A Ternary Ni46 Co40 Fe14 Nanoalloy-Based Oxygen Electrocatalyst for Highly Efficient Rechargeable Zinc-Air Batteries

Cr doping and heterostructure-accelerated NiFe LDH reaction kinetics assist the MoS2 oxygen evolution reaction

Although molybdenum disulfide (MoS2) has garnered significant interest as a potential catalyst for the oxygen evolution reaction (OER), its poor intrinsic activity and few marginal active spots restrict its electrocatalytic activity. Herein, we successfully constructed a catalyst via a simple hydrothermal method by forming a heterostructure of MoS2 with Cr-doped nickel-iron hydroxide (NiFe LDH) to synthesize a MoS2/NiFeCr LDH catalyst to significantly improve the OER catalytic performance. MoS2 plays a crucial function as an electron transport channel in the MoS2/NiFeCr LDH heterostructure, which increases the electron transport rate. Furthermore, a larger active surface area for NiFeCr LDH is provided by the ultrathin layered structure of MoS2, increasing the number of active sites and encouraging the OER. On the other hand, the introduction of Cr element increased the density of the catalytic center and provided additional Cr-OH active sites, which accelerated the oxygen decomposition reaction. These two factors act synergistically to improve the intrinsic structure of MoS2, increase the number of reactive sites, and dramatically enhance the OER catalytic performance. Excellent OER activity is demonstrated by the MoS2/NiFeCr LDH catalyst, which only needs an overpotential of 224 mV to obtain a current density of 10 mA cm-2 and a Tafel slope of 61 mV dec-1. The catalyst also demonstrated outstanding stability, with its activity practically holding steady after 48 h of testing. This work offers novel ideas for enhancing and designing MoS2-based OER catalysts, and it provides a crucial reference for research in the field of clean energy.

Enhancing the bifunctional oxygen reduction and evolution activity of CoNC by introducing a trace amount of Fe

The potential application of zinc air batteries to tackle the energy shortage and environmental crisis has proposed new requirements of bifunctional catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Utilizing the special spatial structure of zeolitic imidazolate framework-67 (ZIF-67) as an ideal research platform, the effect of a trace amount of Fe on the composition and structure of as-obtained Fe-CoNC catalysts was investigated. It was revealed that, due to the increased exposed pore structure and metal species located at the near surface, the active sites for the ORR/OER on Fe-CoNC are highly exposed, greatly boosting the activity to the reduction and evolution of oxygen in alkaline media. ZABs with Fe-CoNC have the highest maximum power density of 200 mW cm-2 when operated at current densities as high as 328 mA cm-2, better than not only Fe-free CoNC, but also precious metal-based references with the same catalyst loading.

Reconstructing 3d-Metal Electrocatalysts through Anionic Evolution in Zinc-Air Batteries

As one of the promising sustainable energy storage systems, academic research on rechargeable Zn-air batteries has recently been rejuvenated following development of various 3d-metal electrocatalysts and identification of their dynamic reconstruction toward (oxy)hydroxide, but performance disparity among catalysts remains unexplained. Here, this uncertainty is addressed through investigating the anionic contribution to regulate dynamic reconstruction and battery behavior of 3d-metal selenides. Comparing with the alloy counterpart, anionic chemistry is identified as a performance promoter and further exploited to empower Zn-air batteries. Based on theoretical modeling, Se-resolved operando spectroscopy, and advanced electron microscopy, a three-step Se evolution is established, consisting of oxidation, leaching, and recoordination. The process generates an amorphous (oxy)hydroxide with O-sharing bonded Se motifs that triggers charge redistribution at metal sites and lowers the energetic barrier of their current-driven redox. A pervasive concept of Se back-feeding is then proposed to describe the underlying chemistry for 3d-metal selenides with diversity in crystals or compositions, and the feasibility to fine-tune their behavior is also presented.

Recent advances of bifunctional catalysts for zinc air batteries with stability considerations: from selecting materials to reconstruction

With the growing depletion of traditional fossil energy resources and ongoing enhanced awareness of environmental protection, research on electrochemical energy storage techniques like zinc-air batteries is receiving close attention. A significant amount of work on bifunctional catalysts is devoted to improving OER and ORR reaction performance to pave the way for the commercialization of new batteries. Although most traditional energy storage systems perform very well, their durability in practical applications is receiving less attention, with issues such as carbon corrosion, reconstruction during the OER process, and degradation, which can seriously impact long-term use. To be able to design bifunctional materials in a bottom-up approach, a summary of different kinds of carbon materials and transition metal-based materials will be of assistance in selecting a suitable and highly active catalyst from the extensive existing non-precious materials database. Also, the modulation of current carbon materials, aimed at increasing defects and vacancies in carbon and electron distribution in metal-N-C is introduced to attain improved ORR performance of porous materials with fast mass and air transfer. Finally, the reconstruction of catalysts is introduced. The review concludes with comprehensive recommendations for obtaining high-performance and highly-durable catalysts.

CoNi Alloys Encapsulated in N-Doped Carbon Nanotubes for Stabilizing Oxygen Electrocatalysis in Zinc-Air Battery

Alloy-based catalysts with high corrosion resistance and less self-aggregation are essential for oxygen reduction/evolution reactions (ORR/OER). Here, via an in situ growth strategy, NiCo alloy-inserted nitrogen-doped carbon nanotubes were assembled on a three-dimensional hollow nanosphere (NiCo@NCNTs/HN) using dicyandiamide. NiCo@NCNTs/HN exhibited better ORR activity (half-wave potential (E_1/2) of 0.87 V) and stability (E_1/2 shift of only -13 mV after 5000 cycles) than commercial Pt/C. NiCo@NCNTs/HN displayed a lower OER overpotential (330 mV) than RuO₂ (390 mV). The NiCo@NCNTs/HN-assembled zinc-air battery exhibited high specific-capacity (847.01 mA h g^-1) and cycling-stability (291 h). Synergies between NiCo alloys and NCNTs facilitated the charge transfer to promote 4e^- ORR/OER kinetics. The carbon skeleton inhibited the corrosion of NiCo alloys from surface to subsurface, while inner cavities of CNTs confined particle growth and the aggregation of NiCo alloys to stabilize bifunctional activity. This provides a viable strategy for the design of alloy-based catalysts with confined grain-size and good structural/catalytic stabilities in oxygen electrocatalysis.

Understanding Synergistic Catalysis on Cu-Se Dual Atom Sites via Operando X-ray Absorption Spectroscopy in Oxygen Reduction Reaction

The construction and understanding of synergy in well-defined dual-atom active sites is an available avenue to promote multistep tandem catalytic reactions. Herein, we construct a dual-hetero-atom catalyst that comprises adjacent Cu-N₄ and Se-C₃ active sites for efficient oxygen reduction reaction (ORR) activity. Operando X-ray absorption spectroscopy coupled with theoretical calculations provide in-depth insights into this dual-atom synergy mechanism for ORR under realistic device operation conditions. The heteroatom Se modulator can efficiently polarize the charge distribution around symmetrical Cu-N₄ moieties, and serve as synergistic site to facilitate the second oxygen reduction step simultaneously, in which the key OOH*-(Cu₁ -N₄ ) transforms to O*-(Se₁ -C₂ ) intermediate on the dual-atom sites. Therefore, this designed catalyst achieves satisfied alkaline ORR activity with a half-wave potential of 0.905 V vs. RHE and a maximum power density of 206.5 mW cm^-2 in Zn-air battery.

Electronic tuning of Ni-Fe-Co oxide/hydroxide as highly active electrocatalyst for rechargeable Zn-air batteries

As a bifunctional oxygen electrocatalyst (oxygen reduction reaction (ORR) and oxygen evolution reaction (OER)), spinel copper cobaltite (CuCo₂O₄) is attracting significant research interest owing to the tailored Co, Cu electronic structure and ease of adjusting the electrochemically active area. However, its poor OER performance (>300 mV at 10 mA cm^-2) limits its practical application for rechargeable zinc-air batteries. Therefore, we construct a CuCo₂O₄/NiFe LDH oxide/hydroxide interface to tune the properties of Ni, Fe and Co for enhancing OER activity and decreasing the charging overpotential of rechargeable zinc-air batteries. The obtained electrocatalysts show a low overpotential of 251 mV (10 mA cm^-2), which is 91 mV lower than the overpotential (342 mV) of CuCo₂O₄. By in situ Raman, XPS and electrochemical analyses, we ascribe the enhanced OER activity to the increasing Ni/Fe oxidation state triggered by the charge transfer of Ni/Fe and Co, which prompts CuCo₂O₄/NiFe LDH to rapidly form an active surface layer. Benefiting from enhanced OER performance, zinc-air batteries with a CuCo₂O₄/NiFe LDH electrode display a high round-trip efficiency with a low voltage gap of ∼0.78 V (10 mA cm^-2) due to the obvious decrease in the charging overpotential. These results suggest the importance of tuning the charge transfer on interfaces for designing high-efficiency electrocatalysts.

Research Progress of Bifunctional Oxygen Reactive Electrocatalysts for Zinc-Air Batteries

Zinc-air batteries (ZABs) have several advantages, including high energy density, cheap price and stable performances with good application prospects in the field of power batteries. The charging and discharging reactions for the air cathode of ZABs are the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), respectively, which play an important role in the whole performance of ZAB. Due to the cost and limited reserves of highly active precious metal catalysts, it is crucial to design alternative efficient and stable dual-functional non-precious metal catalysts. In the present review, we present a systematic summary of the recent progress in the use of transition metal-based electrocatalysts as alternatives to precious metals for the positive poles of ZAB air. Combined with state-of-the-art in situ characterization technologies, a deep understanding of the catalytic mechanism of OER/ORR provided unique insights into the precise design of excellent synthetic non-precious metal catalysts from the perspective of atomic structure. This review further shows that the hybrid electric battery is a new strategy to improve the efficiency of the hybrid electric battery, which could be available to alleviate the problem of resource shortage. Finally, the challenges and research trends for the future development of ZABs were clearly proposed.

Mixed-Ligand-Regulated Self-Enhanced Luminous Eu-MOF as an ECL Signal Probe for an Oriented Antibody-Decorated Biosensing Platform

The self-luminescence behavior of lanthanide MOFs (Ln-MOFs) due to the unique antenna effect is considered to be a promising electrochemiluminescence (ECL) emission for biosensors. It is more challenging for Ln-MOFs on account of the difficulty to stimulate Ln ions with the desired energy-transfer efficiency to produce stronger ECL emissions at a low potential. Here, guided by a second ligand-assisted energy-transfer strategy, we present an efficient self-enhanced luminescence mixed-ligand Eu-MOF as an ECL signal probe for an oriented antibody-decorated biosensing platform with a low detection limit and a broad detection range. Diamino terephthalic acid (NH₂-H₂BDC) and 1,10-phenanthroline (Phen) were selected as the first and second ligands, respectively, to form highly conjugated structures, as well as suppress the nonradiative energy transfer. Impressively, Phen precisely adjusts the energy gap between the triplet ligand and the excited state of Eu³⁺, realizing the self-enhancement of ECL efficiency of the Eu-MOF. The mixed ligand adjusted the molar ratio to obtain the stable and strong ECL signal at a lowered triggering potential (0.83 V). In addition, FeCo@CNT features densely active FeCo sites along with a rich hierarchy conductive carbon nanotube (CNT) network, which is efficiently a co-reaction accelerator to produce more TPA^•+ radicals to accelerate the reduction process of the Eu-MOF for achieving the ECL emission amplification. FeCo@CNT with heptapeptide HWRGWVC (HWR) constructed a matrix biosensing interface that allowed the fragment antigen-binding (Fab) regions to target specific antigens and enhance the incubation efficiency. The present study has gone some way toward designing a self-enhanced luminous Eu-MOF, thus giving new fresh impetus to develop high-performance ECL emitters for biological analysis.

Structural Design Strategy and Active Site Regulation of High-Efficient Bifunctional Oxygen Reaction Electrocatalysts for Zn-Air Battery

Zinc-air batteries (ZABs) exhibit high energy density as well as flexibility, safety, and portability, thereby fulfilling the requirements of power batteries and consumer batteries. However, the limited efficiency and stability are still the significant challenge. Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are two crucial cathode reactions in ZABs. Development of bifunctional ORR/OER catalysts with high efficiency and well stability is critical to improve the performance of ZABs. In this review, the ORR and OER mechanisms are first explained. Further, the design principles of ORR/OER electrocatalysts are discussed in terms of atomic adjustment mechanism and structural design in conjunction with the latest reported in situ characterization techniques, which provide useful insights on the ORR/OER mechanisms of the catalyst. The improvement in the energy efficiency, stability, and environmental adaptability of the new hybrid ZAB by the inclusion of additional reaction, including the introduction of transition-metal redox couples in the cathode and the addition of modifiers in the electrolyte to change the OER pathway, is also summarized. Finally, current challenges and future research directions are presented.

Hierarchically Assembled Cobalt Oxynitride Nanorods and N-Doped Carbon Nanofibers for Efficient Bifunctional Oxygen Electrocatalysis with Exceptional Regenerative Efficiency

Oxygen-based electrocatalysis is an integral aspect of a clean and sustainable energy conversion/storage system. The development of economic bifunctional electrocatalysts with high activity and durability during reversible reactions remains a great challenge. The tailored porous structure and separately presented active sites for oxygen reduction and oxygen evolution reactions (ORR and OER) without mutual interference are most crucial for achieving desired bifunctional catalysts. Here, we report a hybrid composed of sheath-core cobalt oxynitride (CoO_x@CoN_y) nanorods grown perpendicularly on N-doped carbon nanofiber (NCNF). The brush-like CoO_x@CoN_y nanorods, composed of metallic Co₄N cores and oxidized surfaces, exhibit excellent OER activity (E = 1.69 V at 10 mA cm^-2) in an alkaline medium. Although pristine NCNF or CoO_x@CoN_y alone had poor catalytic activity in the ORR, the hybrid showed dramatically enhanced ORR performance (E = 0.78 V at -3 mA cm^-2). The experimental results coupled with a density functional theory (DFT) simulation confirmed that the broad surface area of the CoO_x@CoN_y nanorods with an oxidized skin layer boosts the catalytic OER, while the facile adsorption of ORR intermediates and a rapid interfacial charge transfer occur at the interface between the CoO_x@CoN_y nanorods and the electrically conductive NCNF. Furthermore, it was found that the independent catalytic active sites in the CoO_x@CoN_y/NCNF catalyst are continuously regenerated and sustained without mutual interference during the round-trip ORR/OER, affording stable operation of Zn-air batteries.

FeNi Nanoparticles Coated on N-doped Ultrathin Graphene-like Nanosheets as Stable Bifunctional Catalyst for Zn-Air Batteries

High-performance and low-cost bifunctional catalysts are crucial to energy conversion and storage devices. Herein, a novel oxygen electrode catalyst with high oxygen evolution reaction and oxygen reduction reaction (OER/ORR) performance is reported based on bimetal FeNi nanoparticles anchored on N-doped graphene-like carbon (FeNi/N-C). The complete 2D ultrathin carbon nanosheet is induced by etching and stripping of molten sodium chloride and its ions in the carbonization process at suitable temperature. The obtained FeNi/N-C catalyst exhibits rapid reaction kinetics for OER, efficient four electron transfer for ORR, and outstanding bifunctional performance with reversible oxygen electrode index of 0.87 V for OER/ORR. Zn-air batteries with a high open-circuit voltage of 1.46 V and a stable discharge voltage of 1.23 V are assembled using liquid electrolytes, zinc sheet as Zn-electrode and FeNi/N-C coating on carbon cloth as air-electrode. The specific capacity is as high as 816 mAh g^-1 and there is extremely little decay after charge-discharge cycle time of 275 h for the FeNi/N-C as oxygen electrode catalyst in Zn-air battery, which are much better than that assembled with Pt/C-RuO₂ catalyst.

Laser ablation in air and its application in catalytic water splitting and Li-ion battery

Pulse laser has been widely used in both fundamental science and practical technologies. In this perspective, we highlight the employment of pulse laser ablation in air (LAA) in energy-related catalytic reactions. With LAA, samples are directly ablated in ambient air, which makes this technology facile to conduct. Materials can be modified by LAA in multiple aspects, such as morphology modulation, heterojunction fabrication, or defects engineering, which are desired features for energy-related catalytic reactions. We begin this perspective with a brief introduction of this technology, including the mechanism, the experimental setup, and the characteristic of laser-ablated materials. The recent works utilizing LAA are then summarized to prove the promising prospects of LAA in the energy field. Finally, several opportunities about the future usage of LAA are proposed and discussed.

Co0.7Fe0.3 NPs confined in yolk-shell N-doped carbon: engineering multi-beaded fibers as an efficient bifunctional electrocatalyst for Zn-air batteries

The development of bifunctional catalysts with a delicate structure, high efficiency, and good durability for the oxygen evolution reaction (ORR) and oxygen evolution reaction (OER) is crucial to renewable Zn-air batteries. In this work, Co_0.7Fe_0.3 alloy nanoparticles (NPs) confined in N-doped carbon with a yolk-shell structure in multi-beaded fibers were prepared as a bifunctional electrocatalyst. The confinement structure was composed of an N-doped graphitized carbon shell and a core formed by numerous Co_0.7Fe_0.3 NPs, and was evenly threaded into a one-dimensional fiber. Moreover, this distinctive hierarchical structure featured abundant mesopores, a high BET surface area of 743.8 m² g^-1, good electronic conductivity, and uniformly distributed Co_0.7Fe_0.3/Co(Fe)-N_x coupling active sites. Therefore, the experimentally optimized Co_0.7Fe_0.3@NC_2:1-800 showed excellent OER performance (overpotential reached 314 mV at 10 mA cm^-2) that far exceeded RuO₂ (353 mV), and good ORR catalytic performance (half-wave potential of 0.827 V) comparable to Pt/C (0.818 V). Impressively, the Co_0.7Fe_0.3@NC_2:1-800 Zn-air battery delivered a higher open circuit voltage of 1.449 V, large power density of 85.7 mW cm^-2, and outstanding charge-discharge cycling stability compared with the commercial RuO₂ + 20 wt% Pt/C catalyst. This work provides new ideas for the structural design of electrocatalysts and energy conversion systems.

Evaluation of the Volumetric Activity of the Air Electrode in a Zinc-Air Battery Using a Nitrogen and Sulfur Co-doped Metal-free Electrocatalyst

While numerous oxygen electrocatalysts have been reported to enhance zinc-air battery (ZAB) performance, highly efficient electrocatalysts for the oxygen electrocatalysis need to be developed for broader commercialization of ZABs. Furthermore, areal (instead of volumetric) power density has been used to benchmark the performance of ZABs, often causing ambiguities or confusions. Here, we propose a methodology for evaluating the performance of a ZAB using the volumetric (rather than the areal) power density by taking into consideration the air electrode thickness. A nitrogen and sulfur co-doped metal-free oxygen reduction electrocatalyst (N-S-PC) is used as a model catalyst for this new metric. The electrocatalyst exhibited a half-wave potential of 0.88 V, which is similar to that of the Pt/C electrocatalyst (0.89 V) due to the effects of co-doping and a highly mesoporous structure. In addition, the use of volumetric activity allows fair comparison among different types of air electrodes. The N-S-PC-loaded air electrode demonstrated a higher peak power density (5 W cm^-3) than the carbon felt or paper electrode in the ZAB test under the same testing conditions.

Micelles of Mesoporous Silica with Inserted Iron Complexes as a Platform for Constructing Efficient Electrocatalysts for Oxygen Reduction

Iron, N-codoped carbon materials (Fe-N-C) are promising electrocatalysts toward oxygen reduction reactions due to their high atom utilization efficiency and intrinsic activity. Nanostructuring of the Fe-N-C materials, such as introducing porosity into the carbon structure, would be conducive to further increasing the exposure of active sites as well as improving the mass transfer. Herein, we explore the potential of iron complex-functionalized micelles of mesoporous SiO₂ as a platform for constructing porous Fe-N-C materials. The classical three-dimensional MCM-48 was selected as a proof-of-concept example, which was utilized as the hard template, and cetyltrimethylammonium bromide micelles inside it played the role of the main carbon source. Fe-N_x sites were derived from Fe-1,10-phenanthroline complexes in the micelles introduced by in situ incorporation of 1,10-phenanthroline and post Fe²⁺ insertion in an aqueous solution. After thermal annealing in a nitrogen atmosphere and subsequent removal of the MCM-48 framework, a carbon material that possesses porous structural features with uniformly dispersed Fe-N_x sites (MPC@PhFe) was obtained, which shows superior ORR activity in a 0.1 M KOH solution and great potential for Zn-air battery applications as well. This work demonstrates the feasibility as well as the effectiveness of turning micelles of mesoporous SiO₂ into porous carbon structures and might offer a universal strategy for manufacturing carbon materials for future application in energy storage and conversion.

d-Orbital steered active sites through ligand editing on heterometal imidazole frameworks for rechargeable zinc-air battery

The implementation of pristine metal-organic frameworks as air electrode may spark fresh vitality to rechargeable zinc-air batteries, but successful employment is rare due to the challenges in regulating their electronic states and structural porosity. Here we conquer these issues by incorporating ligand vacancies and hierarchical pores into cobalt-zinc heterometal imidazole frameworks. Systematic characterization and theoretical modeling disclose that the ligand editing eases surmountable energy barrier for *OH deprotonation by its efficacy to steer metal d-orbital electron occupancy. As a stride forward, the selected cobalt-zinc heterometallic alliance lifts the energy level of unsaturated d-orbitals and optimizes their adsorption/desorption process with oxygenated intermediates. With these merits, cobalt-zinc heterometal imidazole frameworks, as a conceptually unique electrode, empowers zinc-air battery with a discharge-charge voltage gap of 0.8 V and a cyclability of 1250 h at 15 mA cm^–2, outperforming the noble-metal benchmarks.

Low intrinsic activity and accessibility of active sites limit the application of metal-organic framework as catalyst for Zn-air battery. Here, authors present a cation substitution strategy to regulate the electronic state of metal sites and modify its porosity, which enables battery operation.

Shaping a Doped Perovskite Oxide with Measured Grain Boundary Defects to Catalyze Bifunctional Oxygen Activation for a Rechargeable Zn-Air Battery

Symmetry broken configurations within a long-range atomic arrangement exhibit new physical properties, and distinctive strategies are needed to resuscitate the localized symmetry by introducing measured defects, which can be attractive in displaying enhanced catalytic activities for energy applications. Our hypothesis is validated by introducing lattice defects due to the strain originating from a slightly higher doped grain boundary (GB) than at the interconnected grains of perovskite oxide. When Pd is doped at the B-site of ABO₃-type La_0.7Sr_0.3CoO_3-δ, a marginally higher ionic radius of Pd⁴⁺ than Co³⁺ enables partial deportation of Pd⁴⁺ to the GB. Consequently, the GB unit cell is relatively expanded with a higher interplanar spacing, as observed by microscopic analysis. When the Pd concentration is increased, oxygen vacancy sites are reduced and both metallic Pd and PdO_x are exsolved at the perovskite oxide surface. With the Pd/Co ratio of 0.05, the defects originating from the Pd-modulated GB can be maximized to 1.29 ± 0.21% which enhances the bifunctional O₂ activation ability by lowering the combined overpotential of oxygen evolution and reduction reactions (OER/ORR) to 0.91 V, duly corroborated by computational studies. The fabricated rechargeable Zn-air battery has a specific capacity of 740 mA·h/g_Zn (851 mW·h/g_Zn) when discharge is performed at 10 mA/cm². Galvanostatic charge-discharge cycling with a 1 h cycle time shows 60 h stable performance. The OER/ORR bifunctional activity is found to be strongly correlated to the repositioned lattice symmetry at the perovskite GB.

Integrated and Binder-Free Air Cathodes of Co3 Fe7 Nanoalloy and Co5.47 N Encapsulated in Nitrogen-Doped Carbon Foam with Superior Oxygen Reduction Activity in Flexible Aluminum-Air Batteries

All-solid-sate Al-air batteries with features of high theoretical energy density, low cost, and environmental-friendliness are promising as power sources for next-generation flexible and wearable electronics. However, the sluggish oxygen reduction reaction (ORR) and poor interfacial contact in air cathodes cause unsatisfied performance. Herein, a free-standing Co₃ Fe₇ nanoalloy and Co_5.47 N encapsulated in 3D nitrogen-doped carbon foam (Co₃ Fe₇ @Co_5.47 N/NCF) is prepared as an additive-free and integrated air cathode for flexible Al-air batteries in both alkaline and neutral electrolytes. The Co₃ Fe₇ @Co_5.47 N/NCF outperforms commercial platinum/carbon (Pt/C) toward ORR with an onset potential of 1.02 V and a positive half-wave potential of 0.92 V in an alkaline electrolyte (0.59 V in sodium chloride solution), which is ascribed to the unique interfacial structure between Co₃ Fe₇ and Co_5.47 N supported by 3D N-doped carbon foam to facilitate fast electron and mass transfer. The high ORR performance is also supported by in-situ electrochemical Raman spectra and density functional theory calculation. Furthermore, the fabricated Al-air battery displays good flexibility and delivers a power density of 199.6 mW cm^-2 , and the binder-free and integrated cathode shows better discharge performance than the traditionally slurry casting cathode. This work demonstrates a facile and efficient approach to develop integrated air cathode for metal-air batteries.

Nano assembly of NiFe spheres anchored on f-MWCNT for electrocatalytic reduction and sensing of nitrofurantoin in biological samples

The current study reports a facile simple, low-cost electrochemical sensor in the detection of nitrofurantoin (NFT) by using NiFe/f-MWCNT hybrid composite as a promising electrocatalyst. NFT is an antibiotic drug that is extensively using in pharmaceuticals and also in animal food production which causes a severe threat for both human and animal environments. Extending the residues of NFT are left into rivers, soils, lakes, and groundwaters either found or discharged leading health issues. To this NiFe/f-MWCNT composite was synthesized using a hydrothermal mechanism and then ultrasonicated to form a hybrid composite for catalytic evaluation and electrochemical detection of NFT for the very first time. Furthermore, the physicochemical properties of NiFe nanospheres conjugated on f-MWCNT are scrutinized using various analytical and spectroscopical techniques. Resulting transmission electron microscopy (TEM) displays a chain like NiFe nanospheres anchored on f-MWCNT with a well-defined spherical shape, without any comprehensive agglomeration. The NiFe/f-MWCNT screen printed carbon paste electrode (SPCE) displayed an excellent electrocatalytic activity for NFT with a LOD of 0.03 µM and a sensitivity of 11.45 µA µM^-1 cm^-2. establishing a new selectivity and with the existence of co-interfering compounds. To enhance the practical abilities analysis were performed in Human serum and urine samples which resulted in satisfactory recoveries with high precision and linear accuracy illustrated in Scheme 1.

Dynamic active-site generation of atomic iridium stabilized on nanoporous metal phosphides for water oxidation

Designing efficient single-atom catalysts (SACs) for oxygen evolution reaction (OER) is critical for water-splitting. However, the self-reconstruction of isolated active sites during OER not only influences the catalytic activity, but also limits the understanding of structure-property relationships. Here, we utilize a self-reconstruction strategy to prepare a SAC with isolated iridium anchored on oxyhydroxides, which exhibits high catalytic OER performance with low overpotential and small Tafel slope, superior to the IrO₂. Operando X-ray absorption spectroscopy studies in combination with theory calculations indicate that the isolated iridium sites undergo a deprotonation process to form the multiple active sites during OER, promoting the O-O coupling. The isolated iridium sites are revealed to remain dispersed due to the support effect during OER. This work not only affords the rational design strategy of OER SACs at the atomic scale, but also provides the fundamental insights of the operando OER mechanism for highly active OER SACs.

Dynamic electrocatalyst with current-driven oxyhydroxide shell for rechargeable zinc-air battery

Recent fruitful studies on rechargeable zinc-air battery have led to emergence of various bifunctional oxygen electrocatalysts, especially metal-based materials. However, their electrocatalytic configuration and evolution pathway during battery operation are rarely spotlighted. Herein, to depict the underlying behaviors, a concept named dynamic electrocatalyst is proposed. By selecting a bimetal nitride as representation, a current-driven “shell-bulk” configuration is visualized via time-resolved X-ray and electron spectroscopy analyses. A dynamic picture sketching the generation and maturation of nanoscale oxyhydroxide shell is presented, and periodic valence swings of performance-dominant element are observed. Upon maturation, zinc-air battery experiences a near two-fold enlargement in power density to 234 mW cm⁻², a gradual narrowing of voltage gap to 0.85 V at 30 mA cm⁻², followed by stable cycling for hundreds of hours. The revealed configuration can serve as the basis to construct future blueprints for metal-based electrocatalysts, and push zinc-air battery toward practical application.

Interest in rechargeable Zn-air batteries has been renewed in recent years, however, their oxygen electrocatalysts remain not fully understood. Here the authors reveal the presence of a current-driven oxyhydroxide shell in a so-called dynamic eletrocatalyst that enables optimized battery performance.

Bifunctional catalysts of CoNi nanoparticle-embedded nitrogen-doped carbon nanotubes for rechargeable Zn-air batteries

It is essentially important to improve the performance of Zn-air batteries by studying bifunctional catalysts for oxygen evolution reactions (OER) and oxygen reduction reactions (ORR) with low-cost, high-efficiency and high-stability properties. Here, CoNi nanoparticles embedded in the bamboo-like N-doped carbon tubes (Co _x Ni _y @NC) were synthesized, where the optimized catalyst of Co₂Ni₁@NC exhibits superior bifunctional electrocatalytic activity, showing a low overpotential of 300 mV under the current density of 10 mA cm^-2 for OER and a large limiting current density of 3.76 mA cm^-2 under 0.40 V for ORR in an alkaline solution. In addition, the Co₂Ni₁@NC also shows excellent electrocatalytic activity in acidic and neutral solutions. Importantly, primary Zn-air batteries based on Co₂Ni₁@NC affords an excellent specific capacity of 834 mAh/g_Zn with a discharge potential of 1.25 V at 5 mA cm^-2. A rechargeable Zn-air battery assembled with Co₂Ni₁@NC shows excellent cycling stability, where the first discharge and charge voltages reach 1.21 and 2.00 V under 1 mA cm^-2, respectively. This finding provides a simple synthesis approach, which allows one to construct bifunctional catalysts based on metal@NC for future energy conversion and storage devices.

Co and CeO2 co-decorated N-doping carbon nanofibers for rechargeable Zn-air batteries

The heterogeneous Co and CeO₂ co-decorated N-doping carbon nanofibers (Co-CeO₂-N-C) were synthesized via the electrospinning technique. As the bifunctional electrocatalyst, Co-CeO₂-N-C nanofibers show excellent oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) performance, owing to the higher degree of graphitization of carbon, the N-doping, and the formation of an interface between Co and CeO₂. The liquid Zn-air battery based on Co-CeO₂-N-C nanofibers displays excellent specific capacities (815.9 mA h g^-1 at 5 mA cm^-2), higher open circuit voltages (1.47 V), and good cycling stability (113 h). The corresponding flexible solid state Zn-air battery shows excellent cycling stability (11 h), and good flexibility. Our finding suggests that Co-CeO₂-N-C nanofibers could serve as a new group of bifunctional electrocatalysts for OER and ORR with excellent performance, and make them promising for use in future electric vehicles, off-grid power sources, and portable electronics.

Reducing the Barrier Energy of Self-Reconstruction for Anchored Cobalt Nanoparticles as Highly Active Oxygen Evolution Electrocatalyst

It is crucial for leaping forward renewable energy technology to develop highly active oxygen evolution reaction (OER) catalysts with fast OER kinetics, and the novel design of high-performance catalysts may come down to unveiling the origin of high catalytic behavior. Herein, a new class of heterogeneous OER electrocatalyst (metallic Co nanoparticles anchored on yttrium ruthenate pyrochlore oxide) is provided for securing fast OER kinetics. In situ X-ray absorption spectroscopy (in situ XAS) reveals that fast OER kinetics can be achieved by the harmonious catalytic synergy of a pyrochlore oxide support to Co nanoparticles. By the facile oxidation of yttrium (A-site) and ruthenium (B-site) cations, the pyrochlore oxide support helps to expel the electrons generated from the catalytic behavior of Co to the inner layers of the support, facilitating the electrostatic adsorption of OH^- ions and reducing the barrier energy for the formation of CoOOH intermediates. This work affords the rational design of transition metal nanoparticles anchored on pyrochlore oxide heterogeneous catalysts and the fundamental insight of catalytic origin associated with self-reconstruction of OER electrocatalysts.