Facilitating charge transfer via a Semi-Coherent Fe(PO3)2-Co2P2O7 heterointerface for highly efficient Zn-Air batteries.

Developing reversible oxygen electrodes for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is crucial for achieving high-performance rechargeable Zn-air batteries (ZABs). This study introduced an nitrogen-doped carbon confined with a semi-coherent Fe(PO3)2-Co2P2O7 heterojunction for bifunctional oxygen electrocatalysis. This nanocomposite yielded an ORR half-wave potential of 0.908 V and an OER overpotential of 291 mV at 10 mA/cm2. ZABs incorporating this catalyst yielded impressive performance, including a peak power density of 203 mW/cm2, a specific capacity of 737 mAh/gZn, and promoted stability. Both experimental and theoretical simulations demonstrated that the unique electric field between Fe(PO3)2 and Co2P2O7 promoted efficient charge transport across the heterointerface. This interaction likely modulated the d-band center of the heterojunction, expedite the desorption of oxygen intermediates, thus improving oxygen catalysis and, consequently, ZAB performance. This work illustrates a significant design principle for creating efficient bifunctional catalysts in energy conversion technologies.

High-performance rechargeable zinc-air batteries enabled by cobalt iron anchored on nitrogen-doped carbon matrix as bifunctional electrocatalyst.

Developing efficient bifunctional oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) electrocatalysts is potential ways for achieving high rechargeable zinc-air (Zn-air) battery performance. Herein, we report an iron (II) acetate-assisted strategy to synthesize Co3Fe7-NC-OAc catalyst with cobalt iron (Co3Fe7) alloy anchored on nitrogen-doped carbon (NC) matrix, which can serve as efficient ORR/OER bifunctional electrocatalysts for rechargeable Zn-air batteries. Apart from alloying with Co to form ORR/OER active Co3Fe7 nanoparticles, the incorporation of iron (II) acetate has expanded the pore size inside the Co3Fe7-NC-OAc catalyst to serve as gas transfer channels, and has induced synergetic electronic coupling between Co3Fe7 nanoparticles and NC matrix for boosting catalytic activity. Therefore, Co3Fe7-NC-OAc exhibits favorable ORR activity with a most positive half-wave potential of 0.90 V vs. RHE, fast ORR kinetics with a highest kinetic current density of 57.4 mA cm-2 at 0.85 V vs. RHE, and fast O2 diffusion and transport that enables smaller mass transport overpotential at high current density up to 800 mA cm-2. Additionally, Co3Fe7-NC-OAc can catalyze OER with low overpotential of 310 mV at 10 mA cm-2. When employed as air electrode for Zn-air batteries, Co3Fe7-NC-OAc achieve high peak power densities of 193 mW cm-2 and 587 mW cm-2 in liquid and solid-state Zn-air batteries. The liquid battery also exhibits high specific capacity and remarkable cycling performance. This work opens up a new opportunity for developing highly efficient bifunctional electrocatalysts for Zn-air battery applications.

A Photo-Assisted Zinc-Air Battery with MoS2/Oxygen Vacancies Rich TiO2 Heterojunction Photocathode.

Converting solar energy into electrochemical energy is a sustainable strategy, but the design of photo-assisted zinc-air battery (ZAB) with efficient utilization of sunlight faces huge challenges. Herein, a photo-assisted ZAB of a three-electrode system using MoS2/oxygen vacancies-rich TiO2 heterojunction as charge cathode and Fe, N-doped carbon matrix (FeNC) as discharge cathode is constructed, where MoS2 is chosen as solar light-responsive catalytic material and TiO2 acts as electron transport layer and hole blocking layer, arising from a train of thought for efficient charging under sunlight irradiation and light-independent discharging. The introduction of oxygen vacancies in TiO2 facilitates the temporary trapping of carriers and triggers rapid carrier transfer at the interface of the heterojunction, which hinders the recombination of photogenerated holes, thereby facilitating their further participation in the oxygen evolution reaction. Moreover, FeNC exhibits superior oxygen reduction reaction performance due to strong d-π interactions. As a result, the well-built ZABs deliver a low charge voltage (0.71 V) under illumination at 0.1 mA cm-2, and a high power density (167.6 mW cm-2) in dark. This work paves a special way for the development of ZABs by directly harvesting solar energy in charging and efficiently discharging regardless of lighting conditions.

Meso/Microporous Single-Atom Catalysts with Curved Fe-N4 sites Boost the Oxygen Reduction Reaction Activity.

Zeolitic-imidazolate frameworks (ZIFs) are among the most efficient precursors for the synthesis of atomically dispersed Fe-N/C materials, which are promising catalysts for enhancing the performance of Zn-air batteries (ZABs) and proton exchange fuel cells (PEMFCs). However, existing ZIF-derived Fe-N/C electrocatalysts mostly consist of microporous materials, leading to insufficient mass transport and inadequate battery/cell performance. In this study, we synthesize an atomically dispersed meso/microporous Fe-N/C material with curved Fe-N4 active sites, denoted as FeSA-N/TC, through the pyrolysis of hemin-modified ZIF films on ZnO nanorods, obtained from the self-assembly reaction between Zn2+ from ZnO hydrolysis and 2-methylimidazole. Density functional theory calculations demonstrate that the curved Fe-N4 active sites can weaken the intermediate adsorptions, resulting in lower free energy barriers and enhanced performance during oxygen reduction reaction (ORR). Specifically, FeSA-N/TC exhibits exceptional ORR performance with half-wave potentials of 0.925 V in alkaline media and 0.825 V in acidic media. When used as the cathodic catalyst in PEMFCs and ZABs, FeSA-N/TC achieves high peak power densities (H2-O2 PEMFC: 1100 mW cm-2; H2-Air PEMFC: 715 mW cm-2; liquid-state ZAB: 228 mW cm-2; solid-state ZAB: 112 mW cm-2), demonstrating its feasibility and efficiency in practical applications.

Prussian Blue-Derived Atomic Fe/Fe3C@N-Doped C Catalysts Supported by Carbon Cloth as Integrated Air Cathode for Flexible Zn-Air Batteries.

The development of an integrated air cathode with superior oxygen reduction reaction (ORR) performance is fundamental to flexible zinc-air batteries (ZABs) for wearable electronics. Herein, a self-assembled metal-organic framework (MOF)-derived strategy is proposed to prepare a atomic Fe/Fe3C@N-doped C catalysts supported by carbon cloth (CC) catalyst for use as an air cathode of flexible ZABs. The Prussian Blue precursor, which self-assembles on the surface of the carbon cloth due to electrostatic attraction, is critical in achieving the uniform dispersion of catalysts with high density loading on carbon cloth substrates. The hollow cubic structure, N-doped carbon layer coating, and the integrated electrode design can provide more accessible active sites and facilitate a rapid electron transfer and mass transport. Density functional theory (DFT) calculation reveals that the electronic interactions between the Fe-N4 and Fe3C dual active sites can optimize the adsorption-desorption behavior of oxygen intermediates formed during the ORR. Consequently, the Fe/Fe3C@N-doped C/CC exhibits an excellent half wave potential (E1/2 = 0.903 V) and superior long-term cycling stability in alkaline environments. With excellent ORR performance, ZABs and flexible ZABs based on Fe/Fe3C@N-doped C/CC air cathode demonstrate excellent overall electrochemical performance in terms of open circuit voltage, maximum power density, flexibility, and cycling stability.

Photoinduced Zn-Air Battery-Assisted Self-Powered Sensor Utilizing Cobalt and Sulfur Co-Doped Carbon Nitride for Portable Detection Device.

Most self-powered electrochemical sensors (SPESs) are limited by low open circuit voltage and power density, leading to a narrow detection range and low sensitivity. Herein, a photoinduced Zn-air battery-assisted SPES (ZAB-SPES) is proposed based on cobalt and sulfur co-doped carbon nitride with the cyano group (Co, S-CN). The cyano functionalization remarkably enhances visible light utilization, and the cyano moiety acts as an electron-withdrawing group to promote electron enrichment. Co and S co-doping can create a p-n homojunction within carbon nitride, enabling the efficient migration and separation of carriers, thereby significantly improving the performance of the oxygen reduction reaction. The synergistic effects endow Co, S-CN photocathode with an open circuit voltage of 1.85 V and the maximum power density of 43.5 µW cm-2 in the photoinduced ZAB. Employing heavy metal copper ions as the target model, the photoinduced ZAB-SPES exhibited dual-mode and sensitive detection. Furthermore, a portable detection device based on the photoinduced ZAB-SPES is designed and exhibits high linearity in the range of 5 ~ 600 nM with a detection limit of 1.7 nM. This work offers a portable detection method based on the photoinduced ZAB-SPES in the aquatic environment.

Innovative Air Cathode with Ni-Doped Cobalt Sulfide in Highly Ordered Macroporous Carbon Matrix for Rechargeable Zn-Air Battery.

To realize the practical application of rechargeable Zn-Air batteries (ZABs), it is imperative to develop a non-noble metal-based electrocatalyst with high electrochemical performance for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, Ni-doped Co9S8 nanoparticles dispersed on an inverse opal-structured N, S co-doped carbon matrix (IO─NixCo9-xS8@NSC) as a bifunctional electrocatalyst is presented. The unique 3D porous structure, arranged in an inverse opal pattern, provides a large active surface area. Also, the conductive carbon substrate ensures the homogeneous dispersion of NixCo9-xS8 nanocrystals, preventing aggregation and increasing the exposure of active sites. The introduction of heteroatom dopants into the Co9S8 structure generates defect sites and enhances surface polarity, thereby improving electrocatalytic performance in alkaline solutions. Consequently, the IO─NixCo9-xS8@NSC shows excellent bifunctional activity with a high half-wave potential of 0.926 V for ORR and a low overpotential of 289 mV at 10 mA cm-2 for OER. Moreover, the rechargeable ZAB assembled with prepared electrocatalyst exhibits a higher specific capacity (768 mAh gZn -1), peak power density (180.2 mW cm-2), and outstanding stability (over 160 h) compared to precious metal-based electrocatalyst.

Poly(Vinyl Alcohol)/Poly(Acrylic Acid) Gel Polymer Electrolyte Modified with Multi-Walled Carbon Nanotubes and SiO2 Nanospheres to Increase Rechargeability of Zn-Air Batteries.

Zn-air batteries (ZABs) are a promising technology; however, their commercialization is limited by challenges, including those occurring in the electrolyte, and thus, gel polymer electrolytes (GPEs) and hydrogels have emerged as substitutes for traditional aqueous electrolytes. In this work, PVA/PAA membranes were synthesized by the solvent casting method and soaked in 6 M KOH to act as GPEs. The thickness of the membrane was modified (50, 100, and 150 µm), and after determining the best thickness, the membrane was modified with synthesized SiO2 nanospheres and multi-walled carbon nanotubes (CNTs). SEM micrographs revealed that the CNTs displayed lengths of tens of micrometers, having a narrow diameter (95 ± 7 nm). In addition, SEM revealed that the SiO2 nanospheres had homogeneous shapes with sizes of 110 ± 10 nm. Physicochemical experiments revealed that SiO2 incorporation at 5 wt.% increased the water uptake of the PVA/PAA membrane from 465% to 525% and the ionic conductivity to 170 mS cm-1. The further addition of 0.5 wt.% CNTs did not impact the water uptake but it promoted a porous structure, increasing the power density and the stability, showing three-times-higher rechargeability than the ZAB operated with the PVA/PAA GPE.

Balancing Edge Defects and Graphitization in a Pt-Fe/Carbon Electrocatalyst for High-Power-Density and Durable Flow Seawater-Al/Acid Hybrid Fuel Cells and Zn-Air Batteries.

Overcoming the trade-off between the graphitization of the carbon substrate and enhanced electronic metal-support interaction (EMSI) and intrinsic activity of Pt-C catalysts remains a major challenge for ensuring the durable operation of energy conversion devices. This article presents a hybrid catalyst consisting of PtFe nanoparticles and single Pt and Fe atoms supported on N-doped carbon (PtFeNPs@PtFeSAs-N-C), which exhibits improved activities in hydrogen evolution and oxygen reduction reactions (HER and ORR, respectively) and has excellent durability owing to the high graphitization, rich edge defects, and porosity of the carbon in PtFeNPs@PtFeSAs-N-C, as well as strong EMSI between the PtFe nanoparticles and edge-defective carbon embedded with Pt and Fe atoms. According to theoretical calculations, the strong EMSI optimizes the H* adsorption-desorption and facilitates the adsorption OOH*, accelerating the HER and ORR processes. A novel flow seawater-Al/acid hybrid fuel cell using the PtFeNPs@PtFeSAs-N-C cathode can serve as a high-efficiency energy conversion device that delivers a high power density of 109.5 mW cm-2 while producing H2 at a significantly high rate of 271.6 L m-2 h-1. Moreover, PtFeNPs@PtFeSAs-N-C exhibits a remarkable performance (high power density of 298.0 mW cm-2 and long-term durability of 1000 h) in a flow Zn-air battery.

Trifunctional Graphene-Sandwiched Heterojunction-Embedded Layered Lattice Electrocatalyst for High Performance in Zn-Air Battery-Driven Water Splitting.

Zn-air battery (ZAB)-driven water splitting holds great promise as a next-generation energy conversion technology, but its large overpotential, low activity, and poor stability for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) remain obstacles. Here, a trifunctional graphene-sandwiched, heterojunction-embedded layered lattice (G-SHELL) electrocatalyst offering a solution to these challenges are reported. Its hollow core-layered shell morphology promotes ion transport to Co3S4 for OER and graphene-sandwiched MoS2 for ORR/HER, while its heterojunction-induced internal electric fields facilitate electron migration. The structural characteristics of G-SHELL are thoroughly investigated using X-ray absorption spectroscopy. Additionally, atomic-resolution transmission electron microscopy (TEM) images align well with the DFT-relaxed structures and simulated TEM images, further confirming its structure. It exhibits an approximately threefold smaller ORR charge transfer resistance than Pt/C, a lower OER overpotential and Tafel slope than RuO2, and excellent HER overpotential and Tafel slope, while outlasting noble metals in terms of durability. Ex situ X-ray photoelectron spectroscopy analysis under varying potentials by examining the peak shifts and ratios (Co2+/Co3+ and Mo4+/Mo6+) elucidates electrocatalytic reaction mechanisms. Furthermore, the ZAB with G-SHELL outperforms Pt/C+RuO2 in terms of energy density (797 Wh kg-1) and peak power density (275.8 mW cm-2), realizing the ZAB-driven water splitting.

Redox Activity of Co Species in the Active Sites of CoNx/CoOx Facilitates Oxygen Electrocatalysis for Zn-Air Batteries.

Developing efficient bifunctional oxygen electrocatalysts is crucial for enhancing the performance of rechargeable Zn-air batteries (ZABs). In this study, cobalt/cobalt oxides embedded in N-doped carbon nanofibers (Co/CoOx/NCNFs) were synthesized through a combination of electrospinning and annealing processes. The resulting Co/CoOx/NCNFs catalysts feature abundant CoNx and CoOx active species, leveraging the large specific surface area of nanofibers to facilitate oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The optimized Co/CoOx/NCNFs-0.1 achieved a half-wave potential (vs. RHE) of 0.82 V and required only 429 mV to reach 10 mA cm-2 in a typical three-electrode system with 0.1 M KOH using an electrochemical workstation equipped with a pine instruments rotator, outperforming the Pt/C+RuO2. The assembled ZABs exhibited high specific capacity (771 mAh gZn -1), substantial power density (981.6 mWh gZn -1), and long-term stability (>325 h). In situ Raman spectroscopy confirmed that the electrocatalytic processes involve the redox activity of Co (II and III) species derived from abundant CoNx and CoOx, elaborating the origin of the catalysts' exceptional oxygen electrocatalysis performance. This work not only presents a straightforward and effective approach for producing bifunctional oxygen electrocatalysts in ZABs but also sheds light on the catalytic mechanisms underlying ORR and OER for CoNx/CoOx-based oxygen electrocatalysts.

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.

Surface-Engineered Ni2P: An Efficient Oxygen Electrocatalyst for Zinc-Air Battery.

The surface engineering of electrocatalysts is one of the promising strategies to increase the intrinsic activity of electrocatalysts. It generates anion/cation vacancy defects and increases the electrochemically active surface area. We describe the surface engineering of Ni2P to favorably tune the bifunctional oxygen electrocatalytic activity and the development of a rechargeable zinc-air battery (ZAB). Ni2P encapsulated with N and P-dual doped carbon (Ni2P@NPC) is synthesized using a single-source precursor complex tris-(2,2'-bipyridine)nickel(II) bis(hexafluorophosphate). The surface engineering of the as-synthesized Ni2P@NPC catalyst is achieved by the controlled acid treatment at room temperature. The surface engineering removes the carbon debris and opens the pores, exfoliates the encapsulating carbon layer, increases the P-vacancy in the crystal lattice, and boosts the electrochemically active surface area. The surface-engineered catalyst exhibits enhanced bifunctional activity towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The electrocatalytically active sites of engineered catalysts are highly accessible for facilitated electron transfer kinetics. P-vacancy favors the facile formation of defect-rich OER active metal oxyhydroxide species. The rechargeable ZAB based on the engineered catalyst delivers a specific capacity of 770.25 mA h gZn -1, energy density of 692 Wh kgZn -1, and excellent charge-discharge cycling performance with negligible voltaic efficiency loss (0.6 %) after 100 h.

Atomically Engineered Defect-Rich Palladium Metallene for High-Performance Alkaline Oxygen Reduction Electrocatalysis.

Defect engineering is a key chemical tool to modulate the electronic structure and reactivity of nanostructured catalysts. Here, it is reported how targeted introduction of defect sites in a 2D palladium metallene nanostructure results in a highly active catalyst for the alkaline oxygen reduction reaction (ORR). A defect-rich WOx and MoOx modified Pd metallene (denoted: D-Pd M) is synthesized by a facile and scalable approach. Detailed structural analyses reveal the presence of three distinct atomic-level defects, that are pores, concave surfaces, and surface-anchored individual WOx and MoOx sites. Mechanistic studies reveal that these defects result in excellent catalytic ORR activity (half-wave potential 0.93 V vs. RHE, mass activity 1.3 A mgPd-1 at 0.9 V vs. RHE), outperforming the commercial references Pt/C and Pd/C by factors of ≈7 and ≈4, respectively. The practical usage of the compound is demonstrated by integration into a custom-built Zn-air battery. At low D-Pd M loading (26 µgPd cm-2), the system achieves high specific capacity (809 mAh gZn -1) and shows excellent discharge potential stability. This study therefore provides a blueprint for the molecular design of defect sites in 2D metallene nanostructures for advanced energy technology applications.

Customized Heteronuclear Dual Single-Atom and Cluster Assemblies via D-Band Orchestration for Oxygen Reduction Reaction.

Advanced oxygen reduction reaction (ORR) catalysts, integrating with well-dispersed single atom (SA) and atomic cluster (AC) sites, showcase potential in bolstering catalytic activity. However, the precise structural modulation and in-depth investigation of their catalytic mechanisms pose ongoing challenges. Herein, a proactive cluster lockdown strategy is introduced, relying on the confinement of trinuclear clusters with metal atom exchange in the covalent organic polymers, enabling the targeted synthesis of a series of multicomponent ensembles featuring FeCo (Fe or Co) dual-single-atom (DSA) and atomic cluster (AC) configurations (FeCo-DSA/AC) via thermal pyrolysis. The designed FeCo-DSA/AC surpasses Fe- and Co-derived counterparts by 18 mV and 49 mV in ORR half-wave potential, whilst exhibiting exemplary performance in Zn-air batteries. Comprehensive analysis and theoretical simulation elucidate the enhanced activity stems from adeptly orchestrating dz 2-dxz and O 2p orbital hybridization proximate to the Fermi level, fine-tuning the antibonding states to expedite OH* desorption and OOH* formation, thereby augmenting catalytic activity. This work elucidates the synergistic potentiation of active sites in hybrid electrocatalysts, pioneering innovative targeted design strategies for single-atom-cluster electrocatalysts.

"One-Stone, Two-Birds": Zinc-Rich Metal-Organic Frameworks as Precursors for High-Entropy Zn-Air Battery Electrocatalysts with Hierarchical Pore Structures.

The active sites of inexpensive transition metal electrocatalysts are sparse and singular, thus high-entropy alloys composed of non-precious metals have attracted considerable attention due to their multi-component synergistic effects. However, the facile synthesis of high-entropy alloy composites remains a challenge. Herein, we report a "one-stone, two-birds" method utilizing zinc (Zn)-rich metal-organic frameworks as precursors, by virtue of the low boiling point of Zn (907 °C) and its high volatility in alloys, high-entropy alloy carbon nanocomposite with a layered pore structure was ultimately synthesized. The experimental results demonstrate that the volatilization of zinc can prevent metal agglomeration and contribute to the formation of uniformly dispersed high-entropy alloy nanoparticles at slower pyrolysis and cooling rates. Simultaneously, the volatilization of Zn plays a crucial role in creating the hierarchically porous structure. Compared to the zinc-free HEA/NC-1, the HEA/NC-5 derived from the precursor containing 0.8 Zn exhibit massive micropores and mesopores. The resulting nanocomposites represent a synergistic effect between highly dispersed metal catalytic centers and hierarchical adsorption sites, thus achieving excellent electrocatalytic oxygen reduction performance with low catalyst loading compared to commercial Pt/C. This convenient zinc-rich precursor method can be extended to the production of more high-entropy alloys and various application fields.

B-site Doping Boosts the OER and ORR Performance of Double Perovskite Oxide as Air Cathode for Zinc-Air Batteries.

Double perovskite oxides are key players as electrocatalytic oxygen catalysts in alkaline media. In this study, we synthesized B-site doped NdBaCoaFe2-aO5+δ (a= 1.0, 1.4, 1.6, 1.8) electrocatalysts, systematically to probe their bifunctionality and assess their performance in zinc-air batteries as air cathodes. X-ray photoelectron spectroscopy analysis reveals a correlation between iron reduction and increased oxygen vacancy content, influencing electrocatalyst bifunctionality by lowering the work function. The electrocatalyst with highest cobalt content, NdBaCo1.8Fe0.2O5+δ exhibited a bifunctional index of 0.95 V, outperforming other synthesized electrocatalysts. Remarkably, NdBaCo1.8Fe0.2O5+δ, demonstrated facilitated charge transfer rate in oxygen evolution reaction with four-electron oxygen reduction reaction process. As an air cathode in a zinc-air battery, NdBaCo1.8Fe0.2O5+δ demonstrated superior performance characteristics, including maximum capacity of 428.27 mA h at 10 mA cm-2 discharge current density, highest peak power density of 64 mW cm-2, with an outstanding durability and stability. It exhibits lowest voltage gap change between charge and discharge even after 350 hours of cyclic operation with a rate capability of 87.14%.

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 0.86 V and Tafel slope of 50.17 mV dec-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 174.1 mW cm-2 and charge/discharge durability for 148 h. 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.

Bimetal Oxides Anchored on Carbon Nanotubes/Nanosheets as High-Efficiency and Durable Bifunctional Oxygen Catalyst for Advanced Zn-Air Battery: Experiments and DFT Calculations.

To meet increasing requirement for innovative energy storage and conversion technology, it is urgent to prepare effective, affordable, and long-term stable oxygen electrocatalysts to replace precious metal-based counterparts. Herein, a two-step pyrolysis strategy is developed for controlled synthesis of Fe2O3 and Mn3O4 anchored on carbon nanotubes/nanosheets (Fe2O3-Mn3O4-CNTs/NSs). The typical catalyst has a high half-wave potential (E1/2 = 0.87 V) for oxygen reduction reaction (ORR), accompanied with a smaller overpotential (η10 = 290 mV) for oxygen evolution reaction (OER), showing substantial improvement in the ORR and OER performances. As well, density functional theory calculations are performed to illustrate the catalytic mechanism, where the in situ generated Fe2O3 directly correlates to the reduced energy barrier, rather than Mn3O4. The Fe2O3-Mn3O4-CNTs/NSs-based Zn-air battery exhibits a high-power density (153 mW cm-2) and satisfyingly long durability (1650 charge/discharge cycles/550 h). This work provides a new reference for preparation of highly reversible oxygen conversion catalysts.

In-depth understanding the synergisms of Cu atomic clusters on Cu single atoms for highly effective electrocatalytic oxygen reduction reaction and Zn-Air battery.

In this paper, a novel, simple and mild soft template assisted strategy and further carbonization approach has been constructed to the size-tunable preparation of porous Cu-N-C/Surfactant catalysts successfully. Note that the pluronic F127 has a significant influence on the synthesis of porous Cu-N-C/F127 with the atomically dispersed Cu-N4 and adjacent Cu atomic clusters (ACs) than other surfactants owing to their particular non-ionic structure. By combining a series of experimental analysis and density functional theory (DFT) calculations, the synergistic effects between the adjacent Cu ACs and atomically dispersed Cu-N4 are favorable for manipulating the binding energy of O2 adsorption and intermediates desorption at the atomic interface of catalysts, resulting in an excellent electrocatalytic ORR performance with a faster kinetics for Cu-N-C/F127 than those of the Cu-N-C, Cu-N-C/CTAB, Cu-N-C/SDS, and comparable with the commercial Pt/C catalyst. This method not only provides a novel approach for synthesizing highly effective copper based single atom catalysts toward ORR, but also offers an in-depth understanding of the synergisms of adjacent ACs on the Cu single atoms (SAs) for highly effective electrocatalytic ORR and Zn-air Battery.