High-performance Oxygen Reduction Reaction Research Articles

Biomass-derived single atom catalysts with phosphorus-coordinated Fe-N3P configuration for efficient oxygen reduction reaction

Exploiting non-precious metal catalysts with excellent oxygen reduction reaction (ORR) performance for energy devices is paramount essential for the green and sustainable society development. Herein, low-cost, high-performance biomass-derived ORR catalysts with an asymmetric Fe-N3P configuration was prepared by a simple pyrolysis-etching technique, where carboxymethyl cellulose (CMC) was used as the carbon source, urea and 1,10-phenanthroline iron complex (FePhen) as additives, and Na3PO4 as the phosphorus dopant and a pore-forming agent. The CMC-derived FeNPC catalyst displayed a large specific area (BET:1235 m2 g−1) with atomically dispersed Fe-N3P active sites, which exhibited superior ORR activity and stability in alkaline solution (E1/2 = 0.90 V vs. RHE) and Zn-air batteries (Pmax = 149 mW cm−2) to commercial Pt/C catalyst (E1/2 = 0.87 V, Pmax = 118 mW cm−2) under similar experimental conditions. This work provides a feasible and cost-effective route toward highly efficient ORR catalysts and their application to Zn-air batteries for energy conversion.

Ordered Pt3Ni intermetallic compound: A high-performance oxygen reduction reaction catalyst for Zn-air batteries

The development of advanced catalysts for oxygen reduction reaction (ORR) is crucial for Zinc-air batteries (ZABs). In this study, we focus on the controlled synthesis of ordered Pt3Ni intermetallic compounds through impregnation and high-temperature annealing, aiming to enhance the ORR performance for ZABs. The ordered Pt3Ni (denoted as Pt3Ni) and conventional alloy Pt3Ni (denoted as A-Pt3Ni) are synthesized at 600 ℃ and 200 ℃, respectively. Detailed structural characterizations confirm the formation of both ordered and disordered structures. Pt3Ni demonstrates superior ORR catalytic activity and stability compared to A-Pt3Ni and commercial Pt/C catalyst, as evidenced by higher half-wave potentials, lower Tafel slopes, and enhanced electrochemical stability. Furthermore, Pt3Ni exhibits exceptional performance in ZABs, with higher power density, specific capacity, and longer cycle life than its counterparts. These findings highlight the potential of ordered Pt3Ni intermetallic compounds as efficient ORR catalysts in ZABs, offering a promising route for the development of advanced energy conversion and storage systems.

A Bifunctional Iron-Nickel Oxygen Reduction/Oxygen Evolution Catalyst for High-Performance Rechargeable Zinc-Air Batteries.

Efficient and robust electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial for fuel cells, metal-air batteries, and other energy technologies. Here, a highly stable, efficient bifunctional OER/ORR electrocatalyst (FeNi-NC@MWCNTs) is reported and demonstrated its integration and robust performance in an aqueous Zinc-air battery (ZAB). The catalyst is based on neighboring iron/nickel sites (FeNiN6) which are atomically dispersed on porous nitrogen-doped carbon particles. The particles are wrapped in electrically conductive multi-walled carbon nanotubes for enhanced electrical conductivity. Electrocatalytic analyses show high OER and ORR performance (OER/ORR voltage difference = 0.69V). Catalyst integration in a ZAB results in excellent performance metrics, including an open circuit voltage of 1.44V, a specific capacity of 782 mAh g-1 (at j = 15mA cm-2), a peak power density of 218mW cm-2 (at j = 260mA cm-2) and long-term durability over 600 charge/discharge cycles. Combined experimental and theoretical (density functional theory) analyses provide an in-depth understanding of the physical and electronic structure of the catalyst and the role of the FeNi dual atom reaction site. The study therefore provides critical insights into the structure and reactivity of high-performance bifunctional OER/ORR catalysts based on atomically dispersed non-critical metals.

Engineering the Local Atomic Environments of Te-Modulated Fe Single-Atom Catalysts for High-Efficiency O2 Reduction.

Atomically dispersed metal-nitrogen-carbon materials (AD-MNCs) are considered the most promising non-precious catalysts for the oxygen reduction reaction (ORR), but it remains a major challenge for simultaneously achieving high intrinsic activity, fast mass transport, and effective utilization of the active sites within a single catalyst. Here, an AD-MNCs consisting of defect-rich Fe-N3 sites dispersed with axially coordinated Te atoms on porous carbon frameworks (Fe1Te1-900) is designed. The local charge densities and energy band structures of the neighboring Fe and Te atoms in FeN3-Te are rearranged to facilitate the catalytic conversion of the O-intermediates. Meanwhile, the negative shift of the d-band center in FeN3-Te reduces the energy barrier limit for effective desorption of the final OH* intermediate. In the electrochemical evaluation, Fe1Te1-900 presents a more positive onset potential and half-wave potentials of 1.03 and 0.89V versus the reversible hydrogen electrode, respectively. Furthermore, the liquid zinc-air batteries assembled with Fe1Te1-900 exhibited excellent performances compared to commercial Pt/C. This work opens up new ideas for the development of high-performance ORR electrocatalysts for applications in various energy conversion and storage technologies.

Rigid Ligand Confined Synthesis of Carbon Supported Dimeric Fe Sites with High-Performance Oxygen Reduction Reaction Activity for Quasi-Solid-State Rechargeable Zn-Air Batteries.

Dimeric metal sites (DiMSs) in carbon-based single atom catalysts (SACs) offer distinct advantages in optimizing the adsorption energies of the catalytic intermediates and reaction pathways over single atom sites, which inspires the investigations on the rational design of DiMSs-based SACs and the accurate discernment of catalytic mechanisms. Here, dimeric Fe sites on carbon blacks (DiFe-N/CBs) are prepared using the precursor of metal-organic complex with a controlled structure, and the rigid ligand confinement secures the preservation of dimeric Fe sites during the thermal treatment. DiFe-N/CBs shows excellent electrocatalytic performance for oxygen reduction reaction (ORR) with a high half-wave potential of 0.917 V, and excellent durability with negligible activity decay. Theoretical studies reveal that the dimeric Fe sites have an optimal adsorption of OOH* with the Yeager-type binding, illustrating the advantages of DiMSs over SAs in catalyzing ORR. The rechargeable aqueous and quasi-solid-state Zn-air batteries assembled using DiFe-N/CBs-based air cathodes achieve small voltage gaps after long term charge/discharge test, showing great promises for practical applications. This synthetic strategy serves a novel platform to produce a scope of catalysts incorporating multimeric metal sites, and studies on the catalytic mechanism lay the foundation for establishing cooperative effect for multidentate adsorption reactions.

Modulating Spin of Atomic Manganese Center for High-Performance Oxygen Reduction Reaction.

Single atom catalysts (SACs) are promising non-precious catalysts for oxygen reduction reaction (ORR). Unfortunately, the ORR SACs usually suffer from unsatisfactory activity and in particular poor stability. Herein, we report atomically dispersed manganese (Mn) embedded on nitrogen and sulfur co-doped graphene as an efficient and robust electrocatalyst for ORR in alkaline electrolyte, realizing a half-wave potential (E1/2) of 0.883 V vs. reversible hydrogen electrode (RHE) with negligible activity degradation after 40,000 cyclic voltammetry (CV) cycles in 0.1 M KOH. Introducing sulfur (S) to form Mn-S coordination changes the spin state of single Mn atom from high-spin to low-spin, verified by electron paramagnetic resonance (EPR) and magnetic susceptibility measurements as well as density functional theory (DFT) calculations, which effectively optimizes the oxygen intermediates adsorption over the single Mn atomic sites and thus greatly improves the ORR activity.

Nitrogen-doped carbon embedded with heterostructured Co3Fe7-Co5.47N nanoalloys for electrocatalytic oxygen reduction reaction in zinc-air battery

The oxygen reduction reaction (ORR) is the cathodic process in zinc-air batteries, but its sluggish kinetics significantly limit the energy conversion efficiency of these batteries. Therefore, developing high-performance ORR electrocatalysts is essential to support the advancement of zinc-air battery technology. Herein, a nitrogen-doped carbon embedded with heterostructured Co3Fe7-Co5.47N nanoalloys (FeCo@NC-900) was fabricated, and the electrocatalytic ORR activity and stability of FeCo@NC-900 were investigated in alkaline media. The FeCo@NC-900 catalyst exhibited a half-wave potential of 0.84 V, a Tafel slope of 76.06 mV·dec−1, and an electron transfer number (n) of approximately 3.83 for ORR. A rechargeable zinc-air battery was assembled using FeCo@NC-900 as the air cathode, achieving an open-circuit voltage of 1.435 V and a maximum power density of 81 mW cm−2, along with good cycling stability.

Lignin-derived Fe–N–C electrocatalyst with 3D porous structure for efficient oxygen reduction reaction

Developing low-cost, high-performance oxygen reduction reaction (ORR) catalysts is crucial for the commercialization of fuel cells and zinc-air batteries. Herein, we report a lignin-derived Fe/N co-doped 3D porous carbon electrocatalyst Fe-NLC-1 as an alternative to commercial Pt/C catalysts, which was synthesized by a green and facile in situ carbonization strategy. Fe-NLC-1 exhibits higher oxygen reduction activity with a half-wave potential (E1/2) of 0.90 V vs. RHE than commercial 20 wt% Pt/C (E1/2 = 0.85 V) in the alkaline conditions, as well as excellent methanol tolerance and stability. Furthermore, the Zn-air battery loaded with Fe-NLC-1 exhibits a maximum power density of 125 mW cm−2, an open circuit voltage of 1.477 V, and stable discharge performance, which are comparable or even better than the commercial Pt/C. This study highlights the potential of biomass-derived porous carbon materials for the development of high-performance ORR electrocatalysts.

In situ-grown nitrogen-sulfur co-doped carbon nanotubes encapsulated with FeS particles as cathode materials for zinc-air batteries

Transition metal sulfides as ideal oxygen reduction reaction (ORR) catalysts have great potential to regulate multiple reaction pathways and understand their corresponding internal reaction mechanisms at cathode in zinc-air batteries (ZABS), effectively. This work adopted a facile one-pot synthesis method based on chemical vapor deposition (CVD), which utilizes the synergistic effect of zeolite imidazolium ester skeleton (ZIF-8) and polypyrrole (PPY) to grow nitrogen-sulfur co-doped carbon nanotubes (NS-CNT) in the shape of colonic with a relatively uniform size and encapsulated with FeS nanoparticles as the main active sites. The synthesized purpose catalyst noted as FeS-NS-CNT-900, in which that the FeS nanoparticles were tightly encapsulated in carbon nanotubes, and this special structure ensures that the FeS particles do not detach during the reaction, thus greatly enhancing their electrochemical activity and stability. As expected, the FeS-NS-CNT-900 catalyst exhibited a half-wave potential of 0.877 V which is higher than that of commercial platinum charcoal (0.847 V), at 0.1 mol KOH. More importantly, the formation of abundant FeS catalytic active sites, the optimal conditions for NS-CNT growth, and the covered mechanisms of the enhanced ORR reaction activity of FeS-NS-CNT-900 were thoroughly investigated. Additionally, whileFeS-NS-CNT-900 was used as an air cathode material for the assembly of a zinc-air battery, it exhibited a peak power density and specific capacity of 123 mW cm−2 and 785.81 mA h g−1, respectively, which were significantly better than that of platinum-carbon cathode (92.8 mW cm−2 and 740.4 mA h g−1). And surprisingly, the battery with FeS-NS-CNT-900 cathode exhibited (delivered/showed) a high cycle stability of 260 h at 5 mA cm−2. Conclusively, present work provides a feasible method for in situ growth of sulfur and nitrogen co-doped carbon nanotube encapsulated transition metal sulfide nanoparticle catalysts, which may pave a new avenue for the preparation of high ORR performance air cathode material for ZABS.

Construction of Fe/Co-N4 Single-Atom Sites for the Oxygen Reduction Reaction in Zinc-Air Batteries.

Insight into the modulation effect of oxygen reduction reaction (ORR) active centers is of profound significance but remains a great challenge. Here, we designed Co, Fe dual-metal single-atom sites (CoFe-DSAs/NC) uniformly anchored on nitrogen-doped multiwalled carbon nanotubes for boosting ORR performance through regulating the 4d electronic orbitals of the Co-N4 active site. Mechanism studies revealed that for the first time the neighboring Fe-N4 atomic sites were able to regulate the d-band center of Co-N4 single-atom active centers while maintaining the balance of adsorption-desorption affinity for O2 and oxygen-containing species on Co-N4, thereby resulting in a superior ORR performance with a positive half-wave potential (0.90 V vs RHE). The assembled zinc-air battery based on CoFe-DSAs/NC exhibited an increased open-circuit voltage (1.48 V) and an elevated specific capacity (782.33 mAh·g-1). The work provides a new clue for reasonably designing high-performance ORR catalysts through adjusting the d-band center of active sites.

N, S Co-Doped Carbon Nanotubes Loaded With Cu Nanoclusters For Efficient Oxygen Reduction Reaction.

Developing highly superior precious-metal-free electrocatalysts for oxygen reduction reaction (ORR) are challenging and great significance. In this study, it is reported that an efficient ORR catalysts with N and S co-doped carbon nanotubes anchored to copper (Cu) nanoclusters by mechanical grinding and high temperature heat treatment. The obtained Cu-S1-N-C electrocatalysts exhibited a high ORR performance with an onset potential (Eonest) of 0.989 V and a half-wave potential (E1/2) of 0.905 V (vs. RHE) in alkaline electrolyte, which was superior to that of commercial Pt/C catalyst. In contrast to N doping alone, the defect structures and active species of the catalysts were optimized by precise modulation of S-atom doping, and moreover, the introduction of S-atoms provided more thiophene-sulfur active sites. This study provides an innovative idea for designing excellent ORR catalysts.

Spartina alterniflora-Derived Carbons for High-Performance Oxygen Reduction Reaction (ORR) Catalysts

Being an alien species, Spartina alterniflora has occupied the living space of native animals and plants, causing irreversible damage to the environment. Converting Spartina alterniflora into carbon or its derivatives offers a valuable solution to manage both invasive biomass and an energy shortage. Herein, through a simple activation process, we successfully prepared Spartina alterniflora-derived carbon (SAC) and its N-doped derivative SANC, and used them as metal-free catalysts for an oxygen reduction reaction (ORR). SAC exhibits good electrochemical performance and holds significant potential in catalysis. After N-doping by melamine as a nitrogen source, electronegativity is redistributed in SANC, leading to enhanced performance (a half-wave potential of 0.716 V vs. RHE, and a four-electron transfer pathway with a H2O2 yield of only 2.05%). This work presents a straightforward and cost-effective approach to the usage of obsolete invasive biomass and shows great potential in energy generation.

Co/CoSe heterojunction as bifunctional oxygen electrocatalysts for rechargeable Zinc–Air batteries

The construction of suitable heterostructures in materials can tune the Fermi energy levels and electron transport rates of materials to achieve attractive oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) properties. In this study, a catalyst anchored in nitrogen-doped carbon nanowires (NCNW) with a heterogeneous interface of Co and CoSe is constructed to realize high-performance ORR and OER bifunctional catalysis. These Co and CoSe heterostructure interfaces can optimize the adsorption of intermediates. The Co/CoSe@NCNW catalyst performs excellent ORR catalytic activity (E1/2 = 0.89 V), and good OER activity (potential at 10 mA/cm2, Ej = 10 = 1.55 V). More importantly, the material shows excellent performance in rechargeable zinc-air batteries (ZABs). The open-circuit voltages of 1.47 and 1.50 V and the peak power densities of 122.56 and 74.49 mW/cm2 in liquid and solid electrolytes, respectively, are superior to those of the ZABs prepared from noble metals. Consequently, the construction of heterogeneous structures can convincingly boost the commercialization of rechargeable ZABs, and be extended to other fields involving ORR and OER.

Zinc Assisted Thermal Etching for Rich Edge-Located Fe-N4 Active Sites in Defective Carbon Nanofiber for Activity Enhancement of Oxygen Electroreduction.

Single-atom catalysts (SACs) with edge-located metal active sites exhibit superior oxygen reduction reaction (ORR) performance due to their narrower energy gap and higher electron density. However, controllably designing such active sites to fully reveal their advantages remains challenging. Herein, rich edge-located Fe-N4 active sites anchored in hierarchically porous carbon nanofibers (denoted as e1-Fe-N-C) are fabricated via an in situ zinc-assisted thermal etching strategy. The e1-Fe-N-C catalyst demonstrates superior alkaline ORR activity compared to counterparts with fewer edge-located Fe-N4 sites and commercial Pt/C. Density functional theory calculations show that the accumulation of more negative charges near the Fe-N and the formation of partially reduced Fe state in the edge-located Fe-N4 sites reduce the energy barrier for the ORR process. Additionally, the unique hierarchically porous structures with mesopores and macropores facilitate full utilization of the active sites and enhance long-range mass transfer. The zinc-air battery (ZAB) assembled with e1-Fe-N-C has a peak power density of 198.9mWcm-2, superior to commercial Pt/C (152.3mWcm-2). The present strategy by facile controlling the amount of the zinc acetate template systematically demonstrates the superiority of edge-located Fe-N4 sites, providing a new design avenue for rational defect engineering to achieve high-performance ORR.

Machine Learning Accelerated Identification of Bifunctional Active Sites in Metal-Organic Framework Derived Metal Oxide Heterostructures for High-Performance Zinc-Air Batteries

The demand for electrochemical energy storage (ESS) systems and their market size has drastically increased in many applications ranging from portable devices through electric vehicles to large-scale grid systems over the past decades. Yet, a more advanced ESS is required due to the safety issues and limited energy density of currently commercialized lithium-ion batteries (LIBs) for wide and matured applications. As a solution to this challenge, zinc-air batteries (ZABs) have gained tremendous attention due to their high energy density, low cost, environmental friendliness, and much lower fire risk characteristics. ZABs utilize oxygen from the atmosphere at their cathode during discharge, where the atmospheric oxygen is reduced to hydroxide via an oxygen reduction reaction (ORR). On the other hand, hydroxide is released as oxygen via oxygen evolution reaction (OER) during charge. The fact that oxygen is drawn directly from the air enables high gravimetric and volumetric energy densities of ZABs compared to those of commercial LIBs. However, the sluggish kinetics of the four-electron transfer steps in ORR and the mass transport of oxygen in OER remain major challenges for the practical application of ZABs. Meanwhile, precious metal-based catalysts such as Pt/C and RuO2 are known to have good catalytic activity towards ORR and OER. However, the integration of different catalysts into the same cathode is very difficult. Additionally, the high cost and natural scarcity of novel metals limit their usage for practical applications.We synthesized a bifunctional CoO/Mn3O4 heterostructure (CMH) OER/ORR electrocatalyst which was derived from metal-organic framework (MOF) for excellent activities in ZABs. The CMH cathode exhibited high ORR and OER performances, as demonstrated by the higher ORR current density than that of the Pt/C catalyst as well as the low OER overpotential exceeding those of the RuO2 catalyst. Remarkably, atomic structures of the CMH were elucidated using global optimization of genetic algorithm integrated with the machine learning force field. By adopting first-principles electronic structure calculations, we further revealed the charge transfer and active sites for both reactions in the identified heterojunction. Furthermore, assembling CMH cathode and Zn metal anode into a ZAB full-cell configuration achieves a ~5.5-fold higher energy density of 879 Wh kg-1 exceeding those of commercial lithium-ion batteries (LIBs), a high-discharge outstanding power density that is 1.39 times higher than novel metal catalysts, and robust cycle stability with negligible voltage decay which is far superior to that of benchmark Pt/C+RuO2 electrocatalysts.

Ultrafine PtFeMo intermetallic compound nanowires for efficient oxygen reduction reaction in proton exchange membrane fuel cells

To advance the application of proton exchange membrane fuel cells (PEMFCs), it is crucial to develop high-performance oxygen reduction reaction (ORR) catalyst. Pt-based alloy nanowires exhibit excellent ORR activity due to their unique one-dimensional structure, but transition metals undergo spontaneous leaching under the harsh operating condition, often leading to decreased activity. Herein, ultrafine PtFeMo intermetallic compound nanowires were successfully synthesized as a high-performance ORR catalyst for PEMFC. The average diameter of the nanowires was 2.1 nm and the incorporation of inexpensive and high melting point metal Mo improved both catalytic performance and structural stability. The as-prepared ultrafine PtFeMo intermetallic compound nanowires exhibited mass activity of 2.56 A mgPt−1 for ORR, which is higher than that of disordered PtFeMo alloy nanowires (1.36 A mgPt−1) and commercial Pt/C (0.24 A mgPt−1) in rotating disk electrode test. And it exhibited peak power density of 2716 mW cm−2 under 250 kPa H2-O2 single-cell and mass activity of 0.62 A mgPt−1 under 100 kPa H2-O2 single-cell test in PEMFC. After long-time durability test, the intermetallic compound nanowires maintained their original structure, composition and electrocatalytic performance well, highlighting the importance of Mo incorporation and ordered phase structure generation.

Highly dispersed Co nanoparticles confined by mesopore-rich N-doped hollow carbon nanotubes for efficient oxygen reduction reaction and Zn-air battery

Oxygen reduction reaction (ORR) is an important reaction process in Zn-air batteries, and the catalyst plays a crucial role as the cathode in the system. However, the reported catalysts often exhibit poor durability and stability in the operation of air batteries. Here, we used g-C3N4 as a precursor to mix Co nanoparticles for carbonization, and synthesized a large number of carbon nanotubes (CNTs) interwoven cluster catalysts, namely Co/CNT-800. The obtained catalyst has a rolling grass like morphology, forming a highly conductive network, which helps to improve the electron transfer ability in the ORR process. At the same time, the influence of materials at different carbonization temperatures on the ORR of Zn-air batteries was studied. In alkaline media, Co/CNT-800 showed the high ORR performance, with a half-wave potential of 0.839 V (vs. RHE, Pt/C 0.845 V). After 5000 cycles, the E1/2 of the Co/CNT-800 catalyst only decreased by 9 mV, and its performance in stability tests and methanol tolerance tests was superior to Pt/C. When Co/CNT-800 catalyst is used as the air cathode for Zn-air batteries, it exhibits an excellent specific capacity of 709.2 mAh/g and a power density of 142.2 mW cm−2.This research achievement provides valuable insights for the development of high-performance Zn-air batteries and innovative guidance for the design of ORR catalysts.

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.

Design of Atomically Dispersed CoN4 Sites and Co Clusters for Synergistically Enhanced Oxygen Reduction Electrocatalysis.

Constructing dual-site catalysts consisting of atomically dispersed metal single atoms and metal atomic clusters (MACs) is a promising approach to further boost the catalytic activity for oxygen reduction reaction (ORR). Herein, a porous CoSA-AC@SNC featuring the coexistence of Co single-atom sites (CoN4) and S-coordinated Co atomic clusters (SCo6) in S, N co-doped carbon substrate is successfully synthesized by using porphyrinic metal-organic framework (Co-TPyP MOF) as the precursor. The introduction of the sulfur source creates abundant microstructural defects to anchor Co metal clusters, thus modulating the electronic structure of its surrounding carbon substrate. The synergistic effect between the two types of active sites and structural advantages, in turn, results in high ORR performance of CoSA-AC@SNC with half-wave potential (E1/2) of 0.86V and Tafel slope of 50.17mVdec-1. Density functional theory (DFT) calculations also support the synergistic effect between CoN4 and SCo6 by detailing the catalytic mechanism for the improved ORR performance. The as-fabricated Zn-air battery (ZAB) using CoSA-AC@SNC demonstrates impressive peak power density of 174.1mWcm-2 and charge/discharge durability for 148h. This work provides a facile synthesis route for dual-site catalysts and can be extended to the development of other efficient atomically dispersed metal-based electrocatalysts.

Asymmetrically Coordinated Calcium Single Atom for High-Performance Oxygen Reduction Reaction.

S-block single atoms represent an ideal catalyst for the oxygen reduction reaction (ORR) as they can suppress the Fenton reaction. However, the symmetry of the s/p orbitals tends to generate either an excessively strong or weak interaction with intermediates. Herein, Ca single atoms coordinated with -S, -OP, and three N atoms (Ca/NPS-HC) were fabricated to modulate the adsorption of intermediates and promote the efficiency of s-block ORR catalysts. The experimental results from ORR demonstrated that the Ca/NPS-HC catalyst exhibited outstanding catalytic capability with a half-wave potential of 0.89 V, a kinetic current density of 56.6 mA cm-2 at 0.85 V, and a Tafel slope of 42 mV dec-1, outperforming commercial Pt/C. The detailed mechanistic studies revealed that the asymmetric coordination of Ca single atoms led to the symmetry-breaking of electron distribution in Ca single atoms, attenuating the s-p hybridization from the intermediate adsorption process, and thereby minimizing the energy barrier of the whole ORR.