Advancing Electrically Conductive Metal-Organic Frameworks for Photocatalytic Energy Conversion

Presents ligand-based solid solutions as a molecularly precise route for tuning N/O chelating environments, band gaps, band positions and conductivity.

Relevance: Core · p. 2319 · Chelating Atoms

Summarises EC-MOF opportunities and sets future directions: broader modular EC-MOF databases, more controllable synthesis, and functional-site design.

Relevance: Core · p. 2322 · Conclusion and Perspectives

Defines the review's thesis: EC-MOFs combine porosity, surface area, electronic conductivity and tunable band positions, but need electronic-structure, morphology and defect control for photocatalysis.

Relevance: Core · p. 2316 · Conspectus

Describes ligand treatment of EC-MOFs as a defect-healing strategy that improves crystallinity, fills missing-linker voids and increases conductivity.

Relevance: Core · p. 2321 · Defect Repair

Develops three design levers for photocatalytic band and charge control: metal-node selection, chelating-atom solid solutions and donor-acceptor pillar functionalisation.

Relevance: Core · p. 2318 · Electronic Structure Manipulation

Uses DPT/pillar functionalisation to show how donor-acceptor motifs and fluorinated pillars can redistribute excited-state charge and increase carrier lifetime.

Relevance: Core · p. 2320 · Functionalized Pillars

Frames photocatalytic energy conversion requirements, limitations of inorganic and organic photocatalysts, and the rationale for EC-MOFs as conductive porous hybrids.

Relevance: Core · p. 2317 · Introduction

Highlights four Park-group primary studies that structure the account: Fe-HHTP redox/ECSA, ligand solid solutions, functionalised pillars for H2O2 production and electrosynthetic Ni-HHTP morphology control.

Relevance: Supporting · p. 2316-2317 · Key References

Argues that metal identity and d-electron configuration influence reactant adsorption, redox activity, charge transfer and band positions in EC-MOFs.

Relevance: Core · p. 2318 · Metal Nodes

Compares growth-direction control in single-crystal EC-MOFs with electrosynthetic Ni-HHTP flower/disc morphologies and their transport/ECSA consequences.

Relevance: Core · p. 2321 · Morphology Control

Links photocatalytic performance to particle morphology, crystal-growth direction, surface area, carrier pathways, defect traps and postsynthetic defect repair.

Relevance: Core · p. 2320 · Morphology and Defect Control

Electronic-structure manipulation routes

The electronic-structure section is explicitly subdivided into metal-node choice, chelating-atom microenvironment control and donor-acceptor pillar insertion.

Categories: metal nodes · chelating atoms · functionalized pillars

p. 2318 · Electronic Structure Manipulation · Figure 1

Critical future research avenues

The conclusion lists three priority directions that can structure the Chapter 1 outlook for conductive MOF photocatalysts.

Categories: broader modular EC-MOF synthesis · more controllable synthesis strategies · chemical functionalisation of EC-MOFs

p. 2322 · Conclusion and Perspectives

Growth-direction morphology in layered EC-MOFs

Layered EC-MOFs are interpreted through growth within the ab-plane versus stacking along c-axis, with morphology controlling accessible surfaces and charge pathways.

Categories: 1D rods from axial stacking · 2D plates from ab-plane growth · flower-like particles · disc particles

p. 2320-2321 · Morphology Control

Ideal photocatalyst criteria and EC-MOF advantages

The review organises the photocatalyst problem around six performance requirements and maps EC-MOF features onto these criteria in Figure 1.

Categories: efficient light absorption · mass transport and reactant adsorption · photon-to-electron conversion efficiency · accessible active sites · selectivity · photochemical stability

p. 2317-2318 · Introduction · Figure 1

Morphology and defect control routes

The review separates physical control into morphology control and defect repair, both intended to improve surface access and charge transport.

Categories: low-dimensional morphology · ab-plane versus c-axis growth · electrosynthetic particle morphology · postsynthetic defect repair

p. 2321 · Morphology and Defect Control

Semiconducting HAB-based copper MOFs subjected to postsynthetic ligand treatment to repair missing-linker defects.

Conduction: Defect healing improves crystallinity and produces a large conductivity increase by reducing carrier traps and missing-linker voids.

Representative materials: Cu3(HAB)2 · HAB-treated Cu-HAB · pristine Cu-HAB

Nodes / linkers: Cu · HAB

p. 2322 · Defect Repair

Copper EC-MOF solid solutions constructed from HAB and TATHB ligands to vary nitrogen/oxygen chelating-atom density.

Conduction: PDOS is described as involving C/N/O pz orbitals and Cu dx2-y2 orbitals; increased nitrogen content reduces band gap and increases conductivity.

Representative materials: Cu3(HAB)x(TATHB)2-x · Cu3(HAB)2 · Cu3(TATHB)2 · Cu3(HAB)(TATHB)

Nodes / linkers: Cu · HAB · TATHB

p. 2319-2320 · Chelating Atoms

MOFs retaining porosity and modularity while exhibiting electronic conductivity through conjugated metal-ligand networks.

Conduction: Electronic conductivity is attributed to d-p conjugation between metal nodes and organic ligands, with narrow band gaps enabling visible-light absorption.

Representative materials: EC-MOFs · 2D EC-MOFs

Nodes / linkers: transition-metal nodes · conjugated organic ligands

p. 2317 · Introduction

Cu-HHB-derived EC-MOFs incorporating DPT pillars and postsynthetic click functionalisation with PA or EFB to tune excited-state charge distribution.

Conduction: Functionalised pillars adjust band gaps/positions and redistribute electrons and holes after excitation, with fluorine localising electrons in EFB-MOF.

Representative materials: DPT-MOF · PA-MOF · EFB-MOF · Cu-HHB

Nodes / linkers: Cu · HHB · DPT · phenylacetylene · 1-ethynyl-4-fluorobenzene

p. 2320 · Functionalized Pillars

Isostructural HITP frameworks with Co, Ni and Cu metal-node combinations used to demonstrate continuous conductivity and band-gap variation.

Conduction: Metal-node alloying adjusts electron configurations and energy levels within an isostructural conductive lattice.

Representative materials: Co3(HITP)2 · Ni3(HITP)2 · Cu3(HITP)2 · M3(HITP)2 alloys

Nodes / linkers: Co · Ni · Cu · HITP

p. 2318 · Electronic Structure Manipulation

2D planar HHTP-based EC-MOF analogues where metal identity affects redox activity, interlayer structure and electrochemical surface area.

Conduction: The review emphasises metal-node redox peaks and charge-transfer potential rather than using these values as primary conductivity rankings.

Representative materials: Fe-HHTP · Ni-HHTP · Cu-HHTP

Nodes / linkers: Fe · Ni · Cu · HHTP

p. 2318-2319 · Metal Nodes

HHTT-based 2D EC-MOFs with atomically precise single-crystal structures and controllable rod/plate morphologies.

Conduction: Used to illustrate anisotropic conductivity, with in-plane conduction higher than out-of-plane conduction.

Representative materials: Cu3HHTT2 · MmHHTTn

Nodes / linkers: Cu · other M nodes · HHTT

p. 2321 · Morphology Control

Nickel HHTP films synthesised electrochemically on nickel foam with flower and disc morphologies controlled by HHTP concentration.

Conduction: Flower morphology shows higher conductivity, lower charge-transfer resistance and higher capacitance/ECSA than disc morphology.

Representative materials: Ni-HHTP-Flower · Ni-HHTP-Disc

Nodes / linkers: Ni · HHTP

p. 2321 · Morphology Control

Chelating-atom solid-solution tuning

Use isomorphic ligands with varied coordinating atoms to continuously adjust the metal-node microenvironment and band structure.

Claimed effects: Provides continuous band-gap and conductivity tuning and could distinguish photocatalytic reactions with close redox potentials.

Controlling variables: HAB:TATHB ratio · nitrogen content · oxygen content · M-X4 coordination motif

Representative materials: Cu3(HAB)x(TATHB)2-x

Caveat: The demonstrated band-position shift is narrow, so the review presents it as mechanistically useful rather than universally sufficient.

p. 2320 · Chelating Atoms

Electrochemical morphology control

Use electrosynthesis to adjust growth parameters in real time and tailor EC-MOF particle morphology on conductive supports.

Claimed effects: Produces Ni-HHTP flower and disc morphologies with different conductivity, charge-transfer resistance, capacitance and ECSA.

Controlling variables: electrochemical conditions · HHTP concentration · nucleation rate · particle adhesion to anode

Representative materials: Ni-HHTP-Flower · Ni-HHTP-Disc

Caveat: Benchmarks come from electrochemical-capacitance context and should be treated as secondary indicators for photocatalyst design.

p. 2321 · Morphology Control

Donor-acceptor pillar functionalisation

Insert functionalizable pillars into an EC-MOF and use click reactions to introduce substituents that spatially separate photogenerated carriers.

Claimed effects: Tunes band positions and charge distribution, increases carrier lifetime and raises photocatalytic H2O2 production in EFB-MOF.

Controlling variables: DPT pillar insertion · click-functionalised substituent · electron-donor/acceptor distribution · fluorine substitution

Representative materials: DPT-MOF · PA-MOF · EFB-MOF

Caveat: The review presents this as a proof-of-concept series rather than a generalised library of functional sites.

p. 2320 · Functionalized Pillars

Crystal growth-direction control

Guide layered EC-MOF growth along the ab-plane or c-axis to produce morphologies with different transport pathways and exposed facets.

Claimed effects: Two-dimensional plate-like growth can enhance carrier transport relative to one-dimensional axial stacking where conductivity is anisotropic.

Controlling variables: in-plane growth · axial stacking · facet expression · crystal dimensionality

Representative materials: Cu3HHTT2 · MmHHTTn

Caveat: The review notes rapid EC-MOF growth kinetics make micromorphology control difficult.

p. 2321 · Morphology Control

Metal-node diversification

Vary metal identity and d-electron count in otherwise related EC-MOFs to tune redox activity, adsorption and charge-transfer energetics.

Claimed effects: Can alter adsorption, electron-transfer resistance, redox activity, ECSA and photocatalytic potential.

Controlling variables: metal node identity · d-electron count · spin state · metal-reactant orbital energy alignment

Representative materials: Fe-HHTP · Cu-HHTP · Ni-HHTP · M3(HITP)2

Caveat: The review frames Fe-HHTP as promising but not yet an extensive photocatalysis benchmark across reactions.

p. 2318 · Metal Nodes

Postsynthetic ligand defect healing

Treat a synthesised EC-MOF with its original ligand so missing ligand sites can be filled after initial growth.

Claimed effects: Repairs in-plane missing ligand defects, improves crystallinity and reduces charge traps, producing major conductivity gains.

Controlling variables: postsynthetic ligand treatment · original ligand identity · missing-linker sites · growth-rate-derived defect density

Representative materials: Cu3(HAB)2 · HAB-treated Cu-HAB

Caveat: Treatment slightly reduces surface area/pore size, so defect repair may trade some porosity for improved charge transport.

p. 2322 · Defect Repair

Current DFT-level EC-MOF databases lack experimentally obtained conductivity values, morphology-dependent surface areas, adsorption energies and photocatalytic efficiencies.

Proposed direction: Build comprehensive databases combining structures, theory, experimental transport, morphology and HER/OER/CO2RR performance.

p. 2322 · Conclusion and Perspectives

EC-MOFs need functional sites with specific and directional photocatalytic activities to exploit spatially separated carriers.

Proposed direction: Functionalise pillar ligands with targeted groups such as cyano groups or CO2-adsorbing aromatic motifs.

p. 2322 · Conclusion and Perspectives

EC-MOFs have not been extensively studied for photocatalytic energy conversion despite plausible light absorption and electron transport advantages.

Proposed direction: Develop systematic EC-MOF photocatalyst studies that connect band structure, morphology, defects and reaction selectivity.

p. 2316 · Conspectus

Limited understanding of EC-MOF electronic structures remains a critical hurdle for photocatalytic design.

Proposed direction: Use modular metal/linker/chelate/pillar libraries with theory and spectroscopy to connect band edges and charge distributions to photocatalysis.

p. 2322 · Conclusion and Perspectives

Highly crystalline catalysts with controlled morphologies are needed because current uncontrolled structures convolute structure-property relationships.

Proposed direction: Obtain large single crystals or controlled low-dimensional morphologies to clarify morphology/transport/performance relationships.

p. 2322 · Conclusion and Perspectives

Fast EC-MOF growth kinetics make it difficult to tailor micromorphology and reduce defect formation.

Proposed direction: Develop controllable syntheses that tune morphology and repair defects while preserving transport and reactant access.

p. 2317 · Introduction

Photocatalytic reactions with closely aligned redox potentials require more precise band-edge control than broad band-gap tuning alone.

Proposed direction: Use chelating-atom solid solutions and metal-node microenvironment control to fine-adjust band positions.

p. 2320 · Chelating Atoms