Palladium Enhanced Iron Active Site – An Efficient Dual-Atom Catalyst for Oxygen Electroreduction

Metal–nitrogen–carbon (M–C/N) electrocatalysts have been shown to have satisfactory catalytic activity and long-term durability for the oxygen reduction reaction (ORR). Here, a strategy to prepare a new electrocatalyst (Fe&Pd–C/N) using a unique metal-containing ionic liquid (IL) is exploited, in which Fe & Pd ions are positively charged species atomically dispersed by coordination to the N of the N-doped C substrate, C/N. X-ray absorption fine structure, XPS and aberration-corrected transmission electron microscopy results verified a well-defined dual-atom configuration comprising Fe^+2.x–N₄ coupled Pd²⁺–N₄ sites and well-defined spatial distribution. Electronic control of a coupled Fe–Pd structure produces an electrocatalyst that exhibits superior performance with enhanced activity and durability for the ORR compared to that of commercial Pt/C (20%, Johnson Matthey) in both alkaline and acid media. Density functional theory calculations indicate that Pd atom can enhance the catalytic activity of the Fe active sites adjacent to Pd sites by changing the electronic orbital structure and Bader charge of the Fe centers. The excellent catalytic performance of the Fe&Pd–C/N electrocatalyst is demonstrated in zinc–air batteries and hydrogen–air fuel cells.     

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.     

High Density Single Fe Atoms on Mesoporous N-Doped Carbons: Noble Metal-Free Electrocatalysts for Oxygen Reduction Reaction in Acidic and Alkaline Media

It remains a challenge to develop efficient noble metal-free electrocatalysts for the oxygen reduction reaction (ORR) in various renewable energy systems. Single atom catalysts have recently drawn great attention as promising candidates both due to their high activity and their utmost atom utilization for electrocatalytic ORR. Herein, the synthesis of an efficient ORR electrocatalyst that is composed of N-doped mesoporous carbon and a high density (4.05 wt%) of single Fe atoms via pyrolysis Fe-conjugated polymer is reported. Benefiting from the abundant atomic Fe–N₄ sites on its conductive, mesoporous carbon structures, this material exhibits an excellent electrocatalytic activity for ORR, with positive onset potentials of 0.93 and 0.98 V in acidic and alkaline media, respectively. Its electrocatalytic performance for ORR is also comparable to that of Pt/C (20 wt%) in both media. Furthermore, it electrocatalyzes the reaction almost fully to H₂O (or barely to H₂O₂). Additionally, it is durable and tolerates the methanol crossover reaction well. Furthermore, a proton exchange membrane fuel cell and a zinc–air battery assembled using it on their cathode deliver high maximum power densities (320 and 91 mW cm⁻², respectively). Density functional theory calculation reveals that the material's decent electrocatalytic performance for ORR is due to its atomically dispersed Fe–N₄ sites.     

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.     

Coordination Engineering of Defective Cobalt–Nitrogen–Carbon Electrocatalysts with Graphene Quantum Dots for Boosting Oxygen Reduction Reaction

Developing efficient and robust metal–nitrogen–carbon electrocatalysts for oxygen reduction reaction (ORR) is of great significance for the application of hydrogen–oxygen fuel cells and metal–air batteries. Herein, a coordination engineering strategy is developed to improve the ORR kinetics and stability of cobalt–nitrogen–carbon (Co–N–C) electrocatalysts by grafting the oxygen-rich graphene quantum dots (GQDs) onto the zeolite imidazole frameworks (ZIFs) precursors. The optimized oxygen-rich GQDs-functionalized Co–N–C (G-CoNOC) electrocatalyst demonstrates an increased mass activity, nearly two times higher than that of pristine defective Co–N–C electrocatalyst, and retains a stability of 90.0% after 200 h, even superior to the commercial Pt/C. Comprehensive investigations demonstrate that the GQDs coordination can not only decrease carbon defects of Co–N–C electrocatalysts, improving the electron transfer efficiency and resistance to the destructive free radicals from H₂O₂, but also optimize the electronic structure of atomic Co active site to achieve a desired adsorption energy of OOH⁻, leading to enhanced ORR kinetics and stability by promoting further H₂O₂ reduction, as confirmed by theoretical calculations and experimental results. Such a coordination engineering strategy provides a new perspective for the development of highly active noble-metal-free electrocatalysts for ORR.     

A Prussian blue route to nitrogen-doped graphene aerogels as efficient electrocatalysts for oxygen reduction with enhanced active site accessibility

Developing high-performance nonpredous-metal electrocatalysts for the oxygen reduction reaction (ORR) is crudal for a variety of renewable energy conversion and storage systems.Toward that end,rational catalyst design principles that lead to highly active catalytic centers and enhanced active site accessibility are undoubtedly of paramount importance.Here,we used Prussian blue nanoparticles to anchor Fe/Fe3C species to nitrogen-doped reduced graphene oxide aerogels as ORR catalysts.The strong interaction between nanosized Fe3C and the graphitic carbon shell led to synergistic effects in the ORR,and the protection of the carbon shell guaranteed stability of the catalyst.As a result,the aerogel electrocatalyst displayed outstanding activity in the ORR on par with the state-of-the-art Pt/C catalyst at the same mass loading in alkaline media,good performance in acidic media,and excellent stability and crossover tolerance that rivaled that of the best nonprecious-metal ORR electrocatalysts reported to date.     

Atomically Dispersed Fe/N4 and Ni/N4 Sites on Separate-Sides of Porous Carbon Nanosheets with Janus Structure for Selective Oxygen Electrocatalysis

Dual single atoms catalysts have promising application in bifunctional electrocatalysis due to their synergistic effect. However, how to balance the competition between rate-limiting steps (RDSs) of reversible oxygen reduction and oxygen evolution reaction (OER) and fully expose the active centers by reasonable structure design remain enormous challenges. Herein, Fe/N₄ and Ni/N₄ sites separated on different sides of the carbon nanosheets with Janus structure (FeNi_jns/NC) is synthesized by layer-by-layer assembly method. Experiments and calculations reveal that the side of Fe/N₄ is beneficial to oxygen reduction reaction (ORR) and the Ni/N₄ side is preferred to OER. Such Janus structure can take full advantage of two separate-sides of carbon nanosheets and balance the competition of RDSs during ORR and OER. FeNi_jns/NC possesses superior ORR and OER activity with ORR half-wave potential of 0.92 V and OER overpotential of 440 mV at J = 10 mA cm⁻². Benefiting from the excellent bifunctional activities, FeNi_jns/NC assembled aqueous Zn–air battery (ZAB) demonstrates better maximum power density, and long-term stability (140 h) than Pt/C+RuO₂ catalyst. It also reveals superior flexibility and stability in solid-state ZAB. This work brings a novel perspective for rational design and understanding of the catalytic mechanisms of dual single atom catalysts.     

Atomically Dispersed Ni–N4 Sites Assist Pt3Ni Nanocages with Pt Skin to Synergistically Enhance Oxygen Reduction Activity and Stability

Currently, the rarity and high cost of platinum (Pt)-based electrocatalysts seriously limit their commercial application in fuel cells cathode. Decorating Pt with atomically dispersed metal–nitrogen sites possibly offers an effective pathway to synergy tailor their catalytic activity and stability. Here active and stable oxygen reduction reaction (ORR) electrocatalysts (Pt₃Ni@Ni–N₄–C) by in situ loading Pt₃Ni nanocages with Pt skin on single-atom nickel–nitrogen (Ni–N₄) embedded carbon supports are designed and constructed. The Pt₃Ni@Ni–N₄–C exhibits excellent mass activity (MA) of 1.92 A mg_Pt⁻¹ and specific activity of 2.65 mA cm_Pt⁻², together with superior durability of 10 mV decay in half-wave potential and only 2.1% loss in MA after 30 000 cycles. Theoretical calculations demonstrate that Ni–N₄ sites significant redistribute of electrons and make them transfer from both the adjacent carbon and Pt atoms to the Ni–N₄. The resultant electron accumulation region successfully anchored Pt₃Ni, that not only improves structural stability of the Pt₃Ni, but importantly makes the surface Pt more positive to weaken the adsorption of *OH to enhance ORR activity. This strategy lays the groundwork for the development of super effective and durable Pt-based ORR catalysts.     

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.     

ZIF‐8/ZIF‐67‐Derived Co‐Nx‐Embedded 1D Porous Carbon Nanofibers with Graphitic Carbon‐Encased Co Nanoparticles as an Efficient Bifunctional Electrocatalyst

Herein, an approach is reported for fabrication of Co‐N_x‐embedded 1D porous carbon nanofibers (CNFs) with graphitic carbon‐encased Co nanoparticles originated from metal–organic frameworks (MOFs), which is further explored as a bifunctional electrocatalyst for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Electrochemical results reveal that the electrocatalyst prepared by pyrolysis at 1000 °C (CoNC‐CNF‐1000) exhibits excellent catalytic activity toward ORR that favors the four‐electron ORR process and outstanding long‐term stability with 86% current retention after 40 000 s. Meanwhile, it also shows superior electrocatalytic activity toward OER, reaching a lower potential of 1.68 V at 10 mA cm^?2 and a potential gap of 0.88 V between the OER potential (at 10 mA cm^?2) and the ORR half‐wave potential. The ORR and OER performance of CoNC‐CNF‐1000 have outperformed commercial Pt/C and most nonprecious‐metal catalysts reported to date. The remarkable ORR and OER catalytic performance can be mainly attributable to the unique 1D structure, such as higher graphitization degree beneficial for electronic mobility, hierarchical porosity facilitating the mass transport, and highly dispersed CoN_xC active sites functionalized carbon framework. This strategy will shed light on the development of other MOF‐based carbon nanofibers for energy storage and electrochemical devices.     

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.     

Bimetallic Oxyhydroxide as a High-Performance Water Oxidation Electrocatalyst under Industry-Relevant Conditions

Developing high-performing oxygen evolution reaction (OER) electrocatalysts under high-current operation conditions is critical for future commercial applications of alkaline water electrolysis for clean energy generation. Herein, we prepared a three-dimensional (3D) bimetallic oxyhydroxide hybrid grown on a Ni foam (NiFeOOH/NF) prepared by immersing Ni foam (NF) into Fe(NO₃)₃ solution. In this unique 3D structure, the NiFeOOH/NF hybrid was composed of crystalline Ni(OH)₂ and amorphous FeOOH evenly grown on the NF surface. As a bimetallic oxyhydroxide electrocatalyst, the NiFeOOH/NF hybrid exhibited excellent catalytic activity, surpassing not only the other reported Ni–Fe based electrocatalysts, but also the commercial Ir/C catalyst. In situ electrochemical Raman spectroscopy demonstrated the active FeOOH and NiOOH phases involved in the OER process. Profiting from the synergy of Fe and Ni catalytic sites, the NiFeOOH/NF hybrid delivered an outstanding OER performance under challenging industrial conditions in a 10.0 mol∙L⁻¹ KOH electrolyte at 80 °C, requiring potentials as small as 1.47 and 1.51 V to achieve the super-high catalytic current densities of 100 and 500 mA∙cm⁻², respectively.     

Engineering Energy Level of FeN4 Sites via Dual-Atom Site Construction Toward Efficient Oxygen Reduction

Single-atom catalysts based on metal–N₄ moieties and embedded in a graphite matrix (defined as M N C) are promising for oxygen reduction reaction (ORR). However, the performance of M N C catalysts is still far from satisfactory due to their imperfect adsorption energy to oxygen species. Herein, single-atom Fe N C is leveraged as a model system and report an adjacent Ru-N₄ moiety modulation effect to optimize the catalyst's electronic configuration and ORR performance. Theoretical simulations and physical characterizations reveal that the incorporation of Ru-N₄ sites as the modulator can alter the d-band electronic energy of Fe center to weaken the Fe O binding affinity, thus resulting in the lower adsorption energy of ORR intermediates at Fe sites. Thanks to the synergetic effects of neighboring Fe and Ru single-atom pairs, the FeN₄/RuN₄ catalyst exhibits a half-wave potential of 0.958 V and negligible activity degradation after 10 000 cycles in 0.1 m KOH. Metal–air batteries using this catalyst in the cathode side exhibit a high power density of 219.5 mW cm⁻² and excellent cycling stability for over 2370 h, outperforming the state-of-the-art catalysts.     

Metal–Organic-Framework-Derived Co2P Nanoparticle/Multi-Doped Porous Carbon as a Trifunctional Electrocatalyst

Developing efficient and low-cost replacements for precious metals as electrocatalysts active in electrochemical reactions—the oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and oxygen reduction reaction (ORR)—is a top priority in renewable energy technology. In this work a highly active and very stable trifunctional electrocatalyst composed of Co₂P embedded in Co, N, and P multi-doped carbon has been synthesized using zeolitic imidazolate frameworks as precursors. The synergistic effects between Co₂P and the multi-heteroatom-doped carbon substrates afford materials having electrocatalytic activities for HER, OER, and ORR, which are comparable—or even superior to—those of commercial RuO₂ or Pt/C catalysts. Density functional theory calculations show that Co₂P has a higher density of states at the Fermi level than Co_nP (0 < n < 2), which promotes electron transfer and intermediates adsorption in the catalytic process. Zinc–air batteries and water splitting devices assembled using the materials as electrode electrocatalysts show good performance and outstanding stability. This work represents a breakthrough in improving the catalytic performance of non-precious metal electrocatalysts for OER, HER, and ORR, and opens new avenues for clean energy generation.     

Altering Ligand Microenvironment of Atomically Dispersed CrN4 by Axial Ligand Sulfur for Enhanced Oxygen Reduction Reaction in Alkaline and Acidic Medium

Because of the instability and Fenton reactivity of non-precious metal nitrogen-carbon based catalyst when processing the oxygen reduction reaction (ORR), seeking for electrocatalysts with highly efficient performance becomes very highly desired to speed up the commercialization of fuel cell. Herein, chromium (Cr)-N₄ electrocatalyst containing extraterrestrial S formed axial S₁-Cr₁N₄ bonds (S₁ Cr₁N₄ C) is achieved via an assembly polymerization and confined pyrolysis strategy. Benefiting from the adjusting  coordination configuration and electronic structure of the metal center through axial coordination, S₁ Cr₁N₄ C exhibits enhanced the intrinsic activity (half-wave potential (E_1/2) is 0.90 V versus reversable hydrogen electrode, RHE) compared with that of Cr N₄ C and Pt/C catalysts. More notably, the catalyst is almost inert in catalyzing the Fenton reaction, and thus shows the high stability. Density functional theory (DFT) results further reveal that the existence of axial S atoms in S₁ Cr₁N₄ C moiety has the better ORR activity than Cr₁N₄ C moieties. The axial S ligand in S₁ Cr₁N₄ C moiety can break the electron localization around the planar Cr₁N₄ active center, which facilitated the rate-limiting reductive release of OH* and accelerated overall ORR process. The present work opens up a new avenue to modulate the axial ligand type of the single-atoms (SAs) active center to enhance intrinsic SAs performances.     

Gradient-Concentration Design of Stable Core–Shell Nanostructure for Acidic Oxygen Reduction Electrocatalysis

Manipulating the surface structure of electrocatalysts at the atomic level is of primary importance to simultaneously achieve the activity and stability dual-criteria in oxygen reduction reaction (ORR) for proton exchange membrane fuel cells. Here, a durable acidic ORR electrocatalyst with the “defective-armored” structure of Pt shell and Pt–Ni core nanoparticle decorated on graphene (Pt–Ni@Pt_D/G) using a facile and controllable galvanic replacement reaction to generate gradient distribution of Pt–Ni composition from surface to interior, followed by a partial dealloying approach, leaching the minor nickel atoms on the surface to generate defective Pt skeleton shell, is reported. The Pt–Ni@Pt_D/G catalyst shows impressive performance for ORR in acidic (0.1 m HClO₄) electrolyte, with a high mass activity of threefold higher than that of Pt/C catalyst owing to the tuned electronic structure of locally concave Pt surface sites through synergetic contributions of Pt–Ni core and defective Pt shell. More importantly, the electrochemically active surface areas still retain 96% after 20 000 potential cycles, attributing to the Pt atomic shell acting as the protective “armor” to prevent interior Ni atoms from further dissolution during the long-term operation.     

Metallic Metastable Hybrid 1T′/1T Phase Triggered Co,P?SnS2 Nanosheets for High Efficiency Trifunctional Electrocatalyst

The development of trifunctional electrocatalyst for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) with deeply understanding the mechanism to enhance the electrochemical performance is still a challenging task. In this work, the distorted metastable hybrid-phase induced 1T′/1T Co,P SnS₂ nanosheets on carbon cloth (1T′/1T Co,P SnS₂@CC) is prepared and examined. The density functional theoretical (DFT) calculation suggests that the distorted 1T′/1T Co,P SnS₂ can provide excellent conductivity and strong hydrogen adsorption ability. The electronic structure tuning and enhancement mechanism of electrochemical performance are investigated and discussed. The optimal 1T′/1T Co,P SnS₂@CC catalyst exhibits low overpotential of ≈94 and 219.7 mV at 10 mA cm⁻² for HER and OER, respectively. Remarkably, the catalyst exhibits exceptional ORR activity with small onset potential value (≈0.94 V) and half-wave potential (≈0.87 V). Most significantly, the 1T′/1T Co,P SnS₂||Co,P SnS₂ electrolyzer required small cell voltages of ≈1.53, 1.70, and 1.82 V at 10, 100, and 400 mA cm⁻², respectively, which are better than those of state-of-the-art Pt-C||RuO₂ (≈1.56 and 1.84 V at 10 and 100 mA cm⁻²). The present study suggests a new approach for the preparation of large-scalable, high performance hierarchical 3D next-generation trifunctional 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.

     

A General Method for Transition Metal Single Atoms Anchored on Honeycomb-Like Nitrogen-Doped Carbon Nanosheets

Excavating and developing highly efficient and cost-effective nonnoble metal single-atom catalysts for electrocatalytic reactions is of paramount significance but still in its infancy. Herein, reported is a general NaCl template-assisted strategy for rationally designing and preparing a series of isolated transition metal single atoms (Fe/Co/Ni) anchored on honeycomb-like nitrogen-doped carbon matrix (M₁-HNC-T₁-T₂, M = Fe/Co/Ni, T₁ = 500 °C, T₂ = 850 °C). The resulting M₁-HNC-500-850 with M-N₄ active sites exhibits superior capability for oxygen reduction reaction (ORR) with the half-wave potential order of Fe₁-HNC-500-850 > Co₁-HNC-500-850 > Ni₁-HNC-500-850, in which Fe₁-HNC-500-850 shows better performance than commercial Pt/C. Density functional theory calculations reveal a choice strategy that the strong p–d-coupled spatial charge separation results the Fe-N₄ effectively merges active electrons for elevating d-band activity in a van-Hove singularity like character. This essentially generalizes an optimal electronic exchange-and-transfer (ExT) capability for boosting sluggish alkaline ORR activity. This work not only presents a universal strategy for preparing single-atom electrocatalyst to accelerate the kinetics of cathodic ORR but also provides an insight into the relationship between the electronic structure and the electrocatalytical activity.     

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.