Oxygen Catalytic Activity Research Articles

Symmetric Electronic Structures of Active Sites to Boost Bifunctional Oxygen Electrocatalysis by MN4+4 Sites Directly from Initial Covalent Organic Polymers

AbstractTransition metal‐nitrogen‐carbon (M‐N‐C) catalysts with CoN4 centers have attracted great attention as a potential alternative to precious metal catalysts for bifunctional oxygen electrocatalysis. However, the asymmetric charge environment of the active site of MN4 obtained by conventional pyrolysis strategy makes the unbalanced adsorption of oxygen molecules, which restricts the activities of both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Herein, a series of well‐defined quasi‐phthalocyanine conjugated 2D covalent organic polymer (COPBTC‐M) is developed with MN4+4 active sites through a pyrolysis‐free strategy. Compared to CoN4 site, the additional subcentral N4 atoms in MN4+4 site in COPBTC‐Co catalyst balance the charge environment and form a symmetric charge distribution, which changes the antibonding orbital of the active metal and regulate the oxygen species adsorption, thus improving the activity of the bifunctional oxygen electrocatalysis. In Silico screening demonstrates that cobalt has the best ORR and OER activity for COPBTC‐M with MN4+4 sites, which can be attributed to the fewer anti‐bonding orbital below the Fermi level, which weakens the oxygen species adsorption. Both theoretical and experimental results verify that the COPBTC‐Co possesses unique CoN4+4 active sites and the harmonious coordinating environment can lead to superior bifunctional oxygen catalytic activity with a high bifunctional oxygen catalytic activity (ΔE [Ej10 – E1/2] = 0.76 V), which is comparable with the benchmark Pt/C‐IrO2 pairs. Accordingly, the as‐assembled Zn–air battery exhibits a maximum power density of 157.7 mW cm −2 with stable operation for >100 cycles under an electric density of 10 mA cm −2. This study provides a characteristic understanding of the intrinsic active species toward MNx centers and could inspire new avenues for designation of advanced bifunctional electrocatalysts that catalyze ORR and OER processes simultaneously.

Starch-based porous carbon microsphere composited NiCo2O4 nanoflower as bifunctional electrocatalyst for zinc-air battery

It is significant to explore and design outstanding bifunctional oxygen electrocatalysts to promote the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in zinc–air batteries. Herein, a novel porous carbon microspheres (CMS2) modified by NiCo2O4 nanoflower (CMS2–NiCo2O4) have been prepared as an ORR and OER catalyst. The hierarchical porous structure of CMS provides high conductivity and abundant active sites for ORR, whereas the synergistic effect of NiCo2O4 nanosheets and a small amount of FeZn oxides act as the positive phase for OER. The efficient oxygen catalytic activity is gained by creating a coupling interface between NiCo2O4 and CMS. The optimized CMS2–NiCo2O4 shows a half–wave potential of 0.82 V toward ORR and an overpotential of 392 mV toward OER. Particularly, CMS2–NiCo2O4 also exhibits an excellent peak power density (175.5 mW cm−2) as a catalyst for zinc–air batteries, which is superior to the commercial Pt/C + RuO2 catalyst (120.5 mW cm−2), and it also demonstrates a remarkable stability even after the charge–discharge cycles of 167 h. The prepared CMS2–NiCo2O4 is promising for the application of the bimetallic oxide catalyst for zinc–air battery.

Hierarchical mesoporous NiO nanosheet arrays as integrated electrode for hybrid sodium-air batteries

Attributed to its environmental friendliness, high theoretical energy density, and abundant sodium resource, rechargeable hybrid sodium-air batteries (HSABs) are expected to become a promising pioneer of the new-generation green energy storage device. However, HSABs suffer from the high voltage gap, low energy conversion efficiency, and poor cycle stability due to the low catalytic activity of catalysts caused by the degradation of polymer binders. Herein, hierarchical mesoporous NiO nanosheet arrays grown on carbon papers (CP) (NiO NA@CP) were synthesized by a facile and efficient hydrothermal route and calcination process, which acts as an integrated electrode for HSABs. Compared with traditional air electrodes that contain a polymer binder and conductive carbon, the integrated NiO NA@CP electrode prevents the aggregation of catalysts, improves the electronic conductivity by good electric contact and ensures its robust mechanical stability. In addition, NiO NA@CP electrode with the abundant porosity and large specific area offers plenty of active sites and shortens ion transfer length and rapid mass transport in ORR/OER process, leading to excellent oxygen catalytic activities. HSABs with NiO NA@CP electrode show a low overpotential of 0.65 V, a state-of-the-art power density (7.53 mW cm−2), as well as an excellent cyclability of 170 cycles (over 170 h) at a current density of 0.1 mA cm−2.

Suppressing the Surface Amorphization of Ba0.5Sr0.5Co0.8Fe0.2O3-δ Perovskite toward Oxygen Catalytic Reactions by Introducing the Compressive Stress.

Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) perovskite has been recognized as a promising oxygen evolution reaction (OER) catalyst due to its superior intrinsic catalytic activity. However, BSCF suffers from serious degradation during the OER process due to its surface amorphization caused by the segregation of A-site ions (Ba2+ and Sr2+). Herein, we construct a novel BSCF composite catalyst (BSCF-GDC-NR) by anchoring the gadolinium-doped ceria oxide (GDC) nanoparticles on the surface of a BSCF nanorod by a concentration-difference electrospinning method. Our BSCF-GDC-NR has greatly improved bifunctional oxygen catalytic activity and stability toward both oxygen reduction reaction (ORR) and OER compared with the pristine BSCF. The improvement of the stability can be related to that anchoring GDC on BSCF effectively suppresses the segregation and dissolution of A-site elements in BSCF during the preparation and catalytic processes. The suppression effects are ascribed to the introduction of compressive stress between BSCF and GDC, which greatly inhibits the diffusions of Ba and Sr ions. This work can give a guidance for developing the perovskite oxygen catalysts with high activity and stability.

Co, N co-doped carbon nanosheets coupled with NiCo2O4 as an efficient bifunctional oxygen catalyst for Zn-air batteries

Developing of inexpensive and efficient bifunctional oxygen catalysts is important for the zinc-air batteries (ZABs). Here, a composite of Co, N co-doped carbon nanosheets coupled with NiCo2O4 (NiCo2O4/CoNC-NS) is developed as oxygen catalyst, which has good bifunctional oxygen catalytic activity and durability. Specifically, the half-wave potential of oxygen reduction reactions (ORR) is 0.849 V, and the overpotential of oxygen evolution reactions (OER) is 1.582 V at a current density of 10 mA cm−2. And the assembled liquid ZABs based on NiCo2O4/CoNC-NS exhibit high open circuit potential (OCP, 1.482 V), high peak power density (148.3 mW cm−2) and large specific capacity (699.9 mAh g−1) with long-term stability. Moreover, the further assembled solid ZABs can also provide high OCP (1.401 V), good power density (58.1 mW cm−2) and superior stability. This work would provide a good reference for the development of other advanced oxygen catalyst in future.

OER highly active encapsulants to improve the electrochemical anticorrosion of Fe–N–C for ultralong-lifespan and high-rate rechargeable zinc–air batteries

Oxygen catalytic activity: ΔE = 0.52 V. Carbon corrosion was alleviated by: (1) encapsulation by LDH that preferentially catalyzes OER and (2) depressing radical generation via fast disproportionation and electro-reduction/oxidation of peroxide.

Constructing asymmetrical dual catalytic sites in manganese oxides enables fast and stable lithium–oxygen catalysis

A general asymmetrical dual-site (Mn–Ru or Mn–Ir) construction strategy on manganese oxides is demonstrated to significantly improve the oxygen catalytic activity and cycling stability toward lithium–oxygen batteries.

A Mass Transfer-Enhanced Pyrolysis-Free Bifunctional Catalyst to Boost Ultralong Lifespan Zinc-Air Batteries

The development of efficient and low-cost bifunctional oxygen catalysts is essential yet a challenge for zinc-air batteries (ZABs). Here, we prepared a pyrolysis-free 3-dimensional hybrid catalyst (COP-Fe@3D-LDH) with bifunctional oxygen-catalytic activity by integrating layered double hydroxides (3D-LDH) and a fully conjugated iron phthalocyanine-based covalent organic polymer (COP-Fe). More hierarchically porous and larger specific surface area (170.4 m 2 g −1 ) can effectively enhance the mass transfer process and active site exposure of cathode, allowing COP-Fe@3D-LDH to exhibit an outstanding peak power density (148.5 mW cm −2 ) and an ultralong lifespan (over 400 h at 10 mA cm −2 ) in ZABs. Accordingly, this work provides a new perspective to enhance the performance of pyrolysis-free catalysts in ZABs.

Understanding the Effect of Nickel Doping in Cobalt Spinel Oxides on Regulating Spin State to Promote the Performance of the Oxygen Reduction Reaction and Zinc–Air Batteries

Metal-doped cobalt spinel oxides are considered to be effective materials to improve the oxygen reduction reaction (ORR) performance. However, the doping sites of nickel in Co3O4 spinel (octahedral sites or tetrahedral sites) remain controversial, leading to a poor understanding of the effects of nickel. Herein, directionally introducing nickel into the octahedral sites of Co3O4 (NiOh-Co3O4) is proposed by exploiting the different redox capabilities of different nickel sources, which yields an encouraging ORR and rechargeable Zn–air battery performance. Magnetic measurements and theoretical calculations reveal that the nickel occupied at the octahedral site can effectively promote the spin-state transition from low spin to higher spin states for cobalt ions and the hybridization of Co 3d–O 2p electrons, resulting in the optimization of the adsorption strength for the oxygen intermediates, thus improving the oxygen catalytic activity of NiOh-Co3O4.

Greatly enhancing the bifunctional oxygen catalytic activities of cobalt-based perovskites by anchoring metal sulfides

Co-based perovskites have been considered as the promising bifunctional oxygen catalysts for zinc-air batteries (ZABs) though their catalytic activities toward oxygen reduction reaction (ORR) are still need to be improved. In this work, we adopt a facile method to anchor MnS, CoS2 with high ORR activity on SrNb0.1Co0.7Fe0.2O3-δ (SNCF) surface. The optimized perovskite hybrid (SNCF-Mn-S4) exhibits the highest bifunctional oxygen catalytic activity among most of the perovskites, and its half-wave potential (E1/2) positively shifts as high as 180 mV compared with that of SNCF. The aqueous ZAB with SNCF-Mn-S4 has the high peak power density of 129.4 mW cm−2 and excellent cycling stability during 4500 charge-discharge cycles. Moreover, the energy efficiency of ZAB with SNCF-Mn-S4 can reach as high as 82%. This can be ascribed to the high oxygen catalytic activity of SNCF-Mn-S4 and hybrid effects of oxygen catalytic reactions and ion conversion reactions caused by CoS2, CoO and Co-based perovskite. Our works provides a feasible strategy for developing the Co-based perovskites with superior bifunctional catalytic properties for the high-performance ZABs.

Electronic Delocalization Regulates the Occupancy and Energy Level of Co 3dz2 Orbitals to Enhance Bifunctional Oxygen Catalytic Activity

AbstractCobalt–nitrogen–carbon is hitherto considered as one of the most satisfactory alternatives to precious metal catalysts for oxygen electrocatalysts. However, precisely tuning the local coordination of Co sites and thus engineering d‐orbital electron configuration to optimize the binding energy of the intermediates remains a huge challenge. Herein, a robust electrostatic self‐assembly strategy is developed to engineer penta‐coordinated Co sites by introducing axial O ligands with atomic‐level precision to form CoN4O1 configurations on MXene nanosheets (CoN4‐O/MX). The optimized CoN4‐O/MX demonstrates outstanding bifunctional electrocatalytic performance with a small potential gap of 0.72 V, significantly outperforming the cobalt–nitrogen–carbon catalyst with plane‐symmetric CoN4 sites and precious metal counterparts. The Zn–air batteries integrated with CoN4‐O/MX provide an outstanding peak power density of 182.8 mW cm−2 and a long‐term cyclability for 250 h. Density functional theory calculations reveal that CoO coordination induces electronic delocalization to draw off partial electrons from the dz2 orbital, which forms unsaturated orbital filling and lifts the energy level, resulting in a stronger Lewis basicity to facilitate electron injection into the intermediate. The study presented here provides not only a novel methodology to achieve precise control of heteroatom coordination, but also a fundamental understanding about the structure–activity relationships of dz2 orbitals.

High-performance alkaline hybrid zinc batteries with heterostructure nickel/cobalt sulfide

Despite their high energy density, great safety, and environmental friendliness, zinc-air batteries (ZABs) has insufficient energy efficiency and low discharge voltage for wide application. Constructing alkaline hybrid zinc battery (AHZB) by coupling ZABs with alkaline zinc-transition metal batteries can effectively address these issues. Herein, we report a nickel/cobalt sulfide heterostructure supported on nickel foam (Ni3S4@CoSx-NF), which exhibits excellent redox properties and high bifunctional oxygen catalytic activities. The aqueous AHZB with Ni3S4@CoSx-NF cathode demonstrates unprecedented energy efficiency (∼90%), high discharge voltage (1.70 V at 50 mA cm−2), and outstanding cycling stability. The evolution of valence states and phases of key materials observed through ex-situ characterizations suggests that Ni4+ and Co4+ contribute to the high redox activity. The solid-state AHZB with polyacrylamide-based gel electrolyte and Ni3S4@CoSx-NF cathode shows high power density over 100 mW cm−2, preceding that of self-supported solid ZAB. Importantly, it can operate at temperatures between −40 and 80 °C.

Achieving high energy efficiency of alkaline hybrid zinc battery by using the optimized Co–Mn spinel cathode

As a potential candidate in the future energy storage system, Zinc-air batteries (ZABs) are impeded by their insufficient discharge voltages and low charge-discharge efficiencies. Building the alkaline hybrid zinc batteries (AHZBs) combining ZAB and alkaline zinc/cobalt batteries (ZCB) at the battery level can supply an effective strategy to solve these problems. In this work, we fabricate a self-supported Mn–Co spinel electrode (named as MnCo2O4) with the porous nanofiber morphology by a facile hydrothermal method and assemble AHZB. Thanks to the large electrochemical active surface area and appropriate ratio of Co2+/Co3+, the as-prepared MnCo2O4 electrode shows both the high bifunctional oxygen catalytic activities for ZABs and metal ion redox properties for ZCBs. AHZB with the self-supported MnCo2O4 electrode possesses two voltage platforms in both charge and discharge processes due to the oxygen evolution/reduction reactions (OER/ORR) ZABs and metal ion redox reaction in ZCBs. Besides of the highly power density and excellent cyclic stability, the charge-discharge efficiency of our AHZB with the self-supported MnCo2O4 electrode can reach 86.2%, almost being the highest value in the recent works. Our work supplies a viable strategy for developing high-performance ZABs with improved discharge voltage and charge-discharge efficiency.

CoFeNi/N-codoped carbon nanotubes with small diameters derived from spherical Prussian blue analog as bifunctional oxygen electrocatalysts for rechargeable Zn-air batteries

Owing to sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), it is still challenging to rationally design and construct bifunctional electrocatalysts with high performance, low-cost and good stability to substitute precious-metal catalysts. Herein, we introduce Ni ions to obtain spherical Prussian blue analog (PBA) doped with Co/Fe/Ni and further to synthesize nitrogen and Co/Fe/Ni co-doped carbon nanotubes (denoted as CoFeNi-CNTs) with small diameters (20–30 nm) by pyrolyzing the mixture of melamine and PBA. The optimized CoFeNi-CNTs have abundant metal-nitrogen-carbon (M-N-C) structures and CoFeNi nanoparticles respectively as effective ORR and OER active sites, which lead to outstanding electrocatalytic activities and durability with a half-wave potential of 0.85 V for ORR and an overpotential of 440 mV for OER. Especially, the rechargeable Zn-air battery based on CoFeNi-CNTs catalyst delivers a high peak power density of 138.7 mW cm -2 , specific capacity of 793 mAh g Zn -1 and stable charge-discharge cycling over 500 h, outperforming the Pt/C-RuO 2 based devices. And all-solid-state Zn-air battery also displays excellent discharge-charge performance and stability. This work explores the optimization of oxygen catalytic activity for carbon nanotubes by reducing diameters and constructing dual-active-sites strategy. • Co/Fe/Ni doped spherical Prussian blue analog (PBA) precursor is developed. • CoFeNi/N-doped carbon nanotubes (CoFeNi-CNTs) with small diameters are synthesized. • The CoFeNi-CNTs consist of Co/Fe/Ni-N-C and CoFeNi nanoparticle active sites. • The catalyst shows oxygen bifunctional catalytic activities with an overpotential of 820 mV. • The CoFeNi-CNTs based Zn-air batteries have high power density and durability.

Sulfur-modulated FeNi nanoalloys as bifunctional oxygen electrode for efficient rechargeable aqueous Zn-air batteries

Currently, FeNi nanoalloys have received considerable attention for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in rechargeable aqueous zinc (Zn)-air batteries (ZABs) because of their high content and good chemical stability. However, their poor electronic conductivity, small surface area, and sluggish activity seriously hinder their catalytic performance. Herein, S-modulated FeNi nanoalloys supported by hierarchically porous carbon (S-FeNi/PC) are synthesized through the thermal treatment of metal-organic precursors for efficient bifunctional oxygen catalysis. S decoration endows S-FeNi/PC with a superior OER performance while maintaining an ORR performance that is comparable to that of Pt/C. Hence, S-FeNi/PC exhibits excellent bifunctional oxygen catalytic activity, outperforming the noble-metal-based composite catalysts of Pt/C and RuO2. Notably, the ZABs assembled with S-FeNi/PC exhibit high specific capacity (792 mA h g−1), high peak power density (123.5 mW cm−2), and remarkable durability for 700 charge/discharge cycles at 10 mA cm−2, which surpasses the performance of commercially available Pt/C-RuO2 and other catalysts in previously reported studies. This study will provide not only new bifunctional oxygen electrodes for efficient ZAB devices but also new insights into the design of FeNi-based materials for a wide range of catalytic applications.

Simultaneously promoting charge and mass transports in carved particle-in-box nanoreactor for rechargeable Zn-air battery

Fundamental understanding of fabricating promoted bi-functional electrocatalyst to achieve fast charge-transfer and smooth mass-transport in oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) through the rational management of catalyst composition and ingenious design of nanostructure is highly desired but still a formidable challenge. Herein, an advanced carved particle-in-box nanoreactor, composed of small Fe-Co-Ni tri-metallic alloy nanoparticles confined in porous nitrogen-doped carbon nanocage, was developed through a spatially-confined pyrolysis strategy. Tri-metal alloy could optimize the electronic structure of the catalyst, thus inducing the charge redistribution, and then regulating the adsorption and desorption energy barriers of intermediates in electrochemical reactions. Unique nano-hole design provided convenient and efficient channels for mass transfer during ORR and OER processes. Thanks to these attributes, the hybrid electrocatalyst delivered decent reversible oxygen catalytic activities, evidenced by a high half-wave potential of 0.850 V towards ORR and a low overpotential of 355 mV at 10 mA/cm2 for OER both in alkaline electrolyte. As a proof-of-concept, this as-developed carved particle-in-box nanoreactor enabled the assembled Zn-air battery to deliver a narrow potential gap of 0.735 V, a decent power density of 315 mW/cm2, a notable specific capacity of 754 mAh/gZn and excellent durability up to 165 h of continuous charge and discharge operations, thus implying the potential applications of this sophisticated catalyst model for promising energy conversion.

FeCo nanoclusters inserted N,S –doped carbon foams as bifunctional electrocatalyst for high-performance rechargeable Zn-air batteries

The availability of high-performance biofunctional electrocatalysts is the enabler for the wide commercialization of Zn-air batteries (ZAB). In this work, a bifunctional electrocatalyst FeCo/1:2/PNSC is developed by embedding FeCo nanoclusters into porous N,S-doped carbon foams (PNSC). The results show that the highly-dispersed FeCo nanoclusters provided more active sits for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The modulated electronic structure of heterojunction is found to accelerate the ORR/OER kinetic behaviors. The optimal FeCo/1:2/PNSC sample exhibits the excellent bifunctional oxygen catalytic activities with the half-wave potential of 0.86 V for ORR and the overpotential of 298 mV for OER at 20 mA cm−2 in alkaline electrolyte. This outperforms the commercial catalysts of Pt/C and RuO2. The constructed FeCo/1:2/PNSC-based ZAB cell displays high power density and long-term cyclability.

Perovskite oxide catalyst having improved oxygen catalytic activity and preparation method thereof

Perovskite oxide catalyst having improved oxygen catalytic activity and preparation method thereof

Co/Co-N/Co-O Rooted on rGO Hybrid BCN Nanotube Arrays as Efficient Oxygen Electrocatalyst for Zn-Air Batteries.

Developing high-performance non-noble metal bifunctional oxygen reduction and evolution reaction electrocatalysts is a critical factor for the commercialization of rechargeable Zn-air batteries. Herein, Co/Co-N/Co-O rooted on reduced graphene oxide (rGO) hybrid boron and nitrogen codoped carbon (BCN) nanotube arrays (BCN/rGO-Co) is prepared by facile low-temperature precross-linking and high-temperature pyrolysis treatment. Benefit from the synergistic effect of its B/N codoping, Co/Co-N/Co-O bifunctional active sites, 3D hybrid porous structure of BCN nanotubes, and highly conductive rGO sheets. The obtained BCN/rGO-Co exhibits superior bifunctional oxygen catalytic activity with a positive ORR half-wave potential (0.85 V) and a low OER potential (1.61 V) at 10 mA cm-2. Additionally, the BCN/rGO-Co-based liquid Zn-air batteries displays a large peak power density of 157 mW cm-2, and a long charge/discharge cycle stability of 200 h, outdoing the commercial Pt/C+Ru/C catalyst.

Synthesis of CuxCo3\u2212xO4 nanocatalyst for degradation of nitrogenous organic wastewater in Fenton-like membrane reactor

Membrane Fenton-like process with cobalt–copper spinel catalyst is proposed to degrade nitrogenous organic hazardous in wastewater. Cu-auxiliary cobalt oxide (CuxCo3–xO4) was synthesized with the dispersion co-precipitation method. As-prepared CuCo2O4 performed as the best catalyst for Fenton degradation on nitrogen-containing organic compound as methylene blue (C16H18N3ClS) in water and N,N-dimethylacetamide [CH3CON(CH3)2] in industrial wastewater. Lattice substation of Cu2+ to Co2+ ion increased the oxygen vacancies and catalytic activity. The catalyst stability was improved owing to hybrid polarization confinement (total metal elution less than 0.8 mg/L). Methylene blue in water (C0 = 100 mg/L) was completely decolorized in 50 min using 0.6 g/L CuCo2O4 and 0.09 M H2O2 at intrinsic pH 6.7. Degradation reaction rate constant was increased by two folds as k = 0.076 min−1 catalyzed by CuCo2O4 over k = 0.039 min−1 by Co3O4. DMAc-contaminant wastewater of high CODs 19,080 mg/L was treated using 2.4 g/L CuCo2O4 and 2.4 M H2O2 at intrinsic pH = 7.6. Removal rate of DMAc was enhanced from 81 to 99% in the ceramic membrane reactor when H2O2 was activated, and self-sweeping effect was suppressed. As a result, Total Organic Nitrogen (2900 mg/L) in the wastewater was mineralized by 99.9% with a fast transformation to inorganic NO3− ion. Biodegradability of the resistant organic wastewater was remarkably improved, and BOD/COD was increased by 18 folds.