Dae-Woon Lim and Hiroshi Kitagawa · Chemical Reviews · 2020
To summarise fundamental principles, design strategies, representative proton-conductive MOFs, computation and characterisation methods for understanding proton transport in MOFs.
The review’s argument is preserved as a navigable set of section summaries.
Reviews acid impregnation strategies using nonvolatile acids and coupled acid-functionalised frameworks, highlighting high conductivities but also stability and crystallinity caveats.
Relevance: Core · 8435 · 4.3. Acid Guest Molecule Inclusion · Figure 26
Reviews MD and related calculations for water- and guest-mediated proton transport in MIL-53, UiO-66 and other MOFs, stressing their value and scarcity.
Relevance: Core · 8445 · 5. Theoretical/Computational Study · Figures 39-40
Discusses charged frameworks where counterions such as ammonium, dimethylammonium, hydronium or sulfate provide charge balance, proton donors and hydrogen-bond pathways.
Relevance: Core · 8426 · 4.1. Counterions in a Charged Network · Figure 12
Combines later design sections on defect control, hydrophilic pore tuning and functional guest inclusion with imidazole, triazole, histamine, POMs or MOPs.
Relevance: Core · 8445 · 4.7. Other Functional Guest Inclusions · Figure 35
Summarises pressure- and light-responsive control of proton transport, noting that examples are scarce and current conductivity switching magnitudes are modest.
Relevance: Supporting · 8437 · 4.4. External Stimuli to Control the Proton Conductivity · Figures 28-30
Covers predesigned and postsynthetic functionalisation of linkers and metal sites, especially acidic, hydroxyl and amine groups as proton sources or hopping sites.
Relevance: Core · 8429 · 4.2. Ligand and Metal Center Functionalization · Figure 18
Introduces proton conduction in fuel-cell and electrochemical contexts, contrasts MOFs with conventional proton conductors, defines Grotthuss and vehicle mechanisms, and states why MOF crystallinity and porosity are attractive.
Relevance: Core · 8417 · 1. Introduction · Figure 1
Organises MOF proton conduction by dimensionality, emphasising 1D and 2D frameworks where ordered hydrogen-bond chains or layered pathways can support high proton transport.
Relevance: Core · 8419 · 3. Low-Dimensional Structures and Proton Conductivity · Figure 2
Explains EIS/IS, single-crystal impedance, SSNMR, PFG-NMR and QENS for assigning pathways, dynamics and mobile species while warning about pellet grain-boundary and circuit-fitting ambiguities.
Relevance: Core · 8453 · 6. Methods for the Characterization of Proton Diffusion and Dynamics · Table 2
Synthesises the main design rules and gaps: carrier concentration, continuous hydrogen-bond networks, stable hosts, single-crystal/computational mechanistic evidence and practical durability.
Relevance: Core · 8459 · 7. Conclusion and Perspectives
Reviews stability requirements under water, ammonia and acid media, and links metal inertness, linker basicity, steric protection and hydrophobicity to practical proton-conductive MOF durability.
Relevance: Core · 8418 · 2. Structural Stability with Conducting Media
Classification systems are attributed to this review and are not treated as a global material registry.
Media selection is tied to intended operating conditions: water is useful below about 100 C, while high-boiling acids or protic organics are used for anhydrous or higher-temperature conduction.
Categories: water-mediated low-temperature conduction · nonvolatile acid-mediated high-temperature conduction · protic organic molecule-mediated anhydrous conduction
8417 · 1. Introduction
The conclusion distils the review into design priorities that can structure a literature-chapter discussion of why high sigma alone is insufficient.
Categories: increase proton-carrier concentration · form continuous hydrogen-bond networks · use stable host materials · visualise and model pathways · improve practical durability
8459 · 7. Conclusion and Perspectives
The review treats dimensionality as a design lever because low-dimensional ordered hydrogen-bond paths can outperform large but less directed void spaces.
Categories: 0D discrete units · 1D chains · pseudo-1D · 2D layers · pseudo-2D · 3D frameworks
8419 · 3. Low-Dimensional Structures and Proton Conductivity · Figure 2
The review classifies proton-conductive MOFs by where mobile protons originate and where hopping occurs; it cautions that real systems often combine multiple types synergistically.
Categories: counterion inclusion · ligand functionalization · metal-centre functionalization · functional guest molecule inclusion · defective MOFs
8417 · 1. Introduction · Figure 1
The review separates conductivity measurement from mechanistic assignment, emphasising that structural and spectroscopic measurements are needed to interpret EIS values.
Categories: pellet impedance · single-crystal impedance · SSNMR line-shape and relaxation · PFG-NMR diffusion · QENS hydrogen dynamics
8453 · 6. Methods
The review uses the conventional distinction between structural proton hopping and molecular diffusion of proton-attached carriers, with activation energy as a first diagnostic rather than a complete proof.
Categories: Grotthuss jump diffusion · vehicle diffusion of protonated species
8418 · 1. Introduction
Review-defined families retain their representative materials and conduction descriptions.
Stable Cr-based MIL-101 frameworks loaded with strong nonvolatile acid guests, sometimes combined with framework sulfonation.
Conduction: Acid guests and water/acid hydrogen bonds increase carrier density and can sustain high conductivity, but host stability and acid retention are limiting concerns.
Representative materials: H3PO4@MIL-101 · TfOH@MIL-101 · H2SO4@MIL-101-SO3H
Nodes / linkers: Cr(III) · BDC · sulfonated BDC
8436 · 4.3. Acid Guest Molecule Inclusion · Figure 26
Anionic or cationic frameworks in which counterions balance charge and may also act as proton donors, carriers or hydrogen-bond nodes.
Conduction: Counterions such as NH4+, Me2NH2+ or Cl-/NH3+ pairs change carrier concentration and hydrogen-bond connectivity.
Representative materials: VNU-15 · (NH2Me2)[Eu(L)] · MIP-202(Zr)
Nodes / linkers: Fe · Eu · Zr · carboxylate · sulfate · phosphonate · amino acid
8428 · 4.1. Counterions · Figure 17
MOFs with dense sulfonic acid groups and framework flexibility that respond to humidity while preserving hydrogen-bond pathways.
Conduction: Sulfonic acid groups increase carrier density while flexible pores may retain connectivity under changing humidity.
Representative materials: BUT-8(Cr) · BUT-8(Cr)A · TMOF-2
Nodes / linkers: Cr(III) · Cu(II) · disulfonated naphthalenedicarboxylate · benzene dimethanesulfonate
8437 · 4.3-4.5 · Figure 27
1D or 2D oxalate-linked coordination frameworks where coordinated or lattice water and counterions form ordered hydrogen-bond chains.
Conduction: Ordered water, ammonium or hydronium-rich hydrogen-bond networks enable proton hopping; cation substitution can strongly alter the pathway.
Representative materials: Fe(ox).2H2O · (NH4)2(adp)[Zn2(ox)3].3H2O · K2(adp)[Zn2(ox)3].3H2O
Nodes / linkers: Fe(II) · Zn(II) · Mn/Cr bimetallic nodes · oxalate · adipate
8420 · 3.1. 1D Structure · Figure 3
MIL-53-type frameworks bearing -H, -NH2, -OH, -COOH or mixed functional groups in channels.
Conduction: Functional group acidity, water uptake and breathing behaviour tune carrier density and hydrogen-bond pathways.
Representative materials: MIL-53(Al)-OH · MIL-53(Al)-NH2 · MIL-53(Fe)-COOH
Nodes / linkers: Al(III) · Fe(III) · BDC derivatives
8430 · 4.2. Ligand and Metal Center Functionalization · Figure 19
MOFs or coordination polymers containing phosphonate/phosphate groups as acidic proton sources and hydrogen-bond acceptor/donor sites.
Conduction: Acidic P-OH groups and coordinated or lattice water produce hydrogen-bond networks; some anhydrous plastic-crystal examples rely on imidazolium mobility.
Representative materials: [Zn(HPO4)(H2PO4)2](ImH2)2 · PCMOF10 · MFM-500(Ni)
Nodes / linkers: Zn(II) · Mg(II) · Ni(II) · Co(II) · orthophosphate · benzene phosphonate · carboxyphosphonate
8421 · 3.1. 1D Structure · Figure 6
MOFs loaded with imidazole, triazole, histamine or related high-boiling proton carriers for anhydrous or high-temperature proton transport.
Conduction: Protic guest molecules provide mobile donor-acceptor networks; host-guest interactions can either promote mobility or trap carriers.
Representative materials: Tz@beta-PCMOF2 · Im@[Al(mu2-OH)(1,4-ndc)] · His@VNU-23
Nodes / linkers: Al(III) · Zr(IV) · Na-containing host frameworks · sulfonate · phosphonate · naphthalenedicarboxylate
8443 · 4.7. Other Functional Guest Inclusions · Figure 35
MOFs for which conductivity was measured along crystallographic directions and compared with pellet behaviour.
Conduction: Single-crystal measurements can expose anisotropic proton migration and avoid pellet grain-boundary artefacts.
Representative materials: CoLa-II · CoCa.4H2O · PCMOF-17 · MOF-74(Co)
Nodes / linkers: Co/La · Co/Ca · In · Co · phosphonate · sulfoisophthalate · dobdc
8454 · 6.1.1. Impedance for Single Crystal Samples · Table 2
Frameworks whose conductivity is modulated by pressure, light or photoisomerisation rather than only humidity or acid loading.
Conduction: Pressure can disrupt pathways by amorphisation; light can release photoacid protons or switch guest interactions through azobenzene isomerisation.
Representative materials: pyranine-doped Zn(HPO4)(H2PO4)2(H2Im)2 · triazole@Cu2(F2AzoBDC)2(dabco) · Zn(HPO4)(H2PO4)2.2H2im under pressure
Nodes / linkers: Zn · Cu · phosphate · azobenzene dicarboxylate
8439 · 4.4. External Stimuli · Figure 30
Zr-carboxylate UiO frameworks where missing linkers, acid groups or postsynthetic functionalisation create proton sources or water-binding sites.
Conduction: Vacant linker sites can host water and improve mobility, while ordered defects alter acidity and can also trap protons.
Representative materials: defective UiO-66 · UiO-66-SO3H · zirconium 2-sulfoterephthalate
Nodes / linkers: Zr6 oxo-hydroxy clusters · terephthalate · sulfo-terephthalate
8440 · 4.5. Defect Control · Figure 31
Review-level synthesis principles remain separate from primary-study recipes.
Impregnate stable porous MOFs with acids such as H2SO4, H3PO4, TfOH or TsOH to increase carrier density and support high-temperature conduction.
Claimed effects: Can produce very high conductivities and low activation energies, especially when framework acid groups and acid guests are coupled.
Controlling variables: host acid stability · acid loading · water retention · acid volatility · pore confinement
Representative materials: H3PO4@MIL-101 · TfOH@MIL-101 · H2SO4@MIL-101-SO3H
Caveat: Strong acid can reduce crystallinity and obscure structural pathway visualisation.
8459 · 7. Conclusion and Perspectives
Design or exploit charged MOFs with protonic counterions that both balance framework charge and participate in hydrogen-bonded transport.
Claimed effects: Can increase carrier concentration and create proton-transfer pathways; non-protonic counterions can suppress conductivity.
Controlling variables: framework charge · counterion acidity · counterion position · water uptake · hydrogen-bond connectivity
Representative materials: (NH4)2(adp)[Zn2(ox)3].3H2O · K2(adp)[Zn2(ox)3].3H2O · VNU-15
Caveat: Counterion positions may be disordered or undefined, making pathway assignment ambiguous.
8428 · 4.1. Counterions in a Charged Network · Figure 12
Create missing-linker or missing-connection sites that alter porosity, water uptake, acidity and proton mobility.
Claimed effects: Defects can improve conductivity by hosting water and increasing pore volume, but can also reduce carrier concentration or create trapping sites.
Controlling variables: metal-to-ligand ratio · monocarboxylic acid additives · defect ordering · acid co-loading · surface sites
Representative materials: defective UiO-66 · zirconium 2-sulfoterephthalate · TMOF-2
Caveat: The review states that defect and surface roles remain under-considered and require exact control.
8441 · 4.5. Defect Control · Figure 32
Use flexible frameworks that can expand, breathe or transform under humidity while preserving hydrogen-bond connectivity.
Claimed effects: May maintain proton conduction under low humidity where rigid frameworks lose connectivity.
Controlling variables: framework flexibility · humidity · cation replacement · pore expansion
Representative materials: BUT-8(Cr) · BUT-8(Cr)A
Caveat: Flexibility must be balanced with structural durability and reproducible hydration state.
8437 · 4.3. Acid Guest Molecule Inclusion · Figure 27
Tune pore surfaces or counterions to improve water affinity and proton-conducting pathways under mild humidity.
Claimed effects: Hydrophilic pores can retain water and enable measurable conductivity at lower humidity.
Controlling variables: alkyl chain length · hydrophilic counterion structure · pore size · water adsorption profile
Representative materials: R-MCr oxalate frameworks · MIT-25
Caveat: Excess water uptake is not sufficient if the adsorbed water does not form a continuous pathway.
8441 · 4.6. Hydrophilicity · Figure 33
Introduce acid, amine or hydroxy groups on linkers before framework synthesis to tune pore acidity, water uptake and hopping sites.
Claimed effects: Acidic groups generally increase proton concentration and can lower activation energy; mixed linkers tune sorption and conductivity.
Controlling variables: functional group pKa · ligand ratio · breathing behaviour · water adsorption
Representative materials: MIL-53(Al)-OH · MIL-53(Al)-NH2 · MIL-53(Fe)-COOH
Caveat: Higher water uptake alone does not guarantee higher conductivity; acidity and framework flexibility also matter.
8430 · 4.2. Ligand and Metal Center Functionalization · Figure 19
Modify an existing stable framework after synthesis, for example oxidising thiols to sulfonic acids or introducing sulfonated surfaces.
Claimed effects: Adds strong proton donor sites while preserving the parent MOF topology when successful.
Controlling variables: postsynthetic conversion extent · acid group density · retained crystallinity · pore accessibility
Representative materials: UiO-66-SO3H · sulfonic acid-decorated PCPs
Caveat: Bulky functional groups or incomplete conversion can reduce surface area or complicate transport interpretation.
8432 · 4.2. Ligand and Metal Center Functionalization · Figure 22
Confine protic organic molecules or supramolecular acid carriers in MOF pores for mobile proton donor-acceptor networks.
Claimed effects: Can support anhydrous or high-temperature conductivity when guest mobility is high and host interactions do not over-trap carriers.
Controlling variables: guest loading · guest boiling point · host-guest interaction · pore hydrophobicity · carrier mobility
Representative materials: Tz@beta-PCMOF2 · histamine@[Al(mu2-OH)(1,4-ndc)] · His@VNU-23
Caveat: Strong host-guest binding can reduce mobility despite higher guest loading.
8444 · 4.7. Other Functional Guest Inclusions · Figure 36
Measure conductivity along known crystallographic directions and compare with pellet behaviour to identify anisotropic pathways and grain-boundary effects.
Claimed effects: Provides stronger evidence for pathway directionality than pellet EIS alone.
Controlling variables: crystal orientation · electrode contact · humidity · phase transition · facet direction
Representative materials: CoLa-II · CoCa.4H2O · MOF-74(Co)
Caveat: Requires large, stable, well-oriented crystals and challenging sample contacts.
8453 · 6.1.1. Impedance for Single Crystal Samples · Table 2
These are the review authors’ synthesis, not newly measured results.
Nonvolatile acid impregnation is a powerful route to high conductivity, especially when paired with framework acid sites, but it depends on exceptional host stability.
Evidence basis: multi_reference
Caveat: Strong acids can lower crystallinity and make the proton-hopping path difficult to visualise.
8435 · 4.3. Acid Guest Molecule Inclusion · Figure 26
The review regards computational simulation as powerful for atomic-scale mechanism insight but still scarce and challenging for proton-conductive MOFs.
Evidence basis: multi_reference
Caveat: No high-throughput prediction study of potential proton-conductive MOFs was found by the review authors.
8452 · 5. Theoretical/Computational Study · Figure 40
Protonic counterions in charged MOFs can both increase carrier concentration and form hydrogen-bond pathways; replacing ammonium with potassium can sharply reduce conductivity.
Evidence basis: single_reference
Caveat: Counterion disorder often prevents unambiguous pathway assignment.
8426 · 4.1. Counterions · Figure 12
Defects can enhance proton conductivity by increasing pore volume, water uptake and available vacant sites, but may also remove carrier-generating ligands or trap protons.
Evidence basis: multi_reference
Caveat: The role of crystal surfaces and exact defect structures remains insufficiently studied.
8441 · 4.5. Defect Control · Figures 31-32
Activation energy is used as an intuitive but not definitive diagnostic: lower Ea is associated with Grotthuss hopping and higher Ea with vehicle-type transport.
Evidence basis: review_reasoning
Caveat: The review also states that structural, conductivity and spectroscopic measurements are needed for overall mechanism assignment.
8418 · 1. Introduction
Flexible sulfonated frameworks are presented as a way to retain or recover hydrogen-bond pathways under humidity changes, improving low-humidity performance relative to rigid analogues.
Evidence basis: single_reference
Caveat: The claim is based on limited examples and depends on maintaining structural integrity.
8437 · 4.3. Acid Guest Molecule Inclusion · Figure 27
Within functionalised MIL-53 derivatives, stronger acidic functional groups correlate with higher conductivity and lower activation energy.
Evidence basis: single_reference
Caveat: Water uptake and structural flexibility also change across functional groups, so acidity is not the only variable.
8430 · 4.2. Ligand and Metal Center Functionalization · Figure 19
For anhydrous or high-temperature guest-mediated systems, carrier mobility and host-guest interactions are as important as carrier concentration.
Evidence basis: multi_reference
Caveat: A strongly bound guest can become immobile even if loading is high.
8444 · 4.7. Other Functional Guest Inclusions · Figure 36
Hydrophilicity is treated as a key design variable for mild-condition proton conduction because it controls water affinity and hence pathway formation.
Evidence basis: multi_reference
Caveat: High humidity can mask differences; low-humidity behaviour is more discriminating.
8441 · 4.6. Hydrophilicity · Figure 33
Low-dimensional frameworks can be advantageous because reduced void space and ordered chains can support efficient proton hopping, despite 3D porosity being attractive for many other MOF applications.
Evidence basis: multi_reference
Caveat: The review does not imply all low-dimensional MOFs outperform 3D MOFs; pathway continuity and hydration state remain decisive.
8419 · 3. Low-Dimensional Structures · Figure 2
MOFs are framed as a useful platform for proton conductors because crystallinity, designability and porosity allow host-guest design and mechanistic interrogation.
Evidence basis: multi_reference
Caveat: The review does not claim MOFs are already practical membranes; it repeatedly notes stability and processing barriers.
8416 · Abstract
NMR and QENS are complementary for proton dynamics: QENS probes shorter timescales, while NMR can cover slower motion and provide diffusion coefficients.
Evidence basis: review_reasoning
Caveat: Technique choice must match the timescale and species of interest.
8459 · 6.3. QENS
Pellet EIS values are vulnerable to grain-boundary effects, electrode interfaces and circuit-fitting ambiguities, so single-crystal and dynamic probes are important for mechanism claims.
Evidence basis: review_reasoning
Caveat: Single-crystal measurements are themselves experimentally difficult.
8453 · 6.1. IS Measurement
For real MOF-based PEM materials, the review prioritises durability, processability, oxidative stability, fuel-crossover control and electrochemical evaluation beyond conductivity alone.
Evidence basis: review_reasoning
Caveat: This is review authors' outlook rather than a direct primary result.
8459 · 7. Conclusion and Perspectives
Single-crystal conductivity measurements can reveal directional proton migration and demonstrate whether bulk pellet conductivity is dominated by specific hydrogen-bond pathways.
Evidence basis: multi_reference
Caveat: The review notes that few single-crystal examples exist.
8454 · 6.1.1. Impedance for Single Crystal Samples · Table 2
Stability toward conducting media is attributed to metal inertness/oxophilicity/oxidation state/radius, linker bonding and hydrophobicity, plus steric protection, interpenetration and flexibility.
Evidence basis: multi_reference
Caveat: High stability must be balanced with proton diffusion and hydrogen-bond network formation.
8419 · 2. Structural Stability
Pressure- and light-responsive control of proton conductivity is possible, but the review judges the example set as small and current modulation modest.
Evidence basis: multi_reference
Caveat: Useful mainly as future-direction context rather than mature design consensus.
8439 · 4.4. External Stimuli · Figure 30
The review warns that conductivity-Ea plots across MOFs are scattered because reported values differ in temperature, humidity, structure, carrier density and measurement criteria.
Evidence basis: review_reasoning
Caveat: Use Table 1 as secondary context only, not as a strict quantitative leaderboard.
8445 · 4.7. Other Functional Guest Inclusions · Figure 38
Water is the dominant low-temperature conducting medium because it provides proton donor and acceptor sites, but water also threatens many MOF coordination bonds.
Evidence basis: review_reasoning
Caveat: Stable host frameworks are required; water uptake alone does not prove a good pathway.
8418 · 2. Structural Stability
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 | proton conductivity | 0.8 x 10^-2 S cm^-1 | 25 C, 98% RH Text · Exact Reported | research_0220 | 8426 · 4.1. Counterions · Figure 12 |
| SecondaryBUT-8(Cr)A | proton conductivity | 1.27 x 10^-1 S cm^-1; Ea = 0.11 eV | 80 C, 100% RH Text · Exact Reported | No verified corpus mapping | 8437 · 4.3. Acid Guest Molecule Inclusion · Figure 27 |
| SecondaryCoLa-II single crystal | directional proton conductivity | 3.05 x 10^-4 S cm^-1 along a-axis; Ea = 0.42 eV | 25 C, 95% RH Text · Exact Reported | No verified corpus mapping | 8453 · 6.1.1. Impedance for Single Crystal Samples · Table 2 |
| Secondarydefective UiO-66 sample 6 | proton conductivity | 6.93 x 10^-3 S cm^-1; Ea = 0.22 eV | 65 C, 95% RH; high stearic acid additive sample Text · Exact Reported | No verified corpus mapping | 8440 · 4.5. Defect Control · Figure 31 |
| Secondarydefective [Zn(H2PO4)2(Tz)2]n sample 5 | anhydrous proton conductivity | 4.6 x 10^-3 S cm^-1; Ea = 0.53 eV | 150 C, N2 atmosphere Text · Exact Reported | No verified corpus mapping | 8441 · 4.5. Defect Control · Figure 32 |
| SecondaryFe(ox).2H2O (ferrous oxalate dihydrate) | proton conductivity | 1.3 x 10^-3 S cm^-1; Ea = 0.37 eV | 25 C, 98% RH Text · Exact Reported | No verified corpus mapping | 8420 · 3.1. 1D Structure · Figure 3 |
| SecondaryH2SO4@MIL-101-SO3H | proton conductivity | 1.82 S cm^-1 at 90 C; 0.92 x 10^-2 S cm^-1 at -40 C; Ea = 0.21 eV | 90 C for maximum value; 3 M H2SO4@MIL-101-SO3H Text · Exact Reported | No verified corpus mapping | 8436 · 4.3. Acid Guest Molecule Inclusion |
| SecondaryHis8.2 subset VNU-23 | proton conductivity | 1.79 x 10^-2 S cm^-1; Ea = 0.27 eV | 95 C, 85% RH Text · Exact Reported | No verified corpus mapping | 8444 · 4.7. Other Functional Guest Inclusions |
| SecondaryMIP-177-SO4H-LT | proton conductivity | 2.6 x 10^-2 S cm^-1 | 25 C, 95% RH Text · Exact Reported | No verified corpus mapping | 8452 · 5. Theoretical/Computational Study |
| SecondaryMIP-202(Zr) | proton conductivity | 1.1 x 10^-2 S cm^-1; Ea = 0.22 eV | 363 K, 95% RH Text · Exact Reported | No verified corpus mapping | 8429 · 4.1. Counterions · Figure 16 |
| SecondaryMOF-74(Co), acid-treated pH 3 single crystal | directional proton conductivity | 3.5 x 10^-3 S cm^-1 along c-axis | 90 C, 95% RH, pH 3 treatment Text · Exact Reported | research_0380 | 8454 · 6.1.1. Impedance for Single Crystal Samples · Table 2 |
| SecondaryPCMOF10 | proton conductivity | 3.55 x 10^-2 S cm^-1; Ea = 0.4 eV | 70 C, 95% RH Text · Exact Reported | No verified corpus mapping | 8432 · 4.2. Ligand and Metal Center Functionalization |
| SecondaryTfOH@MIL-101 | proton conductivity | 8 x 10^-2 S cm^-1; Ea = 0.25 eV at 50% RH and 0.23 eV at 15% RH | 60 C, 100% RH for highest conductivity; acid-loaded MIL-101 Text · Exact Reported | No verified corpus mapping | 8436 · 4.3. Acid Guest Molecule Inclusion |
| SecondaryVNU-15 | proton conductivity | 2.9 x 10^-2 S cm^-1; Ea = 0.22 eV | 95 C, 60% RH Text · Exact Reported | No verified corpus mapping | 8427 · 4.1. Counterions · Figure 14 |
| Secondary[Zn(HPO4)(H2PO4)2](ImH2)2 | anhydrous proton conductivity | 2.6 x 10^-4 S cm^-1; Ea = 0.47 eV | 130 C, anhydrous Text · Exact Reported | No verified corpus mapping | 8421 · 3.1. 1D Structure · Figure 6 |
Open questions are presented as review-author priorities, not conclusions from the primary database.
The review found no high-throughput screening study for potential proton-conductive MOFs.
Proposed direction: Develop screening methods that include water loading, acid sites, hydrogen-bond continuity and proton-transfer energetics.
8459 · 7. Conclusion and Perspectives
Charged MOFs are promising, but undefined counterion positions make conducting pathways ambiguous.
Proposed direction: Use crystallography, neutron methods and spectroscopy to locate counterions and hydrogen atoms under operating humidity.
8429 · 4.1. Counterions
The effect of defects and crystal surfaces has not been considered sufficiently in proton-conductive MOF studies.
Proposed direction: Quantify defect structures, surface contributions and grain boundaries separately using single-crystal and spectroscopic methods.
8441 · 4.5. Defect Control
The review identifies need for alternative conducting media beyond water to achieve practical performance, especially where dehydration breaks pathways.
Proposed direction: Mine high-boiling protic organics, nonvolatile acids and strongly anchored guest systems while retaining crystallinity.
8445 · 4.7. Other Functional Guest Inclusions
Future MOF proton conductors must address durability, membrane/film processability, oxidative stability, fuel crossover and electrochemical testing.
Proposed direction: Move from pellet conductivity toward composite membranes and MEA-level evaluation.
8459 · 7. Conclusion and Perspectives
Single-crystal conductivity studies are limited despite their value for resolving anisotropic pathways.
Proposed direction: Prioritise large stable crystals and operando single-crystal conductivity/XRD workflows.
8459 · 7. Conclusion and Perspectives
Efficient proton diffusion and robust hydrogen-bond networks must be achieved simultaneously with stability toward water, ammonia and strong acids.
Proposed direction: Design hosts with inert metal nodes, stable linkers and accessible hydrophilic pathways rather than optimising stability or conductivity in isolation.
8419 · 2. Structural Stability
Pressure and light examples remain few, and current conductivity changes are not yet large.
Proposed direction: Develop switchable systems where stimulus changes carrier concentration or mobility without structural degradation.
8439 · 4.4. External Stimuli · Figure 30
Mappings show which printed review references have a verified counterpart in the frozen primary corpus.
| Reference | Study | Role and context | Corpus mapping |
|---|---|---|---|
| Ref. 282009 | Rational Designs for Highly Proton-Conductive Metal-Organic Frameworks | counterion_benchmark · low_dimensional_mofUsed by the review as a high-conductivity ammonium-containing oxalate framework example and Table 1 benchmark. | research_0220 |
| Ref. 292016 | Proton-conductive metal-organic frameworks | review_background · taxonomy_supportCited in the review's introductory classification of proton-conductive MOF strategies. | research_0496 |
| Ref. 302012 | Imparting High Proton Conductivity to a Metal-Organic Framework Material by Controlled Acid Impregnation | acid_guest · transport_benchmarkUsed to support acid impregnation of stable MIL-101 as a high-temperature proton-conduction strategy. | Unmapped |
| Ref. 322009 | Anhydrous Proton Conduction at 150 C in a Crystalline Metal-Organic Framework | protic_guest · anhydrous_conductionCited for controlled triazole loading as an anhydrous proton-conduction strategy. | Unmapped |
| Ref. 332017 | A Flexible Metal-Organic Framework with a High Density of Sulfonic Acid Sites for Proton Conduction | flexible_framework · sulfonate · transport_benchmarkUsed for flexible sulfonated framework design and high-humidity conductivity benchmarks. | Unmapped |
| Ref. 422019 | Proton Transfer in Hydrogen-Bonded Degenerate Systems of Water and Ammonia in Metal-Organic Frameworks | ammonia_medium · mechanismCited for NH3 as an alternative conducting medium in functionalised MIL-53 analogues. | research_0274 |
| Ref. 472017 | Unique Proton Dynamics in an Efficient MOF-Based Proton Conductor | counterion · single_crystal · proton_dynamicsUsed for counterion-promoted anisotropic proton dynamics and single-crystal evidence. | Unmapped |
| Ref. 502011 | Wide Control of Proton Conductivity in Porous Coordination Polymers | functional_group · MIL-53Used for acidity and functional-group control in MIL-53 derivatives. | Unmapped |
| Ref. 512019 | Modulating Proton Diffusion and Conductivity in Metal-Organic Frameworks by Incorporation of Accessible Free Carboxylic Acid Groups | carboxylate · QENS · mechanismUsed to connect accessible carboxylate groups with QENS-observed proton diffusion. | Unmapped |
| Ref. 542015 | Superprotonic Conductivity of a UiO-66 Framework Functionalized with Sulfonic Acid Groups by Facile Postsynthetic Oxidation | postsynthetic_modification · sulfonateCited for converting UiO-66 thiol groups into sulfonic acid groups as a postsynthetic strategy. | Unmapped |
| Ref. 552011 | Confinement of Mobile Histamine in Coordination Nanochannels for Fast Proton Transfer | histamine_guest · anhydrous_conductionUsed for confined histamine as a mobile protic guest in MOF nanochannels. | Unmapped |
| Ref. 572019 | MOP x MOF: Collaborative Combination of Metal-Organic Polyhedra and Metal-Organic Framework for Proton Conductivity | MOP_guest · guest_inclusionCited for embedding sulfonated MOPs into mesoporous MOFs to tune hydrophilicity and conductivity. | Unmapped |
| Ref. 582015 | Defect Control to Enhance Proton Conductivity in a Metal-Organic Framework | defect_control · transport_benchmark · PFG-NMRUsed for systematic UiO-66 defect control and mobile proton diffusion evidence. | Unmapped |
| Ref. 592015 | The Role of a Three Dimensionally Ordered Defect Sublattice on the Acidity of a Sulfonated Metal-Organic Framework | defect_control · sulfonate · DFTUsed to show ordered defect sublattices can alter acidity and proton trapping in sulfonated Zr frameworks. | Unmapped |
| Ref. 602016 | Encapsulating Mobile Proton Carriers into Structural Defects in Coordination Polymer Crystals: High Anhydrous Proton Conduction and Fuel Cell Application | defect_control · anhydrous_conduction · fuel_cellUsed for structural-defect encapsulation of mobile phosphate carriers and first MOF solid-state electrolyte fuel-cell demonstration in the review narrative. | Unmapped |
| Ref. 822009 | High Proton Conductivity of One-Dimensional Ferrous Oxalate Dihydrate | low_dimensional · transport_benchmarkUsed as a 1D coordinated-water high proton conductivity benchmark. | Unmapped |
| Ref. 912012 | Coordination-Network-Based Ionic Plastic Crystal for Anhydrous Proton Conductivity | anhydrous_conduction · plastic_crystalUsed as a coordination-network ionic plastic crystal example for anhydrous proton conduction. | Unmapped |
| Ref. 1182014 | Proton Conductivity Control by Ion Substitution in a Highly Proton-Conductive Metal-Organic Framework | counterion_substitution · mechanismUsed to demonstrate ammonium-versus-potassium counterion effects on H-bond networks and conductivity. | Unmapped |
| Ref. 1212016 | High Proton Conductivity at Low Relative Humidity in an Anionic Fe-Based Metal-Organic Framework | counterion · low_humidity · transport_benchmarkUsed as a high-conductivity low-humidity anionic Fe MOF example. | Unmapped |
| Ref. 1232018 | A Robust Zirconium Amino Acid Metal-Organic Framework for Proton Conduction10.1038/s41467-018-07414-4 | cationic_framework · Zr_MOF · transport_benchmarkUsed as a robust amino-acid Zr-MOF with high humid proton conductivity and MC-supported H-bond interpretation. | Unmapped |
| Ref. 1332014 | Highly Proton Conductive Nanoporous Coordination Polymers with Sulfonic Acid Groups on the Pore Surface | sulfonate · postsynthetic_contextUsed for sulfonic-acid-decorated pore surfaces as functionalisation examples. | Unmapped |
| Ref. 1352015 | A Water Stable Magnesium MOF that Conducts Protons Over 10-2 S cm-1 | phosphonate · water_stable · transport_benchmarkUsed for water-stable Mg carboxyphosphonate proton-conduction benchmark. | Unmapped |
| Ref. 1502014 | High Proton Conductivity and Spectroscopic Investigations of Metal-Organic Framework Materials Impregnated by Strong Acids | acid_guest · spectroscopy · transport_benchmarkUsed for strong-acid impregnation and spectroscopic interpretation in MIL-101. | Unmapped |
| Ref. 1522017 | Synergistic Conductivity Effect in a Proton Sources-Coupled Metal-Organic Framework | acid_guest · framework_acid · transport_benchmarkUsed for framework-plus-guest acid source coupling and high conductivity across wide temperature range. | Unmapped |
| Ref. 1552014 | Pressure-Induced Amorphization of a Dense Coordination Polymer and Its Impact on Proton Conductivity | pressure_stimulus · mechanismUsed for pressure-induced amorphisation and reduced proton conductivity in a dense coordination polymer. | Unmapped |
| Ref. 1602017 | Enhanced and Optically Switchable Proton Conductivity in a Melting Coordination Polymer Crystal | photoacid · light_stimulusUsed for photoacid doping and reversible light-controlled proton release in a glassy/melting coordination polymer. | Unmapped |
| Ref. 1682018 | Switching the Proton Conduction in Nanoporous, Crystalline Materials by Light | azobenzene · light_stimulus · SURMOFUsed for azobenzene SURMOF photoswitchable proton-conduction examples. | Unmapped |
| Ref. 1732017 | Missing Metal-Linker Connectivities in a 3-D Robust Sulfonate-Based Metal-Organic Framework for Enhanced Proton Conductivity | defect_control · sulfonateUsed for missing metal-linker connectivity producing free sulfonate groups and enhanced water uptake/conductivity. | Unmapped |
| Ref. 1742012 | Promotion of Low-Humidity Proton Conduction by Controlling Hydrophilicity in Layered Metal-Organic Frameworks | hydrophilicity · low_humidityUsed for controlling hydrophilicity via counterion alkyl chain length in layered MOFs. | Unmapped |
| Ref. 1752018 | Selective Vapor Pressure Dependent Proton Transport in a Metal-Organic Framework with Two Distinct Hydrophilic Pores | hydrophilicity · pore_sizeUsed for two distinct hydrophilic pores and pressure-dependent water uptake/conduction behaviour. | Unmapped |
| Ref. 1822018 | Enhancing Proton Conductivity in a Metal-Organic Framework at T > 80 C by Anchoring Strategy | histamine_guest · anchoring_strategy · transport_benchmarkUsed for histamine anchoring in a sulfonated Zr-MOF and high hydrated proton conductivity. | Unmapped |
| Ref. 1912014 | Enhancing Proton Conduction in 2D Co-La Coordination Frameworks by Solid-State Phase Transition | single_crystal · anisotropic_conductionUsed for single-crystal proton conductivity and phase-transition-linked pathway discussion. | Unmapped |
| Ref. 1932016 | Proton Conduction in a Phosphonate-Based Metal-Organic Framework Mediated by Intrinsic Free Diffusion Inside a Sphere | QENS · phosphonate · mechanismUsed for QENS free-diffusion-in-a-sphere model and phosphonate MOF dynamics. | Unmapped |
| Ref. 1982017 | Single Crystal Proton Conduction Study of a Metal-Organic Framework of Modest Water Stability | single_crystal · low_humidityUsed as a single-crystal example showing anisotropic conductivity and stability limits. | Unmapped |
| Ref. 2032019 | A High Proton Conductive Hydrogen-Sulfate Decorated Titanium Carboxylate Metal-Organic Framework | computational_mechanism · sulfate · transport_benchmarkUsed for AIMD-supported Grotthuss mechanism in a hydrogen-sulfate-decorated titanium MOF. | Unmapped |
| Ref. 2062016 | Proton Transport in a Highly Conductive Porous Zirconium-Based Metal-Organic Framework: Molecular Insight | computational_mechanism · QENS · UiOUsed for QENS/MD molecular insight into water-mediated proton transport in functionalised UiO-66. | research_0236 |
| Ref. 2232013 | Molecular Mechanisms of Water-Mediated Proton Transport in MIL-53 Metal-Organic Frameworks | MD_simulation · MIL-53 · mechanismUsed for aMS-EVB simulation of water-mediated proton transport as a function of water loading and pore state. | Unmapped |
| Ref. 2282017 | Computational Exploration of the Water Concentration Dependence of the Proton Transport in the Porous UiO-66(Zr)-(CO2H)2 Metal-Organic Framework | MD_simulation · water_loading · UiOUsed for water-loading dependence of proton and water self-diffusion in UiO-66(Zr)-(CO2H)2. | Unmapped |
| Ref. 2332018 | High Proton Mobility with High Directionality in Isolated Channels of MOF-74 | single_crystal · anisotropic_conductionUsed for high directional single-crystal proton mobility in MOF-74 channels. | research_0380 |