Daniil I. Kolokolov, Dae-Woon Lim, and Hiroshi Kitagawa · The Chemical Record · 2020
Review how proton conductivity and molecular dynamics in hydrated metal-organic frameworks are characterised, with selected MOF examples used to connect conducting media, structural pathways and mechanism assignment.
The review’s argument is preserved as a navigable set of section summaries.
States that proton-conduction mechanisms in MOFs remain under-investigated and identifies methodological and synthetic needs for PFG-NMR, 2H NMR, neutron scattering and MD.
Relevance: Core · 1311 · 4. Conclusion and Perspective
Details how 2H NMR line-shape and relaxation analysis distinguish protic species, bonding environments and motional modes, with Mg-formate, MOF-74-urea and MFM phosphonate examples.
Relevance: Core · 1305 · 3.1. Deuterium Solid-State Nuclear Magnetic Resonance
Explains why X-ray structures and activation barriers are insufficient, then positions SS NMR, PFG-NMR and neutron scattering as complementary probes over different time and length scales.
Relevance: Core · 1304 · 3. Characterization of Proton Dynamics
Reviews representative hydrated MOFs, showing how countercations, framework functional groups, hydrophilicity, coordinated water, urea-modified open metal sites and hydrophobic nanotubes alter pathways and mechanisms.
Relevance: Core · 1300 · 2.1. Hydrated MOF Proton Conductor
Introduces MOFs as tunable SSPCs, frames water as the dominant conducting medium, lists design strategies by proton source, and defines Grotthuss versus vehicular mechanisms with activation-energy heuristics.
Relevance: Core · 1298 · 1. Introduction
Distinguishes intrinsic from extrinsic proton conductivity and argues that understanding conducting media is prerequisite for general MOF proton-conductor design.
Relevance: Core · 1300 · 2. Conducting Media and Conductive Metal-Organic Frameworks
Defines PFG-NMR as a direct diffusion probe on long length scales and uses the synthetic nanotube example to discuss anisotropic diffusion and Grotthuss-type transfer.
Relevance: Supporting · 1308 · 3.2. Pulse Field Gradient NMR
Explains QENS and INS as atomistic-scale probes of proton mobility and vibrational states, including EISF model validation and examples in ammonium oxalate, UiO-66-COOH and MFM-512.
Relevance: Core · 1308 · 3.3. Quasi Elastic Neutrons Scattering
Classification systems are attributed to this review and are not treated as a global material registry.
The review uses 0.4 eV as an intuitive divider while warning that the heuristic is too general for complex MOF morphologies without structural and dynamic probes.
Categories: Ea below 0.4 eV: often Grotthuss · Ea above 0.4 eV: often vehicular
1300 · 1. Introduction
The introduction organises rational design strategies according to the source of mobile protons and pathways, from H3O+/NH4+/Me2NH2+ counterions to functional groups, acids, defects and stimuli.
Categories: Countercation inclusion · Metal or ligand functionalisation · Acid or functional guest inclusion · Defect control · External stimulus
1298 · 1. Introduction
Water is treated as both proton donor and acceptor; its framework location and hydrogen-bond contacts define conduction pathways and hydration sensitivity.
Categories: Lattice or guest water · Water hydrogen-bonded to framework functional groups · Coordinated solvent water · Water interacting with protonic countercations
1300 · 2.1. Hydrated MOF Proton Conductor
Intrinsic conductivity depends on framework composition and synthetic design; extrinsic conductivity is achieved by adding functional guests or post-synthetic changes.
Categories: Intrinsic proton conductivity designed during MOF synthesis · Extrinsic conductivity by guest impregnation or post-synthetic modification
1300 · 2. Conducting Media and Conductive Metal-Organic Frameworks
Grotthuss transfer involves site-to-site proton jump-diffusion coupled with rotational reorientation, whereas vehicular transport involves diffusion of a larger protonated species such as H3O+ or NH4+.
Categories: Grotthuss or hopping mechanism · Vehicular mechanism
1299 · 1. Introduction · Figure 1
The review frames these methods as complementary, with each probing different motion classes and scales needed to connect conductivity to mechanism.
Categories: 2H SS NMR for reorientation and local species · PFG-NMR for translational diffusion over micrometre scales · QENS for fast local motions over nanometre scales · INS for vibrational states of protic species
1304 · 3. Characterization of Proton Dynamics
QENS separates local rotations and translational motions by Q-dependence, while INS assignments identify protic species and localised hydroxyl/water/hydronium states.
Categories: QENS broadening for thermal mobility · INS peaks for vibrational states · EISF for motional-model validation
1309 · 3.3. Quasi Elastic Neutrons Scattering
Review-defined families retain their representative materials and conduction descriptions.
2D anionic Zn oxalate/adipate frameworks containing NH4+ countercations and lattice water.
Conduction: Continuous hydrogen-bond networks involving NH4+, adipate and water make hydration and countercation mobility central to conductivity.
Representative materials: (NH4)2(adp)[Zn2(ox)3].3H2O · K2(adp)[Zn2(ox)3].3H2O
Nodes / linkers: Zn · Oxalate · Adipic acid/adipate
1300 · 2.1. Hydrated MOF Proton Conductor
Barium MOFs built from terphenyl multi-carboxylic acid linkers with varying accessible acidic protons.
Conduction: Accessible unbound acidic protons and larger cavities in MFM-512 raise conductivity and QENS supports Grotthuss diffusion in a sphere-like model.
Representative materials: MFM-510 · MFM-511 · MFM-512
Nodes / linkers: Ba · Terphenyl tricarboxylate · Terphenyl tetracarboxylate · Terphenyl pentacarboxylate
1311 · 3.3. Quasi Elastic Neutrons Scattering
Dissymmetric 2D bimetallic MnCr oxalate sheets with mono- or dicarboxyl countercation carriers.
Conduction: A more hydrophilic carboxy-face increases water uptake and drives a RH-dependent vehicular-to-Grotthuss transition.
Representative materials: dic-MnCr · moc-MnCr
Nodes / linkers: Mn · Cr · Oxalate · N-butyl carboxylate countercations
1302 · 2.1. Hydrated MOF Proton Conductor · Figure 5
One-dimensional ferrous oxalate chain with coordinated water molecules as acidic proton sources.
Conduction: Coordinated water at Lewis-acidic Fe sites creates a hydrogen-bond pathway while remaining electronically insulating.
Representative materials: [Fe(ox).2H2O] · Humboldtine
Nodes / linkers: Fe(II) · Oxalate · Coordinated water
1303 · 2.1. Hydrated MOF Proton Conductor
2D anionic M-Cr oxalate frameworks whose interlayer hydrophilicity is varied by alkyl ammonium countercations.
Conduction: Water adsorption and low-RH conductivity decrease as hydrophobic alkyl chain length increases.
Representative materials: {NR3(CH2COOH)}[MCr(ox)3].nH2O · Me-FeCr · Et-MnCr · Bu-FeCr · Bu-MnCr
Nodes / linkers: Mn · Fe · Cr · Oxalate · Alkyl ammonium carboxylate counterions
1302 · 2.1. Hydrated MOF Proton Conductor · Figure 4
Pt-based tubular metal-organic framework hosting confined water clusters in hydrophobic and hydrophilic channels.
Conduction: Single-crystal measurements show anisotropic conduction along the channel and PFG-NMR identifies anisotropic proton diffusion.
Representative materials: [Pt(dach)(bpy)Br]4(SO4)4.32H2O
Nodes / linkers: Pt · 4,4-bipyridine · Dach diamine · Sulfate counterions
1303 · 2.1. Hydrated MOF Proton Conductor
Dense metal phosphonate frameworks with acidic hydroxyl groups on crystal surfaces.
Conduction: Hydration creates mobile surface protonic species, but proton transfer is limited by formation/decomposition of D3O+ complexes.
Representative materials: MFM-550(M) · MFM-555(Ho)
Nodes / linkers: La · Ce · Nd · Sm · Gd · Ho · Ba · Biphenyl diphosphonic acid · Benzene diphosphonic acid
1308 · 3.1. Deuterium Solid-State Nuclear Magnetic Resonance
Framework with tight pores and Mg open metal sites binding most water molecules.
Conduction: 2H NMR indicates most protons belong to water tightly bound to Mg sites, limiting H-bond network formation and favouring vehicular transfer.
Representative materials: Hydrated Mg-formate framework
Nodes / linkers: Mg · Formate
1306 · 3.1. Deuterium Solid-State Nuclear Magnetic Resonance
Isostructural Al or Fe MIL-53 frameworks bearing H, NH2, OH or COOH substituents protruding into pores.
Conduction: Functional-group acidity and water interactions tune proton conductivity and activation barrier.
Representative materials: MIL-53-H · MIL-53-NH2 · MIL-53-OH · MIL-53-COOH
Nodes / linkers: Al · Fe · 1,4-benzenedicarboxylate derivatives
1301 · 2.1. Hydrated MOF Proton Conductor · Figure 3
MOF-74(Ni/Mg) frameworks whose open metal sites are occupied by urea to confine water and stabilise hydrogen bonds.
Conduction: Urea decreases void volume, polarises water and stabilises hydronium/water pairs, enabling Grotthuss-type conduction at high humidity.
Representative materials: MOF-74(Ni)-Urea · MOF-74(Mg)-Urea · MOF-74(Ni)-H2O-Urea
Nodes / linkers: Ni · Mg · MOF-74 dobdc-type linker · Coordinated urea
1307 · 3.1. Deuterium Solid-State Nuclear Magnetic Resonance
UiO-66(Zr) framework functionalised with carboxylic acid groups and fully hydrated pores.
Conduction: QENS and MD distinguish fast proton diffusion from slower water diffusion in a stable H-bond network, supporting Grotthuss transport.
Representative materials: UiO-66(Zr)-(CO2H)2
Nodes / linkers: Zr · Carboxylated terephthalate-type linker
1310 · 3.3. Quasi Elastic Neutrons Scattering
Review-level synthesis principles remain separate from primary-study recipes.
Design linkers and cavities so carboxylic acid protons remain unbound and reachable by hydration water.
Claimed effects: MFM-512 outperforms MFM-510 and MFM-511 because it has larger cavities and accessible unbound acidic protons.
Controlling variables: Number of acid groups · Steric accessibility · Cavity size · Hydration water access
Representative materials: MFM-512 · MFM-510 · MFM-511
Caveat: The review frames accessibility as decisive; bound or inaccessible acids give poor conductivity despite acid functionality.
1311 · 3.3. Quasi Elastic Neutrons Scattering
Create a crystalline nanotube analogue so confined water structures and anisotropic conduction can be directly visualised and measured.
Claimed effects: The metal-organic nanotube shows single-crystal anisotropic conductivity and PFG-NMR anisotropic diffusion consistent with Grotthuss transfer along the channel.
Controlling variables: Channel hydrophobicity · Single-crystal quality · H-bond distances · Channel orientation
Representative materials: [Pt(dach)(bpy)Br]4(SO4)4.32H2O
Caveat: Pelletised samples lose much of the single-crystal conductivity, indicating grain-boundary and orientation sensitivity.
1304 · 2.1. Hydrated MOF Proton Conductor
Use Lewis-acidic metal centres to polarise coordinated water so that it can donate protons into a hydrogen-bond network.
Claimed effects: Ferrous oxalate dihydrate is presented as high-conductivity but electronically insulating, showing proton transport rather than mixed electronic transport.
Controlling variables: Metal Lewis acidity · Coordinated-water geometry · Nearby acceptor oxygen atoms · Electronic insulation
Representative materials: [Fe(ox).2H2O]
Caveat: The review treats this as a nanoscale manipulation example rather than a general MOF design law.
1303 · 2.1. Hydrated MOF Proton Conductor
Use cations such as NH4+, H3O+ or Me2NH2+ in anionic MOF pores to increase proton-source concentration and build H-bond networks.
Claimed effects: NH4+ versus K+ replacement sharply changes high-humidity conductivity even with similar host structures.
Controlling variables: Countercation identity · Hydration level · Framework charge and pore geometry
Representative materials: (NH4)2(adp)[Zn2(ox)3].3H2O · K2(adp)[Zn2(ox)3].3H2O
Caveat: Countercation effects require dynamic evidence because activation energies alone can conflate local rotations, carrier formation and vehicular diffusion.
1301 · 2.1. Hydrated MOF Proton Conductor
Install functional groups in the pore, such as COOH, OH or NH2, to alter pKa, water interactions and proton-transfer barriers.
Claimed effects: In MIL-53 derivatives, COOH gives the highest conductivity and lowest activation barrier among the reviewed substituents.
Controlling variables: Functional group identity · pKa · Pore exposure · Relative humidity
Representative materials: MIL-53-COOH · MIL-53-OH · MIL-53-NH2
Caveat: Functional groups must be accessible to water or proton carriers; acidity alone is not a complete design rule.
1301 · 2.1. Hydrated MOF Proton Conductor
Alter alkyl chain length or carboxyl placement to tune water-vapour uptake and low-RH conduction.
Claimed effects: Increasing hydrophobic alkyl character lowers included water and reduces conductivity, whereas carboxyl-rich faces improve humid conduction.
Controlling variables: Hydrophobic chain length · Carboxyl group placement · Water vapour pressure · Layer spacing
Representative materials: Me-FeCr · Bu-FeCr · dic-MnCr · moc-MnCr
Caveat: Conductivity and mechanism can change with RH because water ordering changes.
1302 · 2.1. Hydrated MOF Proton Conductor
Post-synthetically occupy open metal sites with urea to reduce accessible pore volume, add amino H-bonding groups and polarise confined water.
Claimed effects: Fully urea-coordinated MOF-74 samples reach high conductivity and low Ea at high RH; 2H NMR supports hydronium/water gear-like Grotthuss exchange.
Controlling variables: Urea coordination degree · Metal identity · Void size · Hydration level
Representative materials: MOF-74(Ni)-Urea · MOF-74(Mg)-Urea
Caveat: At lower RH or lower urea coordination, the same family can show higher Ea and vehicular behaviour.
1303 · 2.1. Hydrated MOF Proton Conductor
These are the review authors’ synthesis, not newly measured results.
2H NMR line shape and relaxation analysis can identify protic species, bonding environments and motional modes, including chemical exchange relevant to hydronium formation.
Evidence basis: review_reasoning
Caveat: It senses translational displacement mainly when coupled to rotational motion.
1305 · 3.1. Deuterium Solid-State Nuclear Magnetic Resonance
NH4+ countercations increase proton-source concentration and build hydrogen-bond pathways, producing much higher humid conductivity than K+ analogues.
Evidence basis: single_reference
Caveat: The review attributes the difference to H-bonding and proton source effects under high humidity.
1301 · 2.1. Hydrated MOF Proton Conductor
Activation-energy assignment is useful but too general to define the mechanism in morphologically complex MOFs without structural, conductivity and dynamic measurements.
Evidence basis: review_reasoning
Caveat: The 0.4 eV heuristic remains a screening clue, not a proof.
1300 · 1. Introduction
The review identifies Kanda et al. 1979 on a 2D Cu dithiooxamide MOF as the first report of a proton-conductive MOF.
Evidence basis: single_reference
Caveat: This is review framing, not independently verified here.
1298 · 1. Introduction
Hydration state controls hydrogen-bond network continuity and can change conductivity across many orders of magnitude in hydrated ammonium zinc oxalate frameworks.
Evidence basis: single_reference
Caveat: Benchmark values are secondary and should be checked in the primary report before leaderboard use.
1301 · 2.1. Hydrated MOF Proton Conductor
Framework hydrophilicity controls water uptake and therefore low-humidity proton conductivity in layered oxalate MOFs.
Evidence basis: multi_reference
Caveat: Excess hydrophobicity can suppress water adsorption; high humidity can also change phase order and mechanism.
1302 · 2.1. Hydrated MOF Proton Conductor
Despite more than ten years of MOF proton-conduction studies, actual proton-transport mechanisms have not been investigated very much.
Evidence basis: review_reasoning
Caveat: The statement is current to the 2020 review.
1311 · 4. Conclusion and Perspective
Crystalline PCPs/MOFs have become important solid-state proton conductors because porosity, functionality, structural designability and crystallinity allow both performance tuning and pathway analysis.
Evidence basis: multi_reference
Caveat: The review focuses on hydrated MOFs rather than all proton-conductive MOF classes.
1298 · Abstract
PFG-NMR directly probes proton diffusion coefficients but operates over long length scales and cannot by itself distinguish hopping from vehicular mechanisms.
Evidence basis: review_reasoning
Caveat: Requires large crystallites to ensure that measured diffusion is intracrystalline.
1304 · 3. Characterization of Proton Dynamics
Systematic functional-group pKa control in MIL-53 derivatives correlates with proton conductivity and activation barrier.
Evidence basis: single_reference
Caveat: The relation is presented for an isostructural series and may not transfer directly across frameworks.
1301 · 2.1. Hydrated MOF Proton Conductor
Simply hosting water is insufficient for Grotthuss conduction; pore size must allow hydronium formation, rotation and H-bonding to neighbouring water.
Evidence basis: single_reference
Caveat: Based on the Mg-formate example where tight binding produces predominantly vehicular behaviour.
1306 · 3.1. Deuterium Solid-State Nuclear Magnetic Resonance
QENS is especially valuable for proton conductors because incoherent proton scattering selectively follows local translational and rotational motions and allows model validation through Q-dependence and EISF.
Evidence basis: review_reasoning
Caveat: Requires careful separation of framework and conducting-medium signals, often by selective deuteration.
1309 · 3.3. Quasi Elastic Neutrons Scattering
For hydrated UiO-66(Zr)-(CO2H)2, QENS and MD support a percolating H-bond network in which excess protons diffuse faster than water via a Grotthuss mechanism.
Evidence basis: single_reference
Caveat: The review summarises the primary study; primary QENS/MD details should be used for quantitative modelling.
1310 · 3.3. Quasi Elastic Neutrons Scattering
In urea-modified MOF-74, urea both confines/stabilises the water H-bond network and polarises water near open metal sites, creating stable hydronium ions and favouring Grotthuss transfer.
Evidence basis: single_reference
Caveat: Mechanism assignment depends on the review’s reading of 2H NMR relaxation and conductivity agreement.
1307 · 3.1. Deuterium Solid-State Nuclear Magnetic Resonance
Water is the most used conducting medium because conductivity depends on proton-carrier density and diffusion rate, but water loss limits operating temperature and can break pathways.
Evidence basis: review_reasoning
Caveat: Water-mediated conductors face high-temperature stability limits.
1298 · 1. Introduction
Crystallography plus impedance can suggest pathways, but hydrogen positions and mobile proton disorder mean they cannot directly identify actual proton-transfer mechanisms or motional rates.
Evidence basis: review_reasoning
Caveat: Neutron diffraction can help but is also not always sufficient for highly disordered protons.
1304 · 3. Characterization of Proton Dynamics
Every row remains visibly secondary and links to a primary dossier only where the mapping is verified.
| Material | Property | Reported value | Context and quality | Primary evidence | Review source |
|---|---|---|---|---|---|
| Secondary(NH4)2(adp)[Zn2(ox)3].3H2O dehydrated/lower hydration state | Proton conductivity | 6 x 10^-6 S cm^-1 | 70% RH Text · Exact Reported | research_0324 | 1300 · 2.1. Hydrated MOF Proton Conductor |
| Secondary(NH4)2(adp)[Zn2(ox)3].3H2O | Proton conductivity | 8 x 10^-3 S cm^-1 | 298 K, 98% RH Text · Exact Reported | research_0220 | 1300 · 2.1. Hydrated MOF Proton Conductor |
| Secondary(NH4)2(adp)[Zn2(ox)3].3H2O | Activation energy | 0.63 eV | 298 K, 98% RH conductivity context Text · Exact Reported | research_0220 | 1300 · 2.1. Hydrated MOF Proton Conductor |
| Secondarydic-MnCr | Proton conductivity | 1.8 x 10^-3 S cm^-1 | 95% RH Text · Exact Reported | No verified corpus mapping | 1302 · 2.1. Hydrated MOF Proton Conductor |
| Secondary[Fe(ox).2H2O] | Proton conductivity | 1.3 x 10^-3 S cm^-1 | 25 °C, 98% RH Text · Exact Reported | No verified corpus mapping | 1303 · 2.1. Hydrated MOF Proton Conductor |
| Secondary[Fe(ox).2H2O] | Activation energy | 0.37 eV | 25 °C, 98% RH conductivity context Text · Exact Reported | No verified corpus mapping | 1303 · 2.1. Hydrated MOF Proton Conductor |
| SecondaryMe-FeCr layered oxalate MOF | Proton conductivity | 0.8 x 10^-4 S cm^-1 | 65% RH, 298 K figure context Text · Exact Reported | No verified corpus mapping | 1302 · 2.1. Hydrated MOF Proton Conductor |
| SecondaryMFM-512 | Proton conductivity | 2.9 x 10^-3 S cm^-1 | Hydrated Ba multi-carboxylate framework Text · Exact Reported | No verified corpus mapping | 1311 · 3.3. Quasi Elastic Neutrons Scattering |
| SecondaryHydrated Mg-formate framework | Fraction of protons in tightly bound water | p ~ 99.8% | 2H NMR analysis Text · Approximate | No verified corpus mapping | 1306 · 3.1. Deuterium Solid-State Nuclear Magnetic Resonance |
| SecondaryMIL-53-COOH derivative | Proton conductivity | 2.0 x 10^-6 S cm^-1 | 298 K, 95% RH Text · Exact Reported | No verified corpus mapping | 1301 · 2.1. Hydrated MOF Proton Conductor |
| SecondaryMIL-53-COOH derivative | Activation energy | 0.21 eV | MIL-53 functional-group comparison Text · Exact Reported | No verified corpus mapping | 1301 · 2.1. Hydrated MOF Proton Conductor |
| SecondaryMOF-74(Mg)-Urea | Proton conductivity | 2.64 x 10^-2 S cm^-1 | High humidity condition, 95% RH context Text · Exact Reported | No verified corpus mapping | 1303 · 2.1. Hydrated MOF Proton Conductor |
| SecondaryMOF-74(Mg)-Urea-d4 | Correlated rotation barrier | 15 kJ/mol | 2H NMR relaxation analysis; compared with conductivity Ea 16 kJ/mol Text · Exact Reported | No verified corpus mapping | 1307 · 3.1. Deuterium Solid-State Nuclear Magnetic Resonance |
| Secondary[Pt(dach)(bpy)Br]4(SO4)4.32H2O | Single-crystal proton conductivity | 1.7 x 10^-2 S cm^-1 | 55 °C, 95% RH, a-axis Text · Exact Reported | No verified corpus mapping | 1303 · 2.1. Hydrated MOF Proton Conductor |
| Secondary[Pt(dach)(bpy)Br]4(SO4)4.32H2O | Anisotropic proton diffusion coefficient | D_parallel = 2.9 x 10^-11 m2 s^-1; D_perp = 1.6 x 10^-12 m2 s^-1 | PFG-NMR; numeric value is channel-axis diffusion Text · Exact Reported | No verified corpus mapping | 1308 · 3.2. Pulse Field Gradient NMR |
| Secondary(NH4)2(adp)[Zn2(ox)3].3H2O versus K2(adp)[Zn2(ox)3].3H2O | High-humidity conductivity contrast | 0.8 x 10^-2 versus 1.2 x 10^-4 S cm^-1 | 25 °C, 98% RH; numeric value is NH4 analogue Text · Exact Reported | No verified corpus mapping | 1301 · 2.1. Hydrated MOF Proton Conductor |
| SecondaryUiO-66(Zr)-(CO2H)2 | Proton conductivity | 2.3 x 10^-3 S cm^-1 | 90 °C, fully hydrated state, 95% RH Text · Exact Reported | research_0236 | 1310 · 3.3. Quasi Elastic Neutrons Scattering |
| SecondaryUiO-66(Zr)-(CO2H)2 | Proton self-diffusion coefficient | Ds ~ 3.5 x 10^-9 m2 s^-1 | 373 K, QENS fitting at small Q Text · Approximate | research_0236 | 1310 · 3.3. Quasi Elastic Neutrons Scattering |
Open questions are presented as review-author priorities, not conclusions from the primary database.
2H NMR would benefit from broader spin-relaxation analysis and better theory for chemical exchange among multiple protic species.
Proposed direction: Develop adequate simulations for complex chemical exchange in conducting MOFs.
1311 · 4. Conclusion and Perspective
INS application to proton vibrational states in MOF systems is scarce.
Proposed direction: Use INS more widely to identify hydroxyl, water and hydronium vibrational fingerprints, supported by calculations.
1311 · 3.3. Quasi Elastic Neutrons Scattering
Molecular dynamics can now describe H-bond networks and proton transfer, but synergistic use with experiments is not yet routine.
Proposed direction: Apply MD with QENS/NMR/INS as a regular combined workflow for ordered solids.
1311 · 4. Conclusion and Perspective
Actual proton-transport mechanisms in MOFs remain much less investigated than conductivity performance.
Proposed direction: Use dynamics-specific measurements to connect proton mobility to synthetic design and conductivity.
1311 · 4. Conclusion and Perspective
Current NMR measurements do not routinely mimic real fuel-cell membrane operation under a proton gradient.
Proposed direction: Develop in-situ/operando NMR cells for transport-regime measurements.
1311 · 4. Conclusion and Perspective
PFG-NMR needs large crystals to ensure measured diffusivities are intracrystalline rather than interparticle or grain-boundary artefacts.
Proposed direction: Grow larger crystals and study pressure-dependent pelleting to clarify grain-boundary effects.
1311 · 4. Conclusion and Perspective
Neutron studies can suffer interference from flexible/mobile frameworks and host protons.
Proposed direction: Prepare selectively deuterated host frameworks and combine instruments with different resolutions.
1311 · 4. Conclusion and Perspective
Mappings show which printed review references have a verified counterpart in the frozen primary corpus.
| Reference | Study | Role and context | Corpus mapping |
|---|---|---|---|
| Ref. 712016 | Title unavailable | qens · md · transport_benchmarkKey QENS+MD example for fast proton diffusion in carboxylated UiO-66. | research_0236 |
| Ref. 81979 | Title unavailable | historical_framingIdentified by the review as the first proton-conductive MOF report. | Unmapped |
| Ref. 702014 | Title unavailable | qens · countercation_dynamicsSupports neutron-scattering analysis of NH4+ mobility and local gear-like hopping in ammonium zinc oxalate. | Unmapped |
| Ref. 462020 | Title unavailable | hydrophilicity · mechanism_switch · transport_benchmarkUsed for carboxyl-face control and RH-dependent vehicle-to-Grotthuss mechanism transition. | Unmapped |
| Ref. 502020 | Title unavailable | confined_water · pfg_nmr · transport_benchmarkPrimary source for the metal-organic nanotube, confined water clusters, anisotropic conductivity and PFG-NMR diffusion. | Unmapped |
| Ref. 672018 | Title unavailable | 2h_nmr · neutron_scattering · surface_conductionUsed for nonporous phosphonate MOFs combining 2H NMR and neutron scattering to identify vehicular surface proton transport. | Unmapped |
| Ref. 722019 | Title unavailable | qens · accessible_acid_groups · transport_benchmarkSupports the accessible-acid-proton MFM-512 example and QENS free-diffusion-in-a-sphere interpretation. | Unmapped |
| Ref. 172009 | Title unavailable | transport_benchmark · countercation_frameworkPrimary source for the hydrated ammonium zinc oxalate conductivity and activation energy values discussed early in section 2.1. | research_0220 |
| Ref. 452012 | Title unavailable | hydrophilicity · transport_benchmarkSupports the alkyl-chain hydrophilicity and low-RH conductivity comparison in layered oxalate MOFs. | Unmapped |
| Ref. 422014 | Title unavailable | countercation_effect · transport_benchmarkSupports the review’s NH4+ versus K+ comparison and countercation mobility claim. | Unmapped |
| Ref. 412014 | Title unavailable | hydration_structure · transport_benchmarkUsed for systematic hydration-state structures and conductivity changes in ammonium zinc oxalate. | research_0324 |
| Ref. 202020 | Title unavailable | open_metal_site_modification · 2h_nmr · transport_benchmarkCentral example for urea-modified MOF-74 conductivity and 2H NMR mechanism assignment. | Unmapped |
| Ref. 212011 | Title unavailable | functional_group_effect · transport_benchmarkPrimary source for the MIL-53 functional-group/pKa conductivity and activation-energy series. | Unmapped |
| Ref. 592020 | Title unavailable | 2h_nmr · caveatSupports the tight-pore Mg-formate case where bound water favours vehicular transfer. | Unmapped |
| Ref. 472009 | Title unavailable | coordinated_water · transport_benchmarkSupports the ferrous oxalate dihydrate example of coordinated-water acidity and proton conduction. | Unmapped |