Oxygen Catalytic Activity Research Articles

The Proportion of Fe-NX , N Doping Species and Fe3 C to Oxygen Catalytic Activity in Core-Shell Fe-N/C Electrocatalyst.

A bifunctional oxygen electrocatalyst composed of iron carbide (Fe3 C) nanoparticles encapsulated by nitrogen doped carbon sheets is reported. X-ray photoelectron spectroscopy and X-ray absorption near edge structure revealed the presence of several kinds of active sites (Fe-Nx sites, N doping sites) and the modulated electron structure of nitrogen doped carbon sheets. Fe3 C@N-CSs shows excellent oxygen evolution and oxygen reduction catalytic activity owing to the modulated electron structure by encapsulated Fe3 C core via biphasic interfaces electron interaction, which can lower the free energy of intermediate, strengthen the bonding strength and enhance conductivity. Meanwhile, the contribution of the Fe-Nx sites, N doping sites and the effect of Fe3 C core for the electrocatalytic oxygen reaction is originally revealed. The Fe3 C@N-CSs air electrode-based zinc-air battery demonstrates a high open circuit potential of 1.47 V, superior charge-discharge performance and long lifetime, which outperforms the noble metal-based zinc-air battery.

Antiperovskite Intermetallic Nanoparticles for Enhanced Oxygen Reduction

AbstractAntiperovskite Co3InC0.7N0.3 nanomaterials with highly enhanced oxygen reduction reaction (ORR) performance were prepared by tuning nitrogen contents through a metal–organic framework (MOF)‐derived strategy. The nanomaterial surpasses all reported noble‐metal‐free antiperovskites and even most perovskites in terms of onset potential (0.957 V at J=0.1 mA cm−2) and half‐wave potential (0.854 V). The OER and zinc–air battery performance demonstrate its multifunctional oxygen catalytic activities. DFT calculation was performed and for the first time, a 4 e− dissociative ORR pathway on (200) facets of antiperovskite was revealed. Free energy studies showed that nitrogen substitution could strengthen the OH desorption as well as hydrogenation that accounts for the enhanced ORR performance. This work expands the scope for material design via tailoring the nitrogen contents for optimal reaction free energy and hence performance of the antiperovskite system.

Antiperovskite Intermetallic Nanoparticles for Enhanced Oxygen Reduction.

Antiperovskite Co3 InC0.7 N0.3 nanomaterials with highly enhanced oxygen reduction reaction (ORR) performance were prepared by tuning nitrogen contents through a metal-organic framework (MOF)-derived strategy. The nanomaterial surpasses all reported noble-metal-free antiperovskites and even most perovskites in terms of onset potential (0.957 V at J=0.1 mA cm-2 ) and half-wave potential (0.854 V). The OER and zinc-air battery performance demonstrate its multifunctional oxygen catalytic activities. DFT calculation was performed and for the first time, a 4 e- dissociative ORR pathway on (200) facets of antiperovskite was revealed. Free energy studies showed that nitrogen substitution could strengthen the OH desorption as well as hydrogenation that accounts for the enhanced ORR performance. This work expands the scope for material design via tailoring the nitrogen contents for optimal reaction free energy and hence performance of the antiperovskite system.

Robust assembly of urchin-like NiCo2O4/CNTs architecture as bifunctional electrocatalyst in Zn-Air batteries

Cost-effective bifunctional electrocatalysts with desirable oxygen catalytic activity to both of ORR and OER are essential to the large-scale commercial application of metal-air batteries. In this work, a robust hydrothermal assembly strategy is presented to fabricate the three-dimensional (3D) urchin-like hybrid material of acid-treated multiwall CNTs (MWCNTs) and needle-like NiCo2O4 as a cost-effective bifunctional oxygen electrocatalyst. Benefiting from the particular 3D urchin-like mesoporous structure providing rich transport channels for O2 diffusion and electrolyte infiltration and abundant active sites for charge transfer reaction, and the synergistic effect of high electrocatalytically active NiCo2O4 and high conductive MWCNTs network, the optimized NCO@20%MWCNTs composite exhibits a superior OER and ORR catalytic activity. In its practical application, an ultrahigh initial round-trip efficiency of 79.4% and long-term cycle stability (950 cycles) at 10 mA cm−2 are achieved in Zn-air battery. This simple strategy for construction of the cost-effective unique 3D porous urchin-like structure together with the improved electrochemical catalytic activity provides a great potential for material design in oxygen catalysis and metal-air batteries.

Interface Decoration Of N-Doped Carbon Nanotube with Fe For Enhancing Oxygen Catalytic Activity

Oxygen electrocatalytic reactions, including oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are extremely important in energy storage and conversion technology. The ORR is happened in cathode electrode in fuel cells or metal air batteries when discharging, the OER is occurred in anode electrode in water splitting or rechargeable metal air batteries when charging. Currently, the high-performance catalyst developed for ORR still relies on platinum (Pt) and its alloys. On the other hand, ruthenium (Ru) oxides were demonstrated to be high performance electrocatalysts for OER. However, their scarcity, limited stability, and aggregation limited the development of electrochemistry energy storage and conversion. Herein, we synthesize a series of transition metal nanoparticles embedded in nitrogen doped carbon nanotubes (M-CNT) and further decorating the interface of N-CNT with Fe element for enhancing oxygen catalytic activities. The results show that the type of transition metal determine the morphologies of N-CNT and the catalytic performance in ORR and OER. After further modification by introducing Fe element, the Fe-CNT based catalyst displays a superior ORR activity, even surpasses that of Pt/C, the Ni-CNT based catalyst with Fe decoration also showes a significant enhancement in OER. This work provides a feasible strategy to develop highly efficient oxygen catalysts with low-cost, earth-abundant transition metal elements via further decoration.

Inside Back Cover: Redox‐Inert Fe3+ Ions in Octahedral Sites of Co‐Fe Spinel Oxides with Enhanced Oxygen Catalytic Activity for Rechargeable Zinc–Air Batteries (Angew. Chem. Int. Ed. 38/2019)

Inside Back Cover: Redox‐Inert Fe³⁺ Ions in Octahedral Sites of Co‐Fe Spinel Oxides with Enhanced Oxygen Catalytic Activity for Rechargeable Zinc–Air Batteries (Angew. Chem. Int. Ed. 38/2019)

Well-dispersed Co–Co3O4 hybrid nanoparticles on N-doped carbon nanosheets as a bifunctional electrocatalyst for oxygen evolution and reduction reactions

Bifunctional catalysts are vital for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in metal-air batteries. In this work, Co–Co3O4/N-doped carbon nanosheets (NCNs) were developed as highly efficient bifunctional oxygen catalysts via the pyrolysis of a hybrid ZIF-67/CNs precursor. It is found that the introduced CNs play important roles. On one hand, the introduced CNs can tune the surface contents of Co, N and/or O species that are closely correlated with OER and ORR activity. On the other hand, they also facilitate to achieve high specific surface areas for the catalysts. In addition, the introduced CNs helps the formed Co–Co3O4 hybrid nanoparticles with uniform and small sizes to be well-distributed on the NCNs substrates. Despite such important roles, it should be noted that a moderate content of the introduced CNs is required to achieve optimal oxygen catalytic activity. As a result, the optimized ZIF-67/CNs(1)-600 exhibits a low value of η10 (~350 mV) for OER and a high value of E1/2 (~0.85 V) for ORR. Its overall bifunctional activity (ΔE) is as low as ~0.73 V, which is comparable to the recent reported Co-based catalysts.

Redox-Inert Fe3+ Ions in Octahedral Sites of Co-Fe Spinel Oxides with Enhanced Oxygen Catalytic Activity for Rechargeable Zinc-Air Batteries.

Bimetallic cobalt-based spinel is sparking much interest, most notably for its excellent bifunctional performance. However, the effect of Fe3+ doping in Co3 O4 spinel remains poorly understood, mainly because the surface state of a catalyst is difficult to characterize. Herein, a bifunctional oxygen electrode composed of spinel Co2 FeO4 /(Co0.72 Fe0.28 )Td (Co1.28 Fe0.72 )Oct O4 nanoparticles grown on N-doped carbon nanotubes (NCNTs) is designed, which exhibits superior performance to state-of-the-art noble metal catalysts. Theoretical calculations and magnetic measurements reveal that the introduction of Fe3+ ions into the Co3 O4 network causes delocalization of the Co 3d electrons and spin-state transition. Fe3+ ions can effectively activate adjacent Co3+ ions under the action of both spin and charge effect, resulting in the enhanced intrinsic oxygen catalytic activity of the hybrid spinel Co2 FeO4 . This work provides not only a promising bifunctional electrode for zinc-air batteries, but also offers a new insight to understand the Co-Fe spinel oxides for oxygen electrocatalysis.

Redox‐Inert Fe3+ Ions in Octahedral Sites of Co‐Fe Spinel Oxides with Enhanced Oxygen Catalytic Activity for Rechargeable Zinc–Air Batteries

AbstractBimetallic cobalt‐based spinel is sparking much interest, most notably for its excellent bifunctional performance. However, the effect of Fe3+ doping in Co3O4 spinel remains poorly understood, mainly because the surface state of a catalyst is difficult to characterize. Herein, a bifunctional oxygen electrode composed of spinel Co2FeO4/(Co0.72Fe0.28)Td(Co1.28Fe0.72)OctO4 nanoparticles grown on N‐doped carbon nanotubes (NCNTs) is designed, which exhibits superior performance to state‐of‐the‐art noble metal catalysts. Theoretical calculations and magnetic measurements reveal that the introduction of Fe3+ ions into the Co3O4 network causes delocalization of the Co 3d electrons and spin‐state transition. Fe3+ ions can effectively activate adjacent Co3+ ions under the action of both spin and charge effect, resulting in the enhanced intrinsic oxygen catalytic activity of the hybrid spinel Co2FeO4. This work provides not only a promising bifunctional electrode for zinc–air batteries, but also offers a new insight to understand the Co‐Fe spinel oxides for oxygen electrocatalysis.

Porous N-Doped Carbon-Encapsulated CoNi Alloy Nanoparticles Derived from MOFs as Efficient Bifunctional Oxygen Electrocatalysts.

A porous N-doped carbon-encapsulated CoNi alloy nanoparticle composite (CoNi@N-C) was prepared using a bimetallic metal-organic framework composite as the precursor. The optimal prepared Co1Ni1@N-C material at 800 °C exhibited well-defined porosities, uniform CoNi alloy nanoparticle dispersion, a high doped-N level, and scattered CoNi-N x active sites, therefore affording excellent oxygen catalytic activities toward the reduction and evolution processes of oxygen. The oxygen reduction (ORR) onset potential ( Eonset) on Co1Ni1@N-C was 0.91 V and the half-wave potential ( E1/2) was 0.82 V, very close to the parameters recorded on the Pt/C (20 wt Pt%) benchmark. Moreover, it is worth noting that the ORR stability of Co1Ni1@N-C was prominently higher than that of Pt/C. Under the oxygenevolution reaction condition, Co1Ni1@N-C generated the maximum current density at the potential of 1.7 V (8.60 mA cm-2) and the earliest Eonset (1.35 V) among all Co xNi y@N-C hybrids. The Co1Ni1@N-C catalyst exhibited the smallest Δ E value, confirming the superior bifunctional activity. The high surface area and porosity, and CoNi-N x active sites on the carbon surface including the proper interactions between the N-doped C shell and CoNi nanoparticles were attributed as the main contributors to the outstanding oxygen electrocatalytic property and good stability.

Polymer-assisted approach to LaCo1-xNixO3 network nanostructures as bifunctional oxygen electrocatalysts

Energy depletion caused by the consumption of fossil fuels due to increasing population and economic growth has stimulated intense research on electrochemical energy storage systems, including fuel cells and metal-air batteries. Oxygen electrocatalysis, including both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), dominates the performance of these electrochemical energy systems. However, the sluggish kinetics of these two reactions still limits their performance and even the commercialization of these electrochemical energy storage systems. Therefore, development of non-precious metal-based oxygen catalysts, especially with bifunctionality for both OER and ORR, is greatly demanded. In this report, polymer-assisted approach has been employed to synthesize LaCoO3-based perovskite nanoparticles, which interconnected together to form porous network structures. X-ray diffraction indicated that replacement of Co with Ni would lead to a lattice expansion due to larger ionic radius of Ni3+ as compared to that of Co3+. The electrocatalytic activity of these materials in 0.1 M KOH aqueous solution showed that ORR performance of LaCoO3 can be improved through incorporation of Ni into the B-site while their OER performance will also be enhanced which renders these perovskite oxides to exhibit better bifunctional electrocatalytic activity for both OER and ORR. The enhanced performance with Ni-doping might be due to the synergistic effect from the two transition metals as a result of the formation of new redox couples Ni3+/Ni2+ as well as the higher Co3+/Co2+ ratio, which could promote adsorption of oxygen on the catalytic surface with improved the CoO bond strength. Our study not only introduces polymer-assisted method to prepare network structured perovskite nanoparticles, but also highlights the importance of B-site metal doping in perovskites as a simple strategy to enhance their bifunctional oxygen catalytic activities.

N-Doped Carbon Nanosheet Networks with Favorable Active Sites Triggered by Metal Nanoparticles as Bifunctional Oxygen Electrocatalysts

Developing noble metal-free bifunctional oxygen electrocatalysts is vital for metal–air batteries. Herein, we present a facile approach to fabricating N-doped carbon nanosheet networks with metal nanoparticles (M/N-CNSNs) readily converted from metal–organic frameworks. The resultant Co/N-CNSNs show superior bifunctional oxygen catalytic activity attributed to the efficient active sites and fast mass diffusion enabled by the nanosheet structure. It is worth noting that the first-principles studies prove the Co/N–C sites to be the oxygen reduction reaction active sites, where the most favorable ones are the carbon atoms next to Co-coordinated pyridinic N. Interestingly, the cobalt content plays an important role in Co/N–C sites but was not directly involved in the catalytic process. In a Zn–air battery, a small voltage gap without obvious voltage loss is found for the Co/N-CNSNs. This facile approach enables scalable synthesis, representing an essential step toward the popularization of metal–air batteries.

Phosphorus-doped SrCo0.5Mo0.5O3 perovskites with enhanced bifunctional oxygen catalytic activities

Perovskite oxide has attracted wild attentions as a promising bifunctional electrocatalyst family for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in fuel cells and metal-air batteries. Here, phosphorus-doped SrCo0.5Mo0.5O3 perovskites has been prepared and evaluated as bifunctional oxygen electrocatalyst. X–ray diffraction and X-ray photoelectron spectroscopy results show that P-doping benefits the formation of more stable tetragonal phase, and the generation of more surface adsorbed oxygen species. Compared with SrCo0.5Mo0.5O3 perovskites without doping, rotating disk electrode measurements indicates that P-doped SrCo0.5Mo0.5O3 exhibits a positively shifted half-wave potentional of 50 mV for ORR, and a reduced OER overpotential (∼58 mV) at 10 mA cm−2 in 0.1 M KOH solution. The enhanced catalytic activities and stabilities contribute to optimized surface characteristic and stable phase structure. The work not only provides a new strategy to develop efficient bifunctional oxygen catalysts, but also enriches knowledge of perovskite oxides.

One-Pot Synthesis of Co3 O4 /Ag Nanoparticles Supported on N-Doped Graphene as Efficient Bifunctional Oxygen Catalysts for Flexible Rechargeable Zinc-Air Batteries.

Flexible rechargeable zinc-air batteries are considered as one of the most promising power supplies for the emerging flexible and wearable electronic devices. However, the development of flexible zinc-air batteries is stagnant due to the lack of efficient bifunctional catalysts with high oxygen catalytic activity and flexible solid-state electrolytes with high mechanical stability and ionic conductivity. In this work, Co3 O4 /Ag@NrGO composite was synthesized by a facile one-pot method, and the catalyst shows remarkable oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) bifunctional catalytic activity and good long-term stability. In particular, the OER overpotential of Co3 O4 /Ag@NrGO reaches 437 mV, outperforming that of the commercial IrO2 catalyst. This can be attributed to the combined effects of Co3 O4 , Ag, and N-rGO. Furthermore, PAA (polyacrylic acid) and PVA (polyvinyl alcohol) based gel-electrolytes have been developed as flexible solid-state electrolytes for zinc-air batteries. The results show that PAA-based electrolyte is more favorable to the flexible zinc-air battery with a high power density due to its relatively high ionic conductivity. The maximum power density of flexible zinc-air batteries with Co3 O4 /Ag@NrGO catalyst and PAA-based electrolyte can reach 108 mW cm-2 , which is almost the highest value reached in recent reports. This work will provide valuable guidance for the development of flexible rechargeable zinc-air batteries with high power density and stability.

Oxygen Evolution Reaction: Holey 2D Nanosheets of Low‐Valent Manganese Oxides with an Excellent Oxygen Catalytic Activity and a High Functionality as a Catalyst for Li–O2 Batteries (Adv. Funct. Mater. 17/2018)

Oxygen Evolution Reaction: Holey 2D Nanosheets of Low‐Valent Manganese Oxides with an Excellent Oxygen Catalytic Activity and a High Functionality as a Catalyst for Li–O₂ Batteries (Adv. Funct. Mater. 17/2018)

Tunable Bifunctional Activity of Mnx Co3-x O4 Nanocrystals Decorated on Carbon Nanotubes for Oxygen Electrocatalysis.

Noble‐metal‐free electrocatalysts are attractive for cathodic oxygen catalysis in alkaline membrane fuel cells, metal–air batteries, and electrolyzers. However, much of the structure–activity relationship is poorly understood. Herein, the comprehensive development of manganese cobalt oxide/nitrogen‐doped multiwalled carbon nanotube hybrids (MnxCo3−xO4@NCNTs) is reported for highly reversible oxygen reduction and evolution reactions (ORR and OER, respectively). The hybrid structures are rationally designed by fine control of surface chemistry and synthesis conditions, including tuning of functional groups at surfaces, congruent growth of nanocrystals with controllable phases and particle sizes, and ensuring strong coupling across catalyst–support interfaces. Electrochemical tests reveal distinctly different oxygen catalytic activities among the hybrids, MnxCo3−xO4@NCNTs. Nanocrystalline MnCo2O4@NCNTs (MCO@NCNTs) hybrids show superior ORR activity, with a favorable potential to reach 3 mA cm−2 and a high current density response, equivalent to that of the commercial Pt/C standard. Moreover, the hybrid structure exhibits tunable and durable catalytic activities for both ORR and OER, with a lowest overall potential of 0.93 V. It is clear that the long‐term electrochemical activities can be ensured by rational design of hybrid structures from the nanoscale.

Holey 2D Nanosheets of Low‐Valent Manganese Oxides with an Excellent Oxygen Catalytic Activity and a High Functionality as a Catalyst for Li–O2 Batteries

AbstractHoley 2D nanosheets of low‐valent Mn2O3 can be synthesized by thermally induced phase transition of exfoliated layered MnO2 nanosheets. The heat treatment of layered MnO2 nanosheets at elevated temperatures leads not only to transitions to low‐valent manganese oxides but also to the creation of surface hole in the 2D nanosheet crystallites. Despite distinct phase transitions, highly anisotropic 2D morphology of the precursor MnO2 material remains intact upon the heat treatment whereas the diameter of surface hole becomes larger with increasing heating temperature. The obtained holey 2D Mn2O3 nanosheets show promising electrocatalyst performances for oxygen evolution reaction, which are much superior to that of nonporous Mn2O3 crystal. Among the present materials, the holey Mn2O3 nanosheet calcined at 500 °C displays the best electrocatalyst functionality with markedly decreased overpotential, indicating the importance of heating condition in optimizing the electrocatalytic activity. Of prime importance is that this material shows much better catalytic activity for Li–O2 batteries than does nonporous Mn2O3, underscoring the critical role of porous 2D morphology in this functionality. This study clearly demonstrates the unique advantage of holey 2D nanosheet morphology in exploring economically feasible transition metal oxide‐based electrocatalysts and electrodes for Li–O2 batteries.

Design and synthesis of macroporous (Mn1/3Co2/3)O-carbon nanotubes composite microspheres as efficient catalysts for rechargeable Li-O2 batteries

Unique-structured (Mn1/3Co2/3)O-carbon nanotubes (MnCoO-CNT) composite microspheres synthesized by one-pot spray pyrolysis were studied as air electrode for lithium–oxygen (Li-O2) batteries. The (Mn1/3Co2/3)O nanocrystals were first introduced as efficient electrocatalysts for oxygen reduction reactions (ORRs) and oxygen evolution reactions (OERs). In addition, the optimum structure of CNT microspheres was designed as efficient support material for (Mn1/3Co2/3)O nanocatalysts with high electrical conductivity and high accommodation ability for Li2O2 products. The macroporous MnCoO-CNT composite microspheres exhibited excellent bifunctional oxygen catalytic activities in terms of a positive half-wave potential (0.67 V) for ORRs and high limiting diffusion current (35 mA cm−2 at 1.0 V) for OERs. When applied as a cathode material for Li–O2 batteries, the MnCoO–CNT microspheres delivered a high discharge capacity (37142 mA h g−1 at 200 mA g−1), excellent rate capability (4458 mA h g−1 at 2000 mA g−1), and long-term cycle stability (245 cycles at a capacity of 500 mA h g−1 at 200 mA g−1). The synergetic effect of macroporous CNT microspheres with high electrical conductivity and high electrocatalytic activities of the (Mn1/3Co2/3)O nanocatalyst were responsible for the superior performance of MnCoO–CNT composite microspheres as cathode material for Li–O2 batteries.

Oxygen Electrocatalysis on Transition Metal Spinel Oxides

Exploring efficient and low cost oxygen electrocatalysts for ORR and OER is critical for developing renewable energy technologies like fuel cells, metal-air batteries, and water electrolyzers. This presentation will presents a systematic study on oxygen electrocatalysis (ORR and OER) of transition metal spinel oxides.[1] Starting with a model system of Mn-Co spinel, the presentation will introduce the correlation of oxygen catalytic activities of these oxides and their intrinsic chemical properties. The catalytic activity was measured by rotating disk technique and the intrinsic chemical properties were probed by synchrotron X-ray absorption techniques. It was found that molecular orbital theory is able to well-explain their activities.[2,3] The attention was further extended from cubic Mn-Co spinels to tetragonal Mn-Co spinels and it was found that the molecular theory is again dominant in determining the catalytic activies. This mechanistic principle is further applied to explain the ORR/OER activities of other spinels containing other transition metals (Fe, Ni, Zn, Li, and etc.).

Design of 3-Dimensional Hierarchical Architectures of Carbon and Highly Active Transition Metals (Fe, Co, Ni) as Bifunctional Oxygen Catalysts for Hybrid Lithium–Air Batteries

Flexible power sources and efficient energy storage devices with high energy density are highly desired to power a future sustainable community. Theoretically, rechargeable metal–air batteries are promising candidates for the next-generation power sources. The rational design of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts with high catalytic activity is critical to the development of efficient and durable metal–air batteries. Herein, we propose a novel strategy to mass synthesize nonprecious transition-metal-based nitrogen/oxygen codoped carbon nanotubes (CNTs) grown on carbon-nanofiber films (MNO-CNT-CNFFs, M = Fe, Co, Ni) via a facile free-surface electrospinning technique followed by in situ growth carbonization. With a combination of the high catalytic activity of Fe-catalyzed CNTs and the efficient mass-transport characteristics of 3D carbon fiber films, the resultant flexible and robust FeNO-CNT-CNFFs exhibit the highest bifunctional oxygen catalytic activities in t...