Enhanced Proton Conductivity Research Articles

Understanding proton conduction enhancement of MOF-802 through in situ incorporation of imidazole into its channels

In this study, the proton-conducting properties of zirconium-based MOF-802 were investigated. MOF-802 exhibited remarkable thermal, aqueous, and acidic stabilities as well as room temperature superprotonic conduction under 98% relative humidity (RH), however, the proton conduction sharply drops above 318 K due to the release of lattice water molecules. To address this issue, a facile one-pot synthetic method was developed to encapsulate high boiling imidazole molecules in the pores/channels of MOF-802 as proton-transport medium, resulting in Im@MOF-802-S, which showed the enhanced proton conduction regarding MOF-802. We conducted a detailed discussion on the factors contributing to the improvement of the proton-conducting nature of MOF-802.

Proton‐Conducting Hierarchical Composite Hydrogels Producing First Soft Memcapacitors with Switchable Memory

AbstractPerpetual exigency for environment friendly clean energy and powerful soft electronics has elevated the research on hydrogels in past two decades. Hydrogels are the amplifiers of material properties using manipulation in structure–property relationship via simple, economic yet effective routes. Herein, a set of composite and hybrid hydrogels are developed by hierarchical assembling of clay nanosheets and surfactant micelles those divulge the first example of memcapacitor gels and offer exceptional proton conductivity (1.66–4.34 × 10–2 S cm−1) as a gel material. Further, Congo red, Eosin Y, and Orange G are used to hybridize one of the composites to achieve three hybrid hydrogels. Such hybridization is found to regulate the memristive function selectively from the coupled effect of memcapacitance from the composite. The composite hydrogel highlights its volatile memory with encouraging robustness under environmental conditions, established through various current–voltage (I–V) experiments. The electrochemical behaviors including the high proton conductivity are realized from impedance measurements. Material characterizations, experimental results, and in silico optimized structures rationalize composite/hybrid network formation, capacitive/memristive responses, and enhanced proton conduction in the fabricated composite superstructures. Proposed structural models demonstrate two orthogonally oriented structural encryptions to be accountable for the expressed bifunctionality in the hierarchically designed superstructures.

High Entropy Perovskite Electrolytes for Reversible Protonic Ceramic Electrochemical Cells

Reversible protonic ceramic electrochemical cells (R-PCECs) become cornerstones of low-temperature solid oxide electrochemical cells (SOCs) below 600 °C. Low activation energy and high energy conversion efficiency are primary significance of R-PCECs. However, electrolytes of high-performance R-PCECs still suffer from poor tolerance to complex operating conditions. To overcome their low stability and enhance proton conductivity, various cations have been doped into the Ba-based perovskite oxide electrolyte. Developing high entropy oxides by introducing multiple metal cations into A- or B- sites of the perovskite structure can be an effective solution for the structural stability. Due to the effect of the entropy-dominated stabilization in multi-doped perovskite oxides, the material can remain single phase under extreme temperatures and chemical environments. Promising high entropy stabilization concepts were adapted to electrolytes, and finally, durable proton-conducting perovskite oxide was designed. Here, we will present our recent progress on development of high entropy perovskite oxide electrolytes for R-PCECs.

Investigating the Sulfonated Chitosan/Polyvinylidene Fluoride-Based Proton Exchange Membrane with fSiO2 as Filler in Microbial Fuel Cells.

Chitosan (CS), a promising potential biopolymer with exquisite biocompatibility, economic viability, hydrophilicity, and chemical modifications, has drawn interest as an alternative material for proton exchange membrane (PEM) fabrication. However, CS in its original form exhibited low proton conductivity and mechanical stability, restricting its usage in PEM development. In this work, chitosan was functionalized (sulfonic acid (-SO3H) groups)) to enhance proton conductivity. The sulfonated chitosan (sCS) was blended with polyvinylidene fluoride (PVDF) polymer, along with the incorporation of functionalized SiO2 (-OH groups), for fabricating chitosan-based composite proton exchange membranes to enhance microbial fuel cell (MFC) performances. The results show that adding functionalized inorganic fillers (fSiO2) into the membrane enhances the mechanical, thermal, and anti-biofouling behavior. From the results, the PVDF/sCS/fSiO2 composite membrane exhibited enhanced proton conductivity 1.0644 × 10-2 S cm-1 at room temperature and increased IEC and mechanical and chemical stability. Furthermore, this study presents a revolutionary way to generate environmentally friendly natural polymer-based membrane materials for developing PEM candidates for enhanced MFC performances in generating bioelectricity and wastewater treatment.

Bioinspired supramolecular macrocycle hybrid membranes with enhanced proton conductivity

AbstractEnhancing the proton conductivity of proton exchange membranes (PEMs) is essential to expand the applications of proton exchange membrane fuel cells (PEMFCs). Inspired by the proton conduction mechanism of bacteriorhodopsin, cucurbit[n]urils (CB[n], where n is the number of glycoluril units, n = 6, 7, or 8) are introduced into sulfonated poly(ether ether ketone) (SPEEK) matrix to fabricate hybrid PEMs, employing a nature-inspired chemical engineering (NICE) methodology. The carbonyl groups of CB[n] act as proton-conducting sites, while the host–guest interaction between CB[n] and water molecules offers extra proton-conducting pathways. Additionally, the molecular size of CB[n] aids in their dispersion within the SPEEK matrix, effectively bridging the unconnected proton-conducting sulfonic group domains within the SPEEK membrane. Consequently, all hybrid membranes exhibit significantly enhanced proton conductivity. Notably, the SPEEK membrane incorporating 1 wt.% CB[8] (CB[8]/SPEEK-1%) demonstrates the highest proton conductivity of 198.0 mS·cm−1 at 60 °C and 100% relative humidity (RH), which is 228% greater than that of the pure SPEEK membrane under the same conditions. Moreover, hybrid membranes exhibit superior fuel cell performance. The CB[8]/SPEEK-1% membrane achieves a maximum power density of 214 mW·cm−2, representing a 140% improvement over the pure SPEEK membrane (89 mW·cm−2) at 50 °C and 100% RH. These findings serve as a foundation for constructing continuous proton-conducting pathways within membranes by utilizing supramolecular macrocycles as fuel cell electrolytes and in other applications.

Enhanced proton conductivity of SPEEK membranes by constructing hydrogen bond network through doping ionic liquid and graphene oxide

AbstractSo as to improve proton conductivity at medium temperatures while reducing the loss of ionic liquids (ILs), this article fabricated a series of hybrid membranes with sulfonated poly (ether ether ketone) (SPEEK) as their base material, 1‐allyl‐3‐methylimidazolium chloride ([AMIM][Cl]) as their primary proton conductor, and graphene oxide (GO) as their filler. The characterization results showed that the –SO3H groups of SPEEK formed acid–base pairs with the imidazole ring of [AMIM][Cl] at the interface where electrostatic attraction inhibited the main‐chain migration of the SPEEK. At the same time, the large hydrogen bond network formed between [AMIM][Cl], GO and SPEEK provided more jump sites for proton transfer. Proton conduction of the prepared membranes was enhanced by way of low potential energy barriers. At 120°C, SPEEK/IL/GO‐2% exhibited a proton conductivity of 21.35 mS/cm, and the IL loss rate was 20.17%. The characterization results demonstrated that the prepared SPEEK/IL/GO composite membranes had excellent physicochemical properties, dimensional stability, high proton conductivity, and low IL loss, which were expected to be used in practical conditions at medium temperature.Highlights Large hydrogen bonding network provides additional proton hopping sites. Physical cross‐linking limits the leaching of ionic liquid. SPEEK/IL/GO‐2% membrane achieves a conductivity of 21.35 mS/cm at 120°C.

Enhancing proton conduction of high temperature proton exchange membranes based on carbon dots doped polyvinyl chloride nanofibers

Carbon dots (CDs) as the easy-to-get and cheap carbon nanomaterials exhibited the great potential in various high-performance electrolytes. In this research, we constructed high temperature proton exchange membranes with multilayered microstructures through a couple of polyvinyl chloride (PVC) nanofibers layers wrapping a thin CDs layer. In the prepared (PVC/CDs/PVC)es membrane, the CDs provided a mount of sites to anchor phosphoric acid (PA) molecules with the formation of the (PVC/CDs/PVC)es/PA membrane. The proton conduction was accelerated by the continuous proton conduction channels consisting of the CDs layer and PA molecular chains. Notably, the proton conduction behavior was guided by the PVC nanofibers in the (PVC/CDs/PVC)es/PA membrane. Furthermore, a large number of hydrophilic oxygenated functional groups surrounding CDs facilitated the proton conduction process owing to the reduced proton conduction resistance in the hydrophilic membrane. For the PVC/ImCDs/PA membrane, the imidazolium groups could enhance proton conductivity. From our perspective, the imidazolium groups grafted CDs (ImCDs) participated into the proton conduction process through providing imidazolium groups for ameliorating proton conduction network. The enhanced proton conduction was achieved through constructing multilayered structure. Specifically, the (PVC/CDs/PVC)es/PA membrane exhibited the proton conductivity of 5.61 × 10-3 S/cm at 150 °C, which was higher than 7.73 × 10-4 S/cm of the PVC/CDs/PA membrane. Notably, the PA doped membrane could retain the mechanical strength without microstructure expansion.

Numerical modeling of novel cage‐like cross‐linked membranes for enhanced proton conductivity in a high temperature‐polymer electrolyte membrane fuel cell

AbstractPhosphoric acid (PA)‐doped polybenzimidazole (PBI) membranes have encountered several problems associated with high cost, chemical instability, poor solubility in organic solvents, and higher doping level which results in poor mechanical properties and faster degradation of the membrane. Alternative membranes with high proton conductivity and mechanical strength for high‐temperature applications are of great interest, one such membrane being cPBI‐IL X. The cage‐like cross‐linked structure of these membranes shows a dual proton transport path due to which proton conductivity is elevated. The ionic liquid content of these membranes improves the PA absorbing capability and shortens the proton transfer path. These membranes exhibit the highest proton conductivity of 13.3 S/m and better durability compared to existing PBI Membranes. A mathematical model is developed and validated versus published experimental results to account for the proton conductivity of these membranes. The developed model is further investigated for a detailed understanding of polarization phenomena and species distribution.

Advances and challenges in developing protonic ceramic cells

Unlike solid oxide cells (SOCs), which use oxygen ions as charge carriers, protonic ceramic cells (PCCs) utilize protons as primary charge carriers. As a result, PCCs have a unique conduction mechanism that shows higher ionic conductivity with lower activation energy than those of SOCs. Moreover, PCCs have additional critical advantages for commercialization, such as easy gas separation and no fuel dilution at the fuel electrode. At present, PCCs are receiving significant research attention, primarily motivated by their higher performance, superior stability at lower operating temperatures, and greater system simplicity than SOCs. However, despite these advantages and the overall potential of PCCs, their electrochemical performance and stability have not yet significantly exceeded those of SOCs. This review discusses three pathways toward solving the problems currently impacting the PCC development: (1) proton conducting ceramic materials, including proton conducting mechanisms, defects in materials that impact the overall conductivity, and rational design and engineering strategies for enhancing proton conductivity; (2) manufacturing process for fabricating the desired PCC electrolyte layer with large grain size and preserved stoichiometry; (3) improving the interfacial reaction, including enhancing the surface reactivity by controlling the charge-transfer reactant concentrations and increasing the electrolyte/electrode contact area.

Assessing electron conduction mechanisms in highly organized surface water on a model neuronal lipid using quantum chemical methods

A comprehensive characterization of key mechanisms underlying signal transmission within the human brain remains an unsolved problem. The neuronal surface, composed principally of phosphatidylcholine (POPC), has a known ordering effect on water. This produces highly organized water layers (OWLs) at the neuron–water interface—the neurochemical implications of which are not currently understood. The human brain is 75% water by volume, with folds and grooves to maximize surface area, suggesting that characterization of neuronal OWLs may contribute to an understanding of neuronal signal transmission. Previous experimental work has measured enhanced conductivity of POPC OWLs relative to bulk water. The mechanism underlying this conductivity is still debated. Using quantum chemical methods on a POPC–water interface model system, we present data characterizing OWL conductance. Non-equilibrium Green's function calculation results demonstrate that there is negligible electron transfer-based conductivity through the OWL at biological temperatures. This is consistent with existing studies suggesting the Grotthuss mechanism as the most likely explanation for experimentally observed enhanced conductivity at the POPC–water interface. The broader implications of enhanced proton conductivity at the neuron–water interface are discussed.

Unlocking the potential of proton conductivity in guanidinium-based ionic covalent organic nanosheets (iCONs) through pore interior functionalization

Recently, scientists have been exploring the incorporation of proton carriers such as water and phosphoric acid (PA) into the pores and channels of porous materials to enhance proton conduction performance. Ionic covalent organic nanosheets (iCONs) have been identified as promising functional materials due to their inbuilt ionic interfaces, which can facilitate strong interaction with counter ions present inside the pore structure and thus shorten ion transport pathways. However, there is a lack of research related to proton conductivity in iCONs loaded with PA. To address this, we prepared three functionalized guanidinium-based iCONs using a solvothermal condensation reaction between guanidinium amine (TG) and functionalized terephthaldehyde (Da, Dha, and Dma). PA was also incorporated into the iCON structure via ex situ loading to observe its effects on proton conduction performance. The results showed that both the iCONs and PA–iCONs were highly stable in water, organic solvents, acidic and basic media. Amongst these PA–iCONs, one with hydroxyl‑functionalization (PA–DhaTG) displayed high proton conductivity at 90 °C and 95% relative humidity due to a Grotthuss mechanism for protons. These functionalized guanidinium-based iCONs could prove useful for applications in energy conversion devices.

Chemically Gradient Hydrogen‐Bonded Organic Framework Crystal Film

AbstractHydrogen‐bonded organic frameworks (HOFs) are ordered supramolecular solid structures, however, nothing much explored as centimetre‐scale self‐standing films. The fabrication of such crystals comprising self‐supported films is challenging due to the limited flexibility and interaction of the crystals, and therefore studies on two‐dimensional macrostructures of HOFs are limited to external supports. Herein, we introduce a novel chemical gradient strategy to fabricate a crystal‐deposited HOF film on an in situ‐formed covalent organic polymer film (Tam‐Bdca‐CGHOF). The fabricated film showed versatility in chemical bonding along its thickness from covalent to hydrogen‐bonded network. The kinetic‐controlled Tam‐Bdca‐CGHOF showed enhanced proton conductivity (8.3×10−5 S cm−1) compared to its rapid kinetic analogue, Tam‐Bdca‐COP (2.1×10−5 S cm−1), which signifies the advantage of bonding‐engineering in the same system.

Sulfonate-Functionalized Polyoxovanadate-Based Metal-Organic Polyhedra for Enhanced Proton Conduction via the Synergy of Linker and Metal Cluster Vertex

Metal-organic polyhedra (MOPs) have emerged as novel porous platforms for proton conduction, however, the concerted employment of both linker and metal cluster vertex is rarely applied for the fabrication of MOPs-based high conducting materials. Herein we report the synthesis of sulfonate-functionalized polyoxovanadate-based MOPs for enhanced proton conduction via the synergistic effect from linker and metal cluster node. MOPs 1 and 2 exhibit octahedral cage configuration constructed from {V5O9Cl} vertex and 5-sulfoisophthalate linker. Owing to the ordered packing of octahedral cages along three axes, 3D interpenetrated open channels that are lined with high-density sulfonates are thus formed within 2. Coupled with the proton-conductive {V5O9Cl} vertexs as well as protonated counterions, an extensive H-bonded network is therefore generated for facile proton transfer. 2 exhibits high proton conductivity of 3.02×10−2 S cm−1 at 65 °C under 90% RH, recording the highest value for MOPs pellet sample. This value is enhanced ~1 order of magnitude compared with that of carboxylate-functionalized analogue 3, clearly illustrating the advantage of combining linker and metal cluster node for enhanced proton conduction. This work will further promote the exploitation of high proton conductive MOPs-based materials by the synergy design strategy.

Chemically Gradient Hydrogen-Bonded Organic Framework Crystal Film.

Hydrogen-bonded organic frameworks (HOFs) are ordered supramolecular solid structures, however, nothing much explored as centimeter-scale self-standing films. The fabrication of such crystals comprising self-supported films is challenging due to the limited flexibility and interaction of the crystals, and therefore studies on 2D macrostructures of HOFs are limited to external supports. Herein, we introduce a novel chemical gradient strategy to fabricate a crystal-deposited HOF film on an in-situ-formed COP-film (Tam-Bdca-CGHOF). The fabricated film showed versatility in chemical bonding along its thickness from covalent to hydrogen-bonded network. The kinetic-controlled Tam-Bdca-CGHOF showed enhanced proton conductivity (0.83 µS cm-1) compared to its rapid kinetic analogue, Tam-Bdca-COP (0.21 µS cm-1), which signifies the advantage of bonding-engineering in the same system.

High Proton Conductivity of Magnetically Ordered 2D Oxalate-Bridged [MnIICrIII] Coordination Polymers with Irregular Topology.

Two heterometallic coordination polymers {[NH(CH3)2(C2H5)]8[Mn4Cl4Cr4(C2O4)12]}n (1) and {[NH(CH3)-(C2H5)2]8[Mn4Cl4Cr4(C2O4)12]}n (2) were obtained by slow evaporation of an aqueous solution containing the building block [A]3[Cr(C2O4)3] [A = (CH3)2(C2H5)NH+ or (CH3)(C2H5)2NH+] and MnCl2·2H2O. The isostructural compounds comprise irregular two-dimensional (2D) oxalate-bridged anionic layers [Mn4Cl4Cr4(C2O4)12]n8n- with a Shubnikov plane net fes topology designated as (4·82), interleaved by the hydrogen-bonded templating cations (CH3)2(C2H5)NH+ (1) or (CH3)(C2H5)2NH+ (2). They exhibit remarkable humidity-sensing properties and very high proton conductivity at room temperature [1.60 × 10-3 (Ω·cm)-1 at 90% relative humidity (RH) of 1 and 9.6 × 10-4 (Ω·cm)-1 at 94% RH of 2]. The layered structure facilitates the uptake of water molecules, which contributes to the enhancement of proton conductivity at high RH. The better proton transport observed in 1 compared to that in 2 can be tentatively attributed to the higher hydrophilicity of the cations (CH3)2(C2H5)NH+, which is closely related to their affinity for water molecules. The original topology of the anionic networks in both compounds leads to the development of interesting magnetic phases upon cooling. The magnetically ordered ground state can be described as the coupling of ferromagnetic spin chains in which Mn2+ and Cr3+ ions are bridged by bis(bidentate) oxalate groups into antiferromagnetic planes through monodentate-bidentate oxalate bridges in the layers, which are triggered to long-range order below temperature 4.45 K via weaker interlayer interactions.

Pore-Scale Modeling of Liquid Water Transport in Compressed Gas Diffusion Layer of Proton Exchange Membrane Fuel Cells Considering Fiber Anisotropy.

Water management of the gas diffusion layer (GDL) is crucial to the performance of proton exchange membrane fuel cells (PEMFCs). Appropriate water management ensures efficient transport of reactive gases and maintains wetting of the proton exchange membrane to enhance proton conduction. In this paper, a two-dimensional pseudo-potential multiphase lattice Boltzmann model is developed to study liquid water transport within the GDL. Liquid water transport from the GDL to the gas channel is the focus, and the effect of fiber anisotropy and compression on water management is evaluated. The results show that the fiber distribution approximately perpendicular to the rib reduces liquid water saturation within the GDL. Compression significantly changes the microstructure of the GDL under the ribs, which facilitates the formation of liquid water transport pathways under the gas channel, and the increase in the compression ratio leads to a decrease in liquid water saturation. The performed microstructure analysis and the pore-scale two-phase behavior simulation study comprise a promising technique for optimizing liquid water transport within the GDL.

In Situ-Doped Sulfonated Schiff-Base Networks in SPEEK Composite Membranes with Enhanced Proton Conductivity.

Sulfonated polyether ether ketone (SPEEK) has been widely investigated in proton exchange membrane fuel cells (PEMFCs) due to its excellent thermal stability, chemical stability, and low cost compared with Nafion. However, excessive degree of sulfonation will easily lead to the decrease in thermal stabilities and mechanical properties of SPEEK membranes, which limits the enhancement of proton conductivity. In this work, a series of Schiff-base networks (SNWs) with different contents are in situ synthesized in the SPEEK membrane by a Schiff-base co-condensation reaction, and then, the composite membranes are soaked in sulfonic acid for further improvement of proton conductivity. The highest doping amount of the SNW filler in SPEEK can reach 20 wt %. High loading and low leaching rate of H2SO4 are easily achieved owing to the similar size between sulfuric acid molecules and micropores in SNW. Moreover, abundant amino and imine groups in SNW networks contribute to the anchoring of H2SO4 into the pores by acid-base interactions. The proton conductivity of the SPEEK/S-SNW-15 composite membrane can reach 115.53 mS cm-1 at 80 °C and 100% RH. Meanwhile, the composite membrane also exhibits satisfied stability and mechanical property.

Enhanced performance of nanocomposite membrane developed on sulfonated poly (1, 4-phenylene ether-ether-sulfone) with zeolite imidazole frameworks for fuel cell application

Proton exchange membrane fuel cells (PEMFC) have received a lot of interest and use metal–organic frameworks (MOF)/polymer nanocomposite membranes. Zeolite imidazole framework-90 (ZIF-90) was employed as an addition in the sulfonated poly (1, 4-phenylene ether-ether-sulfone) (SPEES) matrix in order to investigate the proton conductivity in a novel nanocomposite membrane made of SPEES/ ZIF. The high porosity, free surface, and presence of the aldehyde group in the ZIF-90 nanostructure have a substantial impact on enhancing the mechanical, chemical, thermal, and proton conductivity capabilities of the SPEES/ZIF-90 nanocomposite membranes. The results indicate that the utilization of SPEES/ZIF-90 nanocomposite membranes with 3wt% ZIF-90 resulted in enhanced proton conductivity of up to 160 mS/cm at 90 °C and 98% relative humidity (RH). This is a significant improvement compared to the SPEES membrane which exhibited a proton conductivity of 55 mS/cm under the same conditions, indicating a 1.9-fold increase in performance. Furthermore, the SPEES/ZIF-90/3 membrane exhibited a remarkable 79% improvement in maximum power density, achieving a value of 0.52 W/cm2 at 0.5 V and 98% RH, which is 79% higher than that of the pristine SPEES membrane.

High Entropy Perovskite Electrolytes for Reversible Protonic Ceramic Electrochemical Cells

Reversible protonic ceramic electrochemical cells (R-PCECs) have become the cornerstone of low-temperature solid oxide electrochemical cells (SOCs) below 600 °C. Low activation energy and high energy conversion efficiency are primary significance of R-PCECs. However, electrolytes of high-performance R-PCECs still suffer from poor tolerance to complex operating conditions. To overcome their low stability and enhance proton conductivity, various cations have been doped into the Ba-based perovskite oxide electrolyte. Developing high entropy oxides by introducing multiple metal cations into A- or B- sites of the perovskite structure can be an effective solution for the structural stability. Due to the effect of the entropy-dominated stabilization in multi-doped perovskite oxides, the material can remain single phase under extreme temperatures and chemical environments. Promising high entropy stabilization concepts were adapted to electrolytes, and finally, durable proton-conducting perovskite oxide was designed. Here, we will present our recent progress on development of high entropy perovskite oxide electrolytes for R-PCECs.

Mixed-ceria reinforced acid functionalized graphene oxide-Nafion electrolyte membrane with enhanced proton conductivity and chemical durability for PEMFCs

Towards the next-gen energy solutions, Nafion, as a state-of-the-art polymer electrolyte to low temperature fuel cell (LTFC) application has been one of the most demanding hydrogen to clean energy conversion device ever achieved. However, the inherent issue of limiting chemical durability and restricted proton conductivity have always been a topic of concern with pure Nafion membranes. To tackle this, we report a mixed-ceria reinforced phosphorylated graphene oxide (sPGO)/Nafion membrane as a potential electrolyte to simultaneously improve the chemical durability and proton conductivity of bare Nafion by utilizing the redox property of ceria nanoparticles and acidic sites of sPGO for accelerated proton transfer. As a progressive method, the single-step phosphorylation of GO introduced short chain branching along with enhanced number of acidic sites in the Nafion matrix whereas incorporation of mixed-ceria nanoparticles improved the chemical durability of the membrane due to its superior radical scavenging property. As a result, mixed-ceria reinforced sPGO/Nafion (Ce-sPGO/NF) electrolyte membrane showed higher proton conductivity (1.2-times) and chemical durability (8.1-times) than bare Nafion. Furthermore, the polymer electrolyte membrane (PEM) was also showcased high enough thermomechanical and electrochemical stability at 80 °C and 100% relative humidity (RH).