Zinc-air Research Articles

Study on the synthesis of CoFe/CoFe2O4@NCNTs derived from ZnFeCo-ZIF with abundant heterostructures and oxygen vacancies as bifunctional catalyst for ORR/OER in zinc-air batteries

The rational design of bifunctional catalysts for oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) in alkaline electrolyte is of great significance for zinc-air batteries (ZABs). In this study, different types of Fe/Co compounds and nitrogen-doped carbon-based composite catalysts from trimetallic zeolitic-imidazole-framework-derived (ZnFeCo-ZIF) were synthesized by adjusting the ratio of Zn/Fe/Co. Among them, the synthesized CoFe/CoFe2O4-N-doped carbon nanotubes (CoFe/CoFe2O4@NCNTs) have abundant Fe-Nx and Co-Nx activity sites, heterostructures and oxygen vacancies. The experimental results reveal that the electrons of CoFe are transferred to CoFe2O4 at the interface of CoFe/CoFe2O4, which not only enhances the electron transfer ability, but also induces oxygen vacancies to improve the adsorption/desorption capacity of O2 and intermediates. Meanwhile, metal atoms are uniformly dispersed in the N-doped carbon nanotubes to form metal–N sites with high catalytic activity. Therefore, the CoFe/CoFe2O4@NCNTs exhibit excellent electrocatalytic performance, possessing a half-wave potential (E1/2) of 0.878 V and a prominent limiting-current densities (JL) of 6.281 mA cm−2 for ORR, and a low overpotential of 344 mV at 10 mA cm−2 for OER. In particular, the CoFe/CoFe2O4@NCNTs-equiped ZAB possesses a higher open-circuit voltage (1.50 V), a greater maximum power density (193.42 mW cm−2) and a longer cycling performance (160 h). The density functional theory (DFT) calculations show that the CoFe/CoFe2O4 heterostructure can induce the rapid transfer of electrons at the CoFe/CoFe2O4 interface, which promotes the change of the surface electronic structure of the catalyst, and thus helps to enhance the ability of the catalyst to transfer electrons.

Multilayer Porous Fe/Co-N-MWCNT Electrocatalyst For Rechargeable Zinc-Air Batteries.

The design of efficient, stable, low-cost non-precious metal-based electrocatalysts with enhanced oxygen reduction reaction (ORR) activity has garnered significant attention in the scientific community. This study introduces a novel electrocatalyst, Fe/Co-N-MWCNT, synthesized through the in-situ growth of ZIF-8 and Fe/Co-Phen on multi-walled carbon nanotubes (MWCNTs), followed by pyrolysis at varying temperatures to optimize its properties. The inclusion of Fe and Co during the pyrolysis process facilitated the creation of metal active sites and Fe-Co, enhancing electron transfer and ORR activity. Compared to Pt/C (E1/2=0.854 V, JL=4.90 mA cm-2), Fe/Co-N-MWCNT exhibited a similar half-wave potential (E1/2=0.812 V) and an improved limiting current density (JL=5.37 mA cm-2). Moreover, Fe/Co-N-MWCNT displayed remarkable stability, showing only a 7 mV negative shift in E1/2 after 2000 cycles. Ampere response testing indicated a current decay of only 7.8 % for Fe/Co-N-MWCNT after 10000 s, while Pt/C experienced a decay of about 18.4 %. The exceptional catalytic stability of Fe/Co-N-MWCNT positions it as a promising candidate for rechargeable zinc-air batteries, attributed to its high pyridinic nitrogen content, unique structure, and abundant metal active sites.

Enhanced oxygen evolution and power density of Co/Zn@NC@MWCNTs for the application of zinc-air batteries

Rechargeable zinc-air batteries (ZABs) are viewed as a promising solution for electric vehicles due to their potential to provide a clean, cost-effective, and sustainable energy storage system for the next generation. Nevertheless, sluggish kinetics of the oxygen evolution reaction (OER), the oxygen reduction reaction (ORR) at the air electrode, and low power density are significant challenges that hinder the practical application of ZABs. The key to resolving the development of ZABs is developing an affordable, efficient, and stable catalyst with bifunctional catalytic. In this study, we present a series of bifunctional catalysts composed of Co/Zn nanoparticles uniformly embedded in nitrogen-doped carbon (NC) and multi-walled carbon nanotubes (MWCNTs) denoted as Co/Zn@NC@MWCNTs. The incorporation of MWCNTs using a facile and non-toxic method significantly decreased the overpotential of the OER from 570 to 430 mV at 10 mA cm−2 and the peak power density from 226 to 263 mW cm−2. Besides, the electrochemical surface area measurements and electrochemical impedance spectroscopy indicate that the three-dimensional (3D) network structure of MWCNTs facilitates mass transport for ORR and reduces electron transfer resistance during OER, leading to a small potential gap of 0.86 V between OER and ORR, high electron transfer number (3.92–3.98) of the ORR, and lowest Tafel slope (47.8 mV dec−1) of the OER in aqueous ZABs. In addition, in-situ Raman spectroscopy revealed a notable decrease in the ID/IG ratio for the optimally configured Co/Zn@NC@MWCNTs (75:25), indicating a reduction in defect density and improved structural ordering during the electrochemical process, which directly contributes to enhanced ORR activity. Hence, this study provides an excellent strategy for constructing a bifunctional catalyst material with a 3D MWCNTs conductive network for the development of advanced ZAB systems for sustainable energy applications.

The application of Co3S4@NCNT/NCHS with excellent bifunctional catalytic activity in aqueous and flexible Zn-air batteries

In this work, we prepared a hybrid structure Co3S4@NCNT/NCHS using SiO2 nanospheres as a template. The structure is supported by hollow carbon spheres (NCHS), which are coated by Co3S4 nanoparticles and cross-linked N-doped carbon nanotubes. The combination of Co3S4 with N-doped carbon material significantly improves the electrocatalytic activity. In addition, the presence of N-doped carbon nanotubes induces more defects, which can regulate the electronic configuration of the material and improve its electrical conductivity. Therefore, Co3S4@NCNT/NCHS has good catalytic performance. At 10 mA cm−2, the OER overpotential of Co3S4@NCNT/NCHS is only 230 mV, which is lower than that of the commercial catalyst RuO2, and the ORR half-wave potential can reach 0.80 V. In the battery discharge test, Co3S4@NCNT/NCHS based ZABs can discharge continuously for 71.5 h, the specific capacity of 790.12 mA h g−1, power density of 113.09 m W cm−2, better than Pt/C+RuO2 battery. When the current density is 3 mA cm−2, ZABs assembled with Co3S4@NCNT/NCHS as catalyst can maintain a voltage gap of 0.62 V to 0.63 V within 300 h without significant change. When the current density is increased to 5 mA cm−2, ZABs based on Co3S4@NCNT/NCHS can be stably cycled for 300 h at a voltage gap between 0.80 V and 0.82 V.

Unveiling the Dynamic Evolution of Catalytic Sites in N-Doped Leaf-like Carbon Frames Embedded with Co Particles for Rechargeable Zn-Air Batteries.

The advancement of cost-effective, high-performance catalysts for both electrochemical oxygen reduction reactions (ORRs) and oxygen evolution reactions (OERs) is crucial for the widespread implementation of metal-air batteries. In this research, we fabricated leaf-like N-doped carbon frames embedded with Co nanoparticles by pyrolyzing a ZIF-L/carbon nanofiber (ZIF-L/CNF) composite. Consequently, the optimized ZIF-L/CNF-700 catalyst exhibit exceptional catalytic activities in both ORRs and OERs, comparable to the benchmark 20 wt% Pt/C and RuO2. Addressing the issue of diminished cycle performance in the Zn-air battery cycle process, further detailed investigations into the post-electrolytic composition reveal that both the carbon framework and Co nanoparticles undergo partial oxidation during both OERs and ORRs. Owing to the varying local pH on the catalyst surface due to the consumption and generation of OH- by OERs and ORRs, after OERs, the product is reduced-size Co particles, while after ORRs, the product is outer-layer Co(OH)2-enveloping Co particles.

Catalyst–Support Interaction in Polyaniline-Supported Ni3Fe Oxide to Boost Oxygen Evolution Activities for Rechargeable Zn-Air Batteries

HighlightsNi3Fe oxide, with an average size of 3.5 ± 1.5 nm, was successfully deposited onto polyaniline (PANI) support through a solvothermal strategy followed by calcination.The catalyst–support interaction between Ni3Fe oxide and PANI can enhance the Ni-O covalency via the interfacial Ni-N bond.Ni3Fe oxide/PANI-assembled Zn-air batteries achieve superior cycling life for over 400 h at 10 mA cm−2 and a low charge potential of around 1.95 V.

Synergetic Charge, Spin, and Stability of Lanthanum-Based Perovskites for Flexible Zn–Air Batteries: A Review

Synergetic Charge, Spin, and Stability of Lanthanum-Based Perovskites for Flexible Zn–Air Batteries: A Review

Boosting the activity of nitrogen-doped carbon catalyst by the guided formation of active sites and enhanced scavenging on reactive oxygen species under the regulation of cerium

The design of nitrogen-doped carbon materials with high density of active sites is of paramount importance for catalysis of the oxygen reduction reaction (ORR). Herein, an efficient oxygen reduction electrocatalyst (CL-Fe/(Fe,Ce)xOy-NC) is developed by planting carbon nanotubes with encapsulated Fe/(Fe,Ce)xOy particles on porous carbon polyhedron particles derived from calcinated ZIF-8 framework. The introduction of Ce evidently promotes the formation of pyridinic nitrogen, graphitic nitrogen and metal nitrogen species in carbon matrix, enhancing the catalytic activity towards the ORR. The Ce oxide in the catalyst effectively scavenges the active oxygen species in ORR process. Under the synergistic effect of high specific surface area with Ce species, the CL-Fe/(Fe,Ce)xOy-NC has a better half-wave potential (0.861 V vs. RHE), faster kinetics (44.13 mV dec−1) and is more stable than the commercial Pt/C catalyst. The zinc-air battery assembled with CL-Fe/(Fe,Ce)xOy-NC has the highest power density of 195 mW cm−2, energy density of 858 Wh kg−1, and better durability. This work presents a novel approach to enhance the efficacy of nitrogen-doped carbon-based catalysts, paving a possible way to substitute the precious platinum catalysts for a variety of electrochemical energy devices.

Synergistic effect of Ru single atoms and MnO2 to boost oxygen reduction/evolution activity via strong electronic interaction

Ru-based single-atomic catalysts have shown great potential application in sustainable electrochemical energy conversion/storage devices. Herein Ru single atoms anchored on the surface of MnO2 nanorods (Ru SAs@MnO2) have been successfully constructed by a facile low-temperature solid-phase reaction, which has been confirmed by X-ray adsorption spectra. The synthesized Ru SAs@MnO2 catalyst exhibits a comparable ORR performance with half-wave potential of 0.83 V and a limiting current density of 7.1 mA cm−2 to commercial Pt/C, and high OER performance with the overpotential of 320 mV at 10 mA cm−2. Theoretical calculation results indicate that Mn sites and Ru sites of Ru SAs@MnO2 act as the catalytic ORR and OER sites, respectively, and the synergistic effect between Ru SAs and MnO2 contributes to the improved catalytic performance via strong electronic interaction. When assembled zinc-air batteries, a maximum power density 230.0 mW cm−2 could be delivered at 318.5 mA cm−2.

Enhanced Low-Temperature Durability of Flexible Zinc–Air Batteries Using NaCl-Doped Dual-Network Hydrogel Electrolytes

Enhanced Low-Temperature Durability of Flexible Zinc–Air Batteries Using NaCl-Doped Dual-Network Hydrogel Electrolytes

Leaf-like Multiphase Metal Phosphides as Bifunctional Oxygen Electrocatalysts toward Rechargeable Zinc-Air Batteries.

Developing a bifunctional oxygen electrocatalyst is crucial to improve the reversibility and cycle life of a rechargeable zinc-air battery (RZAB). Here, transition metal phosphides (TMPs) with a leaf-like hierarchical structure and multiphase composition can be synthesized by the "alloying-dealloying-phosphating" strategy. The as-prepared P-NiCo(1:1) electrode takes advantage of its internal dense nanoholes and synergistic effects induced by NiCoP-containing polyphase to reveal multifunctional catalysis, such as OER and ORR. In combination of these advantages, P-NiCo(1:1) exhibits an extremely low OER overpotential of 220 mV at 10 mA cm-2, a higher half-wave potential of 0.79 V for ORR, and a smaller potential difference (ΔE) of 0.66 V. The liquid RZAB with P-NiCo(1:1) as a cathodic bifunctional catalyst delivers a higher open-circuit voltage (OCV), a larger power density of 175 mW cm-2, and longer cycling life for more than 180 h. Even when applied in solid-state flexible RZABs, the lightweight module could start high-power devices. With theoretical confirmation, the major phase NiCoP of P-NiCo(1:1) is helpful to increase the density of states, regulate the d-band center, and decrease the energy barrier to 2.13 eV, which are significantly superior to those of Co2P and Ni2P. It is believable that the synthetic strategy and activity-promoting mechanism acquired from this research can offer a guide to designing a promising rechargeable zinc-air battery system.

Engineering peripheral S-doped atomic Fe-N4 in defect-rich porous carbon nanoshells for durable oxygen reduction reaction and Zn-air batteries

Iron-nitrogen-carbon (Fe-N-C) single-atom materials have emerged as the most promising catalysts for the oxygen reduction reaction (ORR), which yet suffers from inadequate stability arising from the attack of ·OH and HO2· radicals generated by H2O2. In this study, density functional theory (DFT) calculations reveal that the presence of peripheral S atoms can regulate the electronic structure of the Fe center and suppress the formation of H2O2 to enhance the catalyst's durability. Thereafter, atomic Fe-N4 with peripheral S doping is intricately engineered in defect-rich porous carbon nanoshells (Fe-NS-C) through an adsorption-pyrolysis method. The incorporation of S not only optimizes the coordination microenvironment of Fe-N4 but also induces a larger specific surface area and richer defects. The Fe-NS-C catalyst displays remarkable ORR performance, featuring a half-wave potential (E1/2) of 0.90 V. Its low H2O2 yield (below 1.1 %) and excellent stability (10 mV day in E1/2 after 10,000 cycles) further underscore the superiority of Fe-NS-C. When employed as the cathode for Zn-air battery, Fe-NS-C achieves an impressive peak power density of 230.1 mW cm−2 and stable charge/discharge potentials over an extended duration of 150 h. This study presents an effective strategy for engineering efficient and durable single-atom electrocatalysts for ORR and Zn-air batteries.

Enhancing Zinc-Air Flow Batteries: Single-Atom Catalysis within Cobalt-Encapsulated Carbon Nanotubes for Superior Efficiency.

Amid the world's escalating energy needs, rechargeable zinc-air batteries stand out because of their environmental sustainability, with their performance being critically dependent on the oxygen reduction reaction (ORR). The inherent slow kinetics of the ORR at air electrodes frequently constrains their operational efficiency. Here, we develop a new self-catalytic approach for in situ growth of carbon nanotubes with new cathode material Co@CoN3/CNTs-800 without external additives. Density functional theory calculation reveals this method integrates nonprecious single-atom catalysis with spatial confinement, facilitating large-scale, in situ fabrication of CNTs, which can support dispersed atomic CoN3 sites and enforce spatial confinement on Co nanoparticles. The Co@CoN3/CNTs-800 electrode achieves an electron transfer number close to ideal (3.9 out of 4.0). In rechargeable zinc-air flow batteries, it achieves a peak power density of 169.5 mW cm-2 and a voltage gap that is only 1.6% larger than the original after 700 h. This work surmounts critical challenges in the ORR kinetics for zinc-air batteries.

Built-in Electric Field in 1D/2D Heterostructure Boosts Zinc Air Battery Performance.

The realization of a rechargeable zinc-air battery (ZAB) is hindered by the low intrinsic oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) activities. In this work, an abundant built-in electric field is noticed in a 1D/2D CoO/CoS2 heterostructure, triggering electron transfer from CoO to CoS2 associated with a downshifted d band center of the Co atom mitigating the strong electrochemical adsorption of *OH species on active sites; thereby, boosted OER and ORR performance are achieved. Namely, the OER specific activity of CoO/CoS2 is enhanced by 3.8- and 2.2-fold compared to the counterpart of CoO and CoS2, respectively. Furthermore, the kinetic current density of CoO/CoS2, a fingerprint of intrinsic ORR activity, is promoted by 46 and 6.6 times relative to CoO and CoS2. The rechargeable ZAB performance attains 215.6 mW cm-2, 1.6-times better than Pt/C-IrO2. Moreover, the superior performance remained for 600 h. Besides, the battery performance of the all-solid-state ZAB reaches 83.8 mW cm-2, revealing its promising application in wearable device.

Molten-Salt-Assisted Fabrication of Defect-Rich 2D/3D Nitrogen-Doped Carbon with Embedded Co Nanoparticles for High-Performance Rechargeable Zn–Air Batteries with a High Open-Circuit Voltage

Molten-Salt-Assisted Fabrication of Defect-Rich 2D/3D Nitrogen-Doped Carbon with Embedded Co Nanoparticles for High-Performance Rechargeable Zn–Air Batteries with a High Open-Circuit Voltage

Fabrication of abundant oxygen vacancies in MOF-derived (Fe,Co)3O4 for oxygen evolution reaction and as an air cathode for zinc-air batteries

Metal-organic frameworks (MOFs) find wide-ranging applications owing to their adjustable structures, diverse compositions, and large specific surface area. In this work, MOFs materials were grown in situ on carbon cloth, yielding self-supported electrodes VO-(Fe,Co)3O4@CC rich in oxygen vacancies through a simple high-temperature annealing treatment utilizing NaBH4 as an etchant. Thus the resulting self-supported electrode VO-(Fe,Co)3O4@CC exhibited excellent oxygen evolution reaction (OER) performance, achieving an overpotential of merely 288 mV at 10 mA cm−2, along with a low Tafel slope of 31.39 mV dec-1, and demonstrating robust long-term activity and stability. In addition, a liquid zinc-air battery was assembled utilizing the prepared VO-(Fe,Co)3O4@CC as an air cathode, achieving a high open-circuit voltage of 1.46 V and a high peak power density of 89.06 mW cm−2, and it maintained excellent cycling stability during cyclic charging and discharging (with a current density of 2 mA cm−2) over a 32 h period. Meanwhile, the self-supported electrode VO-(Fe,Co)3O4@CC served as an air cathode for assembling an all-solid-state flexible zinc-air battery (ZAB), demonstrating a high peak power density (38.21 mW cm−2) and exhibiting favorable cycling stability. This experiment offers insights into the potential application of MOF-derived electrocatalysts in water decomposition and zinc-air batteries.

Trifunctional Graphene-Sandwiched Heterojunction-Embedded Layered Lattice Electrocatalyst for High Performance in Zn-Air Battery-Driven Water Splitting.

Zn-air battery (ZAB)-driven water splitting holds great promise as a next-generation energy conversion technology, but its large overpotential, low activity, and poor stability for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) remain obstacles. Here, a trifunctional graphene-sandwiched, heterojunction-embedded layered lattice (G-SHELL) electrocatalyst offering a solution to these challenges are reported. Its hollow core-layered shell morphology promotes ion transport to Co3S4 for OER and graphene-sandwiched MoS2 for ORR/HER, while its heterojunction-induced internal electric fields facilitate electron migration. The structural characteristics of G-SHELL are thoroughly investigated using X-ray absorption spectroscopy. Additionally, atomic-resolution transmission electron microscopy (TEM) images align well with the DFT-relaxed structures and simulated TEM images, further confirming its structure. It exhibits an approximately threefold smaller ORR charge transfer resistance than Pt/C, a lower OER overpotential and Tafel slope than RuO₂, and excellent HER overpotential and Tafel slope, while outlasting noble metals in terms of durability. Ex situ X-ray photoelectron spectroscopy analysis under varying potentials by examining the peak shifts and ratios (Co2+/Co3+ and Mo4+/Mo6+) elucidates electrocatalytic reaction mechanisms. Furthermore, the ZAB with G-SHELL outperforms Pt/C+RuO2 in terms of energy density (797Wh kg-1) and peak power density (275.8mW cm-2), realizing the ZAB-driven water splitting.

Pyridinic N[sbnd]B pair-doped carbon microspheres with refined hierarchical architectures for rechargeable zinc-air batteries

Refined architectures are of vital importance in determining the electrocatalytic activity of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, pyridinic NB pair doped carbon microspheres (NB-CMS) with hierarchical micropore-mesopore structure are prepared via a SiO2 hard template assisted CO2 activation strategy. The pyridinic NB pair accounts for ≈ 59.9 % of all N species in NB-CMS, accelerating the ORR process with onset potential (0.996 V) and half-wave potential (0.889 V). Meanwhile, the NB-CMS also exhibits high OER performance with overpotential of 384 mV at 10 mA cm−2. The assembled Zinc-air battery exhibits maximum power density of 134 mW cm−2 and long-term charging and discharging stability over 358 h. Density functional theory (DFT) simulations reveal that the pyridinic NB pair exhibits the highest electrocatalytic performance in dual-functional catalysis, owing to the highest charge density and readily accepts electrons from *OOH adsorbate of N active site neighboring B.

Cobalt/nitrogen co-doped carbon nanosheets from coal-based graphene quantum dots boosted oxygen reduction

We report on cobalt/nitrogen co-doped carbon nanosheets (Co/NCNs) as a highly efficient electrocatalyst for the oxygen reduction reaction (ORR). The Co/NCNs were synthesized through pyrolysis at 900 °C using coal-based graphene quantum dots that contain nitrogen as a source of both carbon and nitrogen, NaCl as a template, and trace amounts of cobalt salt as a metal source. The Co/NCNs-0.1 exhibited ORR activity that was equivalent to that of Pt/C, with a half-wave potential of 0.85 V and a limiting current density of 4.9 mA cm−2. Furthermore, the zinc-air battery incorporating Co/NCNs-0.1 demonstrated an open circuit voltage of 1.423 V, a maximum power density of 149 mW cm−2, and a specific capacity of 806.5 mAh g−1 at a current density of 20 mA cm−2. The results of density functional theory calculations indicate that metal Co, when protected by graphitic-N-doped carbon, holds a greater negative charge and exhibits a lower energy barrier compared to other types of nitrogen species. This property contributes to the catalytic activity of the ORR.

Manipulating the Electronic Properties of an Fe Single Atom Catalyst via Secondary Coordination Sphere Engineering to Provide Enhanced Oxygen Electrocatalytic Activity in Zinc-Air Batteries.

Oxygen reduction and evolution reactions are two key processes in electrochemical energy conversion technologies. Synthesis of nonprecious metal, carbon-based electrocatalysts with high oxygen bifunctional activity and stability is a crucial, yet challenging step to achieving electrochemical energy conversion. Here, an approach to address this issue: synthesis of an atomically dispersed Fe electrocatalyst (Fe1/NCP) over a porous, defect-containing nitrogen-doped carbon support, is described. Through incorporation of a phosphorus atom into the second coordination sphere of iron, the activity and durability boundaries of this catalyst are pushed to an unprecedented level in alkaline environments, such as those found in a zinc-air battery. The rationale is to delicately incorporate P heteroatoms and defects close to the central metal sites (FeN4P1-OH) in order to break the local symmetry of the electronic distribution. This enables suitable binding strength with oxygenated intermediates. In situ characterizations and theoretical studies demonstrate that these synergetic interactions are responsible for high bifunctional activity and stability. These intrinsic advantages of Fe1/NCP enable a potential gap of a mere 0.65V and a high power density of 263.8mWcm-2 when incorporated into a zinc-air battery. These findings underscore the importance of design principles to access high-performance electrocatalysts for green energy technologies.