' (MOFs') high structural stability, adjustable framework composition, and dense H-bonded networks. Herein, one highly stable Sr(II) MOF, {[Sr(H2tmidc)2(H2O)3]·4H2O}n (1) (H3tmidc = 2-(1H-tetrazolium-1-methylene)-1H-imidazole-4,5-dicarboxylic acid) was successfully fabricated, which was structurally characterized by single-crystal X-ray diffraction and electrochemically examined by the AC impedance determination. The results demonstrated that the σ of the compound manifested a positive dependence on temperature and humidity, and the optimal proton conductivity is as high as 1.22 × 10−2 S/cm under 100 °C and 98% relative humidity, which is at the forefront of reported MOFs with ultrahigh σ. The analysis of the proton conduction mechanism reveals that numerous tetrazolium groups, carboxyl groups, coordination, and crystallization water molecules in the framework are responsible for the high efficiency of proton transport. This work offers a fresh perspective on how to create novel crystalline proton conductive materials. [ABSTRACT FROM AUTHOR]

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Based on the previous work conducted by Fujii et al., NdBaInO4 compounds present modest oxide-ion conductivities. Therefore, it has been an attractive system of significant interest. In this study, we attempted to partially substitute Ca for Nd and the total electrical conductivity was successfully improved due to the generation of oxygen vacancies. The synthesis, crystal structure, density, surface topography, and electrical properties of NdBaInO4 and Ca-doped NdBaInO4 have been studied, respectively. NdBaInO4 and 10% and 20% molar fractions of Ca-doped NdBaInO4 were synthesized through solid-state reactions. The crystal structure of them was obtained from Le Bail refinement of the XRD pattern, giving the result of the monoclinic structure, which belongs to P21/c space group. The highest total electrical conductivity of 4.91 × 10−3 S cm−1 was obtained in the Nd0.9Ca0.1BaInO3.95 sample at a temperature of 760 °C in the dry atmosphere and the activation energy was reduced from 0.68 eV to 0.58 eV when the temperature was above 464 °C (737 K) after doping the NdBaInO4 with a 0.1 molar fraction of Ca2+. Moreover, the total conductivity of Nd0.9Ca0.1BaInO3.95 in the wet atmosphere at moderate temperature was relatively higher than that in the dry atmosphere, which suggests that potential proton conduction may exist in wet atmospheres. In addition, the oxygen diffusion coefficients of Nd0.9Ca0.1BaInO3.95 (D* = 1.82 × 10−8 cm2/s, 850 °C) was about two times higher than that of Nd0.8Ca0.2BaInO3.90 (D* = 7.95 × 10−9 cm2/s, 850 °C) and was increased significantly by two orders of magnitude when compared with the oxygen diffusion coefficient of the undoped NdBaInO4 (D* = 8.25 × 10−11 cm2/s, 850 °C). [ABSTRACT FROM AUTHOR]

Abstract A challenging task in solid oxide fuel cells (SOFCs) is seeking for an alternative electrolyte, enabling high ionic conduction at relatively low operating temperatures, i.e., 300–600 °C. Proton‐conducting candidates, in particular, hold a significant promise due to their low transport activation energy to deliver protons. Here, a unique hierarchical TiO2‐SrTiO3@TiO2 structure is developed inside an intercalated TiO2‐SrTiO3 core as “yolk” decorating densely packed flake TiO2 as shell, creating plentiful nano‐heterointerfaces with a continuous TiO2 and SrTiO3 “in‐house” interfaces, as well the interfaces between TiO2‐SrTiO3 yolk and TiO2 shell. It exhibits a reduced activation energy, down to 0.225 eV, and an unexpectedly high proton conductivity at low temperature, e.g., 0.084 S cm−1 at 550 °C, confirmed by experimentally H/D isotope method and proton‐filtrating membrane measurement. Raman mapping technique identifies the presence of hydrogenated HO─Sr bonds, providing further evidence for proton conduction. And its interfacial conduction is comparatively analyzed with a directly‐mixing TiO2‐SrTiO3 composite electrolyte. Consequently, a single fuel cell based on the TiO2‐SrTiO3@TiO2 heterogeneous electrolyte delivers a good peak power density of 799.7 mW cm−2 at 550 °C. These findings highlight a dexterous nano‐heterointerface design strategy of highly proton‐conductive electrolytes at reduced operating temperatures for SOFC technology.

Achieving rapid ion transport through nanochannels is essential for both biological and artificial membrane systems. Covalent organic frameworks (COFs) with well-defined nanostructures hold great promise for addressing the above challenge. However, due to the limited processability and inadequate interlamellar interaction of COF materials, it is extremely difficult to integrate them to prepare high-performance proton conductors. Herein, inspired by the ingenious bio-adhesion strategy in nature, ultrafast proton conduction is achieved by taking advantage of COF membranes where TP-COF nanosheets are linked by subnanometer nanowires/lignocellulosic nanofibrils composites (SNWs/LCNFs) through electrostatic and π-π interactions to form an ordered and robust structure. Notably, the synthesized SNWs exhibited impressive proton conductivity and adhesion capacity due to their inbuilt phosphotungstic acid (HPW) molecules and multidimensional interactions. Therefore, attributed to the synergistic contribution of TP-COFs and SNWs, the composite membrane achieves ultrahigh proton conductivity (0.395 S cm-1 at 80 °C and 100% RH), superior mechanical property (109.8 MPa), exceptional fuel cell performance (71.6 mW cm-2), and superior operational stability (OCV decay rate is about 1.5 mV h-1), demonstrating outstanding competitiveness. More importantly, the proposed design concept has the potential to be applied in membranes for various electrochemical devices and molecular separations. [ABSTRACT FROM AUTHOR]

Porous aromatic frameworks (PAFs) are an auspicious class of materials that allow for the introduction of sulfonic acid groups at the aromatic core units by post-synthetic modification. This makes PAFs promising for proton-exchange materials. However, the limited thermal stability of sulfonic acid groups attached to aromatic cores prevents high-temperature applications. Here, we present a framework based on PAF-303 where the acid groups were added as methylene sulfonic acid side chains in a two-step post-synthetic route (SMPAF-303) via the intermediate chloromethylene PAF (ClMPAF-303). Elemental analysis, NMR spectroscopy, electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy were used to characterize both frameworks and corroborate the successful attachment of the side chains. The resulting framework SMPAF-303 features high thermal stability and an ion-exchange capacity of about 1.7 mequiv g−1. The proton conductivity depends strongly on the adsorbed water level. It reaches from about 10−7 S cm−1 for 33% RH to about 10−1 S cm−1 for 100% RH. We attribute the strong change to a locally alternating polarity of the inner surfaces. The latter introduces bottleneck effects for the water molecule and oxonium ion diffusion at lower relative humidities, due to electrolyte clustering. When the pores are completely filled with water, these bottlenecks vanish, leading to an unhindered electrolyte diffusion through the framework, explaining the conductivity rise. [ABSTRACT FROM AUTHOR]

As a new type of proton conductor, metal–organic frameworks (MOFs) have attracted much attention because of their superior properties over conventional materials, such as the modifiability of framework, reversibility of coordination bond, high specific surface area, and porosity. It is predicted that the proton conductivities of MOFs can be improved by hole expansion and ionic liquid introduction. In this work, HKUST‐1 and LP‐HKUST‐1 were prepared, which were filled with different proportions of N‐methylimidazole triflate (MIM‐CF3SO3) to prepare composite materials MIM‐CF3SO3@HKUST‐1‐100% and MIM‐CF3SO3@LP‐HKUST‐1‐x (x = 25%, 50%, 75% and 100%). A total of seven kinds of materials were synthesized. The proton conductivities of all the materials at 75% RH were tested from 303 to 353 K. In this environment, MIM‐CF3SO3@LP‐HKUST‐1‐100% shows excellent proton conductivity (σ = 0.341 S·cm−1 at 353 K, 75% relatively humidity [RH]), being 7060 times that of HKUST‐1, and reaches the peak value of MOF family in recent years. Then, the conductivities of parts of the materials were tested in extreme environments, such as in high‐humidity environment (303–353 K, 100% RH), high‐temperature environment (373–423 K, N2 atmosphere), and low‐temperature environment (253–283 K, 75% RH). The results show that under all conditions above, the proton conductivity of MIM‐CF3SO3@LP‐HKUST‐1‐100% is the best, up to 0.341 S·cm−1 at 353 K and 75% RH, 0.179 S·cm−1 at 353 K and 100% RH, 1.31 × 10−3 S·cm−1 at 283 K and 75% RH, and 2.31 × 10−4 S·cm−1 at 423 K and N2 atmosphere, indicating that proton conductivity of HKUST‐1 is improved by hole expansion and ionic liquid introduction. Finally, the stability test showed that MIM‐CF3SO3@LP‐HKUST‐1‐100% was stable in all environments above. Moreover, the conductive mechanism of HKUST‐1 before and after introduction of ionic liquids was also discussed, providing a theoretical basis for the enhancement of proton conductivities of MOFs using ionic liquid introduction and hole expansion. [ABSTRACT FROM AUTHOR]

The extracellular electron transfer (EET) capability of Methanosarcina spp. in direct interspecies electron transfer (DIET) has profoundly increased our understanding of microbial kinetics and energetics in biomethanation systems. In Methanosarcina spp., such EET mechanisms occur in the cell envelope and biofilm matrix. These substances are composed of protein-like, polysaccharide-rich biomolecular structures that were previously thought to contribute only to cell support and shape; while their participation in dynamic processes remains unclear and has gathered widespread interest. This review first addresses the molecular structure and chemical characteristics of the extracellular matrix and cell wall polymers in Methanosarcina spp. Next, we focus on recent theoretical studies on the conduction and EET mechanisms of the extracellular matrix and cell wall polymers: tunnelling, hopping, proton-activated electron transfer and voltage-dependent electron transport. We conclude this review by discussing the state-of-the-art electrochemical techniques and experiments and the associated challenges, i.e., the kinetic isotope effect and on–off resonance switching. The border impacts of such conductive pathways may offer a semi-classical/quantum perspective on microbiology and mark the renaissance of anaerobic biotechnology. [ABSTRACT FROM AUTHOR]

[Display omitted] Obtaining crystalline materials with high structural stability as well as super proton conductivity is a challenging task in the field of energy and material chemistry. Therefore, two highly stable metal-organic frameworks (MOFs) with macro-ring structures and carboxylate groups, Zr-TCPP (1) and Hf-TCPP (2) assembled from low-toxicity as well as highly coordination-capable Zr(IV)/Hf(IV) cations and the multifunctional linkage, meso -tetra(4-carboxyphenyl)porphine (TCPP) have attracted our strong interest. Note that TCPP as a large-size rigid ligand with high symmetry and multiple coordination sites contributes to the formation of the two stable MOFs. Moreover, the pores with large sizes in the two MOFs favor the entry of more guest water molecules and thus result in high H 2 O-assisted proton conductivity. First, their distinguished structural stabilities covering water, thermal and chemical stabilities were verified by various determination approaches. Second, the dependence of the proton conductivity of the two MOFs on temperature and relative humidity (RH) is explored in depth. Impressively, MOFs 1 and 2 demonstrated the optimal proton conductivities of 4.5 × 10−4 and 0.78 × 10−3 S·cm−1 at 100 °C/98 % RH, respectively. Logically, based on the structural information, gas adsorption/desorption features, and activation energy values, their proton conduction mechanism was deduced and highlighted. [ABSTRACT FROM AUTHOR]

Highly reduced polyoxometalates (POMs) are predicted to be used as rather high energy density materials; however, it still suffers from the limited cluster species and reduction ratio. Here we demonstrate that it is possible to employ the building block strategy to generate a highly reduced polyoxomolybdate (C2H8N)14(NH4)4H14[MoV48MoVI26O202(OH)12(SO4)6]·46H2O (Mo74). The fundamental Mo-based {Mox} (x = 4, 5, and 6) building blocks, which are templated by tetra-coordinated anions {MoO4} or, not only lay foundation for the formation of Mo74 featuring an unprecedented reduction ratio of 65%, but also give rise to SBBs-mediated (secondary building blocks) supramolecular dense packing interactions among the isolated Mo74 clusters that are favorable for proton conduction. Remarkably, high proton conductivity (2.04 × 10−2 S cm−1) had been realized at 50 °C and 90% relative humidity, revealing one of the well-known POMs-based crystalline proton conducting materials. This result highlights that this building block approach possesses great potential in producing highly reduced POM systems that can achieve controllable reduced ratio and desirable properties. [ABSTRACT FROM AUTHOR]