Potential For Oxygen Reduction Reaction Research Articles

A first principles analysis of potential-dependent structural evolution of active sites in Fe-N-C catalysts.

Fe-N-C (iron-nitrogen-carbon) electrocatalysts have emerged as potential alternatives to precious metal-based materials for the oxygen reduction reaction (ORR). However, the structure of these materials under electrochemical conditions is not well understood, and their poor stability in acidic environments poses a formidable challenge for successful adoption in commercial fuel cells. To provide molecular-level insights into these complex phenomena, we combine periodic density functional theory (DFT) calculations, exhaustive treatment of coadsorption effects for ORR reaction intermediates, including O and OH, and comprehensive analysis of solvation stabilization effects to construct voltage-dependent ab initio thermodynamic phase diagrams that describe the in situ structure of the active sites. These structures are further linked to activity and stability descriptors that can be compared with experimental parameters such as the half-wave potential for ORR and the onset potential for carbon corrosion and CO2 evolution. The results indicate that pyridinic Fe sites at zigzag carbon edges, as well as other edge sites, exhibit high activity for ORR compared to sites in the bulk. However, edges neighboring the active sites are prone to instability via overoxidation and consequent site loss. The results suggest that it could be beneficial to synthesize Fe-N-C catalysts with small sizes and large perimeter edge lengths to enhance ORR activity, while voltage fluctuations should be limited during fuel cell operation to prevent carbon corrosion of overoxidized edges.

Carbon-isolation induced indirect metal-metal interaction regulates the effect of hierarchical cobalt core on anchored palladium for bifunctional oxygen electrocatalysis

Herein, palladium (Pd)-anchored hierarchical structure metallic Co coated by nitrogen-doped carbon (Pd-NC/Co HS) is constructed as a bifunctional catalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). For Pd-NC/Co HS, the carbon shell isolates the metallic Co core from the electrolyte for avoiding corrosion, while the hierarchical metallic Co enhances the overall structural stability, mass transmission, and intrinsic electron transfer for beneficial electrocatalysis. Notably, the metallic Co core underneath carbon suitably tunes the microstructure of interface Pd nanocrystals, forming electron-deficient Pd2+ which is highly active for OER. Moreover, this carbon-isolation induced indirect metal–metal interaction (IMMI) between metallic Co core and Pd boosts the ORR of the hybrid Pd-NC/Co HS. Theoretical calculations further show that, compared to Pd/C, Pd-NC/Co HS possesses an obvious decreased energy barrier for ORR potential limiting step of *OH desorption and for OER potential limiting step of the conversion from *OH to *O, further confirming the appropriate regulation of Co on Pd via carbon shell. The zinc-air battery (168.25 mW/cm2) and magnesium-air battery (89.98 mW/cm2) driven by Pd-NC/Co HS deliver a higher peak power density than the one driven by precious metal catalysts, along with a longer operation time, showing promising application potentials.

Ni dispersed ultrathin carbon nanosheets as bi-functional oxygen electrocatalyst induced from graphite-like porous supramolecule

Excellent porosity and accessibility are key requirements during carbon-based materials design for energy conversion applications. Herein, a Ni-based porous supramolecular framework with graphite-like morphology (Ni-SOF) was rationally designed as a carbon precursor. Ultrathin carbon nanosheets dispersed with Ni nanoparticles and Ni-Nx sites (Ni@NiNx-N-C) were obtained via in-situ exfoliation during pyrolysis. Due to the hetero-porous structure succeeding from Ni-SOF, the Ni@NiNx-N-C catalyst showed outstanding bifunctional oxygen electrocatalytic activity with a narrow gap of 0.69 V between potential to deliver 10 mA cm−2 oxygen evolution and half-wave potential of oxygen reduction reaction, which even surpassed the Pt/C + IrO2 pair. Therefore, the corresponding zinc-air battery exhibited excellent power output and stability. The multiple Ni-based active sites, the unique 2D structure with a high graphitization degree and large specific surface area synergistically contributed to the excellent bifunctional electrocatalytic activity of Ni@NiNx-N-C. This work provided a novel viewpoint for the development of carbon-based electrocatalyst.

Nitrogen doping regulates microcrystal structure of interconnected Mn oxide particles/rods for oxygen reduction electrocatalysis

Manganese (Mn) oxide possessing considerable catalytic activity toward oxygen reduction reaction (ORR) exhibits promising potential in driving energy conversion technologies. However, small specific surface area, poor electron conductivity, and more importantly uncontrollable microgeometry of crystal greatly restraint their activity. Herein, a crystal regulation strategy induced by nitrogen doping is developed to construct interconnected Mn oxide nano-particles/rods (N-MnOx-Y) with different contents of [MnO6] octahedron for ORR. In N-MnOx-Y, "Y" refers to the mass ratio of melamine to α-MnO2 nanorods during calcination. Nitrogen doping induced increased content of crystalline [MnO6] octahedron is the primary factor boosting the intrinsic activity of N-MnOx-Y. The overall activity of N-MnOx-Y is also determined by electrochemically active area (ECSA) which is closely related to nitrogen doping. The crystal optimal N-MnOx-30 with high content of crystalline [MnO6] octahedron and large ECSA exhibits the highest half-wave potential for ORR and the largest kinetic current density (jk) among the N-MnOx-Y catalysts. When used as a cathodic catalyst, a homemade zinc-air battery driven by N-MnOx-30 delivers a peak power density higher than the one driven by Pt/C, along with better rate performance and a larger discharging specific capacity. This impressive electrocatalytic performance of N-MnOx-30 superior to Pt/C originates from the synergistic effect between crystalline [MnO6] octahedron, active area exposure, oxygen vacancy, Mn-N sites, and the three-dimensional hierarchical structure, which benefiting electronic/mass transmission and structural stability. This work offers a feasible strategy for constructing hierarchical and crystal tunable metal oxides electrocatalysts for efficient energy conversion.

Boosting the bifunctional electrocatalytic activity of nitrogen-doped graphene by electronic effect of heterovalent ion substituted perovskite oxides

Sluggish reaction kinetics of carbon-based catalysts hinder their activity in oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), which further impede commercialization of Zinc-air batteries. Here, a strategy of modifying the electronic structure of nitrogen-doped graphene (NG) through constructing it with cobalt (Co) substituted manganese-based perovskite oxides (LaMn1-xCoxO3) to accelerate its activity in OER and ORR is proposed. Co substitution is beneficial for donating electrons to oxygen-containing intermediates by inducing excessive negative charge on NG to improve kinetics in OER and ORR. The half-wave potential in ORR for LaMn0·6Co0·4O3@NG is 0.74 V, higher than that of LaMnO3@NG and LaCoO3@NG; the overpotential of LaMn0·6Co0·4O3@NG at 10 mA cm−2 is 314 mV for OER, smaller than that of LaMnO3@NG and LaCoO3@NG, supposing the superior electrochemical activity of composite catalyst with Co substitution in OER and ORR. This research offers a way in fabricating high efficient and cost-effective bifunctional electrocatalyst for Zinc-air batteries.

FeNC Catalysts with High Catalytic Activity and Stability for Oxygen Reduction Reaction

Although Pt-based catalysts have been considered as the most effective electrocatalyst for the cathodic oxygen reduction reaction (ORR) of direct methanol fuel cells (DMFCs), they still suffer from the drawbacks of high cost, poor long-term stability and methanol/ CO poisoning effects. Thus, developing low-cost ORR catalysts with high efficiency, durability and antipoisoning ability is of paramount importance. Herein, a series of non-noble metal FeNC materials are prepared through a facile pyrolysis process and used as the electrocatalysts toward ORR in alkaline electrolyte. Results show that the Fe0.50NC-800-1h catalyst pyrolyzed at 800 ºC for 1 h with the mass ratio of Fe(NO3)3•6H2O to melamine being 0.50 exhibits the highest catalytic performance among the as-prepared FeNC catalysts. The half-wave potential of ORR is ca. 0.81 V, which is only 38 mV lower than that on the noble metal Pt/C catalyst. Besides, it also displays higher stability and methanol tolerance than Pt/C. There is almost no change in the current during the chronoamperometric test when methanol is added in the electrolyte whereas significant decrease is found on Pt/C catalyst. This study of FeNC catalysts provides new insights on understanding the ORR mechanism and suggests a promising strategy to develop low-cost and highly efficient non-noble metal electrocatalysts for ORR.

MOF衍生的单原子催化剂中γN原子在ORR反应中的远程作用及其调制机制

The development of fuel cells is conducive to achieving carbon peaking and carbon neutrality goals, but the oxygen reduction reaction (ORR) of its cathodes is still kinetically slow due to multi-step proton-coupled electron transfer. Currently, metal-organic frameworks-derived single-atom catalysts (SACs) are emerging as efficient ORR catalysts. However, the outer layer structure of the active site is difficult to be determined, resulting in the uncertainty of the reaction mechanism. Here, the dual effect of the outer γN atom on its neighboring βC atom and the distant metal center was investigated. The results show that the doping of γN with different locations and amounts changes the electronic configuration of the replaced C sites in Fe-N4/C-γNx structures, which in turn affects the charge distribution of the βC atom closer to the metal center. And these changes indirectly affect the electron distribution and spin of the metal center through long-range effects, significantly enhancing the ORR performance of the 4-e− paths. More importantly, the electronegativity-enhanced βC atoms are thus more likely to adsorb the OH moiety in alkaline electrolyte typically used in experiments. Thus, a γN-modulated βC-assisted pathway was predicted and a higher thermodynamic limiting potential of ORR than that of the common 4-e− pathway was achieved. Further wavefunction analysis, based on the potential limiting steps, provided an understanding on the electronic level and revealed the significance of precise design and characteristics of γN site in analogous SACs.

Activity promotion of bifunctional catalysis by Se-doping and the application in rechargeable zinc-air batteries

Efficient bifunctional catalysts capable of catalyzing both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are required for the air electrode. Herein, the Se-doped FeNiP nanoparticles/N, P dual-doped carbon composite catalysts (FeNiP/SeNPC-2) were developed. The Se elements combine with various elements to form a compact heterogeneous material. At the same time, the Se-doping have modulated the crystal and surface structures, which have improved the catalytic activities of ORR and OER. The overpotential of OER was significantly negatively shifted, accompanied by a significant positive shift of the onset potential of ORR. FeNiP/SeNPC-2 has displayed an overpotential of 269 mV at the current density of 10 mA cm−2 for OER, and with a high half-wave potential (0.86 V) of ORR. The liquid zinc-air battery assembled using FeNiP/SeNPC-2 exhibited a power density of 171 mW cm−2 and stably charge-discharge cycled for 150 h. The solid-state zinc-air battery exhibited a power density of 88 mW cm−2 and stably charge-discharge cycled for 42 h. Subsequently, the solid-state zinc-air batteries of cylindrical hollow design are integrated as modules for driving devices.

Boosting the Electrocatalytic Performance of CoPt Alloy with Enhanced Electron Transfer via Atomically Dispersed Cobalt Sites.

Designing electrocatalysts with strong electronic metal-support interaction can effectively regulate the electronic properties of metal active centers, therefore maximizing the catalytic performance. As a proof of concept, heteroatoms doped carbon with CoPt alloy and isolated Co single atoms (CoPtCoSA@NSC) are synthesized using CoPt bimetallic metal-organic framework as the precursor in this work. The existence of CoSA on the carbon substrate leads to more electron transfer between CoPt and the support, and appropriate upward shift of the d band center of the catalysts, which can effectively reduce the reaction barrier of rate determine step and boost the catalytic performance of CoPt alloy. The enhanced catalytic activity and stability of CoPtCoSA@NSC are demonstrated experimentally. Remarkably, the overpotential for hydrogen evolution reaction is only 23mV at 10mAcm-2 and the half-wave potential for oxygen reduction reaction is 0.90V, both exceeding the commercial Pt/C benchmark. In addition, CoPtCoSA@NSC also exhibits great potential as a cathode electrocatalyst for Zn-air battery, in terms of large open circuit potential of 1.53V, high power density of 184mWcm-2 , as well as superior cycling stability. This work provides a novel strategy for regulating the electronic structure and catalytic performance of alloy based electrocatalysts.

Ag Anchored Atomically Around Nanopores of Porous Co(OH)2 for Efficient Bifunctional Oxygen Catalysis

AbstractVarious clean energy storage and conversion systems highly depend on rational design of efficient electrocatalysts for oxygen reactions. Increasing both gas molecular diffusion and intrinsic activity is critical to boosting its efficiency for bifunctional oxygen electrocatalysis. However, controllable synthesis of catalysts that combines gas molecular diffusion and intrinsic activity remains a fundamental challenge. Herein, a two‐step synthetic strategy is adopted to fabricate a composite oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) bifunctional catalyst (P‐Ag‐Co(OH)2), of which, atomic Ag is anchored in reactive oxygen atoms around nanopores of Co(OH)2 nanosheets. Abundant nanopores provide enough gas molecular diffusion channels, and the special Ag‐O‐Co‐OH catalytic groups around nanopores display high intrinsic catalytic activity, which jointly result in an excellent ORR/OER performance. In alkaline electrolyte, P‐Ag‐Co(OH)2 displays a high half‐wave potential (0.902 V versus RHE) for ORR, and a low overpotential (235 mV at 10 mA cm−2) for OER, which is superior to non‐noble catalysts in previous studies and Pt/C (Ir/C) catalyst. At the same time, the single‐cell zinc‐air battery is prepared with an extremely high discharge peak power density of 435 mW cm−2 and excellent discharge–charge cycle stability.

Electrodeposition of bimetal Ni-Co oxide as a bifunctional electrocatalyst for rechargeable zinc air battery

Zinc air battery is a promising candidate green energy storage due to its high energy density and low-cost. However, most of the preparation of air cathode in the literature involves a lengthy and inefficient process of mixing catalyst powders with a polymeric binder. Herein, we synthesize bimetal Ni-Co oxide through a simple electrodeposition technique followed by annealing at a low temperature under atmospheric conditions. The addition of cobalt at various contents significantly alters surface morphology from tiny nanoparticles to a 2D nano-sheet structure. The performance of the as-prepared catalysts were firstly evaluated toward the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in alkaline solution. Our results show that the incorporating cobalt in the NiO host structure not only improve the OER but also the ORR activities. The required potential to drive OER at a current density of 10 mA/cm2 and the half-wave potential for ORR using the NC-2 catalyst are 1.567 and 0.855 V vs. RHE, respectively, resulting a delta potential of 0.712 V. Furthermore, we demonstrate the practical application of the NC-2 catalyst as the air cathode electrode for assembling a liquid zinc air battery device. The battery test reveals that NC-2 has an open circuit potential of 1.36 V and a specific capacity of 714 mAh/gZn with an excellent stability performance for about 80 h. Our findings suggest that bimetal Ni-Co oxide is a promising catalyst for enhancing the performance of zinc air batteries.

“Substituents optimization” and “push effect” dual strategy for design of cobalt phthalocyanine catalyst on oxygen reduction reaction

Molecular metallocycle electrocatalysts like metalloporphyrins and metallophthalocyanines were found to be effective for oxygen reduction reaction (ORR) due to their M–N4 active sites and large conjugated electronic molecular structures. Herein, the “substituents optimization” strategy combined with “push effect” modification was innovatively employed to target a single Co–N4 active site in three substituted phthalocyaninato cobalt complexes: tetranitrophthalocyaninato cobalt (CoTNPc), tetra(4-nitrophenoxy) phthalocyaninato cobalt (CoTPNPc), and tetraphenoxy phthalocyaninato cobalt (CoTPPc) electrocatalyst, also with 4-phenylpyridine axial coordination on Co–N4 unit. Through substituents screening, the half-wave potential (E1/2) for ORR increases in the order of CoTPNPc (0.75 V) < CoTPPc (0.80 V) < CoTNPc (0.83 V) along with decreased electron-withdrawing ability of their substituents from –OC6H4–NO2, –OC6H5 to –NO2 in the three cobalt phthalocyanine derivatives. CoTNPc with the weakest electron-withdrawing substituent exhibits the best ORR performance among the three compounds. This is attributed to its higher electron delocalization and lifted HOMO energy level with the lower energy barrier in the rate-determining step relative to the other two compounds, which facilitate the electron transfer and reduction of oxygen as evidenced by XPS, UPS, and DRS analysis combined with DFT calculations. Further coordination of 4-phenylpyridine shifts the E1/2 up to 0.78, 0.82, and 0.85 V for CoTPNPc, CoTPPc, and CoTNPc. DFT calculations demonstrate that the introduction of the electron-donating phenylpyridine ligand into the cobalt phthalocyanines breaks the symmetry of the Co–N4 center and also raises the electron density of Co sites, which promotes O2 adsorption and improves ORR performance. After comparing the two strategies, the substituents on metallophthalocyanine are more determined by the electroactivity than the axial group, which directly regulates the coordination environment and then the activation barrier of the ORR process. This work provides theoretical and experimental guidance by two coupling strategies for the design of highly active molecular CoPc-based ORR electrocatalysts in the practical application.

Three-dimensional urchin-like N/S co-doped Mn-based metal-organic frameworks for efficiently enabling oxygen reduction reaction

The exploration of economical and effective non-noble metal catalysts is essential for oxygen reduction reaction (ORR) in energy devices. Recently, heteroatom-doped metal-organic frameworks (MOFs) have shown great potential in ORR due to their high efficiencies and low costs. Herein, three-dimensional (3D) urchin-like N/S co-doped Mn-based MOFs (U–N/S–Mn-MOFs) as an effective ORR catalyst have been successfully prepared by a facile one-step solvothermal methodology. The unique 3D urchin-like structure with a spherical interior and dendritic exterior may provide more catalytic sites and transport channels for ORR. Simultaneously, the doped N and S combined with Mn can promote oxygen adsorption and reduce the reaction energy barrier. These characteristics endow U–N/S–Mn-MOFs with high ORR performance. The present work provides a new opportunity for multiple heteroatom-doped MOFs to achieve high electrocatalytic performance.

Potential-Dependent Oxygen Reduction on FeN4 under Explicit Solvation Environment

Atomically dispersed FeN4 catalysts have been considered promising materials to replace the expensive Pt-based catalysts for oxygen reduction reaction (ORR), the development of which requires a fundamental understanding of the mechanism underlying their catalytic activity. Herein, we simulate the potential-dependent ORR process via density functional theory calculations and find that the O2 adsorption step becomes the rate-determining step (RDS) at slightly higher applied voltages and the onset potential is 0.8 V, which is because the substrate (*) and *OH intermediates are stabilized at constant potential states (CPS), yet the O2 adsorption becomes thermodynamically unfavorable compared to that at neutral charge states (NCS). The weakened O2 adsorption is attributed to the adjusted Fermi level at CPS that broadens the density of state distribution of the Fe 3d orbital. The determined RDS and the onset potential of ORR over FeN4 by performing potential-dependent simulations agree well with experimental findings, which improves the understanding of the ORR catalytic activity at applied potentials.

Cobalt atoms anchored on nitrogen-doped hollow carbon spheres for efficient electrocatalysis of oxygen reduction to H2O2

Electrochemical production of hydrogen peroxide (H2O2) from oxygen reduction reaction (ORR) is a promising alternative to the costly anthraquinone method. However, the sluggish kinetics of ORR on most electrocatalysts restricts its wide application. Therefore, exploring electrocatalysts with high activity and selectivity for two–electron ORR is significant. Herein, cobalt atoms anchored on nitrogen-doped hollow carbon spheres (Co–NHCS) are presented for H2O2 electrosynthesis. The Co–NHCS catalyst exhibits excellent H2O2 electrosynthesis performance in acidic media with high reactivity with an ORR potential of 0.581 V at 1.0 mA cm−2 and H2O2 selectivity up to 90%. Moreover, the H2O2 output in the assembled device reaches 2980 mg l−1 h−1 with high Faraday efficiency. The enhanced performance of Co–NHCS originates from the hollow structure and center sites of Co introduction. This work affords a facile strategy for the fabrication of high-efficient carbon-based materials for H2O2 electrosynthesis.

A Fe-Ni-Zn triple single-atom catalyst for efficient oxygen reduction and oxygen evolution reaction in rechargeable Zn-air batteries

The rechargeable Zn-air battery (ZAB) is a promising device for energy storage. A good bifunctional catalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) plays a decisive role in the ZAB. Here, we prepare a Fe-Ni-Zn triple single-atom catalyst (SAC) anchored in the nitrogen-doped porous carbon framework (NC) denoted as SAC(Fe, Ni, Zn)/NC or A-SAC(Fe, Ni, Zn)/NC (ammonia-treated) for the ZAB study. We found that not only Fe-Nx, Ni-Nx, and Zn-Nx act as excellent catalytic sites for ORR and OER, but the synergetic effect by the three adjacent SAC(Fe, Ni, Zn) in the NC enhances the catalytic performance. As a result, the voltage difference (ΔE) of 0.75 V is achieved (half-wave potential of ORR: 0.88 V and the potential of OER at 10 mA cm−2: 1.63 V). In the rechargeable ZAB study, the battery with the A-SAC(Fe, Ni, Zn)/NC has a good specific capacity of 809 mAh/g @ 50 mA cm−2, the excellent power density of 300 mW cm−2 @ 406 mA cm−2 and superior cycle stability (2150 cycles, 358.3 h @ 10 mA cm−2) while the all-soild-state ZAB showed promising power density of 64.5 mW cm−2 and acceptable cycling durability over 25 h@1 mA cm−2. Triple SAC(Fe, Ni, Zn) in the hierarchical porous NC possesses the bifunctional catalytic capability, high ionic diffusivity, and electron conductivity.

Small-size MOF derived highly active low-platinum catalysts for oxygen reduction reactions

Platinum catalysts derived from MOF have shown excellent potential in oxygen reduction reaction (ORR) of fuel cells. In this paper, we applied a simple and efficient synthesis method to prepare ZIF-67-Rx(x ​= ​0–4) with different sizes. Co@MOF-Rx(x ​= ​0–4) skeleton supports with carbon nanotube structure were obtained by further pyrolysis. Pt/Co@MOF-Rx(x ​= ​0–4) catalysts were synthesized by loading Co@MOF-Rx with 10% Pt. By changing the content of metal precursor, the nanometer size of ZIF-67-Rx was reduced from 722 ​nm to 93 ​nm. Pt/Co@MOF-Rx showed super high oxygen reduction activity and superior cycle stability. At 0.9 ​V, the mass activity(MA) and specific activity(SA) were 9.63 ​mA mgPt−1and 1.33 ​mA ​cm2, respectively, which were 1.54 and 1.23 times higher than those of Pt/C(20%). After 6000 cycles, it shows excellent stability than Pt/C(20%). This work brings new opportunities to design and prepare promising catalyst supports for proton exchange membrane fuel cells.

Photo Energy-Enhanced Oxygen Reduction and Evolution Kinetics in Zn-Air Batteries.

Harvesting solar energy directly to boost the sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) on an air cathode is a promising approach. Herein, we synthesize a step-scheme (S-scheme) titanium dioxide-indium selenide (TiO2-In2Se3) heterojunction catalyst. The onset potential in ORR under light illumination reaches 1.28 V and the onset potential decreases to 0.48 V in OER. When an S-scheme TiO2-In2Se3 heterojunction is exposed to light, photogenerated electrons at the conduction band (CB) of TiO2 migrate to the valence band (VB) of In2Se3 due to the built-in electric field. The photogenerated electrons with strong reduction capability on the CB of In2Se3 and the holes with strong oxidation capability on the VB of TiO2 boost the cathode reaction kinetics (ORR/OER). The excellent outcome reveals tremendous commercial potential of photo-enhanced Zn-air batteries.

Molten-salt confined synthesis of nitrogen-doped carbon nanosheets supported Co3O4 nanoparticles as a superior oxygen electrocatalyst for rechargeable Zn-air battery

Rational design and preparation of high-efficiency oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts is crucial for the large-scale practical application of rechargeable Zn-air batteries. In this work, employing a combined strategy of self-sacrificial template and molten-salt confinement effect, a facile one-step pyrolysis route has been developed to synthesize defect-rich N-doped carbon nanosheets supported Co3O4 nanoparticles (Co3O4@NCNs). The pyrolytic precursor is built up of NaCl encapsulated ZnO@zeolitic imidazolate framework-67 core-shell particles. Thanks to the pore-forming and oxygen source functions of ZnO and the confinement effect of NaCl, the holed NCNs in Co3O4@NCNs are interconnected into a 3D porous carbon structure with a high N-dopant level. The as-prepared Co3O4@NCNs catalyst exhibits excellent bifunctional ORR/OER electrocatalytic activities with a half-wave ORR potential (E1/2) of 0.84 V, an ultralow gap of 0.63 V between OER Ej = 10 mA/cm2 and ORR E1/2 potentials, and prominent long-term durability. Its rechargeable Zn-air battery displays a high power density up to 173.8 mW cm−2 and superior cycling stability. This work highlights a novel strategy for the component and architecture design of high-performance carbon-based electrocatalysts in energy conversion and storage systems.

Bulk preparation of free‐standing single‐iron‐atom catalysts directly as the air electrodes for high‐performance zinc‐air batteries

AbstractThe keen interest in fuel cells and metal‐air batteries stimulates a great deal of research on the development of a cost‐efficient and high‐performance catalyst as an alternative to traditional Pt to boost the sluggish oxygen reduction reaction (ORR) at the cathode. Herein, we report a facile and scalable strategy for the large‐scale preparation of a free‐standing and flexible porous atomically dispersed Fe–N‐doped carbon microtube (FeSAC/PCMT) sponge. Benefiting from its unique structure that greatly facilitates the catalytic kinetics, mass transport, and electron transfer, our FeSAC/PCMT electrode exhibits excellent performance with an ORR potential of 0.942 V at −3 mA cm−2. When the FeSAC/PCMT sponge was directly used as an oxygen electrode for liquid‐state and flexible solid‐state zinc‐air batteries, high peak power densities of 183.1 and 58.0 mW cm−2 were respectively achieved, better than its powdery counterpart and commercial Pt/C catalyst. Experimental and theoretical investigation results demonstrate that such ultrahigh ORR performance can be attributed to atomically dispersed Fe–N5 species in FeSAC/PCMT. This study presents a cost‐effective and scalable strategy for the fabrication of highly efficient and flexible oxygen electrodes, provides a significant new insight into the catalytic mechanisms, and helps to realize significant advances in energy devices.