Zinc-air Research Articles

Reducing corrosion and hydrogen gas release inside an alkaline zinc-air battery by employing ionic liquid

Zn–air batteries are a promising route that might be used in a range of energy sectors. Significant disadvantages, such as passive film and hydrogen gas evolution (HGE) in alkaline corrosive medium; restrict the possible usage of Zn–air batteries. To address these problems and increase the performance of zinc-air batteries, an ionic liquid (tris(2hydroxyethyl) hydroxymethylammonium methyl sulfate [IL]+[MS]-) has been used in this study. The usage of [IL]+[MS]- in 7.0 M KOH solution has a considerable effect on suppressing hydrogen gas creation, with an effectiveness of 86.2 %. Increasing the depth of the Bode-phase angle and the charge transfer resistance by adding [IL]+[MS]- also indicates a slower hydrogen gas production rate. The application of the [IL]+[MS]- additive improves the zinc-air battery's specific discharge capacity and capacity retention. To support these findings, SEM/EDX has been used to analyze the morphological features of Zn anodes in various electrolytes.

Boosting OER activity of Fe-N Moieties via Ni induced d-Orbital Tailoring for durable rechargeable Zn-Air batteries

Fe-N-C-based catalysts are considered the most promising Pt candidates due to their high oxygen reduction reaction (ORR) activity and low cost, whereas their oxygen evolution reaction (OER) performance is extremely poor due to the sluggish O-O coupling process, which hampers the practical application of rechargeable zinc-air batteries. Here, we in situ infiltrate Ni and Fe ions into metal triazolidine (MET)-derived N-doped porous carbon via a microporous confinement-pyrolysis strategy to enhance the OER activity of the Fe-N sites. The introduction of Ni induced the electronic delocalization of Fe atoms at the Fe-N center, which lowered the adsorption energy barriers for the decisive velocity step (O*→OOH*), thus accelerating the O-O bond coupling and OER kinetics. In addition, the preferential formation of NiOOH at high OER potentials ensures the catalytic stability of zinc-air batteries by trapping Fe ions escaping from carbon corrosion to form FeOOH. The optimized catalyst (FeNi-NC) has an overpotential of only 351 mV at a current density of 50 mA cm−2 under alkaline conditions. More importantly, the assembled ZABs can be stably charged and discharged for more than 500 h at 10 mA cm−2, demonstrating excellent battery charging and discharging stability. This work shows the great potential of strong electronic interactions between polymetals to improve Fe-N-C catalysts.

Fe3O4 encapsulated in hierarchically porous nitrogen-doped graphitic carbon layers for efficient oxygen reduction reaction: Enhanced intrinsic activity via directional interfacial charge transfer

Constructing efficient electrocatalysts for the oxygen reduction reaction (ORR) is crucial for the commercialization of metal-air batteries. Iron oxide-based catalysts exhibit promising potential for ORR. However, addressing the issue of inferior catalytic performance is essential, and a comprehensive understanding of the catalytic mechanism of iron oxide-based catalysts is also lacking. In this study, we present Fe3O4 nanoparticles encapsulated in N-doped graphitic carbon layers (NGC) hosted by hierarchically porous carbon (Fe3O4@NGC), achieved through a facile dual melt-salt template strategy. The encapsulation of Fe3O4 nanoparticles protects them from corrosion and exfoliation, endowing the catalysts with superior stability. Density functional theory (DFT) calculations discover that the electronic interaction between Fe3O4 nanoparticles and N-doped graphitic carbon layers induces directional interfacial electron transfer, which effectively modulates the surface electronic structure to improve the binding ability to O2, weaken the OO bond, and optimize the adsorption of intermediates, thus boosting the intrinsic activity. DFT unveils that the C atoms nearest to graphitic-N in NGC are active sites. Finally, the synergistic effects of Fe3O4 nanoparticles and NGC result in outstanding ORR performance and superior stability and methanol tolerance of Fe3O4@NGC, with a half-wave potential of 0.89 V, surpassing that of Pt/C by 50 mV. Fe3O4@NGC also shows better performance than Pt/C when used as the air-electrode catalyst in zinc-air battery.

Architecting double-shelled hollow carbon nanocages embedded bimetallic sites as bifunctional oxygen electrocatalyst for zinc-air batteries

Rational design of complex hollow nanostructures offers a great opportunity to construct various functional nanostructures. A novel in situ disassembly-polymerization-pyrolysis approach was developed to synthesize atomically dispersed Fe single atoms (Fe SAs) and tiny Co nanoparticles (Co NPs) binary sites embedded in double-shelled hollow carbon nanocages (Co NPs/Fe SAs DSCNs) without removing excess templates. The Co NPs/Fe SAs DSCNs displayed excellent bifunctional activity, boosting the realistic rechargeable zinc-air batteries with high efficiency, long-term durability, and reversibility, which is comparable to noble metal catalysts (Pt/C and RuO2). The enhanced catalytic activity should be attributed to as well as the strong interactions between Fe SAs and Co NPs with the nitrogen-doped carbon matrix, the exposure of more active sites, and the high-flux mass transportation. In addition, the confinement effect between the double C-N shells prevented the aggregation and corrosion of metal atoms, thus improving the durability of the Co NPs/Fe SAs DSCNs, further highlighting the structural advantages of carbon nanoreactor. This work provides guidance for further rational design and preparation of complex hollow structure materials with advanced bifunctional air cathodes.

Efficient atomically dispersed Fe catalysts with robust three-phase interface for stable seawater-based zinc-air batteries

The use of seawater-based electrolytes in zinc-air batteries (S-ZABs) presents significant economic and social benefits and mitigates the demand for scarce freshwater resources. However, it is challenging to achieve a metal-nitrogen-carbon (M-N-C) catalyst that exhibits high resistance to corrosive Cl- in seawater-based electrolytes and possesses a strengthened binding affinity with O2, which enables catalysts with an optimized oxygen reduction reaction (ORR) and enhances the applicability of S-ZABs. Herein, we propose a combined wet chemistry-pyrolysis strategy to obtain atomically dispersed Fe-decorated nitrogen-doped mesoporous carbon spheres (N-MCS-Fe-900). Benefiting from the capacity of the Fe decorations to form the edge-hosted aerophilic FeN4-O2 sites at the optimized three-phase interface, N-MCS-Fe-900 affords the enhanced resistance of the active Fe sites to corrosive Cl-, as well as improved interaction with O2, thereby facilitating the ORR process. As expected, the N-MCS-Fe-900 delivers high half wave potential of 0.90V and kinetic current density of 18.61mAcm−2 at 0.85V in seawater-based 0.1M KOH. More importantly, the S-ZABs equipped with N-MCS-Fe-900 exhibited long-term stability under a high current density for over 140h without voltage decay. Theoretical calculations and electrochemical performance evaluations collectively revealed the superior catalytic efficacy and genesis of this activity in N-MCS-Fe-900, which features edge-hosted FeN4-O2 sites at the stable three-phase interface in seawater electrolytes. This study provides new insights for the advancement of ORR catalysts in sustainable energy conversion technologies for seawater-based electrolytes.

Development of an efficient bifunctional electrocatalyst based on Co/CoSe2 nanoparticles embedded in N, Se co-doped carbon for AEMFC and rechargeable Zn-air battery

We suggest a hollow-structured N, Se dual-doped carbon framework embedded with Co/CoSe2 nanoparticles (Co/CoSe2@NSeC) as highly efficient bifunctional electrocatalyst for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The prepared electrocatalyst exhibits high electrochemical active surface area attributed to its unique hollow/porous structure and defective heteroatom doping sites. Furthermore, the strongly coupled heterojunction between Co and CoSe2 species not only provides abundant and highly active sites but also generates built-in electric field, thereby promoting electron transfer during the electrocatalytic reaction. Based on the above considerations, the prepared catalyst shows excellent bifunctional electrocatalytic performance. Leveraging the excellent ORR activity of Co/CoSe2@NSeC, alkaline exchange membrane fuel cells (AEMFC) with the Co/CoSe2@NSeC as air cathode exhibits high power density of 171.23 mW cm2. Furthermore, the rechargeable Zn-air battery employing the Co/CoSe2@NSeC shows high specific capacity (729.4 mAh gZn−1), peak power density (192.88 mW cm2), and sustained stability over 300 cycles.

Electro-functionalized 2D nitrogen-carbon nanosheets decorated with symbiotic cobalt single-atoms/clusters

Two-dimensional (2D) materials loaded with single atoms and clusters are being set at the forefront of catalysis due to their distinctive geometric and electronic features. However, the usually-complicated synthesis procedures impede in-depth clarification of their catalytic mechanisms. To this end, herein we developed an efficient one-step dimension-reduction carbonization strategy, with which we successfully architected a highly-efficient catalyst for oxygen reduction reaction (ORR), featured with symbiotic cobalt single atoms and clusters decorated in two-dimensional (2D) ultra-thin (3.5 nm thickness) nitrogen-carbon nanosheets. The synergistic effects of the two components afford excellent oxygen reduction activity in alkaline media (E1/2=0.823 V vs. RHE) and thereof a high power density (146.61 mW cm−2) in an assembled Zn-air battery. As revealed by theoretical calculations, the cobalt clusters can regulate electrons surrounding those individual atoms and affect the adsorption of intermediate species. As a consequence, the derived active sites of single cobalt atoms lead to a significant improvement of the ORR performance. Thus, our work may fuel interests to delicate architecture of single atoms and clusters coexisting 2D support toward optimal electrocatalytic performance.

Iron, cobalt embedded nitrogen-doped carbon derived from conjugated macrocyclic polymers as electrocatalysts for oxygen reduction reaction

The synthesis of earth-abundant metal-based electrocatalysts for deploying electrochemical energy devices has become an area of considerable interest. Herein, we have illustrated a facile Friedel-Crafts reaction for designing a metalloporphyrin polymer followed by its calcination to synthesize cauliflower-like nitrogen-doped iron-cobalt bimetallic electrocatalyst (FeCoTpp-900-2) and its satisfactory performance toward reducing oxygen. The bimetallic FeCoTpp-900-2 catalyst exhibits a half-wave potential (E1/2) of 0.84 V (vs. reversible hydrogen electrode (RHE)) and an onset potential (Eonset) of 0.95 V (vs. RHE). The notable electrocatalytic activity for oxygen reduction reaction (ORR) of FeCoTpp-900-2 is attributed to the presence of ORR active nitrogen species along with the Fe-Nx/Co-Nx sites. In addition, FeCoTpp-900-2 possesses an appreciable amount of mesopores responsible for the ORR behavior. Notably, the zinc-air battery consisting of FeCoTpp-900-2 as the catalyst for the air cathode presents a maximal power density of 127.53 mW cm−2 and robust durability for 24 hours (h). Therefore, this work can contribute to the facile synthesis of bimetallic electrocatalysts with non-noble metals to explore their applications in ORR.

Coordination polymer derived transition metal phosphide/carbon composites for bifunctional oxygen electrocatalyst

Developing nonprecious electrocatalysts with bifunctional performances for oxygen reduction (ORR) and evolution reactions (OER) remains a crucial challenge in rechargeable Zn-air batteries (RZABs). In this study, we report the synthesis of a three-dimensional (3D) porous N, P-doped carbon-wrapped cobalt phosphide composite (Co2P@3DNPC) via direct calcination of a novel organic/inorganic porous coordination polymer by an in-situ phosphating strategy. DFT calculations demonstrate the intricate interactions occurring during the PEI-directed grinding self-assembly process among Co2+, phytic acid (PA), and polyethylenimine (PEI). Specifically, Co2+ ions initially adsorb onto PEI molecules before integrating with PA to form a 3D coordination polymer matrix. As-fabricated Co2P@3DNPC composite exhibits impressive ORR/OER bifunctional performances, with a half-wave potential of 0.78 V and an overpotential of 1.71 V, respectively. Its bifunctional activities enable a power density of 148.5 mW cm–2 in rechargeable ZABs, with remarkable stability (> 480 h) during a discharge-charge cycle. The interconnected porous structure and embedded Co2P nanoparticles optimize the electrode-electrolyte interfacial contact, boosting energy density and cycle life of as-assembled ZABs. This innovative approach paves the way for efficient, cost-effective production of bifunctional electrocatalysts for RZABs.

Regulating Fe Intermediate Spin States via FeN4‐Cl‐Ti Structure for Enhanced Oxygen Reduction

AbstractModulating the spin states of FeN4 moieties is critical for enhancing the electrocatalytic oxygen reduction reaction (ORR). In this study, Ti4N3Clx and Ti4N3Ox MXenes are synthesized and functionalized with iron phthalocyanine (FePc) to form model catalysts with well‐defined FeN4‐Cl‐Ti and FeN4‐O‐Ti structures, respectively. The FeN4‐Cl‐Ti structure, formed within the Ti4N3Clx/FePc composite, enables precise modulation of FeN4 spin states from low to intermediate spin, significantly enhancing ORR performance. In contrast, the FeN4‐O‐Ti structure in Ti4N3Ox/FePc shows less effective spin state modulation, leading to comparatively lower ORR activity. Compared to FePc and Ti4N3Ox/FePc, Ti4N3Clx/FePc demonstrates superior electrochemical performance, with an ORR half‐wave potential of +0.91 V versus RHE and doubled power densities in Zn–air batteries (214.5 mW cm−2). Theoretical studies confirm that the intermediate spin states induced by the weak‐field ligand‐modified FeN4‐Cl‐Ti structure in Ti4N3Clx/FePc facilitate electron filling in the antibonding orbital composed of Fe 3dz2 and O2 π* orbitals, greatly enhancing O₂ activation and ORR activity. These findings underscore the superior catalytic properties of FeN4‐Cl‐Ti compared to FeN4‐O‐Ti, advancing the understanding of spin state‐related catalytic mechanisms and guiding the design of high‐performance ORR catalysts.

Topological Synthesis of 2D High-Entropy Multimetallic (Oxy)hydroxide for Enhanced Lattice Oxygen Oxidation Mechanism.

Owing to sluggish reaction kinetics and high potential, oxygen evolution reaction (OER) electrocatalysts face a trade-off between activity and stability. Herein, an innovative topological strategy is presented for preparing 2D multimetallic (oxy)hydroxide, including ternary CoFeZn, quaternary CoFeMnZn, and high-entropy CoFeMnCuZn. The key to the synthesis lies in using Ca-rich brownmillerite oxide as a precursor, which possesses inherent structural flexibility enabling tailored elemental adjustments and topologically transforms from a point-shared structure of metal-oxygen octahedrons into an edge-shared structure under alkaline conditions. The presence of Zn in the catalysts causes a shift in the center of the O2p band toward the Fermi level, resulting in more Co4+ species, which drive holes into oxygen ligands to promote intramolecular oxygen coupling. The triggered lattice oxidation mechanism is identified by detecting peroxo-like (O2 2-) negative species using tetramethylammonium chemical probe, along with 18O isotope labeling experiments. As a result, the catalyst demonstrates an overpotential of 267mV at 10 mA cm-2, ranking it among the top-performing non-Ni-based catalysts. Importantly, the catalysts also show high Fe-leaching resistance during OER compared to conventional NiFe and CoFe hydroxides/(oxy)hydroxides. The assembled zinc-air battery enables stable operation for over 225 h at a low charging voltage of 1.93V.

Co2P/CoP embedded in N, P, S triply-doped hollow carbon towards enhanced oxygen electrocatalysis

Simultaneously dispersing phosphide crystallites and multiple heteroatoms in hollow carbon is a significant yet challenging task for achieving high-performance oxygen electrocatalysts of zinc-air batteries. Herein, a simple wrapping-pyrolysis strategy is proposed to prepare Co2P/CoP embedded in N, P, S triply-doped hollow carbon (Co2P/CoP@NPS-HC). Co2P/CoP@NPS-HC composite features hollow polyhedral structure populated with numerous catalytically active Co2P/CoP nanoparticles and N, P, S heteroatoms. This optimized catalyst exhibits excellent activity for oxygen reduction reaction, with a half-wave potential of 0.82 V vs. RHE, and impressive enhancement for oxygen evolution reaction, indicated by an overpotential of 400 mV at 10 mA cm−2. Moreover, Co2P/CoP@NPS-HC catalyst exhibits greater durability and superior methanol tolerance compared to commercial Pt/C. The excellent bifunctional electrocatalytic performance of Co2P/CoP@NPS-HC catalyst is attributed to the synergistic effect of uniformly dispersed Co2P/CoP nanoparticles and N, P, S triply-doped hollow carbon structure. The former provides abundant catalytically active sites, while the latter offers a high accessible specific surface area, as well as enhances catalytic activity and electronic conductivity due to its altered charge distribution.

Main-group element-boosted oxygen electrocatalysis of Cu-N-C sites for zinc-air battery with cycling over 5000 h

Developing highly active and durable air cathode catalysts is crucial yet challenging for rechargeable zinc-air batteries. Herein, a size-adjustable, flexible, and self-standing carbon membrane catalyst encapsulating adjacent Cu/Na dual-atom sites is prepared using a solution blow spinning technique combined with a pyrolysis strategy. The intrinsic activity of the Cu-N4 site is boosted by the neighboring Na-containing functional group, which enhances O2 adsorption and optimizes the rate-determining step of O2 activation (*O2 → *OOH) during the oxygen reduction reaction process. Meanwhile, the Cu-N4 sites are encapsulated within carbon nanofibers and anchored by the carbon matrix to form a C2-Cu-N4 configuration, thereby reinforcing the stability of the Cu centers. Moreover, the introduction of Na-containing functional groups on the carbon atoms significantly reduces the positive charge on their outer shell C atoms, rendering the carbon skeletons less susceptible to corrosion by oxygen species and further preventing the dissolution of Cu centers. Under these multi-type regulations, the zinc-air battery with Cu/Na-carbon membrane catalyst as the air cathode demonstrates long-term discharge/charge cycle stability of over 5000 h. This considerable stability improvement represents a critical step towards developing Cu-N4 active sites modified with the neighboring main-group metal-containing functional groups to overcome the durability barriers of zinc-air batteries for future practical applications.

Anchored Fe3O4/Fe nanoparticles on hollow PPy nanotube@Fe-modified ZIF-8 derivative for enhanced ORR activity in zinc-air batteries

The reasonable design of highly conductive, abundant active sites, and well-stabilized outstanding non-precious metal-based electrocatalysts is vital for promoting the widespread utilization of zinc-air battery. In this research, a highly efficient oxygen reduction reaction (ORR) material was synthesized using a template-assisted pyrolysis strategy. Notably, the polyvinylpyrrolidone-treated polypyrrole (PPy) nanotubes acted as effective structure-directing templates for capturing Zn2+, coordinating with Zn2+ in the ZIF-8 synthesis solution, resulting in strong anchoring of ZIF-8. Therefore, after thermal decomposition process, a designed chain-like ORR catalyst of N-doped porous carbon nanostructure encapsulated Fe3O4/Fe nanoparticles (Fe3O4/Fe@NC@NCT) was successfully synthesized, possessing an excellent stability. And satisfactorily, the Fe3O4/Fe@NC@NCT catalyst exhibits excellent ORR performance, with a half-wave potential (E1/2) of 0.88 V and favorable durability with a loss of only 2 mV in E1/2 after 2000 CV cycles. Furthermore, zinc-air batteries assembled with this catalyst on the air cathode exhibit a high power/specific energy and an excellent cycling stability, both surpassing commercial Pt/C-based zinc-air batteries. The outstanding performance can be ascribed to the large specific surface area, stable composite structure, high conductivity, and high-density catalytic active sites.

A(CoFe)(S2)2/CoFe heterostructure constructed in S, N co-doped carbon nanotubes as an efficient oxygen electrocatalyst for zinc-air battery

Transition metal alloys can exhibit synergistic intermetallic effects to obtain high activities for oxygen reduction/evolution reactions (ORR/OER). However, due to the insufficient stability of active sites in alkaline electrolytes, conventional alloy catalysts still do not meet practical needs. Herein, by using polypyrrole tubes and cobalt-iron (CoFe) Prussian blue analogs as precursors, CoFe sulfides is in-situ formed on CoFe alloys to construct (CoFe)(S2)2/CoFe heterostructure in sulfur (S) and nitrogen (N) co-doped carbon nanotubes (CoFe@NCNTs-nS) via a low-temperature sulfidation strategy. The as-marked CoFe@NCNTs-12.5S exhibits a comparable ORR activity (half-wave potential of 0.901 V) to Pt/C (0.903 V) and a superior OER activity (overpotential of 272 mV at 10 mA cm−2) to RuO2 (299 mV). CoFe@NCNTs-12.5S also exhibits ultralow charge transfer resistances (ORR-6.36 Ω and OER-0.21 Ω) and an excellent potential difference of 0.617 V. The sulfidation-induced (CoFe)(S2)2/CoFe heterojunctions can accelerate interfacial charge transfer process. Tubular structure not only disperses the (CoFe)(S2)2/CoFe heterostructure, but also reduces the corrosion of active-sites to enhance catalysis stability. Zinc-air battery with CoFe@NCNTs-12.5S achieves a high specific capacity (718.1 mAh g−1), maintaining a voltage gap of 0.957 V after 400 h. This work reveals the potential of interface engineering for boosting ORR/OER activities of alloys via in-situ heterogenization.

Ultra-stable air electrodes based on different carbon materials for zinc-air battery

Air electrode is an indispensable crucial component of metal-air batteries and its performance is determined by many factors. Among them, the structure of the gas diffusion layer has a great influence on the overall performance of an air electrode. In this work, different carbon materials such as acetylene black (AB), graphite (GP), carbon nanotube (CNT), and their mixtures are taken to construct the gas diffusion layer of an air electrode to significantly improve the gas transport efficiency of the diffusion layer. The results show that the air electrode AB2@CNT8, which is composed of AB and CNT with the mass ratio of 2:8, reveals superior oxygen reduction reaction (ORR) performance compared to the AB air electrode fabricated with the conventional carbon material AB. Further, we applied the air electrodes AB2@CNT8 and AB to alkaline zinc-air batteries and investigated their discharge performance. Tests show that compared to the AB zinc-air battery, the AB2@CNT8 battery exhibits higher output power and discharge specific capacity of up to 704 mAh·gZn−1. In addition, during the ultra-long time constant current (5 mA) discharge test, the AB2@CNT8 battery can run stably for 1430 h continuously by simply replacing anode Zn sheet and electrolyte, while maintaining a relatively stable discharge voltage. Meanwhile, the performance of the air electrode AB2@CNT8 after long-term operation can be rapidly restored by a simple hot water treatment. Comprehensive testing of the air electrode AB2@CNT8 is a testament to its powerful and excellent long life, good cyclic discharge stability, and durability. This shows that changing the type of carbon materials and regulating the mixing ratio between various carbon materials will be an effective means to design and optimize the structure of the air cathode. In addition, the air electrode preparation method of the present investigation has the characteristics of simple synthesis process, easy operation, safety and environmental friendliness, and low cost. The work provides a new strategy for the industrial-scale production of stable and efficient air electrodes.

WN-CoS2 nanoparticles encapsulated into carbon nanotubes enable a stable and high-performance rechargeable zinc air battery

The battery performance associated with longevity are the priorities for the industrialization of rechargeable zinc air battery (ZAB). Herein, we have reported the construction of WN-CoS2 heterostructure enveloped by nitrogen and phosphorus co-doped carbon nanotubes (WN-CoS2@NPCNT). WN-CoS2@NPCNT performs a superior oxygen evolution reaction (OER) catalytic activity of 279 mV overpotential to reach 10 mA cm−2, lowered by 85 mV with relative to CoS2@NCNT attributing to the heterostructure efficiently modulating the electronic structure of active sites. Besides, the half-wave potential reaches 0.875 V vs. RHE for WN-CoS2@NPCNT under oxygen reduction reaction (ORR) condition, corresponding to a 3.2-time higher kinetic current density compared to commercial Pt/C. Due to the exceptional bifunctionality, the battery performance is 205 mW cm−2 for WN-CoS2@NPCNT, 1.54 times higher than commercial counterpart, Pt/C + IrO2. Impressively, the battery performance sustains for 1000 h for WN-CoS2@NPCNT stemming from the confinement effect caused by NPCNT. In addition, the all-solid-state ZAB shows a high-power density of 55 mW cm−2.

In-situ observation of defects evolution of graphene nanoflakes in Pt/C catalyst for boosting ORR performance

The structural stability of supported metal nanoparticles determines the activity and longevity of heterogeneous catalysts. Unfortunately, the chemical/thermal working environment inevitably accelerates metal sintering to larger crystallites that leads to the degradation of catalytic performance. Here, we demonstrate that the distribution of defects in carbon support as an inherent parameter plays a crucial role in catalyst sintering. Based on in-situ transmission electron microscopy studies, the strong metal-support interaction between platinum (Pt) nanoparticles and defect-rich graphene nanoflakes largely suppresses metal sintering up to 700 °C. Particularly, the optimal carbon support can be achieved in the annealing process, in which the mass transfer and charge transport can be enhanced by accurately manipulating the distribution of defects in carbon matrix and graphitization degree. It is worth noting that the screened Pt/GNs-300 exhibits impressive oxygen reduction reaction performance with high half-wave potential (0.91 V), mass activity (108.1 A g–1Pt) and excellent stability. By its ascendancy in ORR, the Pt/GNs-300 exhibits a high open-circuit voltage of 1.41 V and a maximum power density of 198.6 mW cm−2 in Zn-air battery, implying its brilliant practicability. This work paves a pathway for achieving sinter-resistant metal-loaded catalysts in energy electrocatalysis.

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.