Engineering Natural Pollen Grains as Multifunctional 3D Printing Materials

The development of multifunctional 3D printing materials from sustainable natural resources is a high priority in additive manufacturing. Using an eco-friendly method to transform hard pollen grains into stimulus-responsive microgel particles, we engineered a pollen-derived microgel suspension that can serve as a functional reinforcement for composite hydrogel inks and as a supporting matrix for versatile freeform 3D printing systems. The pollen microgel particles enabled the printing of composite inks and improved the mechanical and physiological stabilities of alginate and hyaluronic acid hydrogel scaffolds for 3D cell culture applications. Moreover, the particles endowed the inks with stimulus-responsive controlled release properties. The suitability of the pollen microgel suspension as a supporting matrix for freeform 3D printing of alginate and silicone rubber inks was demonstrated and optimized by tuning the rheological properties of the microgel. Compared with other classes of natural materials, pollen grains have several compelling features, including natural abundance, renewability, affordability, processing ease, monodispersity, and tunable rheological features, which make them attractive candidates to engineer advanced materials for 3D printing applications.     

Direct 3D Printed Biomimetic Scaffolds Based on Hydrogel Microparticles for Cell Spheroid Growth

Biocompatible hydrogel inks with shear‐thinning, appropriate yield strength, and fast self‐healing are desired for 3D bioprinting. However, the lack of ideal 3D bioprinting inks with outstanding printability and high structural fidelity, as well as cell‐compatibility, has hindered the progress of extrusion‐based 3D bioprinting for tissue engineering. In this study, novel self‐healable pre‐cross‐linked hydrogel microparticles (pcHμPs) of chitosan methacrylate (CHMA) and polyvinyl alcohol (PVA) hybrid hydrogels are developed and used as bioinks for extrusion‐based 3D printing of scaffolds with high fidelity and biocompatibility. The pcHμPs display excellent shear thinning when injected through a syringe and subsequently self‐heal into gels as shear forces are removed. Numerical simulations indicate that the pcHμPs experience a plug flow in the nozzle with minimal disturbance, which favors a steady and continuous printing. Moreover, the pcHμPs show a self‐supportive yield strength (540 Pa), which is critical for the fidelity of printed constructs. A series of biomimetic constructs with very high aspect ratio and delicate fine structures are directly printed by using the pcHμP ink. The 3D printed scaffolds support the growth of bone‐marrow‐derived mesenchymal stem cells and formation of cell spheroids, which are most important for tissue engineering.     

Highly Hydrophobic ZIF‐8/Carbon Nitride Foam with Hierarchical Porosity for Oil Capture and Chemical Fixation of CO2

The introduction of hierarchical porosity into metal‐organic frameworks (MOFs) has been of considerable interest in gas separation and heterogeneous catalysis due to the efficient mass transfer kinetics through meso/macropores. Here, a facile, scalable approach is reported for the preparation of carbon nitride (CN) foams as structural templates with micrometer‐sized pores and high nitrogen content of 25.6 wt% by the fast carbonization of low‐cost melamine foam. The nitrogen functionalities of CN foam facilitate chemical anchoring and growth of ZIF‐8 (zeolitic imidazolate frameworks) crystals, which leads to the development of hierarchical porosity. The growth of ZIF‐8 crystals also renders CN foam, which is hydrophilic in nature, highly hydrophobic exhibiting 135° of water contact angle due to the enhanced surface roughness, thus creating a natural shield for the MOF crystals against water. The introduction of ZIF‐8 crystals onto the CN foam enables selective absorption of oils up to 58 wt% from water/oil mixtures and also facilitates the highly efficient conversion of CO₂ to chloropropene carbonate in a quantitative yield with excellent product selectivity. Importantly, this present approach could be extended to the vast number of MOF structures, including the ones suffering from water instability, for the preparation of highly functional materials for various applications.     

Metal–Organic Frameworks Derived from Zero‐Valent Metal Substrates: Mechanisms of Formation and Modulation of Properties

The replicative construction of metal–organic frameworks (MOFs) templated with solvent‐insoluble solid substrates is of marked importance, as it allows for the assembly of 2D and 3D macro‐ and mesoscopic architectures with properties that are challenging to attain by the conventional solution‐based synthesis approach. This work reports an in situ and direct construction of MOFs from zero‐valent metal substrates via a green hydrothermal oxidation–MOF construction chemistry without the use of any additional metal source, chemical reagents, or acidification of solvent, and elucidates the zero‐valent metal derived formation mechanisms of MOFs and their structure modulation to 1D nanofibers (NFs), 2D film, and 3D core–shell microstructures. Through modulation of the competing surface oxidation‐dissolution and MOF crystallization kinetics, Al@MIL‐53 core–shell microstructures and MIL‐53 (Al) NFs are obtained that exhibit unique morphologies and marked properties superior to the conventional MIL‐53 (Al) powders. The generality of zero‐valent metal‐templated synthesis of MOFs is demonstrated with formation of MIL‐53 (Al), HKUST‐1, and ZIF‐7 polycrystalline films on Al, Cu, and Zn metal meshes, elucidating the significance of the approach utilizing solid metal substrate that can be easily processed into various shapes, architectures, and compositions.     

Selenium‐Containing Polymer@Metal‐Organic Frameworks Nanocomposites as an Efficient Multiresponsive Drug Delivery System

The development of efficient multiresponsive drug delivery systems (DDSs) to control drug release has been widely explored. Herein, a facile strategy is reported that enables the micelles of the selenium‐containing polymer with the drug to be encapsulated in metal‐organic frameworks (MOFs), which serves as multiresponsive drug release by employing the selenium‐containing polymers with redox‐triggered property and the MOFs with pH‐triggered property in DDS. In this case, the micelles of selenium‐containing polymers, as core easily disassembles in the presence of redox agents, can then release the drug in MOFs matrixes. The ZIF‐8 (one type of MOFs) crystal frameworks serving as shell can collapse only under low pH conditions, and the drug can be further released. In the presence of external redox agents as well as the pH stimuli, the prepared nanocomposite (P@ZIF‐8) drug system exhibits the capability of multiresponsive release of the doxorubicin (DOX) and possesses good selectivity in releasing the DOX under low pH conditions instead of normal pH conditions. In addition, the merits of P@ZIF‐8 such as good biocompatibility, multiresponsive release properties, and especially the selective release properties under different pH conditions make the materials highly promising candidates for the realization of controlled drug delivery in tumor tissue systems.     

A High‐Performance Sodium‐Ion Hybrid Capacitor Constructed by Metal–Organic Framework–Derived Anode and Cathode Materials

Sodium‐ion hybrid capacitors (SIHCs) can potentially combine the virtues of high‐energy density of batteries and high‐power output as well as long cycle life of capacitors in one device. The key point of constructing a high‐performance SIHC is to couple appropriate anode and cathode materials, which can well match in capacity and kinetics behavior simultaneously. In this work, a novel SIHC, coupling a titanium dioxide/carbon nanocomposite (TiO₂/C) anode with a 3D nanoporous carbon cathode, which are both prepared from metal–organic frameworks (MOFs, MIL‐125 (Ti) and ZIF‐8, respectively), is designed and fabricated. The robust architecture and extrinsic pseudocapacitance of TiO₂/C nanocomposite contribute to the excellent cyclic stability and rate capability in half‐cell. Hierarchical 3D nanoporous carbon displays superior capacity and rate performance. Benefiting from the merits of structures and performances of anode and cathode materials, the as‐built SIHC achieves a high energy density of 142.7 W h kg^?1 and a high power output of 25 kW kg^?1 within 1–4 V, as well as an outstanding life span of 10 000 cycles with over 90% of the capacity retention. The results make it competitive in high energy and power–required electricity storage applications.     

Preconcentration of Nitroalkanes with Archetype Metal–Organic Frameworks (MOFs) as Concept for a Sensitive Sensing of Explosives in the Gas Phase

Thermal desorption based enrichment is a general concept that can enhance any detection system's sensitivity and selectivity. Given their large interior surface area and chemical versatility, archetype metal–organic frameworks (MOFs) are selected for preconcentration of explosives and their precursors occurring in low concentrations, and are compared to the state‐of‐the‐art sorbent Tenax TA . Applying inverse gas chromatography (iGC), this study shows that several archetype MOFs, namely HKUST‐1 and MIL‐53 , surpass Tenax regarding their specific retention volume for nitromethane, a typical ingredient in improvised explosives. Using linear hydrocarbons as reference probe molecules, the dispersive surface energy is determined for all MOFs along with the specific contribution of the nitro group for HKUST‐1 and ZIF‐8 . Trends from pulse‐chromatographic iGC‐investigations are mostly followed in breakthrough and thermal desorption experiments using a 1000 ppm nitromethane source. In these experiments, HKUST‐1 proves the peak substance, with enrichment factors being 109‐fold higher than for Tenax , followed by MIL‐53 . In case of HKUST‐1 , this factor is successfully reproduced for a 1 ppm concentration scenario. This shows that archetype MOFs can be suitable or even superior candidates for a sensitive sensing of nitroalkane explosives from the gas phase by a concept of preconcentration.     

Self‐Directed Localization of ZIF‐8 Thin Film Formation by Conversion of ZnO Nanolayers

Control of localized metal–organic framework (MOF) thin film formation is a challenge. Zeolitic imidazolate frameworks (ZIFs) are an important sub‐class of MOFs based on transition metals and imidazolate linkers. Continuous coatings of intergrown ZIF crystals require high rates of heterogeneous nucleation. In this work, substrates coated with zinc oxide layers are used, obtained by atomic layer deposition (ALD) or by magnetron sputtering, to provide the Zn²⁺ ions required for nucleation and localized growth of ZIF‐8 films ([Zn(mim)₂]; Hmim = 2‐methylimidazolate). The obtained ZIF‐8 films reveal the expected microporosity, as deduced from methanol adsorption studies using an environmentally controlled quartz crystal microbalance (QCM) and comparison with bulk ZIF‐8 reference data. The concept is transferable to other MOFs, and is applied to the formation of [Al(OH)(1,4‐ndc)]_n (ndc = naphtalenedicarboxylate) thin films derived from Al₂O₃ nanolayers.     

A Self-Thickening and Self-Strengthening Strategy for 3D Printing High-Strength and Antiswelling Supramolecular Polymer Hydrogels as Meniscus Substitutes

3D printing of high-strength and antiswelling hydrogel-based load-bearing soft tissue scaffolds with similar geometric shape to natural tissues remains a great challenge owing to insurmountable trade-off between strength and printability. Herein, capitalizing on the concentration-dependent H-bonding-strengthened mechanism of supramolecular poly(N-acryloyl glycinamide) (PNAGA) hydrogel, a self-thickening and self-strengthening strategy, that is, loading the concentrated NAGA monomer into the thermoreversible low-strength PNAGA hydrogel is proposed to directly 3D printing latently H-bonding-reinforced hydrogels. The low-strength PNAGA serves to thicken the concentrated NAGA monomer, affording an appropriate viscosity for thermal-assisted extrusion 3D printing of soft PNAGA hydrogels bearing NAGA monomer and initiator, which are further polymerized to eventually generate high-strength and antiswelling hydrogels, due to the reconstruction of strong H-bonding interactions from postcompensatory PNAGA. Diverse polymer hydrogels can be printed with self-thickened corresponding monomer inks. Further, the self-thickened high-strength PNAGA hydrogel is printed into a meniscus, which is implanted in rabbit's knee as a substitute with in vivo outcome showing an appealing ability to efficiently alleviate the cartilage surface wear. The self-thickening strategy is applicable to directly printing a variety of polymer-hydrogel-based tissue engineering scaffolds without sacrificing mechanical strength, thus circumventing problems of printing high-strength hydrogels and facilitating their application scope.     

Macro-/mesoporous Metal–Organic Frameworks Templated by Amphiphilic Block Copolymers Enable Enhanced Uptake of Large Molecules

The first synthesis of hierarchical porous metal–organic frameworks (HP-MOFs) is reported through a solvent evaporation-induced co-assembly of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) and MOF building blocks. The growth of MOFs is restricted to confined spaces formed by self-assembled PS-b-PEO, and mesopores and/or macropores are created after removing PS-b-PEO by solvent rinsing. This approach avoids phase separation and competitive interactions between templates and MOF building blocks. Both amorphous and crystalline HP-MOFs can be synthesized by finely controlling MOF growth conditions. Additionally, HP-MOFs (ZIF-L sheets) with honeycomb-like channels show significantly enhanced incorporation of large guest molecules compared to microporous MOFs. This study establishes an efficient synthetic strategy for preparing HP-MOFs with highly accessible mesopores and macropores for applications involving large molecules.     

3D Printing of Multifunctional Hydrogels

3D printing technology has been widely explored for the rapid design and fabrication of hydrogels, as required by complicated soft structures and devices. Here, a new 3D printing method is presented based on the rheology modifier of Carbomer for direct ink writing of various functional hydrogels. Carbomer is shown to be highly efficient in providing ideal rheological behaviors for multifunctional hydrogel inks, including double network hydrogels, magnetic hydrogels, temperature‐sensitive hydrogels, and biogels, with a low dosage (at least 0.5% w/v) recorded. Besides the excellent printing performance, mechanical behaviors, and biocompatibility, the 3D printed multifunctional hydrogels enable various soft devices, including loadable webs, soft robots, 4D printed leaves, and hydrogel Petri dishes. Moreover, with its unprecedented capability, the Carbomer‐based 3D printing method opens new avenues for bioprinting manufacturing and integrated hydrogel devices.     

Fluidic Processing of High‐Performance ZIF‐8 Membranes on Polymeric Hollow Fibers: Mechanistic Insights and Microstructure Control

Recently, a methodology for fabricating polycrystalline metal‐organic framework (MOF) membranes has been introduced – referred to as interfacial microfluidic membrane processing – which allows parallelizable fabrication of MOF membranes inside polymeric hollow fibers of microscopic diameter. Such hollow fiber membranes, when bundled together into modules, are an attractive way to scale molecular sieving membranes. The understanding and engineering of fluidic processing techniques for MOF membrane fabrication are in their infancy. Here, a detailed mechanistic understanding of MOF (ZIF‐8) membrane growth under microfluidic conditions in polyamide‐imide hollow fibers is reported, without any intermediate steps (such as seeding or surface modification) or post‐synthesis treatments. A key finding is that interfacial membrane formation in the hollow fiber occurs via an initial formation of two distinct layers and the subsequent rearrangement into a single layer. This understanding is used to show how nonisothermal processing allows fabrication of thinner (5 μm) ZIF‐8 films for higher throughput, and furthermore how engineering the polymeric hollow fiber support microstructure allows control of defects in the ZIF‐8 membranes. The performance of these engineered ZIF‐8 membranes is then characterized, which have H₂/C₃H₈ and C₃H₆/C₃H₈ mixture separation factors as high as 2018 and 65, respectively, and C₃H₆ permeances as high as 66 GPU.     

Pore Tuning of Metal-Organic Framework Membrane Anchored on Graphene-Oxide Nanoribbon

Although the pore structures and gas transport properties of metal-organic frameworks (MOFs) have been tuned mainly by modifying the framework building blocks, a pore-tuned zeolitic imidazolate framework (ZIF)-8 layer is directly grown on graphene oxide nanoribbons (GONR)-treated polymer substrate. Oxygen-containing functional groups and GONR dangling-carbon bonds facilitated the spontaneous growth of ZIF-8 oriented to the (100) grain on the GONR surface and also enhanced the rigidity by strongly anchoring the ZIF-8 layer by metal-carbon chemisorption. Gas permeation and molecular simulation results confirmed that the effective aperture size of ZIF-8 is adjusted to 3.6 Å. As a result, ultrafast H₂ permeance of 7.6 × 10⁻⁷ mol m⁻² Pa s is achieved while blocking large hydrocarbon molecules. In particular, the membrane showed exceptionally enhanced hydrogen selectivity for the mixture separation than ideal selectivity, owing to the competitive transport between H₂ and large hydrocarbon molecules, and the separation performance surpassed those of ZIF membranes previously fabricated on polymeric supports.     

A Versatile Prodrug Strategy to In Situ Encapsulate Drugs in MOF Nanocarriers: A Case of Cytarabine‐IR820 Prodrug Encapsulated ZIF‐8 toward Chemo‐Photothermal Therapy

Zeolitic imidazolate framework‐8 (ZIF‐8) is an attractive metal organic framework (MOF) in drug delivery. Strong interaction between drugs and ZIF‐8 is essential for high drug loadings through in situ construction of MOFs. However, only limited drugs with unique functional groups (? COOH, ? SO₃H, et al.) can interact with ZIF‐8 and be encapsulated satisfactorily so far. Drugs without these functional groups are difficult to be loaded due to the lack of strong interaction. Herein a versatile prodrug strategy is proposed to solve the problems encountered by MOFs. Cytarabine (Ara) is chosen as a model drug since it cannot be loaded in ZIF‐8 satisfactorily by itself. New indocyanine green (IR820) is utilized to bond with Ara for the formation of prodrug (Ara‐IR820) and endows the prodrug with fluorescence imaging‐guided chemo‐photothermal therapy, in which sulfonic groups strengthen the interaction between prodrug and ZIF‐8. This prodrug loaded ZIF‐8 is further functionalized with hyaluronic acid (HA) to result in active‐targeting HA/Ara‐IR820@ZIF‐8 nanoparticles. The in vitro and in vivo results demonstrate its excellent visual cancer therapy with tumor‐targeted and pH‐responsive release behavior. This design offers a new concept to solve the drug loading problem of MOFs, exhibiting a flexible strategy to expand the biomedical applications of MOFs.     

Hollow Mesoporous Carbon Nanocubes: Rigid‐Interface‐Induced Outward Contraction of Metal‐Organic Frameworks

Novel carbon materials derived from metal‐organic frameworks (MOFs) have attracted much attention, but the commonly inevitable inward contraction during the carbonization process has restricted their structural variety and applications. In this work, a novel rigid‐interface induced outward contraction approach is reported for synthesizing hollow mesoporous carbon nanocubes (HMCNCs) by using ZIF‐8 nanocubes as precursors. HMCNCs exhibit a cubic morphology with the particle sizes slightly larger than ZIF‐8 nanocubes. Due to the unique outward contraction process, uniform carbon nanocubes with a hollow cavity, an outer microporous shell, and an inner mesoporous wall are simultaneously formed with a large pore size (25 nm), high surface area (1085.7 m² g^?1), high porosity (3.77 cm³ g^?1), and high nitrogen content (12.2%). When used as a cathode material for Li–SeS₂ batteries, the HMCNCs deliver a stable capacity of 812.6 mA h g^?1 at 0.2 A g^?1 after 100 cycles and an outstanding rate capability (455.1 mA h g^?1 at 5.0 A g^?1). The findings may pave the way for the construction of distinctive MOF‐derived carbon materials for various applications.     

Direct 3D Printing of High Strength Biohybrid Gradient Hydrogel Scaffolds for Efficient Repair of Osteochondral Defect

The emerging 3D printing technique allows for tailoring hydrogel‐based soft structure tissue scaffolds for individualized therapy of osteochondral defects. However, the weak mechanical strength and uncontrollable swelling intrinsic to conventional hydrogels restrain their use as bioinks. Here, a high‐strength thermoresponsive supramolecular copolymer hydrogel is synthesized by one‐step copolymerization of dual hydrogen bonding monomers, N‐acryloyl glycinamide, and N‐[tris(hydroxymethyl)methyl] acrylamide. The obtained copolymer hydrogels demonstrate excellent mechanical properties—robust tensile strength (up to 0.41 MPa), large stretchability (up to 860%), and high compressive strength (up to 8.4 MPa). The rapid thermoreversible gel ? sol transition behavior makes this copolymer hydrogel suitable for direct 3D printing. Successful preparation of 3D‐printed biohybrid gradient hydrogel scaffolds is demonstrated with controllable 3D architecture, owing to shear thinning property which allows continuous extrusion through a needle and also immediate gelation of fluid upon deposition on the cooled substrate. Furthermore, this biohybrid gradient hydrogel scaffold printed with transforming growth factor beta 1 and β‐tricalciumphosphate on distinct layers facilitates the attachment, spreading, and chondrogenic and osteogenic differentiation of human bone marrow stem cells (hBMSCs) in vitro. The in vivo experiments reveal that the 3D‐printed biohybrid gradient hydrogel scaffolds significantly accelerate simultaneous regeneration of cartilage and subchondral bone in a rat model.     

Phthalocyanine‐Based 2D Conjugated Metal‐Organic Framework Nanosheets for High‐Performance Micro‐Supercapacitors

2D conjugated metal‐organic frameworks (2D c‐MOFs) are emerging as a novel class of conductive redox‐active materials for electrochemical energy storage. However, developing 2D c‐MOFs as flexible thin‐film electrodes have been largely limited, due to the lack of capability of solution‐processing and integration into nanodevices arising from the rigid powder samples by solvothermal synthesis. Here, the synthesis of phthalocyanine‐based 2D c‐MOF (Ni₂[CuPc(NH)₈]) nanosheets through ball milling mechanical exfoliation method are reported. The nanosheets feature with average lateral size of ≈160 nm and mean thickness of ≈7 nm (≈10 layers), and exhibit high crystallinity and chemical stability as well as a p‐type semiconducting behavior with mobility of ≈1.5 cm² V^?1 s^?1 at room temperature. Benefiting from the ultrathin feature, the nanosheets allow high utilization of active sites and facile solution‐processability. Thus, micro‐supercapacitor (MSC) devices are fabricated mixing Ni₂[CuPc(NH)₈] nanosheets with exfoliated graphene, which display outstanding cycling stability and a high areal capacitance up to 18.9 mF cm^?2; the performance surpasses most of the reported conducting polymers‐based and 2D materials‐based MSCs.     

Atomic‐Scale CoOx Species in Metal–Organic Frameworks for Oxygen Evolution Reaction

The activity of electrocatalysts strongly depends on the number of active sites, which can be increased by downsizing electrocatalysts. Single‐atom catalysts have attracted special attention due to atomic‐scale active sites. However, it is a huge challenge to obtain atomic‐scale CoO_x catalysts. The Co‐based metal–organic frameworks (MOFs) own atomically dispersed Co ions, which motivates to design a possible pathway to partially on‐site transform these Co ions to active atomic‐scale CoO_x species, while reserving the highly porous features of MOFs. In this work, for the first time, the targeted on‐site formation of atomic‐scale CoO_x species is realized in ZIF‐67 by O₂ plasma. The abundant pores in ZIF‐67 provide channels for O₂ plasma to activate the Co ions in MOFs to on‐site produce atomic‐scale CoO_x species, which act as the active sites to catalyze the oxygen evolution reaction with an even better activity than RuO₂.     

Oriented Growth of ZIF‐67 to Derive 2D Porous CoPO Nanosheets for Electrochemical‐/Photovoltage‐Driven Overall Water Splitting

Hydrogen generation from water splitting driven by electric/solar energy is highly desirable, which requires efficient and robust bifunctional electrocatalysts for both hydrogen and oxygen evolution reactions. 2D porous hybrids with attractive chemical and structural properties are the first‐class candidates for water splitting, while control over efficient and modulable synthesis remains a huge challenge. This work demonstrates a zeolitic imidazolate framework‐67 (ZIF‐67) nanoplate self‐template approach to fabricate 2D porous oxygen‐incorporated cobalt phosphide (CoPO) ultrathin nanosheets. The synthesis starts with the oriented growth of ZIF‐67 nanoplates along [211] crystal plane, followed by oxidation/phosphorization processes for pore generation and O/P coincorporation in the hybrid. The resultant 2D porous CoPO nanosheets afford very small voltages of 1.52 and 1.98 V for overall water splitting at 10 and 200 mA cm^?2, respectively. This excellent bifunctionality further provides the basis for photovoltage‐driven water splitting at a Faradaic efficiency of 97.6%. These findings offer a general strategy for rational design and modulation of 2D porous catalysts for various electrocatalytic and other applications.     

Engineering Fe–Fe3C@Fe–N–C Active Sites and Hybrid Structures from Dual Metal–Organic Frameworks for Oxygen Reduction Reaction in H2–O2 Fuel Cell and Li–O2 Battery

Dual metal–organic frameworks (MOFs, i.e., MIL‐100(Fe) and ZIF‐8) are thermally converted into Fe–Fe₃C‐embedded Fe–N‐codoped carbon as platinum group metal (PGM)‐free oxygen reduction reaction (ORR) electrocatalysts. Pyrolysis enables imidazolate in ZIF‐8 rearranged into highly N‐doped carbon, while Fe from MIL‐100(Fe) into N‐ligated atomic sites concurrently with a few Fe–Fe₃C nanoparticles. Upon precise control of MOF compositions, the optimal catalyst is highly active for the ORR in half‐cells (0.88 V in base and 0.79 V versus RHE in acid in half‐wave potential), a proton exchange membrane fuel cell (0.76 W cm^?2 in peak power density) and an aprotic Li–O₂ battery (8749 mAh g^?1 in discharge capacity), representing a state‐of‐the‐art PGM‐free ORR catalyst. In the material, amorphous carbon with partial graphitization ensures high active site exposure and fast charge transfer simultaneously. Macropores facilitate mass transport to the catalyst surface, followed by oxygen penetration in micropores to reach the infiltrated active sites. Further modeling simulations shed light on the true Fe–Fe₃C contribution to the catalyst performance, suggesting Fe₃C enhances oxygen affinity, while metallic Fe promotes *OH desorption as the rate‐determining step at the nearby Fe–N–C sites. These findings demonstrate MOFs as model system for rational design of electrocatalyst for energy‐based functional applications.