Bifunctional Oxygen Electrocatalysis Research Articles

An ultrathin defect-rich nickel–cobalt oxide nanosheet array for enhanced bifunctional oxygen electrocatalysis

We report an ultrathin defect-rich nickel–cobalt oxide nanosheet array, which can actively and stably catalyze oxygen evolution and reduction reactions.

Lignin-based nitrogen/sulfur dual-doped nanosheets decorated with Co1−xS nanoparticles as efficient bifunctional oxygen electrocatalysts

The development of efficient, cost-effective, bifunctional cathode catalyst materials to replace precious metals is highly attractive for the fabrication of Zn–air battery. Here, the three–dimensional N and S co–doped carbon nanosheets loaded with cobalt sulfide nanoparticles (Co1-xS@SNFC) for bifunctional oxygen electrocatalysis were synthesized with Co(NO3)2·6H2O as the Co source, lignin as the carbon source, thiourea as the nitrogen/ sulfur source, and MgO as the template. The synergistic effect of multiple active sites gives the Co1-xS@SNFC fast electrochemical kinetic properties and excellent stability to oxygen reduction reactions (ORR) and oxygen evolution reactions (OER). The half-wave potential and overpotential of Co1-xS@SNFC were 0.84 mV and 306 mV, respectively, which is closed to commercial noble metal catalysts. In addition, Co1-xS@SNFC exhibited four–electron transfer characteristics and ultra–low tafel slope. Compared with commercial Pt/C, the Zn–air battery assembled from Co1-xS@SNFC exhibited a low voltage gap of polarization curve (0.75 V) between charging and discharge and high power density (207 mWcm−2) in alkaline electrolyte. This work developed a green and novel fabrication approach for the synthesis of bifunctional electrocatalyst and provides a new idea for high-value utilization of biomass.

NCNT grafted perovskite oxide as an active bifunctional electrocatalyst for rechargeable zinc-air battery

Precious-metal-free electrocatalysts with high activity to bifunctionally activate both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are key enablers for the scalable adoption of zinc-air batteries (ZABs). In this work, a unique hybrid catalyst comprising nitrogen-doped carbon nanotube (NCNT) in-situ grown directly on La0·8Sr0·2Ti0·65Fe0·35O3-δ perovskite oxide (denoted as LSTFO/NCNT) has been developed as a bifunctional ORR and OER electrocatalyst for ZAB applications. The compositionally optimized LSTFO/NCNT hybrid delivers remarkable bifunctional oxygen electrocatalysis performances with a characteristic potential gap (ΔE) of 0.76 V. On a device level, the primary and rechargeable homemade ZABs demonstration using such an LSTFO/NCNT hybrid as an air electrode catalyst exhibit reliable electrochemical performances of high peak power density and cycling stability with a final round-trip efficiency of 62.8% at 10 mA cm−2 during 123 cycles. The active oxygen electrocatalytic activity is believed to be related to the considerable level of pyridinic-N and graphitic-N on NCNT, abundant oxygen vacancies, improved electrical conductivity and the strong electronic interaction between LSTFO and NCNT. The DFT calculation results demonstrated that the electron transfer from NCNT to LSTFO not only reduces the oxygen adsorption and activation energy, but also activates the surface lattice oxygen and favors the formation of O–O bond through reinforcing the Fe/Ti–oxygen covalency, leading to exceptional bi-functionality. This work demonstrates a robust method to obtain exceptional bi-functional oxygen electrocatalysis based on transitional metal oxides for high-performance metal-air batteries.

Molten salt-assisted carbonization and unfolding of Fe, Co-codoped ZIF-8 to engineer ultrathin graphite flakes for bifunctional oxygen electrocatalysis

Zeolitic imidazolate frameworks (ZIFs) are already utilized to synthesis precursors for transition metal and nitrogen co-doped carbon catalysts. However, there are few reports on deliberately tailoring catalyst structure except for the hierarchical pores formed from Zn evaporation during the pyrolysis. Herein, NaCl salt-assisted carbonization and unfolding of Fe, Co-codoped ZIF-8 polyhedron (FeCo/ZIF-8) result in ultrathin Fe, Co, N-codoped graphite flake (FeCo/NG), while FeCo/ZIF-8 pyrolysis without NaCl yields Fe, Co, N-codoped carbon spheres (FeCo/NC). Because of the high specific surface area, porosity, and degree of defects, the active site is further exposed. The synthesized FeCo/NG demonstrates excellent oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) properties with half-wave potential (E 1/2 ) at 0.88 V and overpotential at 460 mV and good cycling stability, superior to those of FeCo/NC. In addition, the assembled Zn-air batteries with FeCo/NG catalysts deliver high peak power density at 109 mW cm −2 , specific capacity at 783 mAh g −1 and an operating time for 100 h. The study will provide a feasible synthesis method to design high-performance electrocatalysts by deliberate tailoring structures with molten salt-assisted carbonization and unfolding of ZIFs. • Molten salt-assisted pyrolysis tailors ZIF-8 polyhedron into ultrathin graphite flake. • Molten NaCl assists carbonization and unfolding of FeCo/ZIF-8 to form ultrathin FeCo/NG. • Evaporation of Zn in pyrolysis and removal of NaCl result in porous FeCo/NG. • FeCo/NG demonstrates excellent bifunctional oxygen electrocatalytic performances. • Zn-air battery with FeCo/NG delivers high peak power density and specific capacity.

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.

Porous carbon nanofibers confined NiFe alloy nanoparticles as efficient bifunctional electrocatalysts for Zn-air batteries

Zn-air batteries (ZABs) present attractive applications for next-generation sustainable energy storage owing to their low cost and intrinsic safety; however, the power density and durability of ZABs are often limited by the poor ion/mass transfer at triple-interfaces. Here, we propose efficient structural engineering to significantly promote the O2 adsorption/transfer and OH- diffusion. By confining NiFe alloy nanoparticles into porous carbon nanofibers, the as-designed bifunctional catalysts (H-NiFe/CNF) feature abundant hierarchical pores and a high specific surface area. The finite element method and oxygen adsorption-desorption measurement convincingly confirm that this ingenious structural design dramatically enlarges the adsorption capacity, diffusion efficiency and transport scale of OH-/oxygen. These charming characteristics allow the H-NiFe/CNF to exhibit remarkable bifunctional activity, delivering an indicator ΔE of 0.67 V, which is superior to most previous reports and noble-metal-based Pt/C+IrO2 benchmark. Accordingly, long-term stability (over 800 cycles at 5 mA cm−2) and excellent rate performances are achieved in liquid ZABs. Correspondingly, the flexible ZABs also exhibit high power density and long-cycling durability. This work highlights ion/mass transfer regulation to design bifunctional oxygen electrocatalysis for the metal-air battery.

Enhanced dual atomic Fe-Ni sites in N-doped carbon for bifunctional oxygen electrocatalysis

Atomically dispersed catalysts with high electrocatalytic performance are emerging as promising electrocatalysts for energy conversion and storage devices. Nevertheless, achieving superior bifunctional catalytic activity with single-atom catalysts toward reactions involving multi-intermediates is still facing great challenges. Herein, dual-atomic Fe-Ni pairs dispersed in hierarchical porous nitrogen-doped carbon (FeNi-HPNC) catalysts were successfully synthesized using a facile mechanochemical strategy. By virtue of the engineered electronic structure of Fe coordinated with Ni, the as-synthesized FeNi-HPNC with atomically dispersed dual-metal active sites and pore-rich structure exhibits remarkable bifunctional activities. A high half-wave potential of 0.868 V for oxygen reduction reaction and a low potential of 1.59 V at 10 mA/cm2 for oxygen evolution reaction have been obtained for FeNi-HPNC, which are superior to the single-atom catalysts of Fe-HPNC and Ni-HPNC, respectively, and are even greater than the precious metal catalysts. Combined experimental and theoretical results have revealed that the enhanced bifunctional catalytic activity of FeNi-HPNC is ascribed to the electronic interaction of Fe-Ni sites, which decreases the adsorption energy of oxygen intermediates during oxygen reduction reaction/oxygen evolution reaction. Furthermore, the practical application of FeNi-HPNC catalysts in Zn-air batteries has been demonstrated; a high peak power density and long-term durability are delivered.

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.

Doping Effect on Mesoporous Carbon-Supported Single-Site Bifunctional Catalyst for Zinc-Air Batteries.

Rechargeable zinc-air batteries (ZABs) require bifunctional electrocatalysts presenting high activity in oxygen reduction/evolution reactions (ORR/OER), but the single-site metal-N-C catalysts suffer from their low OER activity. Herein, we designed a series of single-site Fe-N-C catalysts, which present high surface area and good conductivity by incorporating into mesoporous carbon supported on carbon nanotubes, to study the doping effect of N and P on the bifunctional activity. The additional P-doping dramatically increased the content of active pyridine-N and introduced P-N/C/O sites, which not only act as extra active sites but also regulate the electron density of Fe centers to optimize the absorption of oxygenated intermediates, thereby ultimately improving the bifunctional activity of Fe-N-C sites. The optimized catalyst displayed a half-wave potential of 0.882 V for ORR and a low overpotential of 365 mV at 10 mA cm-2 for OER, which significantly outperforms the counterpart without P, as well as noble-metal-based catalysts. The ZABs with air cathodes containing the N,P-co-doped catalysts exhibited a high peak power density of 201 mW cm-2 and a long cycling stability beyond 600 h. Doping has shown to be an effective way to optimize the performance of single-site catalysts in bifunctional oxygen electrocatalysis, which can be extended to other catalyst systems.

Dealloying-Derived Porous Spinel Oxide for Bifunctional Oxygen Electrocatalysis and Rechargeable Zinc-Air Batteries: Promotion of Activity Via Hereditary Al-Doping.

The large-scale fabrication of highly efficient and low-cost bifunctional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is critical to the development of rechargeable zinc-air batteries (ZABs). Herein, a scalable dealloying strategy was proposed to obtain hierarchically porous spinel-type oxide with minor hereditary Al doping. Benefiting from the well-structured porosity and native dopant, O-np-Ni5 Co10 (Al), namely Al-NiCo2 O4 , exhibited excellent electrocatalytic ORR and OER activities, giving a small potential gap of 0.71 V. The rechargeable ZAB with O-np-Ni5 Co10 (Al) as cathode catalyst delivered a high specific capacity of 757 mAh g-1 , a competitive peak power density of 142 mW cm-2 , and a long-term discharge-charge cycling stability. Furthermore, density functional theory calculations evidenced that appropriate Al doping into NiCo2 O4 could significantly reduce the Gibbs free energy difference to 1.71 eV. This work is expected to inspire the design of performance-oriented bifunctional electrocatalysts for wider applications in renewable energy systems.

Tunable dual cationic redox couples boost bifunctional oxygen electrocatalysis for long-term rechargeable Zn-air batteries

Efficient nonprecious bifunctional electrocatalysts toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are essential for improving the electrochemical performance of Zinc–air (Zn–air) batteries. Herein, we report a cobalt-doped Mn2(OH)3VO3 catalyst prepared by facile hydrothermal method, and the ratios of cationic redox couples of catalysts were tuned with different Co doping amounts. The as-prepared Mn1.8Co0.2(OH)3VO3 (MnCoVO-1) catalyst achieves the highest ratio of (Mn3+Mn4+)/Mn2+ and Co3+/Co2+ redox couples which serve as ORR and OER active sites respectively, and exhibits the enhanced electrocatalytic performance. Furthermore, when employed as air–cathode catalyst for rechargeable Zn–air batteries, the MnCoVO-1 catalyst reveals a high power density (278 mW cm−2), enhanced rate performance and outstanding long-term stability of over 270 h. This work demonstrates the Co-doped Mn2(OH)3VO3 with optimized electronic structure by rational doping engineering can serve as a promising bifunctional catalyst for oxygen electrocatalysis and rechargeable Zn–air batteries.

Engineering d-band center of iron single atom site through boron incorporation to trigger the efficient bifunctional oxygen electrocatalysis

Modulating the microenvironment of single-metal active sites holds excellent promises for developing highly efficiently oxygen electrocatalysts. Herein, by combining theoretical predictions and experiments, we reported a general strategy to engineer the electronic properties of iron-nitrogen-carbon (FeN4/C) catalysts via the incorporation of the boron (B) atom for achieving improved catalytic activity in oxygen electrocatalysis. Our theoretical results revealed that B modulation effectively tunes the d-band center of the iron (Fe) active site to optimize its adsorption strength with oxygenated species, greatly enhancing oxygen reduction reaction (ORR) and oxygen evolution reactions (OER) activity. Our experimental measurements then confirmed the above theoretical predictions: the as-synthesized B-doped FeN4/C (Fe-N4-B) material can perform as an eligible bifunctional catalyst for ORR and OER in alkaline media, and its catalytic activity even outperforms the commercial noble metal benchmarks. The present findings provide a promising strategy to further design the advanced catalysts for a wide range of electrochemical applications.

Electronic Tuning of Core-Shell CoNi Nanoalloy/N-Doped Few-Layer Graphene for Efficient Oxygen Electrocatalysis in Rechargeable Zinc-Air Batteries.

The discovery of highly efficient, durable, and affordable bifunctional ORR/OER electrocatalysts is of great significance for the commercialization of rechargeable metal-air batteries. Herein, we synthesized uniformly sized CoNi alloy nanoparticles encapsulated with N-doped few-layer graphene (N-FLG) sheets via pyrolysis of a CoNi dual metal-organic framework precursor. The developed CoNi/N-FLG catalyst exhibited excellent oxygen reduction activity (comparable to a commercial 20 wt % Pt/C catalyst) and outstanding oxygen evolution activity (superior to a commercial 20 wt % IrO2/C catalyst), thus enabling efficient bifunctional oxygen electrocatalysis and stability when applied in prototype rechargeable zinc-air batteries. The remarkable electrochemical properties of CoNi/N-FLG originate from its unique core-shell structure and favorable electron penetration effects, thereby optimizing the adsorption/desorption strengths of intermediates formed during the oxygen reduction and oxygen evolution reactions.

Peach Gum‐Derived S,N Co‐Doped Nanoporous Carbon Coupled with Layered Double (Ni, Fe) Hydroxide for Efficient Bifunctional Oxygen Electrocatalysis in Zn‐Air Batteries

AbstractLow‐cost and high activity bifunctional oxygen electrocatalysts are at the heart of developing advanced rechargeable Zn‐air batteries (ZABs), but the challenges are great. Herein, a highly efficient hybrid catalyst, consisting of S, N co‐doped nanoporous carbon (SNC) coupled with in‐situ growth layered double (Ni, Fe) hydroxide (LDH), was derived from the biomass peach gum by a series of treatments, including hydrothermal carbonization, alkali activation, S/N co‐doping and metal‐coprecipitation process. Benefiting from the coexistence of active sites for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), the hybrid (NiFe‐LDH/SNC) reveals excellent bifunctional electrocatalytic activity with a small ΔE of 794 mV. Furthermore, as the cathode bifunctional catalyst for ZAB, the battery with NiFe‐LDH/SNC displays a large open‐circuit voltage of 1.36 V, a high power density/specific capacity of 100 mW cm−2/816 mAh gZn−1, and superior cycling durability up to 500 h at a charge/recharge current density of 2 mA cm−2, indicating its great application potential in the rechargeable metal‐air batteries.

Recent Advances in Porphyrin-Based Systems for Electrochemical Oxygen Evolution Reaction.

Oxygen evolution reaction (OER) plays a pivotal role in the development of renewable energy methods, such as water-splitting devices and the use of Zn–air batteries. First-row transition metal complexes are promising catalyst candidates due to their excellent electrocatalytic performance, rich abundance, and cheap price. Metalloporphyrins are a class of representative high-efficiency complex catalysts owing to their structural and functional characteristics. However, OER based on porphyrin systems previously have been paid little attention in comparison to the well-described oxygen reduction reaction (ORR), hydrogen evolution reaction, and CO2 reduction reaction. Recently, porphyrin-based systems, including both small molecules and porous polymers for electrochemical OER, are emerging. Accordingly, this review summarizes the recent advances of porphyrin-based systems for electrochemical OER. Firstly, the electrochemical OER for water oxidation is discussed, which shows various methodologies to achieve catalysis from homogeneous to heterogeneous processes. Subsequently, the porphyrin-based catalytic systems for bifunctional oxygen electrocatalysis including both OER and ORR are demonstrated. Finally, the future development of porphyrin-based catalytic systems for electrochemical OER is briefly prospected.

A clicking confinement strategy to fabricate transition metal single-atom sites for bifunctional oxygen electrocatalysis.

Rechargeable zinc-air batteries call for high-performance bifunctional oxygen electrocatalysts. Transition metal single-atom catalysts constitute a promising candidate considering their maximum atom efficiency and high intrinsic activity. However, the fabrication of atomically dispersed transition metal sites is highly challenging, creating a need for for new design strategies and synthesis methods. Here, a clicking confinement strategy is proposed to efficiently predisperse transitional metal atoms in a precursor directed by click chemistry and ensure successful construction of abundant single-atom sites. Concretely, cobalt-coordinated porphyrin units are covalently clicked on the substrate for the confinement of the cobalt atoms and affording a Co-N-C electrocatalyst. The Co-N-C electrocatalyst exhibits impressive bifunctional oxygen electrocatalytic performances with an activity indicator ΔE of 0.79 V. This work extends the approach to prepare transition metal single-atom sites for efficient bifunctional oxygen electrocatalysis and inspires the methodology on precise synthesis of catalytic materials.

Oxygen‐Rich Cobalt–Nitrogen–Carbon Porous Nanosheets for Bifunctional Oxygen Electrocatalysis

AbstractMetal–nitrogen–carbon (M–N–C) materials have attracted much interest in bifunctional oxygen‐involving electrocatalysis for rechargeable Zn–air batteries. Such M–N–C electrocatalysts with M–Nx sites show good activity for the oxygen reduction reaction (ORR) but moderate activity for the oxygen evolution reaction (OER). Herein, an oxygen‐rich M–N–C material (O–Co–N/C) with a highly porous nanosheet structure is reported as a bifunctional oxygen electrocatalyst, which is prepared by the direct pyrolysis of ultrathin CoO nanosheets decorated with zeolitic imidazolate framework‐8 nanoparticles under an inert atmosphere. Particularly, Co nanoparticles in the O–Co–N/C electrocatalyst contain both Co–Nx and Co–Ox coordination environments to provide intrinsic active sites for the ORR and OER, respectively. Furthermore, electrochemical studies show that the O–Co–N/C catalyst retains comparable ORR activity to common M–N–C materials with a half‐wave potential of 0.85 V vs the reversible hydrogen electrode and better OER activity with an overpotential of 0.29 V at the current density of 10 mA cm−2. This study provides insights into the development of effective oxygen‐involving electrocatalysts with bifunctional metal active centers coordinated by both nitrogen and oxygen atoms.

Linker-Compensated Metal-Organic Framework with Electron Delocalized Metal Sites for Bifunctional Oxygen Electrocatalysis.

Metal-organic frameworks with tailorable coordination chemistry are propitious for regulating catalytic performance and deciphering genuine mechanisms. Herein, a linker compensation strategy is proposed to alter the intermediate adsorption free energy on the Co-Fe zeolitic imidazolate framework (CFZ). This grants zinc-air battery superior high current density capability with a small discharge-charge voltage gap of 0.88 V at 35 mA cm-2 and an hourly fading rate of less than 0.01% for over 500 h. Systematic characterization and theoretical modeling reveal that the performance elevation is closely correlated with the compensation of CFZ unsaturated metal nodes by S-bridging heterogeneous linkers, which exhibit electron-withdrawing characteristic that drives the delocalization of d-orbital electrons. These rearrangements of electronic structures establish a favorable adsorption/desorption pathway for key intermediates (OH*) and a stable coordination environment in bifunctional oxygen electrocatalysis.

Regulating Electronic Structure of Single‐Atom Catalysts toward Efficient Bifunctional Oxygen Electrocatalysis

Electronic structure of single-atom catalysts (SACs) is critical for bifunctional oxygen electrocatalysis by adjusting the binding energy in oxygen-containing intermediates. However, the regulation of electronic structure has always been a challenge to improve catalytic reactivity. Herein, by introducing a heterogenous metal, the electronic structure through a direct bonding interaction to the active center atom is effectively adjusted. Partial charge transfer between the two atoms optimizes the binding energy of intermediates and reducing the energy barrier of the catalytic reaction. Theoretical calculations confirm these effects and the uniform distribution of 3d orbitals, leading to the improvement of bifunctional oxygen electrocatalytic reactivity. Benefiting from these attributes, the as-constructed bifunctional catalyst enables outstanding electrocatalytic performances in both oxygen reduction and hydrogen oxidation in various energy storage systems. The generality and expandability of this strategy is demonstrated by further successful development of other dual-metal catalysts systems with various active metals.

Method to Determine the Bifunctional Index for the Oxygen Electrocatalysis from Theory

AbstractMetal‐air batteries are encountered as a promising solution for energy storage due to their high energy density, cost effectiveness, and environmental benefits. Yet, the application of metal‐air batteries in practice is still not mature, which is also related to the bifunctional oxygen electrocatalysis at the cathode, comprising the oxygen reduction (ORR) and oxygen evolution (OER) reactions during discharge and charge of the battery, respectively. Experimentally, the performance of electrocatalysts in the OER and ORR is described by bifunctional index (BI), but, so far, there is no direct approach to capture the BI on the atomic scale. Herein, we present a method to ascertain the BI from ab initio theory, thereby combining a data‐driven methodology with thermodynamic considerations and microkinetic modeling as a function of the applied overpotential. Our approach allows deriving the BI from simple adsorption free energies, which are easily accessible to electronic structure theory in the density functional theory (DFT) approximation. We outline how our methodology may steer the design of efficient bifunctional catalysts on the atomic scale.