2D Nanoporous Fe−N/C Nanosheets as Highly Efficient Non‐Platinum Electrocatalysts for Oxygen Reduction Reaction in Zn‐Air Battery

It is an ongoing challenge to fabricate nonprecious oxygen reduction reaction (ORR) catalysts that can be comparable to or exceed the efficiency of platinum. A highly active non‐platinum self‐supporting Fe?N/C catalyst has been developed through the pyrolysis of a new type of precursor of iron coordination complex, in which 1,4‐bis(1H‐1,3,7,8–tetraazacyclopenta(1)phenanthren‐2‐yl)benzene (btcpb) functions as a ligand complexing Fe(II) ions. The optimal catalyst pyrolyzed at 700 °C (Fe?N/C?700) shows the best ORR activity with a half‐wave potential (E_1/2) of 840 mV versus reversible hydrogen electrode (RHE) in 0.1 m KOH, which is more positive than that of commercial Pt/C (E_1/2: 835 mV vs RHE). Additionally, the Fe?N/C?700 catalyst also exhibits high ORR activity in 0.1 m HClO₄ with the onset potential and E_1/2 comparable to those of the Pt/C catalyst. Notably, the Fe?N/C?700 catalyst displays superior durability (9.8 mV loss in 0.1 m KOH and 23.6 mV loss in 0.1 m HClO₄ for E_1/2 after 8000 cycles) and better tolerance to methanol than Pt/C. Furthermore, the Fe?N/C?700 catalyst can be used for fabricating the air electrode in Zn–air battery with a specific capacity of 727 mA hg^?1 at 5 mA cm^?2 and a negligible voltage loss after continuous operation for 110 h.     

Biomass Derived N‐Doped Porous Carbon Supported Single Fe Atoms as Superior Electrocatalysts for Oxygen Reduction

Exploring sustainable and high‐performance electrocatalysts for the oxygen reduction reaction (ORR) is the crucial issue for the large‐scale application of fuel cell technology. A new strategy is demonstrated to utilize the biomass resource for the synthesis of N‐doped hierarchically porous carbon supported single‐atomic Fe (SA‐Fe/NHPC) electrocatalyst toward the ORR. Based on the confinement effect of porous carbon and high‐coordination natural iron source, SA‐Fe/NHPC, derived from the hemin‐adsorbed bio‐porphyra‐carbon by rapid heat‐treatment up to 800 °C, presents the atomic dispersion of Fe atoms in the N‐doped porous carbon. Compared with the molecular hemin and nanoparticle Fe samples, the as‐prepared SA‐Fe/NHPC exhibits a superior catalytic activity (E _1/2 = 0.87 V and J _k = 4.1 mA cm^?2, at 0.88 V), remarkable catalytic stability (≈1 mV negative shift of E _1/2, after 3000 potential cycles), and outstanding methanol‐tolerance, even much better than the state‐of‐the‐art Pt/C catalyst. The sustainable and effective strategy for utilizing biomass to achieve high‐performance single‐atom catalysts can also provide an opportunity for other catalytic applications in the atomic scale.     

Single Fe Atom on Hierarchically Porous S,N‐Codoped Nanocarbon Derived from Porphyra Enable Boosted Oxygen Catalysis for Rechargeable Zn‐Air Batteries

Iron–nitrogen–carbon materials (Fe–N–C) are known for their excellent oxygen reduction reaction (ORR) performance. Unfortunately, they generally show a laggard oxygen evolution reaction (OER) activity, which results in a lethargic charging performance in rechargeable Zn–air batteries. Here porous S‐doped Fe–N–C nanosheets are innovatively synthesized utilizing a scalable FeCl₃‐encapsulated‐porphyra precursor pyrolysis strategy. The obtained electrocatalyst exhibits ultrahigh ORR activity (E_1/2 = 0.84 V vs reversible hydrogen electrode) and impressive OER performance (E_{j = 10} = 1.64 V). The potential gap (ΔE = E_{j = 10} ? E_1/2) is 0.80 V, outperforming that of most highly active bifunctional electrocatalysts reported to date. Furthermore, the key role of S involved in the atomically dispersed Fe–Nx species on the enhanced ORR and OER activities is expounded for the first time by ultrasound‐assisted extraction of the exclusive S source (taurine) from porphyra. Moreover, the assembled rechargeable Zn–air battery comprising this bifunctional electrocatalyst exhibits higher power density (225.1 mW cm^?2) and lower charging–discharging overpotential (1.00 V, 100 mA cm^?2 compared to Pt/C + RuO₂ catalyst). The design strategy can expand the utilization of earth‐abundant biomaterial‐derived catalysts, and the mechanism investigations of S doping on the structure–activity relationship can inspire the progress of other functional electrocatalysts.     

UIO‐66‐NH2‐Derived Mesoporous Carbon Catalyst Co‐Doped with Fe/N/S as Highly Efficient Cathode Catalyst for PEMFCs

Efficient, low‐cost catalysts are desirable for the sluggish oxygen reduction reaction (ORR). Herein, UIO‐66‐NH₂‐derived multi‐element (Fe, S, N) co‐doped porous carbon catalyst is reported, Fe/N/S‐PC, with an octahedral morphology, a well‐defined mesoporous structure, and highly dispersed doping elements, synthesized by a double‐solvent diffusion‐pyrolysis method (DSDPM). The morphology of the UIO‐66‐NH₂ precursor is perfectly inherited by the derived carbon material, resulting in a high surface area, a well‐defined mesoporous structure, and atomic‐level dispersion of the doping elements. Fe/N/S‐PC demonstrates outstanding catalytic activity and durability for the ORR in both alkaline and acidic solutions. In 0.1 m KOH, its half‐potential reaches 0.87 V (vs reversible hydrogen electrode (RHE)), 30 mV more positive than that of a 20 wt% Pt/C catalyst. In 0.1 m HClO₄, it reaches 0.785 V (vs RHE), only 65 mV less than that of Pt/C. The catalyst also exhibits excellent performance in acidic hydrogen/oxygen proton exchange membrane fuel cells. A membrane electrode assembly (MEA) with the catalyst as the cathode reaches 700 mA·cm^‐2 at 0.6 V and a maximum power density of 553 mW·cm^‐2, ranking it among the best MEAs with a nonprecious metal catalyst as the cathode.     

ZIF‐8 with Ferrocene Encapsulated: A Promising Precursor to Single‐Atom Fe Embedded Nitrogen‐Doped Carbon as Highly Efficient Catalyst for Oxygen Electroreduction

The oxygen reduction reaction (ORR) plays an important role in the fields of energy storage and conversion technologies, including metal–air batteries and fuel cells. The development of nonprecious metal electrocatalysts with both high ORR activity and durability to replace the currently used costly Pt‐based catalyst is critical and still a major challenge. Herein, a facile and scalable method is reported to prepare ZIF‐8 with single ferrocene molecules trapped within its cavities (Fc@ZIF‐8), which is utilized as precursor to porous single‐atom Fe embedded nitrogen‐doped carbon (Fe–N–C) during high temperature pyrolysis. The catalyst shows a half‐wave potential (E_1/2) of 0.904 V, 67 mV higher than commercial Pt/C catalyst (0.837 V), which is among the best compared with reported results for ORR. Significant electrochemical properties are attributed to the special configuration of Fc@ZIF‐8 transforming into a highly dispersed iron–nitrogen coordination moieties embedded carbon matrix.     

Fe Isolated Single Atoms on S,N Codoped Carbon by Copolymer Pyrolysis Strategy for Highly Efficient Oxygen Reduction Reaction

Heteroatom‐doped Fe‐NC catalyst has emerged as one of the most promising candidates to replace noble metal‐based catalysts for highly efficient oxygen reduction reaction (ORR). However, delicate controls over their structure parameters to optimize the catalytic efficiency and molecular‐level understandings of the catalytic mechanism are still challenging. Herein, a novel pyrrole–thiophene copolymer pyrolysis strategy to synthesize Fe‐isolated single atoms on sulfur and nitrogen‐codoped carbon (Fe‐ISA/SNC) with controllable S, N doping is rationally designed. The catalytic efficiency of Fe‐ISA/SNC shows a volcano‐type curve with the increase of sulfur doping. The optimized Fe‐ISA/SNC exhibits a half‐wave potential of 0.896 V (vs reversible hydrogen electrode (RHE)), which is more positive than those of Fe‐isolated single atoms on nitrogen codoped carbon (Fe‐ISA/NC, 0.839 V), commercial Pt/C (0.841 V), and most reported nonprecious metal catalysts. Fe‐ISA/SNC is methanol tolerable and shows negligible activity decay in alkaline condition during 15 000 voltage cycles. X‐ray absorption fine structure analysis and density functional theory calculations reveal that the incorporated sulfur engineers the charges on N atoms surrounding the Fe reactive center. The enriched charge facilitates the rate‐limiting reductive release of OH* and therefore improved the overall ORR efficiency.     

Atomic‐Level Fe‐N‐C Coupled with Fe3C‐Fe Nanocomposites in Carbon Matrixes as High‐Efficiency Bifunctional Oxygen Catalysts

Highly active and durable bifunctional oxygen electrocatalysts are of pivotal importance for clean and renewable energy conversion devices, but the lack of earth‐abundant electrocatalysts to improve the intrinsic sluggish kinetic process of oxygen reduction/evolution reactions (ORR/OER) is still a challenge. Fe‐N‐C catalysts with abundant natural merits are considered as promising alternatives to noble‐based catalysts, yet further improvements are urgently needed because of their poor stability and unclear catalytic mechanism. Here, an atomic‐level Fe‐N‐C electrocatalyst coupled with low crystalline Fe₃C‐Fe nanocomposite in 3D carbon matrix (Fe‐SAs/Fe₃C‐Fe@NC) is fabricated by a facile and scalable method. Versus atomically FeN_x species and crystallized Fe₃C‐Fe nanoparticles, Fe‐SAs/Fe₃C‐Fe@NC catalyst, abundant in vertical branched carbon nanotubes decorated on intertwined carbon nanofibers, exhibits high electrocatalytic activities and excellent stabilities both in ORR (E_1/2, 0.927 V) and OER (E_J=10, 1.57 V). This performance benefits from the strong synergistic effects of multicomponents and the unique structural advantages. In‐depth X‐ray absorption fine structure analysis and density functional theory calculation further demonstrate that more extra charges derived from modified Fe clusters decisively promote the ORR/OER performance for atomically FeN₄ configurations by enhanced oxygen adsorption energy. These insightful findings inspire new perspectives for the rational design and synthesis of economical–practical bifunctional oxygen electrocatalysts.     

Inflating strategy to fabricate highly dispersed Fe,N co-doped hierarchically porous carbon for ORR and supercapacitor

Doped-carbon nanomaterials as effective electrocatalysts have been received widespread attention in oxygen reduction reaction (ORR) and supercapacitors system. Herein, the high-active Fe atoms dispersed on hierarchically porous N-doped carbon (FeNC-X) is synthesized via inflating the Fe-ion-denatured egg-white, followed by activation and pyrolysis. Among them, the as-prepared FeNC-900 for ORR that has an inner-connecting hierarchically porous structure shows a superior performance with a limiting current density of 5.28 mA cm^?2 and half-wave potential (E_1/2) of 0.839 V (vs RHE), and exhibits a 4 e^? ORR pathway in the alkaline medium. FeNC-900 also shows better durability and good methanol tolerance than those of commercial Pt/C. Besides, FeNC-900 exhibits an outstanding specific capacity of 258 F g^?1 at 1 A g^?1 for supercapacitor. The method presented here may provide a cost-efficient approach to fabricate carbon-based materials for ORR and supercapacitors.

     

Pyridinic‐N Protected Synthesis of 3D Nitrogen‐Doped Porous Carbon with Increased Mesoporous Defects for Oxygen Reduction

Nitrogen (N)‐doped carbons are potential nonprecious metal catalysts to replace Pt for the oxygen reduction reaction (ORR). Pyridinic‐N‐C is believed to be the most active N group for catalyzing ORR. In this work, using zinc phthalocyanine as a precursor effectively overcomes the serious loss of pyridinic‐N, which is commonly regarded as the biggest obstacle to catalytic performance enhancement upon adopting a second pyrolysis process, for the preparation of a 3D porous N‐doped carbon framework (NDCF). The results show only ≈14% loss in pyridinic‐N proportion in the Zn‐containing sample during the second pyrolysis process. In comparison, a loss of ≈72% pyridinic‐N occurs for the non‐Zn counterpart. The high pyridinic‐N proportion, the porous carbon framework produced upon NaCl removal, and the increased mesoporous defects in the second pyrolysis process make the as‐prepared catalyst an excellent electrocatalyst for ORR, exhibiting a half‐wave potential (E_1/2 = 0.88 V) up to 33 mV superior to state‐of‐the‐art Pt/C and high four‐electron selectivity (n > 3.83) in alkaline solution, which is among the best ORR activities reported for N‐doped carbon catalysts. Furthermore, only ≈18 mV degradation in E_1/2 occurs after an 8000 cycles' accelerating stability test, manifesting the outstanding stability of the as‐prepared catalyst.     

Thermodynamically Stable Mesoporous C3N7 and C3N6 with Ordered Structure and Their Excellent Performance for Oxygen Reduction Reaction

Carbon nitrides with a high N/C atomic ratio (>2) are expected to offer superior basicity and unique electronic properties. However, the synthesis of these nanostructures is highly challenging since many parts of the C? N frameworks in the carbon nitride should be replaced with thermodynamically less stable N? N frameworks as the nitrogen content increases. Thermodynamically stable C₃N₇ and C₃N₆ with an ordered mesoporous structure are synthesized at 250 and 300 °C respectively via a pyrolysis process of 5‐amino‐1H‐tetrazole (5‐ATTZ). Polymerization of the precursor to the ordered mesoporous C₃N₇ and C₃N₆ is clearly proved by X‐ray and electron diffraction analyses. A combined analysis including diverse spectroscopy and FDMNES and density functional theory (DFT) calculations demonstrates that the N? N bonds are stabilized in the form of tetrazine and/or triazole moieties in the C₃N₇ and C₃N₆. The ordered mesoporous C₃N₇ represents the better oxygen reduction reaction (ORR) performances (onset potential: 0.81 V vs reversible hydrogen electrode (RHE), electron transfer number: 3.9 at 0.5 V vs RHE) than graphitic carbon nitride (g‐C₃N₄) and the ordered mesoporous C₃N₆. The study on the mechanism of ORR suggests that nitrogen atoms in the tetrazine moiety of the ordered mesoporous C₃N₇ act as active sites for its improved ORR activity.     

Porphyrin-like Fe-N<Subscript>4</Subscript> sites with sulfur adjustment on hierarchical porous carbon for different rate-determining steps in oxygen reduction reaction

We developed a strategy based on coordination polymer to synthesize singleatom site Fe/N and S-codoped hierarchical porous carbon (Fe₁/N,S-PC). The as-obtained Fe₁/N,S-PC exhibited superior oxygen reduction reaction (ORR) performance with a half-wave potential (E_1/2, 0.904 V vs. RHE) that was better than that of commercial Pt/C (E_1/2, 0.86 V vs. RHE), single-atom site Fe/N-doped hierarchical porous carbon (Fe₁/N-PC) without S-doped (E_1/2, 0.85 V vs. RHE), and many other nonprecious metal catalysts in alkaline medium. Moreover, the Fe₁/N,S-PC revealed high methanol tolerance and firm stability. The excellent electrocatalytic activity of Fe₁/N,S-PC is attributed to the synergistic effects from the atomically dispersed porphyrin-like Fe-N₄ active sites, the heteroatom codoping (N and S), and the hierarchical porous structure in the carbon materials. The calculation based on density functional theory further indicates that the catalytic performance of Fe₁/N,S-PC is better than that of Fe₁/N-PC owing to the sulfur doping that yielded different rate-determining steps.

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Ultrathin PtPd‐Based Nanorings with Abundant Step Atoms Enhance Oxygen Catalysis

The lack of highly active and stable catalysts with low Pt usage for the oxygen reduction reaction (ORR) is a major barrier in realizing fuel cell‐driven transportation applications. A general colloidal chemistry method is demonstrated for making a series of ultrathin PtPdM (M = Co, Ni, Fe) nanorings (NRs) for greatly boosting ORR catalysis. Different from the traditional ultrathin nanosheets, the ultrathin PtPdM NRs herein have a high portion of step atoms on the edge, high Pt utilization efficiency, and strong ligand effect from M to Pt and fast mass transport of reactants to the NRs. These key features make them exhibit greatly enhanced electrocatalytic activity for the ORR and the oxygen evolution reaction (OER). Among all the PtPdM NRs, the PtPdCo shows the highest ORR mass and specific activities of 3.58 A mg^?1 and 4.90 mA cm^?2 at 0.9 V versus reversible hydrogen electrode (RHE), 23.9 and 24.5‐fold larger than those of commercial Pt/C in alkaline electrolyte, respectively. The theoretical calculations reveal that the oxygen adsorption energy (E _O) can be optimized under the presence of step atoms exposed on the edge and ligand effect induced by Co. They are stable under ORR conditions with negligible changes after 30 000 cycles.     

Single‐Atom Nanozyme Based on Nanoengineered Fe–N–C Catalyst with Superior Peroxidase‐Like Activity for Ultrasensitive Bioassays

Single‐atom catalysts are becoming a hot research topic owing to their unique characteristics of maximum specific activity and atomic utilization. Herein, a new single‐atom nanozyme (SAN) based on single Fe atoms anchored on N‐doped carbons supported on carbon nanotube (CNT/FeNC) is proposed. The CNT/FeNC with robust atomic Fe–N_x moieties is synthesised, showing superior peroxidase‐like activity. Furthermore, the CNT/FeNC is used as the signal element in a series of paper‐based bioassays for ultrasensitive detection of H₂O₂, glucose, and ascorbic acid. The SAN provides a new type of signal element for developing various biosensing techniques.     

Atomic Fe Dispersed on N‐Doped Carbon Hollow Nanospheres for High‐Efficiency Electrocatalytic Oxygen Reduction

Exploration of high‐efficiency, economical, and ultrastable electrocatalysts for the oxygen reduction reaction (ORR) to substitute precious Pt is of great significance in electrochemical energy conversion devices. Single‐atom catalysts (SACs) have sparked tremendous interest for their maximum atom‐utilization efficiency and fascinating properties. Therefore, the development of effective synthetic methodology toward SACs becomes highly imperative yet still remains greatly challenging. Herein, a reliable SiO₂‐templated strategy is elaborately designed to synthesize atomically dispersed Fe atoms anchored on N‐doped carbon nanospheres (denoted as Fe–N–C HNSs) using the cheap and sustainable biomaterial of histidine (His) as the N and C precursor. By virtue of the numerous atomically dispersed Fe–N₄ moieties and unique spherical hollow architecture, the as‐fabricated Fe–N–C HNSs exhibit excellent ORR performance in alkaline medium with outstanding activity, high long‐term stability, and superior tolerance to methanol crossover, exceeding the commercial Pt/C catalyst and most previously reported non‐precious‐metal catalysts. This present synthetic strategy will provide new inspiration to the fabrication of various high‐efficiency single‐atom catalysts for diverse applications.     

Reduced Graphene Oxide‐Wrapped Co9–xFexS8/Co,Fe‐N‐C Composite as Bifunctional Electrocatalyst for Oxygen Reduction and Evolution

Searching for highly efficient bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) using nonnoble metal‐based catalysts is essential for the development of many energy conversion systems, including rechargeable fuel cells and metal–air batteries. Here, Co_9–xFe_xS₈/Co,Fe‐N‐C hybrids wrapped by reduced graphene oxide (rGO) (abbreviated as S‐Co_9–xFe_xS₈@rGO) are synthesized through a semivulcanization and calcination method using graphene oxide (GO) wrapped bimetallic zeolite imidazolate framework (ZIF) Co,Fe‐ZIF (CoFe‐ZIF@GO) as precursors. Benefiting from the synergistic effect of OER active CoFeS and ORR active Co,Fe‐N‐C in a single component, as well as high dispersity and enhanced conductivity derived from rGO coating and Fe‐doping, the obtained S‐Co_9–xFe_xS₈@rGO‐10 catalyst shows an ultrasmall overpotential of ≈0.29 V at 10 mA cm^?2 in OER and a half‐wave potential of 0.84 V in ORR, combining a superior oxygen electrode activity of ≈0.68 V in 0.1 m KOH.     

Regulating the Coordination Geometry and Oxidation State of Single-Atom Fe Sites for Enhanced Oxygen Reduction Electrocatalysis

Fe N C catalysts demonstrate remarkable activity and stability for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells and Zn–air batteries (ZABs). The local coordination of Fe single atoms in Fe N C catalysts strongly impacts ORR activity. Herein, Fe N C catalysts containing Fe single atoms sites with FeN₃, FeN₄, and FeN₅ coordinations are synthesized by carbonization of Fe-rich polypyrrole precursors. The FeN₅ sites possess a higher Fe oxidation state (+2.62) than the FeN₃ (+2.23) and FeN₄ (+2.47) sites, and higher ORR activity. Density functional theory calculations verify that the FeN₅ coordination optimizes the adsorption and desorption of ORR intermediates, dramatically lowering the energy barrier for OH⁻ desorption in the rate-limiting ORR step. A primary ZAB constructed using the Fe N C catalyst with FeN₅ sites demonstrates state-of-the-art performance (an open circuit potential of 1.629 V, power density of 159 mW cm⁻²). Results confirm an intimate structure-activity relationship between Fe coordination, Fe oxidation state, and ORR activity in Fe N C catalysts.     

High-Activity Fe3C as pH-Universal Electrocatalyst for Boosting Oxygen Reduction Reaction and Zinc-Air Battery

Transition metal catalysts are regarded as one of promising alternatives to replace traditional Pt-based catalysts for oxygen reduction reaction (ORR). In this work, an efficient ORR catalyst is synthesized by confining Fe₃C nanoparticles into N, S co-doped porous carbon nanosheets (Fe₃C/N,S-CNS) via high-temperature pyrolysis, in which 5-sulfosalicylic acid (SSA) demonstrates as an ideal complexing agent for iron (ΙΙΙ) acetylacetonate while g-C₃N₄ behaves as a nitrogen source. The influence of the pyrolysis temperature on the ORR performance is strictly examined in the controlled experiments. The obtained catalyst exhibits excellent ORR performance (E_1/2 = 0.86 V; E_onset = 0.98 V) in alkaline electrolyte, coupled by exhibiting the superior catalytic activity and stability (E_1/2 = 0.83 V, E_onset = 0.95 V) to Pt/C in acidic media. In parallel, its ORR mechanism is carefully illustrated by the density functional theory (DFT) calculations, especially the role of the incorporated Fe₃C played in the catalytic process. The catalyst-assembled Zn-air battery also exhibits a much higher power density (163 mW cm^–2) and ultralong cyclic stability in the charge–discharge test for 750 h with a gap increase down to 20 mV. This study provides some constructive insights for preparation of advanced ORR catalysts in green energy conversion units correlated systems.     

A Polymer Encapsulation Strategy to Synthesize Porous Nitrogen‐Doped Carbon‐Nanosphere‐Supported Metal Isolated‐Single‐Atomic‐Site Catalysts

A novel polymer encapsulation strategy to synthesize metal isolated‐single‐atomic‐site (ISAS) catalysts supported by porous nitrogen‐doped carbon nanospheres is reported. First, metal precursors are encapsulated in situ by polymers through polymerization; then, metal ISASs are created within the polymer‐derived p‐CN nanospheres by controlled pyrolysis at high temperature (200–900 °C). Transmission electron microscopy and N₂ sorption results reveal this material to exhibit a nanospheric morphology, a high surface area (≈380 m² g^?1), and a porous structure (with micropores and mesopores). Characterization by aberration‐corrected high‐angle annular dark‐field scanning transmission electron microscopy and X‐ray absorption fine structure confirms the metal to be present as metal ISASs. This methodology is applicable to both noble and nonprecious metals (M‐ISAS/p‐CN, M = Co, Ni, Cu, Mn, Pd, etc.). In particular, the Co‐ISAS/p‐CN nanospheres obtained using this method show comparable (E_1/2 = 0.838 V) electrochemical oxygen reduction activity to commercial Pt/C with 20 wt% Pt loading (E_1/2 = 0.834 V) in alkaline media, superior methanol tolerance, and outstanding stability, even after 5000 cycles.     

Well‐Defined Single‐Atom Cobalt Catalyst for Electrocatalytic Flue Gas CO2 Reduction

Single‐atom Co catalyst Co‐Tpy‐C with well‐defined sites is synthesized by pyrolysis of a Co terpyridine (Tpy) organometallic complex. The Co‐Tpy‐C catalyst exhibits excellent activity for the electrochemical CO₂ reduction reaction in aqueous electrolyte, with CO faradaic efficiency (FE) of over 95% from ?0.7 to ?1.0 V (vs RHE). By comparison, catalysts without Co or Tpy ligand added do not show any high CO FE. When simulated flue gas with 15% of CO₂ is used as the source of CO₂, CO FE is kept at 90.1% at ?0.5 V versus RHE. During gas phase flow electrolysis using simulated flue gas, the CO partial current density is further increased to 86.4 mA cm^?2 and CO FE reached >90% at the cell voltage of 3.4 V. Experiments and density functional theory calculations indicate that uniform single‐atom Co–N₄ sites mainly contribute to the high activity for CO₂ reduction.     

Silk‐Derived 2D Porous Carbon Nanosheets with Atomically‐Dispersed Fe‐Nx‐C Sites for Highly Efficient Oxygen Reaction Catalysts

Controlled synthesis of highly efficient, stable, and cost‐effective oxygen reaction electrocatalysts with atomically‐dispersed Me–N_x–C active sites through an effective strategy is highly desired for high‐performance energy devices. Herein, based on regenerated silk fibroin dissolved in ferric chloride and zinc chloride aqueous solution, 2D porous carbon nanosheets with atomically‐dispersed Fe–N_x–C active sites and very large specific surface area (≈2105 m² g^?1) are prepared through a simple thermal treatment process. Owing to the 2D porous structure with large surface area and atomic dispersion of Fe–N_x–C active sites, the as‐prepared silk‐derived carbon nanosheets show superior electrochemical activity toward the oxygen reduction reaction with a half‐wave potential (E_1/2) of 0.853 V, remarkable stability with only 11 mV loss in E_1/2 after 30 000 cycles, as well as good catalytic activity toward the oxygen evolution reaction. This work provides a practical and effective approach for the synthesis of high‐performance oxygen reaction catalysts towards advanced energy materials.