Bifunctional Oxygen Electrocatalysts Research Articles

Bifunctional oxygen electrocatalysts for rechargeable zinc-air battery based on MXene and beyond

Bifunctional oxygen electrocatalysts for rechargeable zinc-air battery based on MXene and beyond

FeZrRu Trimetallic bifunctional oxygen electrocatalysts for rechargeable Zn-air batteries

The development of high active and stable bifunctional electrocatalysts for metal-air batteries remains a challenge due to the slow reaction kinetics both in oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, a trimetallic electrocatalyst with efficient ORR and OER bifunctional catalytic activities has been fabricated by a one-step high-temperature pyrolysis methodology. The catalyst shows higher catalytic ORR and OER performance than the commercial 46% TKK platinum carbon and IrO2 catalysts, respectively, with a half-wave potential (E1/2) of 0.912 V vs. RHE for ORR in 0.1 M KOH and an overpotential of 250 mV at 10 mA/cm2 for OER in 1 M KOH. Moreover, the carbon encapsulation ensures the high stability of FeZrRu/C catalysts both for both ORR and OER electrocatalysis. The Zn–air batteries using the obtained FeZrRu/C catalysts exhibit a power density as high as 221.34 mW/cm2. This work provides a universal strategy for the synthesis of high-performance trimetal-doped bifunctional electrocatalysts for metal-air batteries and fuel cells.

Carbon‐Nanotube‐Bridging Strategy for Integrating Single Fe Atoms and NiCo Nanoparticles in a Bifunctional Oxygen Electrocatalyst toward High‐Efficiency and Long‐Life Rechargeable Zinc–Air Batteries

AbstractThe development of highly efficient and robust bifunctional electrocatalysts for oxygen reduction (ORR) and evolution reactions (OER) is the key issue for realizing high‐performance and long‐life rechargeable zinc–air batteries (ZABs). However, it is still a great challenge to integrate independent ORR and OER sites in a catalyst with high activity. Here, a carbon nanotube‐bridging strategy is proposed to synthesize such a bifunctional oxygen electrocatalyst enriched with highly active single‐atom Fe sites for the ORR and high‐performance nanosized NiCo hydroxides for the OER. Consequently, the developed catalyst shows a small overpotential difference of 0.686 V. When used as an oxygen electrode catalyst, the corresponding ZAB exhibits a large power density of 219.5 mW cm−2, a small charge–discharge voltage gap of 0.72 V at 10 mA cm−2, and outstanding discharge–charge durability without attenuation after more than 700 cycles. This work proposes a new idea to realize multifunctional catalysts and drives the practical application of ZABs.

Rational Design for Efficient Bifunctional Oxygen Electrocatalysts by Artificial Intelligence

Rational Design for Efficient Bifunctional Oxygen Electrocatalysts by Artificial Intelligence

Manganese-doped cobalt spinel oxide as bifunctional oxygen electrocatalyst toward high-stable rechargeable Zn-air battery

High-performance and low-cost bifunctional electrocatalysts for ORR and OER are urgently required for rechargeable Zn-air batteries. Herein, a series of Mn-doped Co3O4 nanoparticles grown on carbon nanotubes (Mn-Co3O4@CNTs) bifunctional electrocatalysts are designed. Owing to the moderate doped Mn atoms, the Mn-Co3O4 heightens ORR activity via the synergistic effect between Co and Mn atoms, and more Co3+ active sites are exposed on the surface of Mn-Co3O4 to enhance the OER rate. As a result, the 40% Mn-doped Mn-Co3O4@CNTs electrocatalyst exhibits higher ORR (E1/2 = 0.84 V) and OER (η10 = 356 mV at 10 mA cm−2) performance. More significantly, the Mn-Co3O4@CNTs equipped with rechargeable ZAB displays a high power density of 116 mW cm−2, a low charge-discharge voltage gap of 0.94 V at 10 mA cm−2, and superior cycling stability of over 425 h and 1200 cycles, being much more outperforming than Pt- and Ru-based ZABs.

Preventing surface passivation of transition metal nanoparticles in oxygen electrocatalyst to extend the lifespan of Zn-air battery

• A MOFs-derived bifunctional oxygen electrocatalyst was prepared. • The electron transfer from Ru to Co/Fe could improve the OER performance. • The porous carbon structure caused by Zn evaporation could promote both the ORR and OER activity. • A quasi in-situ electrochemical test in the battery cell was used to observe the surface passivation of transition metal nanoparticles. Prolonging the lifespan of oxygen catalysts in Zn-air batteries was urgently required for the potential commercialization. Herein, two interactional active species were integrated into porous N-doped carbon microspheres (Co-Fe-Ru/PNCS) to act as bifunctional oxygen electrocatalysts. Due to the electron transfer from Ru to Co/Fe element, the high value state of Ru could promote OER performance and reduce the charge voltage of the battery. An extended cycle stability of 200 h was achieved in Co-Fe-Ru/PNCS-based battery. Moreover, the quasi in-situ potentiodynamic sweep of air-electrode in battery cell confirmed it was the incorporation of Ru that avoided the passivation of Co/Fe-based nanoparticles. Accordingly, this novel electrocatalyst may provide a new strategy of designing durable bifunctional oxygen electrocatalyst for Zn-air batteries.

La0.75Sr0.25MnO3-based perovskite oxides as efficient and durable bifunctional oxygen electrocatalysts in rechargeable Zn-air batteries

Efficient and durable bifunctional oxygen electrocatalysts are critical for advanced rechargeable zinc-air (Zn-air) batteries. However, the obstacle to the development of bifunctional electrocatalysts for the oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) lies in the different requirements of the ORR and OER for catalytic materials. Herein, La0.75Sr0.25Mn0.5X0.5O3 (X = Co, Ni, and Fe) perovskite nanoparticles were created by rationally screening targeted ORR/OER components and precisely controlling their electronic structures to achieve bifunctional oxygen electrocatalysis, in which La0.75Sr0.25Mn0.5Fe0.5O3 (LSFMO) displayed superior ORR performance (Eonset of 0.932 V and n of 3.59) and significantly enhanced electrocatalytic activity in the OER process (an Ej=10 of 1.658 V and overpotential of 428 mV), corresponding to excellent bifunctional properties (ΔE = 0.94 V). Furthermore, density functional theory (DFT) calculations demonstrated that Mn and Fe dual sites generated by partial substitution had a significant synergistic effect on the electrocatalytic process. The rechargeable Zn-air batteries delivered an unprecedented small charge-discharge voltage polarization (0.76 V), high reversibility and stability over many charge-discharge cycles (60 h). These excellent results demonstrate that Mn-based perovskites with Fe doping are undoubtedly promising bifunctional electrocatalysts for rechargeable Zn-air batteries.

N, S co-doped carbon with embedment of FeNi alloy as bifunctional oxygen electrocatalysts for rechargeable Zinc-air batteries

Zinc-air batteries (ZABs) have sparked great interest, but their wide-ranging applications are limited by sluggish cathode reactions (ORR and OER). In this work, a multifunctional 3D catalyst (FeNi alloy/porous carbon) was easily fabricated by introducing Fe3+ and Ni2+ to modulate in-situ vapor phase grown carbon nanotubes. The as-prepared catalyst FNSNC73-800 displays abundant mesoporous, massive structural defects, and multiple active sites, which greatly facilitate the transport of oxygen species and charge transfer during the reaction. Due to the excellent ORR and OER performance, FNSNC73-800 shows a narrow voltage gap (ΔE) of 0.76 V, which is superior to recent reports. Notably, the secondary zinc-air battery with this catalyst displays a high-peak power density (210 mW cm−2), while maintaining an ultra-low potential gap (0.74 V) after a long-term charge-discharge cycle of 200 h. This effort presents a facile strategy for designing economical and efficient 3D catalysts for zinc-air batteries and more energy devices.

Two-in-one strategy to construct bifunctional oxygen electrocatalysts for rechargeable Zn-air battery

Integrating two different catalytic active sites into one composite is a useful 2-in-1 strategy for designing high-efficient bifunctional catalysts, which can easily tailor the activity of each reaction. Hence, we adopt the 2-in-1 strategy to design the metal oxyhydroxide supported on N-doped porous carbons (PA-CoFe@NPC) as the oxygen bifunctional catalyst, where NPC provides the activity for oxygen reduction reaction (ORR) while the metal oxyhydroxide is responsible for oxygen evolution reaction (OER). Results demonstrate that the PA-CoFe@NPC indeed exhibits both super ORR and OER activities. Impressively, using bifunctional PA-CoFe@NPC as the oxygen electrode, the resulting Zn-air battery exhibits outstanding charge and discharge performance with the peak power density of 156.3 mW cm–2, and also exhibits a long-term cycle stability with continuous cyclic charge and discharge of 170 hours that is obviously better than the 20% Pt/C+IrO2 based one. The 2-in-1 strategy in this work can be efficiently extended to design other bi- or multi-functional electrocatalysts.

Mixed-valence cobalt oxides bifunctional electrocatalyst with rich oxygen vacancies for aqueous metal-air batteries

As the bifunctional oxygen electrocatalysts, the mixed-valence metal oxide with multiple oxidation state of metal ions usually gives analogous alloy effect. However, the irreversible surface reconstruction of the electrocatalyst during the electrochemical catalysis usually changes the oxidation state of metal ions in the near-face to higher oxidation state especially in the mixed-valence metal oxide. For the modulation equilibrium, we adopt a new approach to prepare the mixed-valence cobalt oxide with the regulatable ratio of Co2+/Co3+ by inducing air at a certain temperature during the cooling procedure. The obtained Co/CoO/Co3O4/NCS with hollow nanosphere possesses multiple heterointerfaces accompanying rich oxygen vacancies. Together with the contribution of the mixed valence and oxygen vacancies, Co/CoO/Co3O4/NCS exhibits an exceptional ORR activity with a half-wave potential of 0.844 V and superb OER activity with a low overpotential of 285 mV at 10 mA cm−2. The as-fabricated Zn-air batteries with Co/CoO/Co3O4/NCS catalyst exhibit a remarkable open-circuit voltage (1.47 V), a competitive power density of 146.5 mW cm−2, and good durability without nearly no performance decay for over 400 h at 5.0 mA cm−2. More attractively, when constructed into Mg-air batteries, Co/CoO/Co3O4/NCS cathode realizes an excellent stable discharge voltage over 90 h at 20 mA cm−2.

In situ formation of self‐antistacking FeCoOx on N‐doped graphene: A 3D‐on‐2D nanoarchitecture for long‐life Zn–air batteries

AbstractBefore the practical application of rechargeable Zn–air batteries (ZABs), a critical issue regarding the inherent slow reaction kinetics of the oxygen reduction (ORR) and oxygen evolution (OER) must be addressed. Here, we fabricate a cost‐effective bifunctional oxygen electrocatalyst with a self‐antistacking structure, where three‐dimensional (3D) Fe–Co bimetallic oxide particles (FeCoOx) are directly grown on 2D N‐doped graphene (NG). The in situ grown FeCoOx particles can alleviate the NG interlaminar restacking, ensuring abundant channels for diffusion of O2/OH− species, while the NG allows rapid electron flow. Benefiting from this self‐antistacking 3D‐on‐2D structure and synergetic electrocatalysis, FeCoOx@NG demonstrated excellent activity for both ORR and OER (ΔE = 0.78 V), which is superior to that of the binary mixtures of Pt/C and RuO2 (ΔE = 0.83 V). A homemade ZAB with 20%‐FeCoOx@NG delivers a specific capacity of 758.9 mAh g−1, a peak power density of 215 mW cm−2, and long‐term cyclability for over 400 h. These research results suggest that designing a bimetallic oxide/N‐doped carbon 3D‐on‐2D nanoarchitecture using an in situ growth strategy is an attractive and feasible solution to overcome electrocatalytic problems in ZABs.

The in situ growth of FeCo nanoalloys in NiFeCoP nanosheets arrays with superhydrophilicity and surperaerophobicity for efficient overall water splitting

The high-efficient bifunctional electrocatalysts for oxygen and hydrogen evolution reactions are important but still challenging in water electrolysis. Herein, a novel NiCoFeP/CC nanocomposite with in situ embedded FeCo nanoalloys (FeCo@NiFeCoP/CC) was fabricated on carbon cloth, forming a Mott-Schottky heterojunction. Benefiting from the strong synergistic effect between the interfaces of FeCo nanoalloys and NiCoFeP nanosheets, the unique 3D structure formed by vertically staggered 2D nanosheets on carbon fibers, as well as the superhydrophilic/superaerophobic electrode surface, as-prepared FeCo@NiFeCoP/CC electrodes exhibit enhanced electrocatalytic activities with low overpotentials of 185 mV for OER and 105 mV for HER at the current density of 10 mA cm−2 in 1.0 M KOH. In addition, FeCo@NiCoFeP/CC electrodes are applied as both anode and cathode to constitute a two-electrode system for overall water splitting, achieving a low cell voltage of 1.55 V to attain 10 mA cm−2 in 1.0 M KOH. The method of in situ fabrication of FeCo nanoalloys@NiFeCoP on carbon cloth could be broadened to other substrates to explore novel bifunctional catalysts for highly efficient overall water splitting.

High-performance bifunctional oxygen electrocatalysts for zinc-air batteries over nitrogen-doped carbon encapsulating CoNi nanoparticles

The nitrogen doped carbon (NC) encapsulating metal particles (metal/NC) are promising low-cost bifunctional oxygen electrocatalysts for rechargeable Zn-air batteries. However, the states of the art catalytic performance are still significantly restricted by the limited content of active sites for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, a series of NC encapsulating CoNi samples as a bifunctional catalyst for both ORR and OER were synthesized via a simple pyrolysis method. Large surface area and high content M–N x active sites promote the ORR activity and accelerate the surface reconstruction layer for high OER performance. The NC encapsulating CoNi with optimized Co/Ni ratio (2:1) shows high ORR activity with a half-wave of potential (0.85 V) and a low overpotential of 309 mV for OER. Rechargeable Zn-air battery assembled by an air cathode with the NC encapsulating CoNi exhibits a power density of 143 mW cm−2 and good cyclability over 100 h at 10 mA cm−2. This mechanism work provides a feasible strategy for developing high activity and low cost bifunctional oxygen electrocatalysts.

In situ decoration of Co3O4 on N-doped hollow carbon sphere as an effective bifunctional oxygen electrocatalyst for oxygen evolution and oxygen reduction reactions

Transition metal oxide based materials are believed as a sustainable and effective electrocatalysts for oxygen evolution and oxygen reduction reactions (OER/ORR). However, poor conductivity, specific surface area, and tunable crystallography are major bottlenecks. To alleviate such issues, we developed a highly active spinel Co3O4 decorated N-doped hollow carbon sphere (Co3O4/NHCS) by single step decoration using cobalt phthalocyanine (CoPc) precursor for the first time. The introduction of various extents of CoPc significantly affects the sphere wall thickness, defect sites, doping amount of cobalt content, and the concentration of Co3+ and Co2+ sites. The resulting optimum loading of 0.2 g of Co3O4/NHCS-0.2, exhibits a highly uniform hollow carbon sphere with a high wall thickness (61 nm), better surface area (445 m2 g−1), and moderate defect sites. Notably, an exterior concentration of octahedral Co3+ (35.50%) and tetrahedral Co2+ (26.54%) sites serve as the active centres for OER and ORR, respectively. Remarkably, the obtained material exhibits exceptional OER performance with a potential of 1.80 V vs. RHE in 0.1 M KOH medium for achieving a current density of 10 mA cm−2, outperforming the benchmark RuO2 material. In addition, Co3O4/NHCS-0.2 demonstrates an impressive ORR electrocatalytic activity with onset potential of 0.89 V vs. RHE, excellent current density of 5.0 mA cm−2, lower Tafel slope of 60 mV dec−1 and close to four electron transfer. Moreover, the moderate carrier concentration, flat band potential, higher tetrahedral Co2+ and pyridinic N sites significantly improved the ORR activity and methanol oxidation tolerance ability.

MOF-Derived Nanoporous Carbon As an Efficient Bifunctional Oxygen Electrocatalyst for Erzabs

Zinc-air batteries are cost-effective batteries that possess a high energy density (1086 Wh Kg-1), compared to other conventional battery systems. In order to improve the electrochemical performance of electrically rechargeable zinc-air batteries (ERZABs), an effective bifunctional oxygen electrocatalyst is required. Hence, the development of non-noble metal bifunctional catalysts for ORR and OER is of prime importance. The transition metal-based catalysts have increasing demand since they are promising alternatives, in terms of cost and durability, to noble metal catalysts. Metal-organic frameworks (MOF) based catalysts show high catalytic activity due to adjustable pore size, ultra-high surface area, and structural designability[1].Increasing porosity can augment the catalytic activity by increasing the surface area, thereby enhancing the ORR kinetics.In the present work, a CFZ-NPC (CoFeZn-MOF derived nanoporous carbon) was synthesized via hydrothermal method and investigated as a bifunctional catalyst for rechargeable zinc-air batteries[2]. The catalyst shows a high electrochemical activity towards oxygen reduction reaction with a half-wave potential of 830 mV vs. RHE and a comparable oxygen evolution activity (overpotential of 379 mV vs. RHE at 10 mA cm-2 ) with IrO2 (Over potential of 377 mV at 10 mA cm-2). The binder-free CFZ-NPC air electrode when applied into a Zinc-air battery system, delivers a low charge-discharge potential gap of 862 mV at 5 mA cm-2. Interestingly, the catalyst possesses an excellent electrochemical performance in the electrically rechargeable Zn-air battery over 1000 cycles at selected DOD for 157 h with a specific capacity of 890 mAh g(Zn) -1 without much efficiency drop.Financial support from Department of Science and Technology, Govt. of India under research grant number DST/TMD/MECSP/2K17/20 is gratefully acknowledged References; [1] Ren, Shuangshuang et al. 2020. “Bifunctional Electrocatalysts for Zn-Air Batteries: Recent Developments and Future Perspectives.” Journal of Materials Chemistry A 8(13): 6144–82.[2] Tang, Jing et al. 2016. “Bimetallic Metal-Organic Frameworks for Controlled Catalytic Graphitization of Nano porous Carbons.” Nature Publishing Group (April): 1-8.

Effects of Catalyst Composition, Loading, and Spray Parameters on the Performance of Unitized Regenerative Fuel Cell Membrane Electrode Assemblies

Proton exchange membrane unitized regenerative fuel cells (PEM-URFCs) combine the ability to both produce power (in fuel cell mode) and generate fuel and oxidant (in electrolysis mode) from the same cell. Compared with discrete fuel cell and electrolyzer systems, URFCs provide the potential for lower mass, volume, and cost. The composition and structure of the bifunctional oxygen catalyst layer (CL), which facilitates the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at the same electrode, significantly affects performance and stability, particularly given the wide potential differences and different mass transport phenomena involved under operation in fuel cell or electrolysis mode. We previously showed bimetallic nanoframes provide bifunctional oxygen electrocatalysts with significantly higher activity compared with monometallic structures, evaluated using a rotating disk electrode configuration.1 Here, we investigated the effects of the oxygen CL composition, loading, and spray parameters on the performance of URFC membrane electrode assemblies (MEAs). Pt black and IrO2 catalysts were combined at different ratios and deposited at different mass loadings. Catalyst layers were sprayed directly onto membranes using an ultrasonic spray system. Within ultrasonically sprayed catalyst layers, higher spray rates resulted in improved fuel cell performance. Higher catalyst loadings improved both fuel cell and electrolyzer performance, but reached a region of diminishing returns at higher loadings. The ratio of the ORR catalyst (Pt) to the OER catalyst (IrO2) modulated the performance in both fuel cell and electrolyzer modes. Different catalyst ratios influence the catalyst utilization at higher loadings. The comparison of URFC performance at same Pt or IrO2 loadings indicates that in addition to the active catalyst itself, the non-catalytically active component influences MEA performance. This result is in line with our previous evaluation of synergistic effects of Pt and IrO2 within rotating disk electrode measurements1 and supports that in addition to the significant effects of catalyst material structure on performance, the electrode structure plays a critical role in fuel cell and electrolyzer performance in URFC MEAs. Repeated switching of URFC MEAs between fuel cell and electrolysis modes indicates that reasonable performance is maintained over the initial cycles within our single cell test configuration. References Godínez-Salomón, F.; Albiter, L.; Mendoza-Cruz, R.; Rhodes, C.P. Bimetallic Two-dimensional Nanoframes: High Activity Acidic Bifunctional Oxygen Reduction and Evolution Electrocatalysts. ACS Appl. Energy Mater. 2020, 3, 2404-2421. http://dx.doi.org/10.1021/acsaem.9b02051

(Digital Presentation) Development of Bifunctional Oxygen Electrocatalysts for Electrically Rechargeable Zinc-Air Batteries

Zinc-air battery is a promising battery system as it possesses high theoretical energy density and is cost-effective3. The theoretical energy density of a Zinc-air battery is 1086 Wh kg-1, which is five times greater than that of lithium-ion batteries2. Moreover, zinc metal is one of the most abundant metals in the earth’s crust and is inexpensive. Rechargeable metal-air batteries operate based on two fundamental electrochemical reactions as Oxygen Reduction Reaction (ORR) during discharge and Oxygen Evolution Reaction (OER) during recharge processes, respectively3. Electrocatalytic activity of the bifunctional electrocatalyst towards these two oxygen reactions will decide the performance of the battery1. Recent advancements in catalyst development are the fabrication of rechargeable air electrodes using a single active material that is capable of bifunctionally catalyzing ORR and OER3. The development of bifunctional catalysts with high activity is necessary for rechargeable metal-air batteries, such as zinc-air batteries3.In this work, a perovskite-type LaFeO3 material was synthesized using a citric acid-assisted sol-gel method and is investigated as bifunctional oxygen electrocatalyst for electrically rechargeable zinc-air batteries. Structural studies using X-ray diffraction revealed the formation of phase pure LaFeO3 in space group Pbnm. This catalyst displayed considerable bifunctional catalytic activity for both oxygen reduction (0.74 V vs. RHE) and oxygen evolution reactions (0.40 V vs. RHE at 10 mA cm-2) in 1 M KOH electrolyte. Electrically rechargeable zinc-air batteries assembled using LaFeO3 as the oxygen electrocatalyst deliver a specific capacity of 936.38 mAh g( Zn) -1 after the 1st discharge. Further details will be discussed in the poster.Financial support from Department of Science and Technology, Govt. of India under research grant number DST/TMD/MECSP/2K17/20 is gratefully acknowledged.

Nonprecious Multi-Principal Metal Systems As the Air Electrode for a Solid-State Rechargeable Zinc-Air Battery

Zinc-air battery technology is gaining recognition as a promising energy storage device to be used in portable electronics and electric vehicles. Despite possessing high theoretical energy density, environmental and operational safety, and easy accessibility of zinc reservoirs, the successful commercialization of zinc-air batteries suffers due to the poor oxygen electrocatalysis kinetics at the air cathode. The kinetically inept oxygen reduction and oxygen evolution reactions at the cathode lead to a large overpotential barrier and poor charge-discharge cyclic performance of the rechargeable zinc-air battery. This work demonstrates designing a multi-principal metal bifunctional electrocatalyst that is directly deposited on conductive, porous, and flexible substrates to eliminate the necessity of polymeric binders. The flexible bifunctional oxygen electrocatalyst used for the cathode of solid-state ZAB is assembled with gel polymer electrolyte and zinc anode giving excellent charge-discharge cyclic stability and constant discharge voltage (close to 1.65 V). These multi-principal metal electrocatalysts constituting quasi-equimolar concentration, provide numerous combinations of surface functionality, multiple adsorption sites, and electronic environments thus enabling better optimization of the catalytic performance.

Rational design of ultrafine cobalt free electrospun nanofibers as efficient and durable binfunctional oxygen electrocatalysts for rechargeable zinc-air battery

Rational design of efficient and stable bifunctional oxygen electrocatalyst is of significant importance for research and progress of rechargeable zinc-air battery (ZAB). Herein, ultrafine cobalt free perovskite type oxide Sr2Fe1.5Mo0.5O6-δ nanofibers (SFM NF) and SFM nanoparticles (SFM NP) have been prepared via the electrospinning technique and combustion technique, respectively, and their electrochemical behaviors in the field of ZAB have been studied. Our study demonstrates that SFM NF catalyst has better bifunctional electrocatalytic activities and more durable charge–discharge cycling stability than SFM NP catalyst. When used as cathode catalysts for ZABs, SFM NF electrode exhibits a higher peak power density of 137 mW cm−2 than 107.9 mW cm−2 for SFM NP electrode. In addition, SFM NF electrode presents a lower galvanostatic charge–discharge voltage gap (ΔE) of 0.94 V than 1.13 V for SFM NP electrode when operated at 10 mA cm−2, which can be explained by the enhanced bifunctional electrocatalytic activities. More importantly, SFM NF electrode presents a significantly low ΔE degradation rate of 0.01 V/100 h during the 300-hour operation, indicating its excellent change-discharge stability. Our findings indicate that SFM NF catalyst is a greatly promising cathode candidate of efficient and durable rechargeable ZAB, and the electrospinning technique is an effective strategy to prepare efficient electrocatalysts for energy storage and conversion application.

Composing atomic transition metal sites for high-performance bifunctional oxygen electrocatalysis in rechargeable zinc–air batteries

Rechargeable zinc–air batteries have attracted extensive attention as clean, safe, and high-efficient energy storage devices. However, the oxygen redox reactions at cathode are highly sluggish in kinetics and severely limit the actual battery performance. Atomic transition metal sites demonstrate high electrocatalytic activity towards respective oxygen reduction and evolution, while high bifunctional electrocatalytic activity is seldomly achieved. Herein a strategy of composing atomic transition metal sites is proposed to fabricate high active bifunctional oxygen electrocatalysts and high-performance rechargeable zinc–air batteries. Concretely, atomic Fe and Ni sites are composed based on their respective high electrocatalytic activity on oxygen reduction and evolution. The composite electrocatalyst demonstrates high bifunctional electrocatalytic activity (ΔE = 0.72 V) and exceeds noble-metal-based Pt/C + Ir/C (ΔE = 0.79 V). Accordingly, rechargeable zinc–air batteries with the composite electrocatalyst realize over 100 stable cycles at 25 mA cm−2. This work affords an effective strategy to fabricate bifunctional oxygen electrocatalysts for high-performance rechargeable zinc–air batteries.