Oxygen Reduction Reaction Kinetics Research Articles

Atomically dispersed dual iron and manganese anchored nitrogen doped reduced graphene as robust cathode catalyst for direct methanol fuel cell and aluminium air battery

A noble metal-free atomically dispersed dual metal (Fe and Mn) anchored nitrogen (N)-doped reduced graphene oxide (rGO) is synthesized as a high-performance oxygen reduction reaction (ORR) electrocatalyst for alkaline direct methanol fuel cell and aluminium-air battery (AAB). The as-synthesized FeMn-NrGO catalyst exhibits a half-wave potential of 0.84 V for ORR and a low onset potential of 0.96 Vvs (RHE). The theoretical study reveals that the synergetic coupling of Mn and Fe with pyridinic and pyrrolic nitrogen weakening adsorption bond strength of the O* intermediates to the active site of the catalyst, thereby improving the for ORR performance. The synthesized Fe3Mn1-NrGO cathode catalyst assembled alkaline direct methanol fuel cell (DMFC) demonstrates a peak power density of 65 mW/cm2 extending an effective strategy to enhance the ORR kinetics of the non-noble metal-based catalyst for fuel cell application. Furthermore, the synthesized Fe3Mn1-NrGO also exhibits excellent ORR activity in 3.5 wt% NaCl solution and demonstrates a peak power density of 11.2 mW/cm2 aqueous NaCl electrolyte-based AAB system.

Enhanced Oxygen Accumulation for a Hydrophobic Cathode in Lean-Oxygen Seawater Batteries.

The unsatisfactory oxygen reduction reaction (ORR) kinetics caused by the inherent lean-oxygen marine environment brings low power density for metal-dissolved oxygen seawater batteries (SWBs). In this study, we propose a seawater/electrode interfacial engineering strategy by constructing a hydrophobic coating to realize enhanced mass transfer of dissolved oxygen for the fully immersed cathode of SWBs. Accumulation of dissolved oxygen from seawater to the catalyst is particularly beneficial for improving the ORR performance under lean-oxygen conditions. As a result, SWB assembled with a hydrophobic cathode achieved a power density of up to 2.32 mW cm-2 and sustained discharge at 1.3 V for 250 h. Remarkably, even in environments with an oxygen concentration of 4 mg L-1, it can operate at a voltage approximately 100 mV higher than that of an unmodified SWB. The introduction of a hydrophobic interface enhances the discharge voltage and power of SWBs by improving interfacial oxygen mass transfer, providing new insights into improving the underwater ORR performance for practical SWBs.

Fabrication of biocarbon catalyst for ORR by modulating the cellulose fraction of wheat stalk

Direct Methanol fuel cells (DMFC) have been limited in their utilization due to their slow cathodic oxygen reduction reaction (ORR) kinetics and the expensive cost of commercial Pt/C catalysts. It is critical to design an oxygen reduction process with high-efficiency catalysts. An approach for modulating the ratio of cellulose, hemicellulose, and lignin in the wheat stalk (WS)/wheat stalk binder (WS binder) precursor materials is proposed in this work. WS binder from alkalization and hydrothermal treatment was added to the WS to change the structure and shape of WS-based carbon materials by varying the ratios, which increased the ORR catalytic activity. The half-wave potential (E1/2) of the produced carbon material (15 wt% N/C (WS)) is 0.76 V, which was enhanced by 80 mV by adjusting the ratio of the WS/WS binder compared to 0 wt% N/C(WS). The E1/2 of 15 wt% Fe–N/C (WS) (0.85 V) was greater than that of commercial Pt/C (0.84 V). Besides, its catalytic oxygen reduction process was close to the 4-electron transfer pathway and had good methanol tolerance. The power density obtained with a cathode catalyst of 15 wt% Fe–N/C (WS) for DMFC was 1.39 mW cm−2 at 30 °C and 3.33 mW cm−2 at 60 °C. At different temperatures, the power densities were 1.59 and 1.54 times greater than those of commercial Pt/C catalysts, respectively.

Efficient industrial-current-density H2O2 production in neutral medium via external-shell boron regulation on single-atom VN4 sites

The unamiable electrolyte environment and insufficient kinetics of electrochemical two-electron oxygen reduction reaction (2e− ORR) hinders its application in producing H2O2. To address this issue, nitrogen-coordinated single atom vanadium with external shell boron regulation is designed for efficient H2O2 production in neutral medium. The optimal catalyst VN4B/NC showcase a 2e− ORR pathway selectivity of 96.6 % in 0.1 M Na2SO4. And the high current density (1.1 A cm−2) and excellent production rate (16.23 mmol cm−1 h−1) in flow cell further confirm its superior activity. Moreover, VN4B/NC exhibits potential application in solid electrolyte reactor, which is demonstrated by the production rate of 10.18 mmol cm−1 h−1 and long-term stability up to 100 h. Mechanism study suggest the external shell B regulation optimize the adsorption of OOH* intermediates on V sites, boosting the 2e− ORR pathway. This work provides novel insights to rational design of electrocatalysts for commodity chemicals production.

Phosphorus-Doping Enables the Superior Durability of a Palladium Electrocatalyst towards Alkaline Oxygen Reduction Reactions.

The sluggish kinetics of oxygen reduction reactions (ORRs) require considerable Pd in the cathode, hindering the widespread of alkaline fuel cells (AFCs). By alloying Pd with transition metals, the oxygen reduction reaction's catalytic properties can be substantially enhanced. Nevertheless, the utilization of Pd-transition metal alloys in fuel cells is significantly constrained by their inadequate long-term durability due to the propensity of transition metals to leach. In this study, a nonmetallic doping strategy was devised and implemented to produce a Pd catalyst doped with P that exhibited exceptional durability towards ORRs. Pd3P0.95 with an average size of 6.41 nm was synthesized by the heat-treatment phosphorization of Pd nanoparticles followed by acid etching. After P-doping, the size of the Pd nanoparticles increased from 5.37 nm to 6.41 nm, and the initial mass activity (MA) of Pd3P0.95/NC reached 0.175 A mgPd-1 at 0.9 V, slightly lower than that of Pd/C. However, after 40,000 cycles of accelerated durability testing, instead of decreasing, the MA of Pd3P0.95/NC increased by 6.3% while the MA loss of Pd/C was 38.3%. The durability was primarily ascribed to the electronic structure effect and the aggregation resistance of the Pd nanoparticles. This research also establishes a foundation for the development of Pd-based ORR catalysts and offers a direction for the future advancement of catalysts designed for practical applications in AFCs.

Insightful Understanding of Synergistic Oxygen Reduction on PtCo3(111) Toward Zinc-Air Batteries.

Theory-guided materials design is an effective strategy for designing catalysts with high intrinsic activity whilst minimizing the usage of expensive metals like platinum. As proof-of-concept, herein it demonstrates that using density functional theory (DFT) calculations and experimental validation that intermetallic PtCo3 alloy nanoparticles offer enhanced electrocatatalytic performance for the oxygen reduction reaction (ORR) compared to Pt nanoparticles. DFT calculations established that PtCo3(111) surfaces possess better intrinsic ORR activity compared to Pt(111) surfaces, owing to the synergistic action of adjacent Pt and Co active sites which optimizes the binding strength of ORR intermediates to boost overall ORR kinetics. With this understanding, a PtCo3/NC catalyst, comprising PtCo3 nanoparticles exposing predominantly (111) facets dispersed on an N-doped carbon support, is successfully fabricated. PtCo3/NC demonstrates a high specific activity (3.4mAcm-2mgPt -1), mass activity (0.67AmgPt -1), and cycling stability for the ORR in 0.1M KOH, significantly outperforming a commercial 20wt.% Pt/C catalyst. Moreover, a zinc-air battery (ZAB) assembled with PtCo3/NC as the air-electrode catalyst delivered an open-circuit voltage of 1.47V, a specific capacity of 775.1mAhgZn -1 and excellent operation durability after 200 discharge/charge cycles, vastly superior performance to a ZAB built using commercial Pt/C+IrO2 as the air-electrode catalyst.

Single-atom Mn sites confined into hierarchically porous core–shell nanostructures for improved catalysis of oxygen reduction

Applications of zinc-air batteries are partially limited by the slow kinetics of oxygen reduction reaction (ORR); Thus, developing effective strategies to address the compatibility issue between performance and stability is crucial, yet it remains a significant challenge. Here, we propose an in situ gas etching-thermal assembly strategy with an in situ-grown graphene-like shell that will favor Mn anchoring. Gas etching allows for the simultaneous creation of mesopore-dominated carbon cores and ultrathin carbon layer shells adorned entirely with highly dispersed Mn-N4 single-atom sites. This approach effectively resolves the compatibility issue between activity and stability in a single step. The unique core–shell structure allows for the full exposure of active sites and effectively prevents the agglomerations and dissolution of Mn-N4 sites in cores. The corresponding half-wave potential for ORR is up to 0.875 V (vs. reversible hydrogen electrode (RHE)) in 0.1 M KOH. The gained catalyst (Mn-N@Gra-L)-assembled zinc-air battery has a high peak power density (242 mW cm−2) and a durability of ∼ 115 h. Furthermore, replacing the zinc anode achieved a stable cyclic discharge platform of ∼ 20 h at varying current densities. Forming more fully exposed and stable existing Mn-N4 sites is a governing factor for improving the electrocatalytic ORR activity, significantly cycling durability, and reversibility of zinc-air batteries.

Ti Single Atom Enhancing Pt‐Based Intermetallics for Efficient and Durable Oxygen Reduction

AbstractThe insufficient durability of Pt‐based catalysts and the sluggish kinetics of oxygen reduction reaction (ORR) is hampering the development of proton exchange membrane fuel cells (PEMFCs) for commercialization. Herein, a single atom Ti‐modified activated nitrogen‐doped porous carbon (Ti‐a‐NPC) is designed to equalize O2‐activation/*OH‐removal through regulating the charge rearrangement of ultra‐small L12‐Pt3Co for efficient and durable oxygen reduction. The Ti single‐atom modified in the surface/pore of Ti‐a‐NPC can anchor the Pt‐based intermetallic nanoparticles (NPs) not only guarantees Pt‐based intermetallics’ ultra‐fine size (≈2.62 nm) but also maintains Pt‐based intermetallics during ORR process. The enhanced catalyst (L12‐Pt3Co/Ti‐a‐NPC) achieves 11‐fold mass activity (1.765 A mgPt−1) compared to commercial Pt/C. Notably, after 30 000 cycles of accelerated durability tests, the mass activity of the L12‐Pt3Co/Ti‐a‐NPC only decreased by 3.7%, while that of commercial Pt/C decreased by 37.1%. Rationalized by theoretical simulation, the introduction of Ti atoms can form charge channels between L12‐Pt3Co NPs and Ti‐a‐NPC, accelerating the charge transfer in the ORR process. Furthermore, the charge of L12‐Pt3Co will accumulate to Ti atoms and buffer the electron transfer of L12‐Pt3Co to the N atoms, thus optimizing the adsorption performance of the active site to the oxygen‐containing intermediate and improving the intrinsic activity of the catalyst.

Covalent organic framework‐derived Fe, Co‐nitrogen codoped carbon as a bifunctional electrocatalyst for rechargeable efficient Zn–air batteries

AbstractThe development of cathode materials with controllable physicochemical structures and explicit catalytic sites is important in rechargeable Zn–air batteries (ZABs). Covalent organic frameworks (COFs) have garnered increasing attention owing to their facile synthesis methods, ordered pore structure, and selectivity of functional groups. However, the sluggish kinetics of oxygen evolution reaction (OER) or oxygen reduction reaction (ORR) inhibit their practical applications in ZABs. Herein, nucleophilic substitution is adopted to synthesize pyridine bi‐triazine covalent organic framework (denoted as O‐COF), and meanwhile, ionothermal conversion synthesis is employed to load MOx (M=Fe, Co) onto carbon nanosheet (named as FeCo@NC) to modulate the electronic structure. The Fe, Co‐N codoped carbon material possesses a large portion of pyridinic N and M‐N, high graphitization, and a larger BET surface area. An outstanding bifunctional activity has been exhibited in FeCo@NC, which provides a small voltage at 10 mA cm−2 for OER (E10 = 1.67 V) and a remarkable half‐wave voltage for ORR (E1/2 = 0.86 V). More impressively, when assembling ZABs, it displays notable rate performance, significant specific capacity (783.9 mAh gZn−1), and satisfactory long‐term endurance. This method of regulating covalent organic framework and ionothermal synthesis can be extended to design diverse catalysts.

Heterostructure catalyst coupled wood-derived carbon and cobalt-iron alloy/oxide for reversible oxygen conversion

As promising energy-storage devices, zinc–air batteries (ZABs) exhibit slow reaction kinetics for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) occurring at their electrodes. High-performance bifunctional catalysts must thus be synthesized to accelerate the reversible conversion of oxygen and improve the rate and overall performance of ZABs. Herein, we reported the promising prospects of self-supported composite electrodes composed of wood-derived carbon (WDC) and bimetallic cobalt-iron alloys/oxides (CoFe-CoFe2O4@WDC) as efficient electrocatalysts for alkaline ORR/OER. WDC provided a favorable three-phase interface for heterogeneous reactions owing to its layered porous structure and genetic stability, thereby enabling mass diffusion and improving reaction kinetics. The CoFe2O4 spinel surface was reduced to bimetallic CoFe alloy to form abundant heterostructure interfaces that promote electron transfer. Under alkaline conditions, the optimized composite electrode exhibited a remarkable high half-wave potential of 0.85 V and an exceptionally low overpotential of 1.49 V. It also exhibited stable performance over an impressive 2340 cycles in a ZAB. Theoretical calculations also confirmed that the heterointerface addresses the issue of proton scarcity throughout the reaction and actively facilitates the creation of O–O bonds during the reversible transformation of oxygen. This study introduces a new concept for developing bifunctional and efficient electrocatalysts based on charcoal and encourages the sustainable and high-value use of forest biomass resources.Graphical

Bimetallic-doped three-dimensional carbon skeleton porous material as efficient catalysts for oxygen reduction reaction

The slowness of the oxygen reduction reaction (ORR) kinetics of the fuel cell cathode has terrifically inhibited its development process. Now it is of considerable importance to research low-cost, multi-defect, high-performance non-noble metal ORR catalysts. Specifically, CuO nanosheets are grown in situ on ZIF-8 to form a composite material (zif-8@CuO), and then undergo a high-temperature carbonization process. Finally, the Zn-Cu codoped composite material Zn-xCu-N/C with a porous structure supported by a three-dimensional carbon skeleton can be obtained. The material has a 3D carbon skeleton support and a rich pore structure, which can expose more active sites. The combination of bimetallic Zn and Cu with carbon materials also increases the overall stability and conductivity of the material, which is beneficial to improvement of catalytic performance. The electrochemical performance test results show that the onset potential and half-wave potential of the Zn-0.1Cu-N/C material are 0.889 V and 0.803 V respectively, with a low Tafel slope of 62 mV dec−1 and excellent long-term stability. After 10000 cycles, the ORR curve only changed 18 mV, while the carbon skeleton can still maintain unchanged.

Asymmetric Coordination of Bimetallic Fe-Co Single-Atom Pairs toward Enhanced Bifunctional Activity for Rechargeable Zinc-Air Batteries.

The advancement of rechargeable zinc-air batteries (RZABs) faces challenges from the pronounced polarization and sluggish kinetics of oxygen reduction and evolution reactions (ORR and OER). Single-atom catalysts offer an effective solution, yet their insufficient or singular catalytic activity hinders their development. In this work, a dual single-atom catalyst, FeCo-SAs, was fabricated, featuring atomically dispersed N3-Fe-Co-N4 sites on N-doped graphene nanosheets for bifunctional activity. Introducing Co into Fe single-atoms and secondary pyrolysis altered Fe coordination with N, creating an asymmetric environment that promoted charge transfer and increased the density of states near the Fermi level. This catalyst achieved a narrow potential gap of 0.616 V, with a half-wave potential of 0.884 V for ORR (vs the reversible hydrogen electrode) and a low OER overpotential of 270 mV at 10 mA cm-2. Owing to the superior activity of FeCo-SAs, RZABs exhibited a peak power density of 203.36 mW cm-2 and an extended cycle life of over 550 h, exceeding the commercial Pt/C + IrO2 catalyst. Furthermore, flexible RZABs with FeCo-SAs demonstrated the promising future of bimetallic pairs in wearable energy storage devices.

Preparation of high-performance multiphase heterostructures IT-SOFC cathode materials by Pr-induced in situ assembly

Here, in situ assembly in La0.6Sr0.4Co0.2Fe0.8O3-δ and CoFe2O4 composite (LSCFC) cathode was induced by Pr to form La0.6Sr0.4CoxFeyO3-δ/PrCoO3/Co3O4/PrO2 (LSCFC-PI) multiphase heterostructures. The surface of LSCFC-PI forms uniform nanoparticles, and the unique core-shell structure prevents Sr segregation, thereby enhancing CO2 tolerance and increasing oxygen reduction reaction (ORR) active sites. Furthermore, compared with LSCFC, LSCFC-PI increases the oxygen vacancy content of the cathode due to the existence of multiphase heterostructure, improves the ORR kinetics, and the conductivity is also greatly improved. The peak power density (PPD) of LSCFC-PI as a single-cell cathode at 700 ℃ reached 1.51 W cm−2, which was 2.65 times higher than that of LSCFC's 0.57 W cm−2, and in the long-term stability test at a constant voltage ∼0.8 V for 100 hours, showing excellent stability. In situ assembly of multiphase heterostructures is expected to become a new strategy for developing high-performance IT-SOFC cathodes.

Single-atom Al precisely modulate the strain of Pt3Co intermetallic for superior oxygen catalytic performance

Precisely controlling the strain of Pt-based intermetallic to ensure high performance and stability is a massive task for sustainable proton-exchange-membrane-fuel-cells. Herein, the Al single-atom was trapped into the L12-Pt3Co intermetallic core to precisely tailor the strain state on the Pt-skin for fast oxygen reduction reaction kinetics. Theoretical calculations firstly predicted that only tailored tension can accelerate the protonation of O2 on L12-Pt3Co@Pt without creating an additional energy barrier for subsequent oxygen-containing intermediates desorption. Experimentally, Al single-atom confined in the L12-Pt3Co lattice by substituting partial Co occupancy, imposing tailored ∼ 0.2 % tension on Pt-skin compared to the L12-Pt3Co. L12-Al-Pt3Co@Pt/C exhibits enhanced mass activity which is ten-time improvement over commercial Pt/C. More significantly, XAS and DFT results reveal that the Al single-atom can strengthen the Pt-Co bonding, enhancing the stability of L12-Al-Pt3Co@Pt/C in oxygen reduction. This work provides an avenue to design the strain by single-atom for sustainable energy conversion technologies.

Enhanced Mass Activity and Durability of Bimetallic Pt-Pd Nanoparticles on Sulfated-Zirconia-Doped Graphene Nanoplates for Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cell Applications.

Developing highly active and durable Pt-based electrocatalysts is crucial for polymer electrolyte membrane fuel cells. This study focuses on the performance of oxygen reduction reaction (ORR) electrocatalysts composed of Pt-Pd alloy nanoparticles on graphene nanoplates (GNPs) anchored with sulfated zirconia nanoparticles. The results of field emission scanning electron microscopy and transmission electron microscopy showed that Pt-Pd and S-ZrO2 are well dispersed on the surface of the GNPs. X-ray diffraction revealed that the S-ZrO2 and Pt-Pd alloy coexist in the Pt-Pd/S-ZrO2-GNP nanocomposites without affecting the crystalline lattice of Pt and the graphitic structure of the GNPs. To evaluate the electrochemical activity and reaction kinetics for ORR, we performed cyclic voltammetry, rotating disc electrode, and EIS experiments in acidic solutions at room temperature. The findings showed that Pt-Pd/S-ZrO2-GNPs exhibited a better ORR performance than the Pt-Pd catalyst on the unsulfated ZrO2-GNP support and with Pt on S-ZrO2-GNPs and commercial Pt/C.

Reverse Atom Capture on Perovskite Surface Enabling Robust and Efficient Cathode for Protonic Ceramic Fuel Cells.

Protonic ceramic fuel cells (PCFCs) hold potential for sustainable energy conversion, yet their widespread application is hindered by the sluggish kinetics and inferior stability of cathode materials. Here, a facile and efficient reverse atom capture technique is developed to manipulate the surface chemistry of PrBa0.5Sr0.5Co1.5Fe0.5O5+ δ (PBSCF) cathode for PCFCs. This method successfully captures segregated Ba and Sr cations on the PBSCF surface using W species, creating a (Ba/Sr)(Co/Fe/W)O3- δ (BSCFW)@PBSCF heterostructure. Benefiting from enhanced kinetics of proton-involved oxygen reduction reaction and strengthened chemical stability, the single cell using the optimized 2W-PBSCF cathode demonstrates an exceptional peak power density of 1.32W cm-2 at 650°C and maintains durable performance for 240h. Theoretical calculations unveil that the BSCFW perovskite delivers lower oxygen vacancy formation energy, hydration energy, and proton transfer energy compared to the PBSCF perovskite. This protocol offers new insights into advanced atom capture techniques for sustainable energy infrastructures.

A magnetic/force coupling assisted lithium-oxygen battery based on magnetostriction and piezoelectric catalysis of CoFe2O4/BiFeO3 cathode

The high energy density of Li−O2 batteries surpasses all existing batteries, and it holds the potential to emerge as the most outstanding solution for energy storage in the future. However, the insulated, insoluble discharge product (Li2O2) has impeded the practical applications. Conventional catalyst design based on electronic structure and interfacial charge transfer descriptors are incapable of overcoming these limitations of Li2O2. Herein, a magnetic/force coupling assisted Li−O2 battery based on magnetostrictive and piezoelectric catalysis with CoFe2O4/BiFeO3 core-shell structure cathode was established for the first time. An external magnetic field is introduced to produce a magnetostrictive stress on CoFe2O4, contributing to the piezoelectric electron hole transport by the generated piezoelectric potential energy with a built-in electric field based on the piezoelectric catalytic mechanism, and thus promoting the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics, and reducing the overpotential during charge/discharge. The magnetic/force coupling assisted Li−O2 battery equipped with the unique CoFe2O4/BiFeO3 cathode deliver an ultra-low charging platform of 3.49 V and an ultra-high discharge platform of 2.83 V. This unique magnetic/force assisted strategy provides an important insight into solving the high overpotential in metal-air battery systems.

Axially Modified Square-Pyramidal CoN4-F1 Sites Enabling High-Performance Zn-Air Batteries.

Cobalt-nitrogen-carbon (Co-N-C) catalysts with a CoN4 structure exhibit great potential for oxygen reduction reaction (ORR), but the imperfect adsorption energy toward oxygen species greatly limits their reduction efficiency and practical application potential. Here, F-coordinated Co-N-C catalysts with square-pyramidal CoN4-F1 configuration are successfully synthesized using F atoms to regulate the axial coordination of Co centers via hydrothermal and chemical vapor deposition methods. During the synthesis process, the geometry structure of the Co atom converts from six-coordinated Co-F6 to square-pyramidal CoN4-F1 in the coordinatively unsaturated state, which provides an open binding site for the O2. The introduction of axial F atoms into the CoN4 plane alters the local atomic environment around Co, significantly improving the ORR activity and Zn-air batteries performance. In situ spectroscopy proves that CoN4-F1 sites strongly combine with the OOH* intermediate and facilitate the splitting of O-O bond, making OOH* readily decompose into O* and OH* via a dissociative pathway. Theoretical calculations confirm that the axial F atom effectively reduces the electronic density of the Co centers and facilitates the desorption of the OH* intermediate, efficiently accelerating the overall ORR kinetics. This work advances a feasible synthesis mechanism of axial ligands and provides a route to construct efficient high-coordination catalysts.

Tailoring Oxygen Reduction Reaction Kinetics of Fe-N-C Catalyst via Spin Manipulation for Efficient Zinc-Air Batteries.

The interaction between oxygen species and metal sites of various orbitals exhibits intimate correlation with the oxygen reduction reaction (ORR) kinetics. Herein, a new approach for boosting the inherent ORR activity of atomically dispersed Fe-N-C matrix is represented by implanting Featomic clusters nearby. The as-prepared catalyst delivers excellent ORR activity with half-wave potentials of 0.78 and 0.90V in acidic and alkaline solutions, respectively. The decent ORR activity can also be validated from the high-performance rechargeable Zn-air battery. The experiments and density functional theory calculations reveal that the electron spin-state of monodispersed Fe active sites is transferred from the low spin (LS, t2g 6 eg 0) to the medium spin (MS, t2g 5 eg 1) due to the involvement of Fe atomic clusters, leading to the spin electron filling in σ∗ orbit, by which it favors OH- desorption and in turn boosts the reaction kinetics of the rate-determining step. This work paves a solid way for rational design of high-performance Fe-based single atom catalysts through spin manipulation.

Self-Catalyzed Growth of Co4N and N-Doped Carbon Nanotubes toward Bifunctional Cathode for Highly Safe and Flexible Li-Air Batteries.

The practical application of high-energy density lithium-oxygen (Li-O2) batteries is severely impeded by the notorious cycling stability and safety, which mainly comes from slow kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at cathodes, causing inferior redox overpotentials and reactive lithium metal in flammable liquid electrolyte. Herein, a bifunctional electrode, a safe gel polymer electrolyte (GPE), and a robust lithium anode are proposed to alleviate above problems. The bifunctional electrode is composed of N-doped carbon nanotubes (N-CNTs) and Co4N by in situ chemical vapor deposition self-catalyzed growth on carbon cloth (N-CNTs@Co4N@CC). The self-supporting, binder-free N-CNTs@Co4N@CC electrode has a strong and stable three-dimensional (3D) interconnected conductive structure, which provides interconnectivity between the active sites and the electrode to promote the transfer of electrons. Furthermore, the N-CNT-intertwined Co4N ensures efficient catalytic activity. Hence, the electrode demonstrates improved electrochemical properties even under a large current density (2000 mA g-1) and long cycling operation (250 cycles). Moreover, a highly safe and flexible rechargeable cell using the 3D N-CNTs@Co4N@CC electrode, GPE, and robust lithium anode design has been explored. The open circuit voltage is stable at ∼3.0 V even after 9800 cycles, which proves the mechanical durability of the integrated GPE cell. The stable cable-type Li-air battery was demonstrated to stably drive the light-emitting diodes (LEDs), highlighting the reliability for practical use.