Efficient Bifunctional Oxygen Electrocatalysts Research Articles

Fish bone-derived N, S co-doped interconnected carbon nanofibers network coupled with (Fe, Co, Ni)9S8 nanoparticles as efficient bifunctional electrocatalysts for rechargeable and flexible all-solid-state Zn-air battery

Rational design of efficient, cost-effective and robust bifunctional oxygen electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is of vital significance to the large-scale application of rechargeable Zn-air battery (ZAB). Herein, we demonstrate a novel and simple strategy for the synthesis of (Fe, Co, Ni)9S8 nanoparticles embedded in nitrogen and sulfur co-doped interconnected carbon nanofibers network ((Fe, Co, Ni)9S8/NSCFs) derived from fish bone as an efficient bifunctional catalyst. The (Fe, Co, Ni)9S8/NSCFs shows large specific surface area (750 m2g − 1), well-defined interconnected nanofibers network structure with high conductivity, synergistic chemical coupling effects between (Fe, Co, Ni)9S8 and NSCFs with doped heteroatoms of N and S. As expected, in alkaline medium, excellent catalytic activity and outstanding durability toward both ORR and OER are obtained. Moreover, the homemade all-solid-state ZAB based on (Fe, Co, Ni)9S8/NSCFs displays outstanding battery capacity and power density together with excellent durability and flexibility. As an additional advance, a digital display screen powered by (Fe, Co, Ni)9S8/NSCFs-based rechargeable ZAB works steadily at twisted, extruded, combusting, and punctured states, making our bifunctional electrocatalysts attractive for wearable energy storage applications.

Pyrolysis-Derived Carbon Auto-Coated Co–Ni Oxide-based Nanoparticles on Graphene-like Nanosheets for High-Performance Oxygen Electrocatalysis

Engineering transition-metal-based bifunctional oxygen electrocatalysts with high activity and stability has always been a problem. Traditional bare transition-metal-based nanoparticles supported on the outer surface of carbon materials are susceptible to the Ostwald-ripening effect in a catalytic process, consequently suffering from poor long-term operation. However, constructing a highly efficient and stable bifunctional oxygen electrocatalyst is still challenging. Here, we report graphene-like carbon nanosheets modified with carbon shell-coated binary Co–Ni oxide-based nanoparticles (CoNiOx@C/G-NSs) by one-step pyrolysis method, in which the hybrids show a three-dimensional fluffy and hierarchical porous nanostructure and large numbers of carbon shell-coated binary Co–Ni oxide-based nanoparticles (CoNiOx@C) dispersed on graphene-like carbon nanosheets evenly. More excitingly, the carbon nanosheets are nitrogen-doped. When applied for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), the onset potential (Eonset) of OER reached 1.26 V, and onset potential of ORR and half-wave potential (E1/2) reached 0.90 and 0.78 V, respectively. The hybrids showed enhanced methanol tolerance, with few changes in the ORR performance with or without adding methanol, and high stability, with 84% activity retention after 10 h continuous reaction. The productivity of H2O2 is about 5% and the number of electron transfer (n) is about 3.9 in the process of catalyzing ORR; density functional theory calculation reveals its high selectivity in the 4e– pathway. Its excellent performance is mainly attributed to the synergistic enhancement effect: three-dimensional fluffy and hierarchical porous nanostructure provided a large catalytic activity area, which enabled the effective participation of species and facilitated rapid mass transfer; the rapid adsorption of O2 by N-doped graphene-like carbon nanosheets ensured fast electron transport; synergistic reactivity between carbon shell and CoNiOx enhanced the activity, and numerous CoNiOx@C nanoparticles reconciled the electron density of the carbon shell, which introduced more active sites; and the carbon shell weakened the Ostwald-ripening effect and ensured the stability of the nanoparticle. All advantages synergistically enhance the catalytic efficiency and make it one of the best bifunctional oxygen electrocatalysts.

Facile construction of S-containing Co-based metal organic framework core-shell microspheres as an efficient bifunctional oxygen electrocatalyst.

A cost-effective non-noble metal bifunctional electrocatalyst towards the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is very important for energy-related applications. Micro/nanomaterials with core-shell structures have emerged as potential non-noble metal catalyst candidates. Herein, an efficient bifunctional oxygen electrocatalyst, S-containing Co-based metal organic framework core-shell microspheres (Co-MOF-CSMSs), has been designed and constructed by using 2,2':5',2''-terthiophene-5,5''-dicarboxylic acid as a novel ligand through a facile one-step hydrothermal method. Due to the integrated favorable structural characteristics of the core-shell structure and MOFs for electrocatalysis, Co-MOF-CSMSs are revealed as a good bifunctional electrocatalyst for the ORR and OER, including an onset potential of 0.93 V vs. RHE (reversible hydrogen electrode), a half-wave potential of 0.78 V vs. RHE and an overpotential of 0.35 V at 10 mA cm-2. This work provides a low-cost and facile method to design and construct advanced micro/nanomaterials with core-shell structures to targetedly develop high-performance bifunctional oxygen electrocatalysts.

Waste to wealth: spent catalyst as an efficient and stable bifunctional oxygen electrocatalyst for zinc–air batteries

The spent catalysts obtained from catalytic decomposition of methane are often considered as waste and typically subjected to energy intensive processes such as high-temperature combustion for recycling or chemical treatment for metal reclamation.

Cobalt sulfides constructed heterogeneous interfaces decorated on N,S-codoped carbon nanosheets as a highly efficient bifunctional oxygen electrocatalyst

The Co9S8/Co1−xS@NSC heterostructures have been prepared by a one-pot salt template-assisted pyrolysis procedure, which exhibit superior bifunctional oxygen electrocatalysis and zinc–air battery performances.

Metal alkoxide-derived Co@NC/NCNS as a highly efficient bifunctional oxygen electrocatalyst.

A promising bifunctional catalyst integrating Co@NC units and porous structure carbon nanosheets (Co@NC/NCNS) is in situ prepared by the calcination and subsequent acid etching of a mixture containing metal alkoxide and melamine. Benefiting from the synergism among the active sites and porous structure, the optimal Co@NC/NCNS-800 exhibits superior activity for the ORR/OER.

Macroporous microspheres consisting of thickness-controlled bamboo-like CNTs and flower-like Co3O4 nanoparticles as highly efficient bifunctional oxygen electrocatalysts for Zn–air batteries

Co3O4 nanoparticle-decorated porous hollow microspheres composed of N-doped CNTs are synthesized by spray pyrolysis. When tested as electrocatalysts for a Zn–air battery cathode, they exhibit superior bifunctional oxygen catalytic activities.

Engineering heterointerfaces coupled with oxygen vacancies in lanthanum–based hollow microspheres for synergistically enhanced oxygen electrocatalysis

3Co–LaMOH|O V @NC hollow microsphere is achieved through pyrolysis with spontaneous cobalt doping and it can be applied as high–active and stable bifunctional oxygen electrocatalyst for rechargeable ZAB. The development of high–efficiency and low–cost bifunctional oxygen electrocatalysts is critical to enlarge application of zinc–air batteries (ZABs). However, it still remains challenges due to their uncontrollable factor at atomic level during the catalysts preparation, which requires the precise regulation of active sites and structure engineering to accelerate the reaction kinetics for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, a novel Co–doped mixed lanthanum oxide and hydroxide heterostructure (termed as Co–LaMOH|O V @NC) was synthesized by pyrolysis of La–MOF–NH 2 with spontaneous cobalt doping. Synergistic coupling of its hollow structure, doping effect and abundant oxygen vacancies creates more active sites and leads to higher electroconductivity, which contribute to the better performance. As employed as a bifunctional oxygen electrocatalyst, the resulting 3Co–LaMOH|O V @NC exhibits superior electrocatalytic activity for both ORR and OER. In assembled ZAB, it also demonstrates an excellent power density of 110.5 mW cm −2 , high specific capacity of 810 mAh g Zn −1 , and good stability over 100 h than those of Pt/C + RuO 2 . Density functional theory (DFT) calculation reveals that the heterointerfaces coupled with oxygen vacancies lead to an enhanced charge state and electronic structure, which may optimize the conductivity, charge transfer, and the reaction process of catalysts. This study provides a new strategy for designing highly efficient bifunctional oxygen electrocatalysts based on rare earth oxide and hydroxides heterointerface.

Fused Hybrid Linkers for Metal–Organic Frameworks-Derived Bifunctional Oxygen Electrocatalysts

Noble metal free M-N-C oxygen electrocatalysts are generaly synthesized using inorganic salts, organometallic precursors, nanostructured carbon nanotubes, several dopants and carbonization under modifying environments such as NH3 or H2. Reducing synthesis steps or bringing versatility in post product is quite rare. We have introduced a series of metal-organic frameworks using iron/benzimidazole as the only primary precursor to obtain a uniform material. By merging catechol and imidazole units together, we prepared efficient bifunctional oxygen electrocatalyst. The proposed material outperforms the Pt-based materials with respect to electrocatalytic properties in alkaline media (ORR: Eon = 1.01 V, E1/2 = 0.87 V vs. RHE in 0.1 M KOH; OER: 1.60 V @10 mA cm–2 in 0.1 M KOH; ΔE = 0.73 V). It was also established that fine-tuning of organic linker can help to modulate the electrochemical properties of the single precursor based electro-catalyst material.

Preparation of Ni3Fe2@NC/CC Integrated Electrode and Its Application in Zinc-Air Battery

Reasonable design and development of a low-cost and high-efficiency bifunctional electrocatalyst for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is essential for promoting the development of Zinc-air battery technology. Herein, we obtained an integrated catalytic electrode, NiFe nanoparticles supported on nitrogen-doped carbon (NC) directly grown on the carbon cloth (designated as Ni3Fe2@NC/CC), by pyrolysis of bimetallic NiFe metal-organic framework (MOF) precursor. There is a synergistic effect between nickel and iron component, which enhances the bifunctional catalytic activity. In addition, the underlying carbon cloth is conducive to the efficient electron transfer and also benefits the uniform loading of catalytically active materials. Thus, the integrated electrode shows good OER/ORR dual-functional catalytic performance, and the OER overpotential is much lower than that of the traditional drop-coating electrode and precious metal catalyst (IrO2). Moreover, the Ni3Fe2@NC/CC integrated electrode used in zinc-air batteries shows good flexibility and cycle stability. Our findings provide a new avenue for the development of efficient and stable bifunctional oxygen electrocatalysts.

Defects enriched hollow porous Co-N-doped carbons embedded with ultrafine CoFe/Co nanoparticles as bifunctional oxygen electrocatalyst for rechargeable flexible solid zinc-air batteries

The construction and design of highly efficient and inexpensive bifunctional oxygen electrocatalysts substitute for noble-metal-based catalysts is highly desirable for the development of rechargeable Zn-air battery (ZAB). In this work, a bifunctional oxygen electrocatalysts of based on ultrafine CoFe alloy (4-5 nm) dispersed in defects enriched hollow porous Co-N-doped carbons, made by annealing SiO2 coated zeolitic imidazolate framework-67 (ZIF-67) encapsulated Fe ions. The hollow porous structure not only exposed the active sites inside ZIF-67, but also provided efficient charge and mass transfer. The strong synergetic coupling among high-density CoFe alloys and Co-Nx sites in Co, N-doped carbon species ensures high oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity. First-principles simulations reveal that the synergistic promotion effect between CoFe alloy and Co-N site effectively reduced the formation energy of from O* to OH*. The optimized CoFe-Co@PNC exhibits outstanding electrocatalytic stability and activity with the overpotential of only 320 mV for OER at 10 mA·cm−2 and the half-wave potential of 0.887 V for ORR, outperforming that of most recent reported bifunctional electrocatalysts. A rechargeable ZAB constructed with CoFe-Co@PNC as the air cathode displays long-term cyclability for over 200 h and high power density (152.8 mW·cm−2). Flexible solid-state ZAB with our CoFe-Co@PNC as the air cathode possesses a high open circuit potential (OCP) up to 1.46 V as well as good bending flexibility. This universal structure design provides an attractive and instructive model for the application of nanomaterials derived from MOF in the field of sustainable flexible energy applications device.

In situ synthesis of Co3O4 nanoparticles confined in 3D nitrogen-doped porous carbon as an efficient bifunctional oxygen electrocatalyst

The rational exploitation of non-precious metal catalyst with high activity, strong durability and low cost for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is of vital importance for metal–air batteries. Herein, a composite of Co3O4 nanoparticles confined in three-dimensional (3D) N-doped porous carbon (Co-NpCs) was prepared by a simple freeze-drying and in situ pyrolysis method. The effect of different dosages of Co(NO3)2 on the catalytic performance was discussed. The Co-NpC-12% exhibits the best catalytic performance (E1/2 = 0.78 V, better stability than 20% Pt/C) in ORR and in OER among all the as-synthesized samples. Furthermore, it also exhibits the best bifunctional activity (ΔE = 0.849 V). The excellent properties of Co-NpCs are mainly due to the synergy between Co3O4 and carbon. Firstly, a high Co3O4 loading amount can boost the defect level of the N-doped hierarchical porous carbon and expose more active sites. Secondly, the unique in situ pyrolysis guarantees a large-area contact between Co3O4 and carbon as well as a strong C–O–Co bonding, which promotes charge transfer, avoids the peeling of Co3O4 nanoparticles and effectively improves the stability of the material. This work is expected to offer a feasible strategy to produce metal oxide/carbon nanocomposite and push forward the development of bifunctional electrocatalyst with high activity and stability.

Co/nitrogen-doped carbon nanocomposite derived from self-assembled metallogels as efficient bifunctional oxygen electrocatalyst for Zn-air batteries

Rational design and exploration of highly efficient nonprecious metal-based bifunctional electrocatalysts are vital for metal-air batteries. Herein, a folic acid based metal–organic gels (MOG) is synthesized based on coordination induced self-assemble strategy, which affords well-defined dispersion cobalt implanted into N-doped porous carbon (CoNC-MOG-x) via pyrolysis. The as-obtained CoNC-MOG-x possesses well distributed Co nanoparticles and larger accessible surface areas than the CoNC without self-assemble process. Taking advantage of the unique structure, the CoNC-MOG-9 exhibits good oxygen reduction reaction activity, and the half-wave potentials for oxygen reduction reaction is 0.815 V. In addition, it also displays high oxygen evolution reaction activity with overpotential of 0.40 V at 10 mA cm−2 and a Tafel slope of 76 mV dec-1. Furthermore, integrated CoNC-MOG-9 cathode in an all-solid-state zinc-air battery exhibits a high specific power of 63 mW cm−2 as well as excellent stability and durability.

In-situ synthesis of hybrid nickel cobalt sulfide/carbon nitrogen nanosheet composites as highly efficient bifunctional oxygen electrocatalyst for rechargeable Zn-air batteries

ABSTRACT In this work, an in-situ synthetic, pyrolytic and carbonized method is elaborately demonstrated to prepare the nickel cobalt sulphide (NiCo2S4) nanoparticles (NPs)/carbon nitrogen nanosheets (CNNs) composites as a highly efficient bifunctional oxygen electrocatalyst for rechargeable Zn-air batteries (ZABs). Specifically, the in-situ synthesized NiCo2S4 NPs confined in cages of CNNs create a well-defined electron transfer hetero-interface with more exposed active sites. The combined NiCo2S4 NPs with the CNNs generate a synergistic effect, which provides effective electron transfer pathways to enhance the electrocatalytic behaviors, yielding a more positive half-wave potential (0.83 V) for oxygen reduction reaction (ORR) and a lower overpotential (360 mV at 10 mA cm−2) for oxygen evolution reaction (OER). As a proof of concept, the equipped ZABs exhibit a high peak power density of 92 mW cm−2 and a superior energy density of 1025 Wh kg−1 with robust cycling stability over 1000 cycles for 180 h, which are better than that of a commercially available Pt/C-RuO2 catalyst. The findings highlight the practical viability of the NiCo2S4/CNNs composites in rechargeable ZABs and provide a new approach for the efficient synthesis of bifunctional oxygen electrocatalyst in the future.

Ultrafine Fe/Fe3C decorated on Fe-N -C as bifunctional oxygen electrocatalysts for efficient Zn-air batteries

Abstract Efficient bifunctional oxygen electrocatalysts for ORR and OER are fundamental to the development of high performance metal-air batteries. Herein, a facile cost-efficient two-step pyrolysis strategy for the fabrication of a bifunctional oxygen electrocatalyst has been proposed. The efficient non-precious-metal-based electrocatalyst, Fe/Fe3C@Fe-Nx-C consists of highly curved onion-like carbon shells that encapsulate Fe/Fe3C nanoparticles, distributed on an extensively porous graphitic carbon aerogel. The obtained Fe/Fe3C@Fe-Nx-C aerogel exhibited superb electrochemical activity, excellent durability, and high methanol tolerance. The experimental results indicated that the assembly of onion-like carbon shells with encapsulated Fe/Fe3C yielded highly curved carbon surfaces with abundant Fe-Nx active sites, a porous structure, and enhanced electrocatalytic activity towards ORR and OER, hence displaying promising potential for application as an air cathode in rechargeable Zn-air batteries. The constructed Zn-air battery possessed an exceptional peak power density of ~147 mW cm−2, outstanding cycling stability (200 cycles, 1 h per cycle), and a small voltage gap of 0.87 V. This study offers valuable insights regarding the construction of low-cost and highly active bifunctional oxygen electrocatalysts for efficient air batteries.

Earth-abundant coal-derived carbon nanotube/carbon composites as efficient bifunctional oxygen electrocatalysts for rechargeable zinc-air batteries

The exploration of active and robust electrocatalysts for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is the bottleneck to realize the commercialization of rechargeable metal-air batteries and regenerative fuel cells. Here we report facile synthesis of three-dimensional (3D) carbon nanotube (CNT)/carbon composites using earth-abundant coal as the carbon source, hydrogen reductant and heteroatom dopant to grow CNTs. The prepared composite featuring 3D structural merits and multiple active sites can efficiently catalyze both ORR and OER, affording high activity, fast kinetics, and long-term stability. With the additional incorporation of manganese, the developed catalyst afforded a potential difference of 0.80 V between ORR at the half wave potential and OER at a current density of 10 mA cm−2. The optimized sample has presented excellent OER performance within a constructed solar-powered water splitting system with continuously generating oxygen bubbles at anode. Notably, it can be further used as a durable air-electrode catalyst in constructed Zn-air battery, delivering an initial discharge/charge voltage gap of 0.73 V, a remained voltaic efficiency of 61.2% after 160 cycles and capability to power LED light for at least 80 h. This study provides an efficient approach for converting traditional energy resource i.e. coal to value-added alternative oxygen electrocatalysts in renewable energy conversion systems.

Continuous nitrogen-doped carbon nanotube matrix for boosting oxygen electrocatalysis in rechargeable Zn-air batteries

Interconnected Carbon Nanotube Network: Continuous nanocarbon matrix composed of abundant interconnected nitrogen-doped carbon nanotubes demonstrates efficient and stable oxygen electrocatalysis for long-life rechargeable Zn-air batteries. Developing robust oxygen electrocatalyst with high-performance is very significant for practical rechargeable Zn-air battery. We report herein the preparation of three-dimensional continuous nanocarbon network composed of interconnected nitrogen-doped carbon nanotubes and its application as oxygen electrocatalysis in rechargeable Zn-air battery. Except the excellent electrochemical bifunctionality, this carbon nanotube matrix also delivers an impressive battery performance. Specifically, an open-circuit voltage of 1.50 V as well as a high power density of 220 mW cm −2 with remarkable cycling stability for 1600 h is achieved in the rechargeable Zn-air battery. The study not only provides an efficient bifunctional oxygen electrocatalyst but more importantly may pave significant concepts in designing robust electrode for long-life rechargeable Zn-air battery and other energy technologies.

Recent Advances on Self-Supported Arrayed Bifunctional Oxygen Electrocatalysts for Flexible Solid-State Zn-Air Batteries.

Flexible solid-state Zn-air batteries have been rapidly developed benefiting from the uprising demand for wearable electronic devices, wherein the air electrode integrated with efficient bifunctional oxygen electrocatalysts plays an important role to achieve high performance. Binder-free self-supported bifunctional catalysts can provide large active surface area, fast electron transport path, easy ion diffusion, and excellent structural stability and flexibility, thus acting as promising flexible air cathodes. In this review, recent advances on the application of nanoarrayed electrocatalysts as air cathodes in flexible Zn-air batteries are reviewed. Especially, various types of bifunctional oxygen electrocatalysts, including carbonaceous material arrays, transition metal compound arrays, transition metal/carbon arrays, transition metal compound/carbon arrays, and other hybrid arrays, are discussed. The applications of flexible Zn-air batteries with two configurations (i.e., planar stacks and cable fibers) are also introduced. Finally, perspectives on the optimization of arrayed air cathodes for future development to achieve high-performance flexible Zn-air batteries are shared.

Controlled synthesis of FeNx-CoNx dual active sites interfaced with metallic Co nanoparticles as bifunctional oxygen electrocatalysts for rechargeable Zn-air batteries

Efficient bifunctional oxygen electrocatalysts are essential for high-performance rechargeable Zn-air batteries (rZABs). Herein, a porous hollow carbon nanoshell (H-Co@FeCo/N/C) in which FeNx and CoNx metal sites are atomically dispersed and interfaced intimately with metallic Co nanoparticles was derived from pyrolysis of polydopamine-coated ZnCo-ZIFs adsorbed with Fe3+; the chemical interactions among different organic and metal species during the polymer-coating process was inverstigated; their role in regulating the size of the Co nanoparticles, the structure of the hollow carbon nanoshell and the formation of the FeNx-CoNx dual active sites was revealed. The H-Co@FeCo/N/C showed superior bifunctional oxygen electrocatalytic activity (ΔE = 0.698 V) and mass activity of 6.8 A gcat.−1 at 0.9 V, outperforming the commercial Pt/C/RuO2 catalysts or the Fe/N/C or Co/N/C counterparts. When assembled for rZABs, the H-Co@FeCo/N/C cathode displayed a long cycle life of 200 h (Egap of about 1.0 V@10 mA cm-2).

Bubble-like Fe-encapsulated N,S-codoped carbon nanofibers as efficient bifunctional oxygen electrocatalysts for robust Zn-air batteries

Efficient, robust and cost-effective bifunctional oxygen electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are of vital importance to the widespread utilization of Zn-air batteries. Here we report the fabrication of a bubble-like N,S-codoped porous carbon nanofibers with encapsulated fine Fe/Fe5C2 nanocrystals (∼ 10 nm) (FeNSCs) by a facile one-pot pyrolysis strategy. The novel FeNSC nanostructures with high Fe content (37.3 wt.%), and synergetic N and S doping demonstrate remarkable ORR and OER catalytic activities in alkaline condition. Particularly for ORR, the optimal FeNSC catalyst exhibits superior performance in terms of current density and durability in both alkaline and acidic media. Moreover, as catalysts on the air electrodes of Zn-air batteries, the optimal FeNSCs show a high peak power density of 59.6 mW/cm2 and extraordinary discharge-charge cycling performance for 200 h with negligible voltage gap change of only 8% at current density of 20 mA/cm, surpassing its noble metal counterpart (i.e. Pt). The impressive battery stability can be attributed to favorable electron transfer resulting from appropriate graphitization of the bubble-like carbon nanofibers and thorough protection of Fe/Fe5C2 nanoparticles by carbon wrapping to prevent oxidation, agglomeration and dissolution of Fe nanoparticles during battery cycling. The present FeNSC catalyst, which is highly active, robust yet affordable, shows promising prospects in large-scale applications, such as metal-air batteries and fuel cells.