Bifunctional Oxygen Electrocatalysis Research Articles

A ΔE= 0.63 V Bifunctional Oxygen Electrocatalyst Enables High-Rate and Long-Cycling Zinc-Air Batteries.

Rechargeable zinc-air batteries constitute promising next-generation energy storage devices due to their intrinsic safety, low cost, and feasibility to realize high cycling current density and long cycling lifespan. Nevertheless, their cathodic reactions involving oxygen reduction and oxygen evolution are highly sluggish in kinetics, requiring high-performance noble-metal-free bifunctional electrocatalysts that exceed the current noble-metal-based benchmarks. Herein, a noble-metal-free bifunctional electrocatalyst is fabricated, which demonstrates ultrahigh bifunctional activity and renders excellent performance in rechargeable zinc-air batteries. Concretely, atomic Co-N-C and NiFe layered double hydroxides (LDHs) are respectively selected as oxygen reduction and evolution active sites and are further rationally integrated to afford the resultant CoNC@LDH composite electrocatalyst. The CoNC@LDH electrocatalyst exhibits remarkable bifunctional activity delivering an indicator ΔE of 0.63V, far exceeding the noble-metal-based Pt/C+Ir/C benchmark (ΔE = 0.77V) and most reported electrocatalysts. Correspondingly, ultralong lifespan (over 3600 cycles at 10mAcm-2 ) and excellent rate performances (cycling current density at 100mAcm-2 ) are achieved in rechargeable zinc-air batteries. This work highlights the current advances of bifunctional oxygen electrocatalysis and endows high-rate and long-cycling rechargeable zinc-air batteries for efficient sustainable energy storage.

Activating inverse spinel NiCo2O4 embedded in N-doped carbon nanofibers via Fe substitution for bifunctional oxygen electrocatalysis

To improve the structure-dominant activity, rational design of oxide-based materials remains challengeable in bifunctional oxygen electrocatalysis, especially from the perspective of electronic modulation. Herein, we demonstrate that the electron configuration of inverse spinel NiCo2O4 can be activated by controllable substitution of Fe into the octahedral centers. Fe-substituted NiCo2O4 nanoparticles embedded in porous N-doped carbon nanofibers (NiCo2-xFexO4/NCNF), which were synthesized by scalable electrospinning, exhibit a correlated relationship with Fe atomic content and achieve an optimal bifunctional activity (ΔE = 0.74 V) at 0.25 at.%. Theoretical calculation shows that the substitution of Co3+ by Fe3+ modulates the electrons filling in eg orbital of octahedral cation via delocalizing the electrons around O anions. The increased density of states around the Fermi level further regulate the adsorption energy of oxygen intermediates and lead to better bifunctional performance than commercial Pt/C + RuO2 in rechargeable Zn-air battery. This work provides a new pathway to develop cost-effective bifunctional electrocatalysts for electrochemical energy storage and conversion.

GdFeO3 Perovskite Oxide Decorated by Group X Heterometal Oxides and Bifunctional Oxygen Electrocatalysis.

Bifunctional electrocatalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are necessary in the renewable energy systems. However, the kinetically slow and large energy-demanding procedures of oxygen electrocatalysis make the preparation of bifunctional catalysts difficult. In this work, we report a novel hierarchical GdFeO3 perovskite oxide of a spherelike nanostructure and surface modification with the group X heterometal oxides. The nanostructured GdFeO3 layer behaved as a bifunctional electrocatalyst in the oxygen electrocatalysis of OER and ORR. Moreover, the surface decoration with catalytically active PtOx + Ni/NiO nanoparticles enhanced the electrocatalytic performances substantially. Incorporation of mesoporous PtOx + Ni/NiO nanoparticles into the porous GdFeO3 nanostructure enlarged the electrochemically active surface area and provided the interconnected nanostructures to facilitate the OER/ORR. The nanostructures were visualized by scanning electron microscopy and transmission electron microscopy images, and the surface area and pore size of nanoparticles were analyzed from N2 adsorption/desorption isotherms. Tafel analysis indicates that surface modification effectively improves the kinetics of oxygen reactions and accordingly increases the electrocatalytic efficiency. Finally, the 2 wt % PtOx + NiO|GdFeO3 (x = 0, 1, and 2) electrode achieved the enhanced OER performance with an overpotential of 0.19 V at 10 mA/cm2 in an alkaline solution and a high turnover frequency of 0.28 s-1 at η = 0.5 V. Furthermore, the ORR activity is observed with an onset potential of 0.80 V and a half-wave potential (E1/2) of 0.40 V versus reversible hydrogen electrode.

Molten Salt-Assisted Carbonization and Unfolding of Fe, Co-Codoped ZIF-8 to Engineer Ultrathin Graphite Flakes for Bifunctional Oxygen Electrocatalysis

Molten Salt-Assisted Carbonization and Unfolding of Fe, Co-Codoped ZIF-8 to Engineer Ultrathin Graphite Flakes for Bifunctional Oxygen Electrocatalysis

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.

In situ encapsulation engineering boosts the electrochemical performance of highly graphitized N-doped porous carbon-based copper-cobalt selenides for bifunctional oxygen electrocatalysis.

Transition-metal selenides are gaining prominence as promising electrode materials for energy storage applications owing to their low electronegativity and environment-friendliness compared with metal sulfides/oxides. Herein, a CuCoSe@NC nanocomposite with copper-cobalt selenides embedded in highly graphitized N-doped porous carbon was synthesized by an in situ encapsulation strategy with metal-organic framework crystals (CuCo-BDC) as templates followed by selenization, and used as a bifunctional electrocatalyst for Zn-air batteries in lye. The result shows that the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalytic activity of the optimal CuCoSe@NC-2 was enhanced, and the assembled Zn-air batteries exhibited a remarkable electrochemical performance with the use of the CuCoSe@NC-2 electrode, including a high power density (137.1 mW cm-2) and excellent charge-discharge cycling stability, which were better than those of the Pt/C + RuO2 electrocatalyst. Such improvement is attributed not only to the higher porosity and larger specific surface area (342 m2 g-1) of the carbon matrix, which increased the contact area with oxygen-containing species, but also the encapsulation effect of the highly graphitized N-doped carbon layer and the high content of pyridine-N species also further improved the conductivity of selenide composites. This work has introduced N-doped bimetallic selenides as an ideal candidate for bifunctional electrocatalysts.

A graphene-like nanoribbon for efficient bifunctional electrocatalysts

A graphene-like nanoribbon has been synthesized by a one-step heat treatment method. And which have excellent bifunctional oxygen electrocatalysis due to their efficient synergistic effect between Fe, Co, N and F, and full exposure of active sites.

A “Ship-in-a-Bottle” strategy to anchor CoFe nanoparticles inside carbon nanowall-assembled frameworks for high-efficiency bifunctional oxygen electrocatalysis

Elaborate design of cost-effective and highly-efficiency bifunctional electrocatalysts towards the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is critically essential for the advancement of rechargeable metal-air batteries. Herein, we develop a straightforward and scalable hydrogel-bridged pyrolysis strategy for the exquisite construction of a “ship-in-a-bottle”-structured bifunctional catalyst consisting of fine CoFe nanoparticles encapsulated inside the carbon nanowall-assembled frameworks (abbreviated as [email protected] hereafter). The deliberate design of such intriguing hierarchical honeycomb-like architecture with tightly confined CoFe nanoparticles and open configuration endows the as-fabricated [email protected] with sufficient well-dispersed active sites, rapid charge transfer efficiency, accelerated mass diffusion and robust mechanical strength. Consequently, the resultant [email protected] catalyst shows outstanding catalytic performance toward the ORR and OER with high activity and long-term stability. More encouragingly, a rechargeable Zn–air battery using [email protected] as the air cathode displays superb energy density, high energy efficiency and robust reversibility, surpassing the state-of-the-art precious Pt/C + RuO2–assembled counterpart. The developed methodology for the fabrication of “ship-in-a-bottle” architectures may open new opportunities to low-cost, mass production of high-efficiency bifunctional oxygen electrocatalysts for a variety of renewable energy technologies and beyond.

Structural regulation of N-doped carbon nanocages as high-performance bifunctional electrocatalysts for rechargeable Zn-air batteries

The development of highly active, inexpensive, and stable bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts to replace noble metal Pt and RuO2 catalysts remains a considerable challenge for highly demanded reversible fuel cells and metal-air batteries. Herein, a novel nitrogen doped carbon nanocage (N–CNC-900) is fabricated via facile carbonization of bimetal-organic framework (BMOF). The newly obtained N–CNC-900 catalyst is featured by multiple carbon layers with a wide lattice spacing of 0.434 nm and the aperture of approximate 10 nm, ultrahigh specific surface area and abundant N doping amount as well. As results, the optimized N–CNC-900 exhibits a low overpotential of 1.52 V toward OER at a current density of 10 mA/cm2, and also show a large half-wave potential of 0.90 V for ORR, respectively. High activity and stability toward the bifunctional oxygen electrocatalysis are also demonstrated on the N–CNC-900. When explored as air cathode for rechargeable Zn-air battery, a high open-circuit voltage (1.54 V) and long-term stability (after cycling 200 h) can be realized, outperforming the commercial Pt/C + RuO2 association. This outstanding performance can be attributed to improved reaction kinetics of both ORR and OER, which originates from the enlarged lattice spacing in the few-layer conductive carbon nanocage structure and the existing metal-nitrogen-carbon (M-Nx-C). These results forebode the optimized N–CNC-900 presenting a promising application in metal-air batteries, as well the lattice modulation of carbon materials providing a novel approach for designing advanced electrocatalysts.

Ceria Nanodots Anchored on ZIF67-Derived Framework By Atomic Layer Deposition for Efficient Bifunctional Oxygen Electrocatalysis

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which are the two most important reactions for electrocatalytic activities, has been widely studied for sustainable and renewable electrochemical applications, including fuel cells[1] , [2], metal-air batteries[3] and water electrolysis[4]. For the development of new catalysts alternative to noble metal-based materials, metal organic frameworks (MOFs) are being actively used as the precursor structure. ZIF-67, a kind of MOF structure made of cobalt nitrate and 2-methylimidazole ligands, has proved to be a good candidate for ORR catalysis due to their rich of Co-N-C active sites. However, ZIF-67 tends to aggregate during the pyrolysis process by breaking C-H or C-O bonds.In this study, atomic layer deposition (ALD) was applied to coat an atomically thin cerium oxide (CeO2, ceria) coatings the MOF structure, which is expected to incur synergistic catalytic activity and suppress the thermal agglomeration. ALD is a self-limiting surface chemistry process, and is able to create highly conformally layer-by-layer thin film on any complex 3D structure with controllable thickness at an atomic level.[5] Ceria has shown good synergistic effect with other metals for OER performance due to its ability for electron exchange and ion reduction.[6] We demonstrates a facile synthesis of Co/Ce co-doped porous carbon nanomaterials by pyrolyzing the ceria-coated ZIF structure. The resultant samples showed uniform crystal structure which are in well accordance with ZIF-67 precursors. The as-prepared samples also showed enhanced electrocatalytic activities for both ORR and OER comparable to that of noble metal benchmarks (Pt/C and IrO2) and in terms of onset potential, half-wave potential, and current density. A sample prepared by performing 15 cycles of ceria ALD followed a pyrolysis at 700 °C shows the highest onset potential (0.95 V versus RHE) for ORR and superior stability in comparison to commercialized Pt/C. Meanwhile, a sample with 5 cycles of ceria ALD exhibits an excellent OER performance (1.48 V at 10 mA cm-2) and maintained a good OER durability performance (from 1.48 V to 1.50 V after 2,000 potentiodynamic cycles).

Filling the in situ-generated vacancies with metal cations captured by C−N bonds of defect-rich 3D carbon nanosheet for bifunctional oxygen electrocatalysis

Filling the in situ-generated vacancies with metal cations captured by C−N bonds of defect-rich 3D carbon nanosheets produces a superior ORR/OER bifunctional catalyst for a rechargeable Zn-air battery. • A Janus-featured bifunctional ORR/OER catalyst was derived from defect-rich carbon. • The C–N bonds at defects of carbon capture metal cations in synthesis. • The M–N–C moieties is responsible for the ORR and bimetallic particles for the OER. • In-situ formed graphene layers with an interconnected structure facilitate electron transport. • The catalyst is highly active and stable for ORR/OER in a rechargeable Zn-air battery. Nitrogen-doped carbon materials with vacancies/defects have been developed as highly efficient ORR electrocatalysts but with poor activity for OER, which limits their application in rechargeable metal-air batteries. Filling the vacancies/defects with heteroatoms is expected to be an effective strategy to obtain surprising catalytic activities and improve their stability especially under the strongly oxidizing conditions during the OER process. Herein, we successfully transformed the defect-rich 3D carbon nanosheets (DCN) into a bifunctional ORR/OER electrocatalyst (DCN-M) by utilizing the in-situ generated vacancies to capture metal cations via a modified salt-sealed strategy. By varying the metal (Fe, Ni) content, the captured metal cations in DCN-M existed in different chemical states, i.e., metal atoms were stabilized by C−N bonds at low metal contents, while at high metal contents, bimetal particles were covered by graphene layers, taking responsibility for catalyzing the ORR and OER, respectively. In addition, the in-situ formed graphene layers with an interconnected structure facilitate the electron transport during the reactions. The Janus-feature of DCN-M in structures ensures superior bifunctional activity and good stability towards ORR/OER for the rechargeable Zn-air battery. This work provides an effective strategy to design multifunctional electrocatalysts by heteroatom filling into vacancies of carbon materials.

A High-Performance Ruddlesden–Popper Perovskite for Bifunctional Oxygen Electrocatalysis

Highly active and stable bifunctional materials for the oxygen evolution/reduction reaction (OER/ORR) are critical for developing high-performance metal–air batteries and fuel cells. This study dem...

Electronic structure tuning of FeCo nanoparticles embedded in multi-dimensional carbon matrix for enhanced bifunctional oxygen electrocatalysis

It is highly desirable to develop efficient, affordable and durable electrocatalysts to accelerate sluggish kinetics of both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) for expanding the applications of Zn-air batteries (ZABs). Here, Fe1Co2 alloy nanoparticles (NPs) embedded in N-doped carbon nanotubes/carbon nanosheets (CNTs/CNSs) (denoted as Fe1Co2-NC) were synthesized in situ by pyrolyzing Fe-chitosan, Co-chitosan chelates and urea. It is demonstrated that the interaction of Fe and Co can effectively modulate electronic structure of Fe and Co, in which ionic state cobalt and iron were partially oxidized, contributing to the enhanced intrinsic catalytic activity. Meanwhile, CNTs/CNSs multi-dimensional porous carbon frameworks facilitated adequate exposure of active sites and mass/electron smooth transport. Accordingly, the resulting Fe1Co2-NC catalyst exhibited a high half-wave potential of 0.88 V (vs. RHE) for ORR and a small over potential (0.356 V) for OER, rendering it with an ultralow potential difference (0.706 V) that can rival that of Pt/C + RuO2 (0.69 V). Impressively, the assembled ZABs with Fe1Co2-NC as a cathode catalyst achieved a high open circuit voltage (1.501 V), maximum power density (203.4 mW cm−2), energy density (820.30 W h kg−1) and robust durability with a slightly increased voltage gap (0.058 V) after 209 h charge-discharge test, shedding light on the great application potential.

Ionic liquid derived active atomic iron sites anchored on hollow carbon nanospheres for bifunctional oxygen electrocatalysis

Rational design of highly active bifunctional catalysts with satisfactory cost-performance as alternatives to precious metals for oxygen reduction and evolution reaction (ORR/OER) still poses challenges. Herein, highly catalytic active atomic Fe sites anchored to hollow carbon nanospheres (Fe-Nx-HCS) have been designed with optimized geometric features by introducing a new Fe-containing ionic liquid followed by a self-sacrificing, template-assisted, and controlled pyrolysis. Morphological and structural characterizations revealed abundant atomic Fe catalytic sites (Fe-N4 and Fe3 species) have a homogeneous dispersion throughout the HCS framework, resulting in high catalytic activity. The bifunctional Fe-Nx-HCS electrocatalyst had a more positive half-wave potential, higher diffusion-limiting ORR current density, as well as a lower overpotential for OER in both 0.1 M KOH and 0.05 M H2SO4. The stability of active sites and structural integrity of Fe-Nx-HCS significantly contributed to long-term cycling stability even after 10,000 potential cycles under alkaline conditions. Moreover, a rechargeable zinc-air battery device fabricated with Fe-Nx-HCS showed superior performance compared to state-of-the-art Pt/C catalyst. Density functional theory (DFT) calculations verified that the Fe3 active species enhanced Fe-N4 catalytic activity and promoted both ORR and OER. This work provides a new insight into the design and fabrication of highly active bifunctional electrocatalysts.

A Zeolitic-Imidazole Frameworks-Derived Interconnected Macroporous Carbon Matrix for Efficient Oxygen Electrocatalysis in Rechargeable Zinc-Air Batteries.

Nanostructures derived from zeolitic-imidazole frameworks (ZIFs) gain much interest in bifunctional oxygen electrocatalysis. However, they are not satisfied well for long-life rechargeable zinc-air batteries due to the limited single particle morphology. Herein, the preparation of an interconnected macroporous carbon matrix with a well-defined 3D architecture by the pyrolysis of silica templated ZIF-67 assemblies is reported. The matrix catalyst assembled zinc-air battery exhibits a high power density of 221.1 mW cm-2 as well as excellent stability during 500 discharging/charging cycles, surpassing that of a commercial Pt/C assembled battery. The synergistic effect from the interconnected macroporous structure together with abundant cobalt-nitrogen-carbon active sites justify the excellent electrocatalytic activity and battery performance. Considering the advanced nanostructures and performance, the as-synthesized hybrid would be promising for rechargeable zinc-air batteries and other energy technologies. This work may also provide significant concept in the view of electrocatalysis design for long-life battery.

Sulfurated Metal–Organic Framework-Derived Nanocomposites for Efficient Bifunctional Oxygen Electrocatalysis and Rechargeable Zn–Air Battery

The development and rational design of highly efficient and Earth-abundant bifunctional nanomaterials for electrocatalytic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) act as...

Synergistic effect of B site co-doping with Co and Ce in bifunctional oxygen electrocatalysis by oxygen deficient brownmillerite Ba2In2O5

Specificity in oxygen reduction and evolution reactions is pivotal in bifunctional catalysts in advanced energy devices which are expected to be active in a wide potential window and stable in both electrochemically reducing and oxidising atmospheres. State of the art noble metal catalysts for these reactions are fraught with issues whereas, metal oxides are expected to be stable in large potential window and can be tuned to have better bifunctional activity. Catalytically active metals, redox centres, oxygen vacancies etc. are some of the features of structured oxides which can be exploited in oxygen electrocatalysis. Brownmillerite family of compounds with general formula, A2B2O5 has high concentrations of ordered oxygen vacancy in a layer and can be promising bifunctional oxygen electrocatalysts, by appropriate B site doping. Ba2In2O5 is a well-studied system for its oxide ion conductivity and proximity of active B sites to O vacancies provide good O adsorption sites which are catalytically active. Here, cobalt and cerium are co-doped in Ba2In2O5, anticipating a synergistic effect of Ce(III)/Ce(IV) redox centre in ORR and Co activity in OER along with O vacancies providing adsorption sites. We have studied the structural changes associated with the doping by Rietveld refinement of the XRD patterns and correlated the structure to bifunctional oxygen electrocatalytic activity which is found to enhance on increasing the Co and Ce content.

Sulphur modulated Ni3FeN supported on N/S co-doped graphene boosts rechargeable/flexible Zn-air battery performance

Exploring feasible strategy for preparation of sulfur (S) modulated NiFe compounds and meanwhile clarifying the performance promoting mechanism of such catalysts has triggered numerous interest in rechargeable Zinc-air battery research field. Herein, S modulated Ni3FeN supported on N/S co-doped graphene (S-Ni3FeN/NSG) is synthesized via controlling the nitriding process of NiFe disulfides. The beneficial effect of the design strategy and S decoration on electrocatalytic activity are determined and analysed systematacially. The S-Ni3FeN/NSG-700 delivers excellent bifunctional oxygen electrocatalysis performance with half-wave potential of 0.878 V for ORR and low OER overpotential of 260 mV at 10 mA cm−2. Density Functional Theory (DFT) calculations demonstrate that S decoration effectively promotes the formation of OOH* intermediates and observably decreases the maximum of change of the Gibbs free energies for four primitive OER steps. Notably, when S-Ni3FeN/NSG-700 as air electrode applied in Zn-air battery test, the device shows superb durability for 1200 discharge/charge cycles at 10 mA cm-2. The corresponding all-solid Zinc-air battery exhibits excellent mechanical flexibility and a high power density of 140.1 mW cm-2. Two Zinc-air batteries in series can long-term stably power a self-made water-splitting device. This work provides new insights into highly efficient and low-cost bifunctional oxygen electrocatalyst designing.

Transition metal alloy integrated tubular carbon hybrid nanostructure for bifunctional oxygen electrocatalysis

Synthesis of cost-effective, robust, and efficient bifunctional electrocatalyst for the development of rechargeable Zn-air batteries (ZAB) is of considerable interest. Herein, we demonstrate the synthesis of NiCo alloy integrated nitrogen-doped tubular carbon (TC) nanostructure (NiCo–N-TC) using metal-organic self-assembly of M(II)-melamine-dipicolinic acid (DPA) (M: Ni(II), Co(II)). The NiCo alloy particles of as-synthesized NiCo–N-TC catalyst are confined at the tip like a cork. The as-synthesized catalyst was structurally engineered by acid treatment. The engineered catalyst (NiCo–N-TC-H) has an open-head hollow nanoarchitecture with uniform distribution of ultrafine NiCo alloy particles on the TC framework. The NiCo–N-TC-H catalyst follows desired 4-electron pathway for the electroreduction of oxygen in both alkaline and acidic pH. It has outstanding bifunctional electrocatalytic activity towards oxygen reduction and oxygen evolution reaction in alkaline electrolyte with a very low potential gap (ΔE) of 0.74 V. Acid-treatment-induced increase in surface area, and graphitic-N and carbon content facilitates the overall bifunctional activity. The bifunctional activity of NiCo–N-TC-H is successfully utilized for the development of rechargeable ZAB. It has long cycling stability and delivers high open circuit voltage (1.54 V), power density of 148.8 mW cm−2, and high voltaic efficiency.

Author Correction: Lattice-strained metal–organic-framework arrays for bifunctional oxygen electrocatalysis

Author Correction: Lattice-strained metal–organic-framework arrays for bifunctional oxygen electrocatalysis