Ultrasmall Metal Nanoparticles Confined within Crystalline Nanoporous Materials: A Fascinating Class of Nanocatalysts

Crystalline nanoporous materials with uniform porous structures, such as zeolites and metal–organic frameworks (MOFs), have proven to be ideal supports to encapsulate ultrasmall metal nanoparticles (MNPs) inside their void nanospaces to generate high‐efficiency nanocatalysts. The nanopore‐encaged metal catalysts exhibit superior catalytic performance as well as high stability and catalytic shape selectivity endowed by the nanoporous matrix. In addition, the synergistic effect of confined MNPs and nanoporous frameworks with active sites can further promote the catalytic activities of the composite catalysts. Herein, recent progress in nanopore‐encaged metal nanocatalysts is reviewed, with a special focus on advances in synthetic strategies for ultrasmall MNPs (<5 nm), clusters, and even single atoms confined within zeolites and MOFs for various heterogeneous catalytic reactions. In addition, some advanced characterization methods to elucidate the atomic‐scale structures of the nanocatalysts are presented, and the current limitations of and future opportunities for these fantastic nanocatalysts are also highlighted and discussed. The aim is to provide some guidance for the rational synthesis of nanopore‐encaged metal catalysts and to inspire their further applications to meet the emerging demands in catalytic fields.     

MOF‐Confined Sub‐2 nm Atomically Ordered Intermetallic PdZn Nanoparticles as High‐Performance Catalysts for Selective Hydrogenation of Acetylene

Controllable synthesis of ultrasmall atomically ordered intermetallic nanoparticles is a challenging task, owing to the high temperature commonly required for the formation of intermetallic phases. Here, a metal–organic framework (MOF)‐confined co‐reduction strategy is developed for the preparation of sub‐2 nm intermetallic PdZn nanoparticles, by employing the well‐defined porous structures of calcinated ZIF‐8 (ZIF‐8C) and an in situ co‐reduction therein. HAADF‐STEM, HRTEM, and EDS characterizations reveal the homogeneous dispersion of these sub‐2 nm intermetallic PdZn nanoparticles within the ZIF‐8C frameworks. XRD, XPS, and EXAFS measurements further confirm the atomically ordered intermetallic phase nature of these sub‐2 nm PdZn nanoparticles. Selective hydrogenation of acetylene evaluation results show the excellent catalytic properties of the sub‐2 nm intermetallic PdZn, which result from the energetically more favorable path for acetylene hydrogenation and ethylene desorption over the ultrasmall particles than over larger‐sized intermetallic PdZn as revealed by density functional theory (DFT) calculations. Moreover, this protocol is also extendable for the preparation of sub‐2 nm intermetallic PtZn nanoparticles and is expected to provide a novel methodology in synthesizing ultrasmall atomically ordered intermetallic nanomaterials by rationally functionalizing MOFs.     

Electrocatalytic N‐Doped Graphitic Nanofiber – Metal/Metal Oxide Nanoparticle Composites

Carbon‐based nanocomposites have shown promising results in replacing commercial Pt/C as high‐performance, low cost, nonprecious metal‐based oxygen reduction reaction (ORR) catalysts. Developing unique nanostructures of active components (e.g., metal oxides) and carbon materials is essential for their application in next generation electrode materials for fuel cells and metal–air batteries. Herein, a general approach for the production of 1D porous nitrogen‐doped graphitic carbon fibers embedded with active ORR components, (M/MO_x, i.e., metal or metal oxide nanoparticles) using a facile two‐step electrospinning and annealing process is reported. Metal nanoparticles/nanoclusters nucleate within the polymer nanofibers and subsequently catalyze graphitization of the surrounding polymer matrix and following oxidation, create an interconnected graphite–metal oxide framework with large pore channels, considerable active sites, and high specific surface area. The metal/metal oxide@N‐doped graphitic carbon fibers, especially Co₃O₄, exhibit comparable ORR catalytic activity but superior stability and methanol tolerance versus Pt in alkaline solutions, which can be ascribed to the synergistic chemical coupling effects between Co₃O₄ and robust 1D porous structures composed of interconnected N‐doped graphitic nanocarbon rings. This finding provides a novel insight into the design of functional electrocatalysts using electrospun carbon nanomaterials for their application in energy storage and conversion fields.     

Nanofence Stabilized Platinum Nanoparticles Catalyst via Facet‐Selective Atomic Layer Deposition

A facet‐selective atomic layer deposition method is developed to fabricate oxide nanofence structure to stabilize Pt nanoparticles. CeO_x is selectively deposited on Pt nanoparticles' (111) facets and naturally exposes Pt (100) facets. The facet selectivity is realized through different binding energies of Ce precursor fragments chemisorbed on Pt (111) and Pt (100), which is supported by in situ mass gain experiment and corroborated by density functional theory simulations. Such nanofence structure not only has exposed Pt active facets for carbon monoxide oxidation but also forms ceria–metal interfaces that are beneficial for activity enhancement. The composite catalysts show excellent sintering resistance up to 700 °C calcination. CeO_x anchors Pt nanoparticles with a strong metal oxide interaction, and nanofence structure around Pt nanoparticles provides physical blocking that suppresses particles migration. The study reveals that forming oxide nanofence structure to encapsulate precious metal nanoparticles is an effective way to simultaneously enhance catalytic activity and thermal stability.     

Super‐Stable,Highly Efficient,and Recyclable Fibrous Metal–Organic Framework Membranes for Precious Metal Recovery from Strong Acidic Solutions

Precious metals such as palladium (Pd) and platinum (Pt) are marvelous materials in the fields of electronic and catalysis, but they are tapering day by day. Zr(IV)‐based metal–organic frameworks (MOFs) are competent for their recovery, notably in harsh environments, while the general powder form limits their practical application. Porous MOF‐based membranes with ultraefficient metal ion permeation, strong stability, and high selectivity are, therefore, strikingly preferred. Herein, a set of polymeric fibrous membranes incorporated with the UiO‐66 series are fabricated; their adsorption/desorption capabilities toward Pd(II) and Pt(IV) are evaluated from strongly acidic solutions; and the MOF–polymer compatibilities are investigated. Polyurethane (PU)/UiO‐66‐NH₂ showed strong acid resistance and high chemical stability, which are attributable to strong π–π interactions between PU and MOF nanoparticles with a high configuration of energy. The as‐fabricated MOF membranes show extremely good adsorption/desorption performances without ruptures/coalitions of nanofibers or leak of MOF nanoparticles, and successfully display the efficacy in a gravity‐driven or even continuous‐flow system with good recycle performance and selectivity. The as‐fabricated MOF membranes set an example of potential MOF–polymer compatibility for practical applications.     

Growth of Au Nanoparticles on 2D Metalloporphyrinic Metal‐Organic Framework Nanosheets Used as Biomimetic Catalysts for Cascade Reactions

Inspired by the multiple functions of natural multienzyme systems, a new kind of hybrid nanosheet is designed and synthesized, i.e., ultrasmall Au nanoparticles (NPs) grown on 2D metalloporphyrinic metal‐organic framework (MOF) nanosheets. Since 2D metalloporphyrinic MOF nanosheets can act as the peroxidase mimics and Au NPs can serve as artificial glucose oxidase, the hybrid nanosheets are used to mimic the natural enzymes and catalyze the cascade reactions. Furthermore, the synthesized hybrid nanosheets are used to detect biomolecules, such as glucose. This study paves a new avenue to design nanomaterial‐based biomimetic catalysts with multiple complex functions.     

Size‐Controlled Synthesis of Sub‐10 nm PtNi3 Alloy Nanoparticles and their Unusual Volcano‐Shaped Size Effect on ORR Electrocatalysis

Dealloyed Pt bimetallic core–shell catalysts derived from low‐Pt bimetallic alloy nanoparticles (e.g, PtNi₃) have recently shown unprecedented activity and stability on the cathodic oxygen reduction reaction (ORR) under realistic fuel cell conditions and become today's catalyst of choice for commercialization of automobile fuel cells. A critical step toward this breakthrough is to control their particle size below a critical value (≈10 nm) to suppress nanoporosity formation and hence reduce significant base metal (e.g., Ni) leaching under the corrosive ORR condition. Fine size control of the sub‐10 nm PtNi₃ nanoparticles and understanding their size dependent ORR electrocatalysis are crucial to further improve their ORR activity and stability yet still remain unexplored. A robust synthetic approach is presented here for size‐controlled PtNi₃ nanoparticles between 3 and 10 nm while keeping a constant particle composition and their size‐selected growth mechanism is studied comprehensively. This enables us to address their size‐dependent ORR activities and stabilities for the first time. Contrary to the previously established monotonic increase of ORR specific activity and stability with increasing particle size on Pt and Pt‐rich bimetallic nanoparticles, the Pt‐poor PtNi₃ nanoparticles exhibit an unusual “volcano‐shaped” size dependence, showing the highest ORR activity and stability at the particle sizes between 6 and 8 nm due to their highest Ni retention during long‐term catalyst aging. The results of this study provide important practical guidelines for the size selection of the low Pt bimetallic ORR electrocatalysts with further improved durably high activity.     

Metal–Organic Framework‐Derived Bamboo‐like Nitrogen‐Doped Graphene Tubes as an Active Matrix for Hybrid Oxygen‐Reduction Electrocatalysts

In this work, large size (i.e., diameter > 100 nm) graphene tubes with nitrogen‐doping are prepared through a high‐temperature graphitization process of dicyandiamide (DCDA) and Iron(II) acetate templated by a novel metal–organic framework (MIL‐100(Fe)). The nitrogen‐doped graphene tube (N‐GT)‐rich iron‐nitrogen‐carbon (Fe‐N‐C) catalysts exhibit inherently high activity towards the oxygen reduction reaction (ORR) in more challenging acidic media. Furthermore, aiming to improve the activity and stability of conventional Pt catalysts, the ORR active N‐GT is used as a matrix to disperse Pt nanoparticles in order to build a unique hybrid Pt cathode catalyst. This is the first demonstration of the integration of a highly active Fe‐N‐C catalyst with Pt nanoparticles. The synthesized 20% Pt/N‐GT composite catalysts demonstrate significantly enhanced ORR activity and H₂‐air fuel cell performance relative to those of 20% Pt/C, which is mainly attributed to the intrinsically active N‐GT matrix along with possible synergistic effects between the non‐precious metal active sites and the Pt nanoparticles. Unlike traditional Pt/C, the hybrid catalysts exhibit excellent stability during the accelerated durability testing, likely due to the unique highly graphitized graphene tube morphologies, capable of providing strong interaction with Pt nanoparticles and then preventing their agglomeration.     

Facile Synthesis of Ultrasmall CoS2 Nanoparticles within Thin N‐Doped Porous Carbon Shell for High Performance Lithium‐Ion Batteries

Cobalt sulfide (CoS₂) is considered one of the most promising alternative anode materials for high‐performance lithium‐ion batteries (LIBs) by virtue of its remarkable electrical conductivity, high theoretical capacity, and low cost. However, it suffers from a poor cycling stability and low rate capability because of its volume expansion and dissolution of the polysulfide intermediates in the organic electrolytes during the battery charge/discharge process. In this study, a novel porous carbon/CoS₂ composite is prepared by using nano metal–organic framework (MOF) templates for high‐preformance LIBs. The as‐made ultrasmall CoS₂ (15 nm) nanoparticles in N‐rich carbon exhibit promising lithium storage properties with negligible loss of capacity at high charge/discharge rate. At a current density of 100 mA g^?1, a capacity of 560 mA h g^?1 is maintained after 50 cycles. Even at a current density as high as 2500 mA g^?1, a reversible capacity of 410 mA h g^?1 is obtained. The excellent and highly stable battery performance should be attributed to the synergism of the ultrasmall CoS₂ particles and the thin N‐rich porous carbon shells derieved from nanosized MOF precusors.     

A General and Straightforward Route to Noble Metal‐Decorated Mesoporous Transition‐Metal Oxides with Enhanced Gas Sensing Performance

Controllable and efficient synthesis of noble metal/transition‐metal oxide (TMO) composites with tailored nanostructures and precise components is essential for their application. Herein, a general mercaptosilane‐assisted one‐pot coassembly approach is developed to synthesize ordered mesoporous TMOs with agglomerated‐free noble metal nanoparticles, including Au/WO₃, Au/TiO₂, Au/NbO_x, and Pt/WO₃. 3‐mercaptopropyl trimethoxysilane is applied as a bridge agent to cohydrolyze with metal oxide precursors by alkoxysilane moieties and interact with the noble metal source (e.g., HAuCl₄ and H₂PtCl₄) by mercapto (? SH) groups, resulting in coassembly with poly(ethylene oxide)‐b‐polystyrene. The noble metal decorated TMO materials exhibit highly ordered mesoporous structure, large pore size (≈14–20 nm), high specific surface area (61–138 m² g^?1), and highly dispersed noble metal (e.g., Au and Pt) nanoparticles. In the system of Au/WO₃, in situ generated SiO₂ incorporation not only enhances their thermal stability but also induces the formation of ε‐phase WO₃ promoting gas sensing performance. Owning to its specific compositions and structure, the gas sensor based on Au/WO₃ materials possess enhanced ethanol sensing performance with a good response (R_air/R_gas = 36–50 ppm of ethanol), high selectivity, and excellent low‐concentration detection capability (down to 50 ppb) at low working temperature (200 °C).     

Improving Polysulfides Adsorption and Redox Kinetics by the Co4N Nanoparticle/N‐Doped Carbon Composites for Lithium‐Sulfur Batteries

Improved conductivity and suppressed dissolution of lithium polysulfides is highly desirable for high‐performance lithium‐sulfur (Li‐S) batteries. Herein, by a facile solvent method followed by nitridation with NH₃, a 2D nitrogen‐doped carbon structure is designed with homogeneously embedded Co₄N nanoparticles derived from metal organic framework (MOF), grown on the carbon cloth (MOF‐Co₄N). Experimental results and theoretical simulations reveal that Co₄N nanoparticles act as strong chemical adsorption hosts and catalysts that not only improve the cycling performance of Li‐S batteries via chemical bonding to trap polysulfides but also improve the rate performance through accelerating the conversion reactions by decreasing the polarization of the electrode. In addition, the high conductive nitrogen‐doped carbon matrix ensures fast charge transfer, while the 2D structure offers increased pathways to facilitate ion diffusion. Under the current density of 0.1C, 0.5C, and 3C, MOF‐Co₄N delivers reversible specific capacities of 1425, 1049, and 729 mAh g^?1, respectively, and retains 82.5% capacity after 400 cycles at 1C, as compared to the sample without Co₄N (MOF‐C) values of 61.3% (200 cycles). The improved cell performance corroborates the validity of the multifunctional design of MOF‐Co₄N, which is expected to be a potentially promising cathode host for Li‐S batteries.     

Catalytic properties of Pt cluster-decorated CeO2 nanostructures

Uniform clusters of Pt have been deposited on the surface of capping-agent-free CeO₂ nanooctahedra and nanorods using electron beam (e-beam) evaporation. The coverage of the Pt nanocluster layer can be controlled by adjusting the e-beam evaporation time. The resulting e-beam evaporated Pt nanocluster layers on the CeO₂ surfaces have a clean surface and clean interface between Pt and CeO₂. Different growth behaviors of Pt on the two types of CeO₂ nanocrystals were observed, with epitaxial growth of Pt on CeO₂ nanooctahedra and random growth of Pt on CeO₂ nanorods. The structures of the Pt clusters on the two different types of CeO₂ nanocrystals have been studied and compared by using them as catalysts for model reactions. The results of hydrogenation reactions clearly showed the clean and similar chemical surface of the Pt clusters in both catalysts. The support-dependent activity of these catalysts was demonstrated by CO oxidation. The Pt/CeO₂ nanorods showed much higher activity compared with Pt/CeO₂ nanooctahedra because of the higher concentration of oxygen vacancies in the CeO₂ nanorods. The structure-dependent selectivity of dehydrogenation reactions indicates that the structures of the Pt on CeO₂ nanorods and nanooctahedra are different. Thes differences arise because the metal deposition behaviors are modulated by the strong metal-metal oxide interactions.     

Interface Metal Oxides Regulating Electronic State around Nickel Species for Efficient Alkaline Hydrogen Electrocatalysis

Heterogeneous electrocatalysis typically depends on the surface electronic states of active sites. Modulating the surface charge state of an electrocatalysts can be employed to improve performance. Among all the investigated materials, nickel (Ni)-based catalysts are the only non-noble-metal-based alternatives for both hydrogen oxidation and evolution reactions (HOR and HER) in alkaline electrolyte, while their activities should be further improved because of the unfavorable hydrogen adsorption behavior. Hereto, Ni with exceptional HOR electrocatalytic performance by changing the d-band center by metal oxides interface coupling formed in situ is endowed. The resultant MoO₂ coupled Ni heterostructures exhibit an apparent HOR activity, even approaching to that of commercial 20% Pt/C benchmark, but with better long-term stability in alkaline electrolyte. An exceptional HER performance is also achieved by the Ni-MoO₂ heterostructures. The experiment results are rationalized by the theoretical calculations, which indicate that coupling MoO₂ with Ni results in the downshift of d-band center of Ni, and thus weakens hydrogen adsorption and benefits for hydroxyl adsorption. This concept is further proved by other metal oxides (e.g., CeO₂, V₂O₃, WO₃, Cr₂O₃)-formed Ni-based heterostructures to engineer efficient hydrogen electrocatalysts.     

Effect of ceria on carbon supported platinum catalysts for methanol electrooxidation

Pt–CeO₂/C catalysts were synthesized by a one-step microwave polyol process and compared with Pt/C (E-TEK) catalyst in terms of the electrochemical activity for methanol oxidation using the cyclic voltammetry and chronoamperometry. The results demonstrated that Pt–CeO₂/C catalysts exhibited lower onset potential, higher current peak and better stability for methanol electrooxidation than Pt/C (E-TEK) catalyst. The effect of ceria on the catalytic activity was investigated by electrochemical measurements and the highest electrochemical activity was obtained at the molar ratio of Pt to Ce by 2:1. The preliminary mechanism of the enhanced electrocatalytic performance for methanol oxidation was discussed.     

Confinement Impact for the Dynamics of Supported Metal Nanocatalyst

Supported metal nanoparticles play key roles in nanoelectronics, sensors, energy storage/conversion, and catalysts for the sustainable production of fuels and chemicals. Direct observation of the dynamic processes of nanocatalysts at high temperatures and the confinement of supports is of great significance to investigate nanoparticle structure and functions for practical utilization. Here, in situ high‐resolution transmission electron microscopy photos and videos are combined with dynamics simulations to reveal the real‐time dynamic behavior of Pt nanocatalysts at operation temperatures. Amorphous Pt surface on moving and deforming particles is the working structure during the high operation temperature rather than a static crystal surface and immobilization on supports as proposed before. The free rearrangement of the shape of Pt nanoparticles allows them to pass through narrow windows, which is generally considered to immobilize the particles. The Pt particles, no matter what their sizes, prefer to stay inside nanopores even when they are fast moving near an opening at temperatures up to 900 °C. The porous confinement also blocks the sintering of the particles under the confinement size of pores. These contribute to the continuous high activity and stability of Pt nanocatalysts inside nanoporous supports during a long‐term evaluation of catalytic reforming reaction.     

Single Pt Atoms Confined into a Metal–Organic Framework for Efficient Photocatalysis

It is highly desirable yet remains challenging to improve the dispersion and usage of noble metal cocatalysts, beneficial to charge transfer in photocatalysis. Herein, for the first time, single Pt atoms are successfully confined into a metal–organic framework (MOF), in which electrons transfer from the MOF photosensitizer to the Pt acceptor for hydrogen production by water splitting under visible‐light irradiation. Remarkably, the single Pt atoms exhibit a superb activity, giving a turnover frequency of 35 h^?1, ≈30 times that of Pt nanoparticles stabilized by the same MOF. Ultrafast transient absorption spectroscopy further unveils that the single Pt atoms confined into the MOF provide highly efficient electron transfer channels and density functional theory calculations indicate that the introduction of single Pt atoms into the MOF improves the hydrogen binding energy, thus greatly boosting the photocatalytic H₂ production activity.     

CeO<Subscript>2</Subscript> and Co<Subscript>3</Subscript>O<Subscript>4</Subscript>–CeO<Subscript>2</Subscript> nanoparticles: effect of the synthesis method on the structure and catalytic properties in COPrOx and methanation reactions

CeO₂ and Co₃O₄–CeO₂ nanoparticles were synthesized, thoroughly characterized, and evaluated in the COPrOx reaction. The CeO₂ nanoparticles were synthesized by the diffusion-controlled precipitation method with ethylene glycol. A notably higher yield was obtained when H₂O₂ was used in the synthesis procedure. For comparison, two commercial samples of CeO₂ nanoparticles (Nyacol^®)—one calcined and the other sintered—were also studied. Catalytic results of bare CeO₂ calcined at 500 °C showed a strong influence of the method of synthesis. Despite having similar BET area values, the CeO₂ synthesized without H₂O₂ was the most active sample. Co₃O₄–CeO₂ catalysts with three different Co/(Co + Ce) atomic ratios, 0.1, 0.3, and 0.5, were prepared by the wet impregnation of the CeO₂ nanoparticles. TEM and STEM observations showed that impregnation produced mixed oxides composed of small CeO₂ nanoparticles located both over the surface and inside the Co₃O₄ crystals. The mixed oxide catalysts prepared with a cobalt atomic ratio of 0.5 showed methane formation, which started at 200 °C due to the reaction between CO₂ and H₂. However, above 250 °C, the reaction between CO and H₂ became important, thus contributing to CO elimination with a small H₂ loss. As a result, CO could be totally eliminated in a wide temperature range, from 200 to 400 °C. The methanation reaction was favored by the reduction of the cobalt oxide, as suggested by the TPR experiments. This result is probably originated in Ce–Co interactions, related to the method of synthesis and the surface area of the mixed oxides obtained.     

Aerosol Spray Drying Guided Synthesis of Ultrasmall Alloyed Bimetallic Nanoparticles Supported on Silica for Catalytic Semihydrogenation

Supported bimetallic nanoparticles (NPs) with ultrasmall sizes and homogeneous alloying are attractive for catalysis. However, facile synthesis of this type of material remains very challenging. Here, the aerosol drying impregnation method for rapid, scalable, and general synthesis of silica-supported bimetallic NPs is proposed. The method relies on aerosol spray drying to promote the mixing and dispersing of binary metal precursors on SiO₂. It is capable of controlling the composition and size of bimetallic NPs and avoids the use of expensive metal complex salts and complicated experiment procedures. Twelve permutations combining a noble metal (Pd, Ru, and Pt) and a base one (Fe, Co, Ni, and Cu) with ultrasmall sizes (1.4–2.2 nm in average size), uniform dispersion, and good alloying are synthesized. Interesting activity and selectivity trends in catalytic semihydrogenation of phenylacetylene over the supported Pd-based NPs can be observed. The silica-supported PdNi NPs deliver both high activity and styrene selectivity. Spectroscopic and density functional theory calculation results reveal the improved chemoselectivity originated from the suitably down-shifted d-band center of the PdNi NPs inducing an increased energy barrier for overhydrogenation and a weakened styrene adsorption.     

Integration of Metal Nanoparticles into Metal–Organic Frameworks for Composite Catalysts: Design and Synthetic Strategy

Metal–organic frameworks (MOFs) are constructed by periodically alternate metal ions with organic ligands, which offer structural diversity and a wide range of interesting properties as an attractive classification of crystalline porous materials. Integration of MOFs with other size‐limited functional centers can supply new multifunctional composites, which exhibit both the properties of the components and new characteristics due to the combination of MOFs with the selected loadings. In recent years, integration of metal/metal oxide nanoparticles (MNPs) into MOFs to form the composite catalysts has attracted considerable attention due to the superior performance. In this review, the latest studies and up‐to‐date developments on the design and synthetic strategy of new MNP@MOF composite catalysts are specifically highlighted. Both the achievements and problems are evaluated and proposed, and the opportunities and challenges of MNP@MOF composite catalysts are discussed.     

Boosting the Loading of Metal Single Atoms via a Bioconcentration Strategy

Increasing the mass loading of transition metal single atoms coordinated with nitrogen in carbon‐based materials (M‐N‐C) is still challenging. Herein, inspired by the bioconcentration effect in the living body, a biochemistry strategy for the synthesis of Fe‐N‐C single atoms is demonstrated. Through introducing ferrous glycinate into the growth of fungus, the Fe atoms are bioconcentrated in hyphae. The highly dispersed Fe‐N‐C single atoms in hyphae‐derived carbon fibers (labeled as Fe‐N‐C SA/HCF) are prepared by the pyrolysis of Fe‐riched hyphae. In the bioconcentration process, the uptake of Fe ions by hyphae promotes the secretion of glutathione and ferritin, which provides additional coordination sites for Fe ions. Accordingly, the mass content of Fe in bioconcentrated Fe‐N‐C SA/HCF reaches 4.8%, which is 5.3 times larger than that of the sample prepared by the conventional pyrolysis process. The present bioconcentration strategy is further extended to the preparation of Co, Ni, and Mn single atoms. Owing to the high content of Fe‐N‐C single atoms, Fe‐N‐C SA/HCF shows the onset potential (E_onset) of 0.931 V versus reversible hydrogen electrode (RHE) and half‐wave potential (E_1/2) of 0.802 V versus RHE in oxygen reduction reaction measurements, which is comparable to the commercial Pt/C catalysts.