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Herein, four different metal-free nitrogen containing Covalent Triazine Frameworks (CTFs) based on their applied monomers (DCP, DCBP, m DCB and p DCB) are synthesized via a classical ionothermal synthesis route (ZnCl 2 , 400/600 °C). These materials are fully characterized and their electrochemical activities for ORR are tested and compared to each other including Carbon Super P and Pt black as standards in 0.1 M KOH. While DCP provides similar catalytic activity to Carbon Super P showing mostly a 2eˉ process (n=2.95) with high H 2 O 2 formation of 52.6 %, the other three CTFs (DCBP, m DCB and p DCB) possess higher ORR activities, surprisingly even much higher limiting current densities than Pt black, proving that O 2 is mainly reduced via direct 4eˉ pathway since n values are in the range of 3.52 to 3.62 and the detected H 2 O 2 values are in the range of 19–23.9 %. Among the studied CTFs, m DCB reaches a limiting current density of −5.61 mA cm-2 (1.21 mA cm-2 larger than that for Pt black, −4.40 mA cm-2) with 0.11 V larger onset potential compared to Pt black. The significant electrochemical performances of the CTF materials in ORR via a 4eˉ process are correlated to the high specific surface areas (up to 2500 m2 g-1), large pore volumes (up to 2.05 cm3 g-1) and the largest total N-graphitic/quaternary contents as well as micro-mesoporous structure properties. [Display omitted] • Four N-containing Covalent Triazine Frameworks (CTF) were synthesized via a classical ionothermal route. • Three CTFs provide higher ORR activities, with much larger limiting current densities than Pt black. • O 2 is mostly reduced through a direct 4eˉ process rather than 2eˉ process at three CTFs. • The N-graphitic/quaternary sites are the active sites for oxygen reduction reaction (ORR). [ABSTRACT FROM AUTHOR]

The potential of polyoxometalates (POMs) as alternatives to noble metal-based bifunctional electrocatalysts for air electrode, i.e., for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), was analyzed herein. Five POMs containing transition metal (Mn, Fe, Co, Ni, or Cu) were prepared and combined with reduced graphene oxide (rGO). Kenning structure of POMs with nanolamellae-like morphology and multi-layered graphene sheets of rGO were confirmed by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy, transmission electron microscopy and Raman spectroscopy analysis. Different POM:rGO ratios were tested to optimize the composition, and a ratio of 1:5 Ni-POM:rGO was found to be the most electrocatalytically active for OER (Tafel slope as low as 42 mV dec−1, overpotential at 10 mA cm−2 of 354 mV and current density at 400 mV overpotential as high as 83.4 mA cm−2), notably better than IrO 2. As for ORR, Co-POM/rGO carried the lowest Tafel slope of 165 mV dec−1, half-wave potential of 0.711 V and a mixed 2- and 4-electron ORR mechanism. Moreover, these non-precious metal electrocatalysts showed stability in alkaline media with no change in their structure. [Display omitted] • Synergistic effect of transition metal-POM and rGO enhances activity for OER/ORR. • Co-POM/rGO and Ni-POM/rGO outperform IrO 2 as benchmark electrocatalyst for OER. • The price of the catalyst per generated current is lower than in the case of costly IrO 2. • Co-POM/rGO demonstrates the best bifunctional character for ORR/OER. [ABSTRACT FROM AUTHOR]

In response to the escalating environmental impact of fossil fuels, there's a growing demand for clean energy solutions, particularly efficient metal-air batteries. Metal-air batteries are promising for energy storage, boasting abundant materials and low cost. However, their efficiency is hindered by slow oxygen reduction and evolution reactions. Synthesizing effective and stable oxygen electrocatalysts is crucial for enhancing battery performance. Here, this work used a simple solvothermal method to synthesize Iron–Cobalt metal-organic framework (FeCo-MOF), Manganese–Iron–Cobalt metal-organic framework (MnFeCo-MOF), and their composites with (1, 3, and 5) wt% rGO and characterized via using XRD, SEM, FTIR, and Raman spectroscopy. Electrochemical testing was conducted in 1 M KOH solution for both OER and ORR. The 3 wt% rGO MnFeCo-MOF shown the lowest overpotential of 54 mV at 10 mA/cm2 and the lowest Tafel slope of 63.4 mV/dec, with highest current density of 79.42 mA/cm2 at 25 mV/s scan rate for OER indicating excellent electrocatalytic activity superior to already reported in literature due to synergistic effect of Mn, Fe, Co, and rGO facilitating rapid electron transfer and more active sites. The 3 wt% rGO MnFeCo-MOF exhibited the halfwave potential of 0.74 V for ORR showing excellent activity comparable to commercial catalysts Pt/C. The lower potential gap ΔE 0.66 V from the overall combined plot of OER/ORR shows efficient and stable bifunctional activity of the 3 wt% rGO MnFeCo-MOF. These exceptional electrocatalytic properties pave the way for future advancements in metal-air batteries. [Display omitted] • FeCo-MOF, MnFeCo-MOF, and their composites with rGO were synthesized solvothermaly at 120 °C. • 3 wt% rGO MnFeCo-MOF showed lowest TAFEL slope 63.4 mV/dec and overpotential of 54 mV at 10 mA/cm2 for OER. • 3 wt% rGO MnFeCo-MOF for ORR has a halfwave potential of 0.74 V. • Exhibited excellent stability studied via chronopotentiometry experiment. • Synergic effect among rGO and Mn, Fe, Co MOF active sites. [ABSTRACT FROM AUTHOR]

In order to develop economical and environment-friendly metal-air batteries, herein, we report aluminium-air batteries (AABs) using low-cost commercially available aluminium (Al) sheets and waste from Al beverage canister as metal anodes and MoSe 2 , NiCo 2 O 4 , and NiCo 2 O 4 –MoSe 2 hybrid nanostructure as cathodes. The electrocatalytic activity of cathode materials have been examined using three-cell electrochemical configuration in 1 M KOH electrolyte, which shows best oxygen reduction behaviour of hybrid nanostructure attributed to large number of active sites, and synergistic effect between NiCo 2 O 4 and MoSe 2. The developed batteries utilize dual electrolyte (KOH-methanol and KOH-water) system to reduce the unwanted corrosion of Al anode and improve the electrocatalytic activity of cathode. Among designed AABs in the present work, AAB with Al canister as anode and NiCo 2 O 4 –MoSe 2 hybrid nanostructure as cathode shows best performance like higher discharging potential of 1.05 V at a current density of 10 mA cm−2 and higher specific capacity of 1304 mAh g−1. The assembled AABs with hybrid electrocatalyst show almost stable performance for more than 50 h by mechanically replacing the Al anode, once consumed. [Display omitted] • Synthesis of NiCo 2 O 4 –MoSe 2 hybrid nanostructure as electrocatalyst. • High specific capacity of 1305 mAh g−1 Al-air battery using NiCo 2 O 4 –MoSe 2 (cathode) and Al beverage canister (anodes). • Dual electrolyte reduces corrosion of Al anode. • Demonstration of mechanically rechargeable Al-air batteries using NiCo 2 O 4 –MoSe 2 as cathode materials. [ABSTRACT FROM AUTHOR]

The sluggish oxygen reduction reaction (ORR) has been one of the most majority bottlenecks of fuel cells and metal-air batteries. It is extremely desirable but challenging to explore low cost, highly active, stable catalysts toward ORR to replace commercial Pt/C catalysts. Herein, a novel hybrid system consisting of trace copper and bi-nonmetallic (N/S) modified the commercial ketjenblack (KB) carbon (Cu–NS–C) has been successfully fabricated by a pyrolysis of Cu–MOF/KB and thiourea to transform crystalline Cu/Cu2O nanoparticles into copper sulfide nanoparticles and the subsequent acid leaching. The optimized Cu–NS–C delivers a half-wave potential of 0.81 V versus RHE and a limiting-current density of 5.0 mA cm−2, which is next to those of commercial 20 wt% Pt/C catalyst. Furthermore, this catalyst demonstrates much better durability and methanol tolerance than Pt/C catalyst. [ABSTRACT FROM AUTHOR]

The effects of B‐site substitution (B═Mn, Fe, and Co) in La‐based perovskite oxides (LPOs); LaMnO3, LaFeO3, LaCoO3, as bifunctional electrocatalysts during oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in metal–air batteries (MABs) under an alkaline electrolyte (pH = 13) are investigated using density functional theory (DFT). It is found that LaMnO3 exhibits higher ORR activity than others with ORR overpotential (ηORR) of 0.57 V, but its OER activity is poor with OER overpotential (ηOER) of 1.12 V. The ηORR (0.59 V) and ηOER (1.13 V) of LaMn0.75Fe0.25O3 closely resemble those of LaMnO3, suggesting that Fe substitution does not yield appreciable enhancements in activity. Fe substitution reduces the ORR and OER activity because the adsorption energies of intermediate species on Fe‐substituted LPOs surfaces are too strong to obtain a potential determining step for ORR and OER. According to Sabatier's principle, the LaMn0.25Co0.75O3 demonstrates superior OER activity compared to the other composition, while ORR activity approximates that of LaMnO3, evidenced by ηORR of 0.65 V and ηOER of 0.53 V. The Co‐terminated LaMn0.25Co0.75O3 shows bifunctional activity higher than Mn/Co termination, indicating that Co is an active site for OER and Mn is a promoter for improved ORR activity. [ABSTRACT FROM AUTHOR]

Li-N2 batteries present a relatively novel approach to N2 immobilization, and an advanced N2/Li3N cycling method is introduced in this study. The low operating overpotential of metal–air batteries is quite favorable to their stable cycling performance, providing a prospect for the development of a new type of battery with extreme voltage. The battery system of Li-N2 uses N2 as the positive electrode, lithium metal as the negative electrode, and a conductive medium containing soluble lithium salts as the electrolyte. In accordance with its voltage-distribution trend, a variety of lithium-nitrogen molecule intermediates are produced during the discharge process. There is a lack of theoretical description of material changes at the microscopic level during the discharge process. In this paper, the first-principles approach is used to simulate and analyze possible material changes during the discharge process of Li-N2 batteries. The discharge process is simulated on a 4N-graphene anode substrate model, and simulations of its electrostatic potential, Density of States (DOS), HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) aspects confirm that the experimentally found Li3N becomes the final stabilized product of the Li-N2 battery. It can also be seen in the density of states that graphene with adsorption of 4N transforms from semiconducting to metallic properties. In addition, the differential charge also indicates that the Li-N2 material has a strong adsorption effect on the substrate, which can play the dual role of electricity storage and nitrogen fixation. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) represents a cornerstone for many clean energy conversion technologies such as fuel cells and metal‐air batteries. Nevertheless, the commercialization of these technologies is largely impeded by the slow kinetics of ORR, for which active, durable and cost‐effective ORR catalysts are needed. In recent years, zeolitic imidazolate framework (ZIF) derived carbon materials emerge as a new class of non‐precious metal catalysts (NPMCs) toward ORR, largely benefiting from their high surface area, abundant porosity, tunable chemical/electronic structure, and superior ORR activity which is comparable or even surpasses those state‐of‐the‐art Pt‐based ORR catalysts. This review offers a comprehensive overview of the recent advances in ZIF‐derived carbons for ORR. The synthesis strategies and the key factors affecting the ORR performance of ZIF‐derived carbon materials are discussed. Future research directions and perspectives on exploring ZIF derived carbons as efficient ORR catalysts are highlighted, with a focus on the principles of rationally engineering the coordination structures of active sites. [ABSTRACT FROM AUTHOR]

The oxidation of carbon in conventional gas diffusion electrodes is a limiting factor for the life of secondary metal-air batteries. Replacement of carbon with zeolite is a possible solution to avoid its oxidation in the gas-diffusion electrodes (GDE) and thus to increase the battery lifetime. Due to the fact that the technology provides the required number of charge/discharge cycles, it is applicable for solar energy storage. Zeolites are a large group of natural or synthetic porous aluminosilicate minerals. Their porous structure provides good gas permeability. The gas diffusion layer of the electrode must also have good hydrophobicity. To prevent leakage of electrolyte from the battery, the zeolite was mixed with an appropriate amount of polytetrafluoroethylene, and the electrode was subjected to hot pressing according to a specially developed procedure. The experiments were performed in a specially designed test cell. Its construction ensures measurements of the bifunctional gas-diffusion electrode in a half-cell configuration applying a reference hydrogen electrode. The stationary volt-ampere characteristics and impedance tests were performed on the zeolite electrodes at certain operating points. The cell was subjected to cycling at charge/discharge current ± 2 mA/cm2, respectively. The obtained experimental results show that zeolite is a suitable material for carbon substitution in secondary metal air batteries. The zeolite/polytetrafluoroethylene (PTFE) ratio needs to be optimised in order to improve the gas permeability of the gas diffusion layer without compromising hydrophobicity. [ABSTRACT FROM AUTHOR]

As the kinetic processes of oxygen reduction (ORR) and oxygen evolution reaction (OER) in metal-air batteries are slow, developing bifunctional catalysts with high performances is an essential requirement for boosting metal-air battery application. FeCo alloy is considered an excellent bifunctional active material, its weak corrosion resistance precludes its practical use in bifunctional catalysts. In this work, through dipping and annealing operations, FeCo alloy nanoparticles are doped on the porous carbon spheres (FeCo/PCNs). Strong FeCo nanoparticle-nitrogen-doped porous carbon sphere interaction results in a noticeable improvement in electrocatalytic activity and stability. FeCo/PCNs catalyst shows impressive bifunctional electrocatalytic activity, half-wave potential (E 1/2) of 0.905 V for ORR, and overpotential of 344 mV at a current density of 10 mA cm−2 (E j = 10) for OER, which are better than commercial Pt/C (E 1/2 = 0.865 V) and RuO 2 (E j = 10 = 351 mV) catalysts. Furthermore, the Zinc-air battery (ZABs) prepared by FeCo/PCNs catalyst (ZAB-FeCo/PCNs), exhibits high open circuit voltage (1.53 V), high power density (135 mW cm−2), and good long-term cycle stability, which further proves that FeCo/PCNs has excellent ORR/OER bifunctional activity. Therefore, the unique FeCo/PCNs catalyst provides a new perspective for the construction of ZABs bifunctional catalysts. [Display omitted] • FeCo/PCNs catalyst is prepared via impregnation and pyrolysis processes. • FeCo alloy in FeCo/PCNs catalyst promotes the graphitization the PCNs skeleton. • FeCo alloy and Fe/Co-N x active sites endow catalyst with high OER/ORR activity. • ZABs with FeCo/PCNs catalyst show better property than Pt/C + RuO 2. [ABSTRACT FROM AUTHOR]

Traditional energy resource, i.e. coal, is converted to value-added electrode materials in electrochemical energy conversion systems. [Display omitted] • Traditional coal energy resource is converted to value-added electrode material for electrochemical energy conversion system. • The intrinsic N- and S-heteroatoms in coal effectively enhance the ORR performance. • The electrode exhibited excellent performance in Zn-air batteries with both liquid and solid electrolytes. Coal-based oxygen electrocatalysts hold immense promise for cost-effective applications in rechargeable Zn-air batteries (ZABs) and the value-added, clean utilization of traditional coal resources. Herein, an electrospun membrane electrode comprising coal-derived carbon nanosheets and directly grown carbon nanotubes (CNS/CMF@CNT) was successfully synthesized. The hierarchical porous structure of the electrode, composed of multiple components, significantly facilitates mass and ion transportation, resulting in exceptional electrochemical performance. Employing Fe as the catalyst for CNT growth, the CNS/CMF@CNT electrode exhibits a remarkable onset potential of 0.96 V and a half-wave potential of 0.87 V in the oxygen reduction reaction (ORR). In-situ surface-enhanced Raman spectroscopy reveals that hydroxyl radical desorption on the surface of CNS/CMF@CNT(Fe) is the rate-determining step of the ORR. Notably, the aqueous ZAB featuring the CNS/CMF@CNT(Fe) electrode achieved a peak power density of 216.0 mW cm−2 at a current density of 414 mA cm−2 and maintained a voltage efficiency of 65.1 % after 2000 charge/discharge cycles at 5 mA cm−2. Furthermore, the all-solid-state ZAB incorporating this electrode displayed an open-circuit voltage of 1.43 V, a peak power density of 70.1 mW cm−2 at a current density of 110 mA cm−2, and a voltage efficiency of 66.5 % after 150 charge/discharge cycles. The utilization of abundant coal as the raw material for electrode fabrication not only brings conceivable economic benefits in ZAB construction, but also commendably advances the effective application of traditional coal resources in a more sustainable manner. [ABSTRACT FROM AUTHOR]

[Display omitted] The design and development of high-performance and long-life Pt-free catalysts for the oxygen reduction reaction (ORR) is of great important with respect to metal-air batteries and fuel cells. Herein, a new low-cost covalent organic frameworks (COFs)-derived Co N C single-atoms catalyst (SAC) is fabricated and compared with the engineered nanoparticle (NP) counterpart for ORR activity. The ORR performance of the SAC catalyst (Co SA @NC) surpasses the NP counterpart (Co NP -NC) under the same operation condition. Co SA @NC also achieves improved long-term durability and better methanol tolerance compared with the Pt/C. The zinc-air battery assembled by the Co SA @NC cathode delivers a higher power density and energy density than that of commercial Pt/C catalyst. Molecular dynamics (MD) is performed to explain the spontaneous evolution from clusters to single-atom metal configuration and density functional theory (DFT) calculations find that Co SA @NC possesses lower d -band center, resulting in weaker interaction between the surface and the O-containing intermediates. Consequently, the reductive desorption of OH*, the rate-determine step, is further accelerated. [ABSTRACT FROM AUTHOR]

Metal-free catalysts are made by the elements with infinite reserve in nature and, therefore, show the potential for large-scale applications in energy devices including metal–air batteries. The construction of metal–air batteries prefers using self-supporting catalysts with favorable activity as well as fast kinetics. However, it is challenging due to the limited electropositivity of metal-free catalysts for O–O bond formation in oxygen evolution reaction (OER), scaling relationship restrictions between OER and oxygen reduction reaction, and difficulty in porosity construction on the monolith electrode surface. In this contribution, through developing a facile methodology of quenching high-temperature carbon clothes in liquid nitrogen, a self-supported carbon cloth with bifunctional active graphene skin and fast kinetics is well constructed to serve as the air cathode in metal–air batteries. Regulated oxygen species and three-dimensionally hierarchical porosity are well constructed on the carbon fiber surfaces, contributing high intrinsic activity and prominently enhanced kinetics, which leads to favorable performances in aqueous as well as flexible rechargeable zinc–air batteries. The work proposed a promising strategy in the rational design and smart synthesis of fast-kinetic monolith electrodes, which refreshes concepts and strategies of advanced material fabrication, and also bridges material science and practical energy devices. [ABSTRACT FROM AUTHOR]

Fuel cells and metal‐air batteries are examples of renewable energy technologies that depend on having highly effective electrocatalysts for the oxygen evolution reaction (OER). In this study, a mesoporous nanostructure composed of Fe3O4‐Carbon nanocomposites was synthesised using a simple and economically viable approach at a relatively low temperature. The observed catalytic activity of the prepared defected Fe3O4‐Carbon nanocomposites mesoporous nanostructure was found to be remarkable. Additionally, the nanostructure exhibited a high tolerance to methanol and demonstrated durability towards the oxygen evolution reaction (OER) in alkaline media. In the course of the experiment, it was observed that the catalyst exhibited noteworthy activity in the Oxygen Evolution Reaction (OER) when compared to the commercially available RuO2 catalyst. This was evident through a more overpotential value of 325 mV at current density of 10 mA/cm2. The catalyst's notable capacity for high oxygen reaction activity may potentially enhance the synergistic effect resulting from the combination of defect sites and the porous structure of Fe3O4‐Carbon nanocomposites. The findings of this study indicate that the Fe3O4‐Carbon nanocomposites nanostructures exhibit promising attributes as an electrocatalyst for the oxygen evolution reaction (OER) in real‐world scenarios. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) is the bottleneck of metal‐air batteries and fuel cells. Strain regulation can change the geometry and adjust the surface charge distribution of catalysts, which is a powerful strategy to optimize the ORR activity. The introduction of controlled strain to the material is still difficult to achieve. Herein, we present a temperature‐pressure‐induced strategy to achieve the controlled lattice strain for metal coordination polymers. Through the systematic study of the strain effect on ORR performance, the relationship between geometric and electronic effects is further understood and confirmed. The strained Co‐DABDT (DABDT=2,5‐diaminobenzene‐1,4‐dithiol) with 2 % lattice compression exhibits a superior half‐wave potential of 0.81 V. Theoretical analysis reveals that the lattice strain changes spin‐charge densities around S atoms for Co‐DABDT, and then regulates the hydrogen bond interaction with intermediates to promote the ORR catalytic process. This work helps to understand the catalytic mechanism from the atomic level. [ABSTRACT FROM AUTHOR]

Driven by the goal of establishing a fossil‐fuel‐free and nuclear‐power‐free economy based on renewable energy, metal‐air batteries are regarded as promising energy conversion and storage devices. Developing efficient oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) bifunctional electrocatalysts for the air electrode of metal‐air batteries is becoming increasingly important. In this work, 36 transition metal (TM) single‐atom catalysts are designed based on MXenes Ti2CT2 with different surface terminal atoms (T = O, S, Cl), and their ORR/OER catalytic activity and stability are evaluated by the density functional theory. Ni@Ti2CO2, Pd@Ti2CS2, and Co@Ti2CCl2 are found to exhibit good catalytic activity with ORR/OER overpotentials of.54 V/.62 V,.59 V/.29 V,.44 V/.40 V. The aggregation behavior of three catalysts is estimated by comparing the average binding energy of one, two, three, and four TM atoms anchored on Ti2CT2. This work cannot only provide a theoretical guide to develop bifunctional single‐atom catalysts, but also help us understand the effect of terminal atoms on the electronic structures and catalytic activity of TM@Ti2CT2. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) is the bottleneck of metal‐air batteries and fuel cells. Strain regulation can change the geometry and adjust the surface charge distribution of catalysts, which is a powerful strategy to optimize the ORR activity. The introduction of controlled strain to the material is still difficult to achieve. Herein, we present a temperature‐pressure‐induced strategy to achieve the controlled lattice strain for metal coordination polymers. Through the systematic study of the strain effect on ORR performance, the relationship between geometric and electronic effects is further understood and confirmed. The strained Co‐DABDT (DABDT=2,5‐diaminobenzene‐1,4‐dithiol) with 2 % lattice compression exhibits a superior half‐wave potential of 0.81 V. Theoretical analysis reveals that the lattice strain changes spin‐charge densities around S atoms for Co‐DABDT, and then regulates the hydrogen bond interaction with intermediates to promote the ORR catalytic process. This work helps to understand the catalytic mechanism from the atomic level. [ABSTRACT FROM AUTHOR]

The expensiveness of oxygen reduction reaction (ORR) catalyst materials especially Pt has hindered the commercialization of next-generation energy conversion devices including metal–air batteries and polymer electrolyte membrane fuel cells. Fe– N –C has drawn attention as a nonprecious metal catalyst owing to its high but commercially unsatisfactory ORR performance; nevertheless, additional heteroatom co-doping could help augment its ORR activity. Here we report nitrogen/fluorine-coordinated iron-co-doped carbon (Fe@NFC) catalysts with improved ORR performance in alkaline media. The annealing temperature affects the nitrogen/fluorine doping and functional group formation, as ascertained by an analysis of control samples annealed at various temperatures. To assess the synergy between the doped fluorine and nitrogen-coordinated iron, we compare the catalyst annealed at 700 °C (Fe@NFC700) with control samples containing different heteroatom dopants but annealed at 700 °C (Fe@NC, Fe@FC). Fe@NFC700 shows improved ORR kinetics and onset potential than those of Fe@NC and commercial Pt/C, respectively, in alkaline media. • The most optimal annealing temperature of the Fe@NFC is found at 700 °C for the ORR. • F-doping increases the ORR favorable N -functional group ratio like Fe-N x. • The high ECSA from N -functional groups enhances the ORR performance. • F-functional groups like semi-ionic C –F bonds provide remarkable ORR kinetics. • The Fe@NFC700 catalyst exhibits higher onset potential than Pt/C in 0.1 M KOH. [ABSTRACT FROM AUTHOR]

Thermal safety issues of batteries have hindered their large‐scale applications. Nonflammable electrolytes improved safety but solvent evaporation above 100 °C limited thermal tolerance, lacking reliability. Herein, fire‐tolerant metal‐air batteries were realized by introducing solute‐in‐air electrolytes whose hygroscopic solutes could spontaneously reabsorb the evaporated water solvent. Using Zn/CaCl2‐in‐air/carbon batteries as a proof‐of‐concept, they failed upon burning at 631.8 °C but self‐recovered then by reabsorbing water from the air at room temperature. Different from conventional aqueous electrolytes whose irreversible thermal transformation is determined by the boiling points of solvents, solute‐in‐air electrolytes make this transformation determined by the much higher decomposition temperature of solutes. It was found that stronger intramolecular bonds instead of intermolecular (van der Waals) interactions were strongly correlated to ultra‐high tolerance temperatures of our solute‐in‐air electrolytes, inspiring a concept of non‐van der Waals electrolytes. Our study would improve the understanding of the thermal properties of electrolytes, guide the design of solute‐in‐air electrolytes, and enhance battery safety. [ABSTRACT FROM AUTHOR]

Thermal safety issues of batteries have hindered their large‐scale applications. Nonflammable electrolytes improved safety but solvent evaporation above 100 °C limited thermal tolerance, lacking reliability. Herein, fire‐tolerant metal‐air batteries were realized by introducing solute‐in‐air electrolytes whose hygroscopic solutes could spontaneously reabsorb the evaporated water solvent. Using Zn/CaCl2‐in‐air/carbon batteries as a proof‐of‐concept, they failed upon burning at 631.8 °C but self‐recovered then by reabsorbing water from the air at room temperature. Different from conventional aqueous electrolytes whose irreversible thermal transformation is determined by the boiling points of solvents, solute‐in‐air electrolytes make this transformation determined by the much higher decomposition temperature of solutes. It was found that stronger intramolecular bonds instead of intermolecular (van der Waals) interactions were strongly correlated to ultra‐high tolerance temperatures of our solute‐in‐air electrolytes, inspiring a concept of non‐van der Waals electrolytes. Our study would improve the understanding of the thermal properties of electrolytes, guide the design of solute‐in‐air electrolytes, and enhance battery safety. [ABSTRACT FROM AUTHOR]

The performance of electrocatalysts in oxygen reduction reactions is crucial for clean energy technologies such as fuel cells and metal-air batteries. Developing highly active and low-cost oxygen reduction catalysts remains a significant challenge. In this work, a silver loaded nitrogen doped graphene sheet (Ag-NGs) nanocomposite with high ORR catalytic performance was synthesized by a microwave plasma technique. XPS analysis reveals that silver nanoparticles preferentially adsorb onto the graphite-nitrogen site structure, resulting in improved catalytic activity for ORR, a conclusion confirmed by first principles calculations. And the incorporation of high-level nitrogen doping into graphene with a pyridine structure also contributes to the improved performance of the ORR catalyst. Moreover, the Ag-NGs nanocomposite not only demonstrates exceptional catalytic activity for the four-electron pathway of oxygen reduction reactions, but also exhibits remarkable stability. This study underscores the potential of the Ag-loaded nitrogen-doped graphene nanocomposite as a promising electrocatalyst for utilization in clean-energy devices. [Display omitted] • Ag/NGs is in-situ synthesized by a nitrogen-containing polymer organic substance. • The pyridine nitrogen in NGs provides a large number of catalytic active sites. • Ag-graphitic N structure is responsible for the 4-electron transfer process. [ABSTRACT FROM AUTHOR]

Alkaline metal‐air batteries are advantageous in high voltage, low cost, and high safety. However, metal anodes are heavily eroded in strong alkaline electrolytes, causing serious side reactions including dendrite growth, passivation, and hydrogen evolution. To address this limitation, we successfully synthesized an organic N‐heterocycle compound (NHCC) to serve as an alternative anode. This compound not only exhibits remarkable stability but also possesses a low redox potential (−1.04 V vs. Hg/HgO) in alkaline environments. To effectively complement the low redox potential of the NHCC anode, we designed a dual‐salt highly concentrated electrolyte (4.0 M KOH+10.0 M KCF3SO3). This electrolyte expands the electrochemical stability window to 2.3 V through the robust interaction between the O atom in H2O molecule with the K+ of KCF3SO3 (H−O⋅⋅⋅KCF3SO3). We further demonstrated the K+ uptaken/extraction storage mechanism of NHCC anodes. Consequently, the alkaline aqueous NHCC anode‐air batteries delivers a high battery voltage of 1.6 V, high‐rate performance (101.9 mAh g−1 at 100 A g−1) and long cycle ability (30,000 cycles). Our work offers a molecular engineering strategy for superior organic anode materials and develops a novel double superconcentrated conductive salt electrolyte for the construction of high‐rate, long‐cycle alkaline aqueous organic anode‐air batteries. [ABSTRACT FROM AUTHOR]

Alkaline metal‐air batteries are advantageous in high voltage, low cost, and high safety. However, metal anodes are heavily eroded in strong alkaline electrolytes, causing serious side reactions including dendrite growth, passivation, and hydrogen evolution. To address this limitation, we successfully synthesized an organic N‐heterocycle compound (NHCC) to serve as an alternative anode. This compound not only exhibits remarkable stability but also possesses a low redox potential (−1.04 V vs. Hg/HgO) in alkaline environments. To effectively complement the low redox potential of the NHCC anode, we designed a dual‐salt highly concentrated electrolyte (4.0 M KOH+10.0 M KCF3SO3). This electrolyte expands the electrochemical stability window to 2.3 V through the robust interaction between the O atom in H2O molecule with the K+ of KCF3SO3 (H−O⋅⋅⋅KCF3SO3). We further demonstrated the K+ uptaken/extraction storage mechanism of NHCC anodes. Consequently, the alkaline aqueous NHCC anode‐air batteries delivers a high battery voltage of 1.6 V, high‐rate performance (101.9 mAh g−1 at 100 A g−1) and long cycle ability (30,000 cycles). Our work offers a molecular engineering strategy for superior organic anode materials and develops a novel double superconcentrated conductive salt electrolyte for the construction of high‐rate, long‐cycle alkaline aqueous organic anode‐air batteries. [ABSTRACT FROM AUTHOR]

Soft robots and wearable technologies benefit significantly from stretchable batteries, yet the rigid nature of high‐capacity electrodes creates large trade‐offs in battery performance and stretchability. This study introduces a new approach for realizing stretchable batteries by allowing the electrodes to slide along a stretchable electrolyte. When the sliding‐electrodes battery is stretched, the forces are transmitted through the hydrogel electrolyte and elastomeric enclosure, while the rigid electrodes slide relative to the hydrogel to maintain interfacial contact. The sliding‐electrodes approach allows 100% of the unstretched battery area to be covered by thick electrodes so that the battery areal capacity and power are improved by up to 10X of prior stretchable designs. Three metal‐air batteries achieve areal capacities of up to 104 mWh cm−2. Further mechanical testing, electrochemical characterization, and integration into soft robotic systems demonstrate the potential of these stretchable batteries in practical applications. The sliding‐electrodes battery can stably power multiple servo motors and sensing circuits under stretching, twisting, bending, and after impact. [ABSTRACT FROM AUTHOR]

The high overpotential caused by the slow kinetics of oxygen reduction (ORR) and oxygen evolution (OER) has greatly limited the practical application of lithium‐oxygen (Li−O2) batteries. The adoption of force‐field‐assisted system based on a newly developed piezocatalysis is promising in reducing the overpotential. Herein, a force‐assisted Li−O2 battery is first established by employing MoS2/Pd nanocomposite cathode, in which the piezoelectric polarization as well as built‐in electric field are formed in MoS2 piezoelectric catalyst under ultrasound activation, leading to the continuously separated electrons and holes to enhance the ORR and OER kinetics. Moreover, the introduction of Pd can promote the electrons transfer and further inhibit the complexation of electron–hole pairs, contributing to enhanced catalytic activity in the decomposition/generation of discharge products, resulting in reduced discharge/charge overpotentials. Thus, the force‐assisted MoS2/Pd‐based Li−O2 battery is capable of adjusting the output and input energies by the assisted ultrasonic wave. An ultra‐low charging platform of 2.86 V and a high discharging platform of 2.77 V are achieved. The proposed unique force‐assisted strategy can also be applied to lithium carbon dioxide battery system through the effective reduction and separation of CO2 and CO32−, providing significant insights in achieving efficient energy conversion for metal−air batteries. [ABSTRACT FROM AUTHOR]

This effective modulation of interface charge redistribution is primarily governed by the interfaces at the junctions between the heterogeneous materials NiCo LDH and NiCoO 2 , resulting in enhanced performance in the context of OER electrocatalysis and Zn-air battery systems. [Display omitted] • Controlled 3D leaf-vein heterostructures can modulate the interface charge redistribution for achieving high performance. • NiCoO 2 @NiCo LDH exhibits OER performance with an overpotential of 272 mV and maintains a stability of 99.76 % over 12 h. • The Zn-air batteries achieved a high power density of 149 mW cm−2 and long-cycle life for 340 h at 5 mA cm−2. Rechargeable zinc-air batteries (ZABs) have garnered attention as a viable choice for large-scale energy storage due to their advantageous characteristics, such as high energy density and cost-effectiveness. Strategies aimed at improving the kinetics of the oxygen evolution reaction (OER) through advanced electrocatalytic materials or structural designs can significantly enhance the efficiency and longevity of ZABs. In this study, we introduce a three-dimensional (3D) leaf-vein system heterojunction architecture. In this structure, NiCoO 2 nanowire arrays form the central vein, surrounded by an outer leaf composed of NiCo layered double hydroxide (LDH) nanosheets. All these components are integrated onto a substrate made of Ni foam. Notably, when tested in an alkaline environment, the NiCoO 2 @NiCo LDH exhibited an overpotential of 272 mV at a current density of 10 mA cm−2, and extended durability evaluations over 12 h underscored its robustness at 99.76 %. The rechargeable ZABs achieved a peak power density of 149 mW cm−2. Furthermore, the NiCoO 2 @NiCo LDH demonstrated stability by maintaining high round-trip efficiencies throughout more than 680 cycles (equivalent to 340 h) under galvanostatic charge–discharge cycling at 5 mA cm−2. The leaf-vein system heterojunction significantly increased the active sites of the catalysts, facilitating charge transport, improving electronic conductivity, and enhancing overall stability. [ABSTRACT FROM AUTHOR]

Exorbitant cost and limited availability of platinum-based electrocatalysts for the oxygen reduction reaction (ORR) in metal–air batteries and alkaline fuel cells pose significant obstacles to the large-scale commercialization of these clean-energy technologies. Herein, we employed a cost-effective and sustainable bacterial cellulose biomass as the precursor to prepare a nitrogen and fluorine codoped metal-free ORR electrocatalyst (BCC-NF-900) by direct pyrolysis regulation. The BCC-NF-900 inherited the three-dimensional framework of bacterial cellulose, exhibiting a robust porous structure with a Brunauer–Emmett–Teller surface area of 196.9 m2·g−1. The pyridinic N (0.6 at%) and semi-ionic F (0.34 at%) species formed in the inert sp2 carbon skeletons synergistically regulated the electron spin and charge density of the adjacent C atoms. Such rational combination of a rapid transport pathway and effective active site led to high ORR activity (onset potential 0.89 V vs. RHE), methanol resistance, and electrochemical stability (merely 6.9% current loss) in alkaline electrolyte. Importantly, compared to the mere F-doped BCC-F-900 (onset potential 0.82 V vs. RHE) and N-doped BCC-N-900 (onset potential 0.77 V vs. RHE) catalysts, the BCC-NF-900 catalyst exhibited a markedly enhanced ORR performance, as evidenced by the measured onset potential. This study provides an available reference for the design of efficient metal-free catalysts for ORR, presenting a promising alternative to Pt/C catalysts in metal–air batteries and alkaline fuel cells. [ABSTRACT FROM AUTHOR]

The elaborately constructed CoN/MnO heterojunction immobilized onto ultrathin N -doped carbon nanosheets as an excellent bifunctional electrocatalyst for Zn-air batteries. [Display omitted] • The fabrication of abundant CoN/MnO heterointerfaces is achieved in ultrathin carbon nanosheets. • The CoN/MnO@NC exhibits high bifunctional activities with an extremely small potential gap of 0.69 V between OER and ORR. • The application of CoN/MnO@NC as an excellent air cathode is demonstrated by both liquid and flexible quasi-solid-state rechargeable Zn-air batteries. • The CoN/MnO heterointerfaces optimize chemisorption energies for reaction intermediates and accelerate reaction kinetics. Designing bifunctional electrocatalysts with outstanding reactivity and durability towards the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) has remained a long-term aim for metal-air batteries. Achieving the high level of fusion between two distinct metal components to form bifunctional catalysts with optimized heterointerfaces and well-defined morphology holds noteworthy implications in the enhancement of electrocatalytic activity yet challenging. Herein, the fabrication of numerous heterointerfaces of CoN/MnO is successfully realized within ultrathin carbon nanosheets via a feasible self-templating synthesis strategy. Experimental results and theoretic calculations verify that the interfacial electron transfer from CoN to MnO at the heterointerface engenders an ameliorated charge transfer velocity, finely tuned energy barriers concerning reaction intermediates and ultimately accelerated reaction kinetics. The as-prepared CoN/MnO@NC demonstrates exceptional bifunctional catalytic performance, excelling in both OER and ORR showcasing a low reversible overpotential of 0.69 V. Furthermore, rechargeable liquid and quasi-solid-state flexible Zn-air batteries employing CoN/MnO@NC as the air-cathode deliver remarkable endurance and elevated power density, registering values of 153 and 116 mW cm−2 respectively and exceeding Pt/C + RuO 2 counterparts and those reported in literature. Deeply exploring the effect of electron-accumulated heterointerfaces on catalytic activity would contribute wisdom to the development of bifunctional electrocatalysts for rechargeable metal-air batteries. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Developing highly efficient and low‐cost electrocatalysts towards oxygen evolution reaction (OER) is essential for practical application in water electrolyzers and rechargeable metal‐air batteries. Although Fe‐based oxyhydroxides are regarded as state‐of‐the‐art non‐noble OER electrocatalysts, the origin of performance enhancement derived from Fe doping remains a hot topic of considerable discussion. Herein, we demonstrate that in situ generated Fe vacancies in the pristine CoFeOOH catalyst through a pre‐conversion process during alkaline OER result from dynamic Fe dissolution, identifying the origin of Fe‐vacancy‐induced enhanced OER kinetics. Density functional theory (DFT) calculations and experimental results including X‐ray absorption fine‐structure spectroscopy, in situ UV‐Vis spectroscopy, and in situ Raman spectroscopy reveal that the Fe vacancies could significantly promote the d‐band center and valence states of adjacent Co sites, alter the active site from Fe atom to Co atom, accelerate the formation of high‐valent active Co4+ species, and reduce the energy barrier of the potential‐determining step, thereby contribute to the significantly enhanced OER performance. [ABSTRACT FROM AUTHOR]

As battery technologies that can potentially increase the energy density and expand application scenarios of the lithium‐ion batteries, rechargeable metal‒air batteries have attracted extensive research interests. Among a variety types of metal anodes investigated, zinc (Zn)‒air and lithium (Li)‒air batteries hold best prospects for real‐world applications and attract the most scientific community interests. It has been more than 10 years since Cho et al. first compared Li–air and Zn–air batteries, during which great progress has been made. In this review, these two representative metal‒air battery technologies are compared in view of the most recent progresses and improvements in the last decade, especially efforts that push these technologies toward real world applications. It starts with the fundamentals of Zn–air and Li–air batteries, and discusses the progress made in electrolyte design, anode protection, and cathode catalysts development. It ends with an evaluation of the current research state along with an overall future perspective. Such a comprehensive comparison of typical non‐aqueous and aqueous battery systems with a focus on practical application criteria would be a timely review of metal‒air battery development in the last decade, which shed light for fundamental and applied research, eventually leading to real‐world application. [ABSTRACT FROM AUTHOR]

Cost-effective and high-efficiency catalysts play a central role in various sustainable electrochemical energy conversion technologies that are being developed to generate clean energy while reducing carbon emissions, such as fuel cells, metal–air batteries, water electrolyzers, and carbon dioxide conversion. In this context, a recent climax in the exploitation of advanced earth-abundant catalysts has been witnessed for diverse electrochemical reactions involved in the above mentioned sustainable pathways. In particular, polymer catalysts have garnered considerable interest and achieved substantial progress very recently, mainly owing to their pyrolysis-free synthesis, highly tunable molecular composition and microarchitecture, readily adjustable electrical conductivity, and high stability. In this review, we present a timely and comprehensive overview of the latest advances in organic polymers as emerging materials for powerful electrocatalysts. First, we present the general principles for the design of polymer catalysts in terms of catalytic activity, electrical conductivity, mass transfer, and stability. Then, the state-of-the-art engineering strategies to tailor the polymer catalysts at both molecular (i.e., heteroatom and metal atom engineering) and macromolecular (i.e., chain, topology, and composition engineering) levels are introduced. Particular attention is paid to the insightful understanding of structure–performance correlations and electrocatalytic mechanisms. The fundamentals behind these critical electrochemical reactions, including the oxygen reduction reaction, hydrogen evolution reaction, CO2 reduction reaction, oxygen evolution reaction, and hydrogen oxidation reaction, as well as breakthroughs in polymer catalysts, are outlined as well. Finally, we further discuss the current challenges and suggest new opportunities for the rational design of advanced polymer catalysts. By presenting the progress, engineering strategies, insightful understandings, challenges, and perspectives, we hope this review can provide valuable guidelines for the future development of polymer catalysts. [ABSTRACT FROM AUTHOR]

The rational design and exploration of efficient, low‐cost and durable bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are key to the development of rechargeable metal−air batteries. Here, we report a novel approach to in‐situ synthesize Fe0.64Ni0.36 nanoalloy encapsulated in nitrogen‐doped porous carbon nanotubes (FeNi@N−CNTs) as bifunctional electrocatalyst derived from Ni‐modified Prussian blue, on which the ORR/OER can be promoted by the N−CNTs surface due to the electron modulation caused by electron transfer from the inner FeNi nanoalloy to the N−CNTs surface. The abundant wide‐size range of mesopores in N−CNTs can offer rapid mass transport channels to facilitate the catalytic reactions. In addition, the encapsulation structure endows the outer N−CNTs acting as a "shield" to prevent the inner FeNi nanoalloy from corrosion in strong basic medium. Thanks to the synergistic effect between the N−CNTs and FeNi nanoalloy, the obtained FeNi@N−CNTs exhibits excellent bifunctional oxygen catalytic activity together with outstanding performance and cycling durability in rechargeable Zn−air battery. This work will open new avenues for the development of advanced bifunctional electrocatalysts for other metal−air batteries. [ABSTRACT FROM AUTHOR]

Molecular electrocatalysis requires the immobilization of molecular catalysts on electrode materials for practical uses. Direct adsorption of catalyst molecules on electrode materials is simple, but grafting molecules through chemical bonds can significantly improve electrocatalytic efficiency and durability. However, designing and synthesizing catalyst molecules to simultaneously improve catalytic activities and realize easy grafting on electrodes is challenging. The study herein reports on a one‐pot strategy to graft Co corroles on pyridine‐modified carbon nanotubes (CNTs) for oxygen electrocatalysis. By modifying CNTs with pyridines, the resulting pyridine‐modified CNTs can function as platforms to grab in situ generated Co corroles through the axial pyridine ligation on Co. Such an immobilization strategy combines three effects for the regulation of electrocatalysis, including the axial ligand effect, the electron transfer effect, and the chemical bond effect. The resulting hybrid materials show high efficiency for oxygen electrocatalysis, and the Zn–air battery assembled using these materials displays comparable performance as the Pt/Ir‐based battery. Moreover, the electrocatalytic efficiency of these hybrid materials can be systematically tuned by using different pyridines, highlighting the controllable feature of this strategy. Therefore, this work is significant to present a one‐pot three‐in‐one strategy to immobilize catalyst molecules on CNTs for electrocatalysis. [ABSTRACT FROM AUTHOR]

Fe–N–C materials have emerged as promising alternatives to precious metals for oxygen reduction reaction/oxygen evolution reaction (ORR/OER). In this study, a strategy is presented to investigate the influence of different chemical states of iron species in Fe–N–C materials on their electrocatalytic performance. Three Fe–N–C catalysts, containing either zero-valent Fe or Fe3O4 nanoparticles, are synthesized using acid pickling, high-speed centrifugation and ultrasound-assisted hydrothermal methods, respectively. The findings manifest that the chemical state of iron significantly affects the electrocatalytic activity of Fe–NX active sites, namely zero-valent Fe enhancing Fe–NX activity while Fe3O4 weakening its activity. Notably, the Fe@FeNC catalyst containing only zero-valent iron, demonstrates the only 0.621 V potential difference between the ORR half-wave potential and the OER potential at 10 mA cm−2. Furthermore, the rechargeable Zn–air battery assembled with Fe@FeNC as the air cathode exhibits a remarkable peak power density of 179.0 mW cm−2, excellent cycling stability over 210 h (with a cycle frequency of one every 10 min), and the minimal voltage gap of 0.710 V. These results reveal the significance of different chemical states of metal-based nanoparticles in Fe–NX activity of Fe–N–C catalysts and offer insights into the rational design of electrocatalysts with exceptional activity and versatile applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Diameter can improve the catalytic performance of SACs for ORR/OER. • Local strain and curvature effects causes abnormal d -band center model of OH on SACs. • Co@N 4 CNTs diameter adjusts Co d -orbitals, enhancing catalyst activity. • Co@N 4 CNTs have good selectivity for ORR rather than HER. The advancement of metal-air batteries relies significantly on the development of highly efficient bifunctional catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, we investigate the potential application of Co@N 4 -doped carbon nanotubes (Co@N 4 CNTs) as bifunctional catalysts using density functional theory calculations. We explore the stability and electronic properties of Co@N 4 CNTs by analyzing energies, bond lengths, conducting ab initio molecular dynamics simulations, and examining the density of states. Notably, the diameter of the nanotubes has a notable impact on the catalytic performance of Co@N 4 CNTs. A remarkable 54% improvement in catalytic activity when transitioning from (4, 4) to (24, 4) Co@N 4 CNTs, with η Bi from changing from 1.40 to 0.64 V. We have several exceptional catalysts with low overpotentials, including (18, 4), (22, 4), and (24, 4) Co@N 4 CNTs, which exhibit η Bi values of 0.68, 0.67, and 0.64 V, respectively. Moreover, we link the increased activity of Co@N 4 CNTs to the change of Co atom's partial d orbital energy, facilitated by adjustments in the diameter of Co@N 4 CNTs. This revelation offers valuable insights into the underlying factors driving the enhancement of catalytic activity through alterations in orbital energy levels. Our research uncovers several excellent catalysts and provides valuable insights for the design and development of efficient catalysts for metal-air batteries. [ABSTRACT FROM AUTHOR]

[Display omitted] Nitrogen-doped carbon-based electrodes are among the most promising alternatives to platinum-based electrodes in the cathode of fuel cells and metal-air batteries, where the oxygen reduction reaction (ORR) takes place. Among the approaches for improving ORR activity, nitrogen functionalities and well-developed textural properties have proved very effective. Nonetheless, the question of which between nitrogen active sites or textural properties are more crucial in N -doped carbon materials remains unanswered. This work proposes a comparative and critical approach through the selective functionalization of four commercial activated carbons with different textural properties. This study highlights the greater importance of N -doping in relation to the textural properties of carbon materials, and provides fundamental insights for conclusively addressing the ongoing debate within the carbon community about the significance of these two factors in the context of ORR. [ABSTRACT FROM AUTHOR]

Clean energy devices such as fuel cells and metal-air batteries can effectively solve the problems of environmental pollution and energy shortage. The common electrochemical reactions on hydrogen electrode (oxidation as HOR and evolution as HER) and oxygen electrode (reduction as ORR and evolution as OER) are important reaction in the conversion process of chemical energy and electric energy. However, the electrochemical conversion of these reactions is relatively low, with high overpotential (ƞ) even on Pt and Ru based catalysts, respectively, in addition to the high cost, which hinder the successful commercialization. Therefore, it is of great important to develop novel catalysts with acceptable ƞ at the same time cost effective. Here, the novel Cd–N–C-doped graphene catalyst systems with active center configuration (ACC) formed by low-boiling point non-precious metals Cd with a carbon and nitrogen coexist coordination environment are reported through a detailed study of density functional theory (DFT). The stability of catalyst was proved by energy calculations and dynamic simulations. Based on Gibbs free energy change (ΔG), ƞ and mechanisms of catalytic reactions were studied. Cd–N 1 C 3 -gra is a high efficiency HER and HOR catalyst with ƞ as low as 0.01 V. Cd–N 2 C 2 -o-gra is an efficient ORR and OER bifunctional catalyst with ƞOER = 0.48 V and ƞORR = 0.64 V. Based on the comparison of the free energy variation of principal and secondary reactions, their negligible yield of hydrogen peroxide was confirmed. Our research has further promoted the development of low-boiling point non-precious metals in electrocatalysis. [Display omitted] • Using N-doped, Cd atoms anchored on graphene as catalyst substrate. • The overpotential of HER at Cd–N 1 C 3 -gra is 0.01 V. • Cd–N 2 C 2 -o-gra is an efficient ORR and OER bifunctional catalyst with ƞOER = 0.48 V and ƞORR = 0.64 V. [ABSTRACT FROM AUTHOR]

[Display omitted] Development of the hydrogen economy requires the design of catalysts that increase the rate of the accompanying sluggish kinetic oxygen evolution reaction (OER). This is a key process in electrochemical energy conversion and storage, such as water splitting and metal-air batteries. The OER needs high overpotential and typically expensive precious metal-based catalysts. Therefore, designing low-cost and efficient electrocatalysts for OER is of paramount importance. In addition to focusing on the number of active sites or high specific surface area, the correlation between catalyst particle shape and performance should be considered. This work presents an electrocatalytic activity comparison of cobalt-containing carbons with different morphologies in the OER process. Employing metal–organic frameworks as carbon and metal precursors, the materials in the shape of polyhedrons, needles, unique spherical hedgehogs, and sea urchins were obtained. The effect of MOF template infiltration with additional carbon source on the physicochemical properties of electrocatalysts was also examined. The furfuryl alcohol-impregnated needle-shaped particles were characterized by a high content of cobalt active sites, surrounded by nitrogen-containing graphite layers. Electrochemical tests confirmed their best activity (overpotential 317 mV@10 mA/cm2), long stability (up to 20 h), as well as low reagents diffusion limitations (Tafel slope 57 mV/dec up to 24 mA/cm2). The vertically aligned structure of the catalyst contributed to improved detachment of the oxygen bubbles produced. [ABSTRACT FROM AUTHOR]

[Display omitted] Oxygen reduction reaction (ORR) is an essential half-reaction in next-generation energy storage and conversion systems, such as metal-air batteries and fuel cells. However, its practical application is restricted by the slow intrinsic kinetics, and the high price and low storage of noble metal electrocatalysts. Herein, unique CoFe nanoparticles encapsulated in N -doped carbon (CoFe-NC-Z8-900) with high content graphite-N derived from CoFe-g-C 3 N 4 @ZIF-8 via stepwise pyrolysis is reported as effective ORR catalysts. The increase of graphitic nitrogen content can enhance both the electrical conductivity and the adsorption of oxygen-containing intermediates, resulting in improved catalytic performance. Fortunately, CoFe-NC-Z8-900 exhibits an exceptionally high half-wave potential (E 1/2) of 0.914 V in a 0.1 M KOH solution. The excellent ORR electrocatalytic activity can be mainly attributed to the synergistic effect of the CoFe bimetal and the relatively high content of graphite-N. This study offers a unique method for creating powerful nitrogen-doped carbon coated metal nanoparticle electrocatalysts. [ABSTRACT FROM AUTHOR]

Efficient oxygen evolution reaction (OER) electrocatalysts are widely required in the realm of water electrolysis and rechargeable metal-air batteries. This work describes an easy and simple method for the synthesis of copper salen (Cu(Salen))-functionalized multiwalled carbon nanotubes (MWCNTs) nanocomposite materials (Cu(Salen)/MWCNTs). It has been used for OER in the basic medium (0.1 M KOH). The resulting nanocomposite, Cu(Salen)/MWCNTs, has been studied using spectroscopic and microscopic techniques such as Fourier transform infrared (FT-IR), UV-visible spectroscopy, powder X-ray diffraction (p-XRD), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDAX). The electrochemical characterization of prepared Cu(Salen)/MWCNTs nanocomposite based modified glassy carbon (GC) electrodes (GC/Cu(Salen)/MWCNTs) and their application towards OER have been performed using an electrochemical method. The Tafel slope of nanocomposite material is 159.6 mV/dec in 0.1 M KOH solution, indicating that GC/Cu(Salen)/MWCNTs could be a promising and cost-effective electrode material for the OER. This study demonstrates a novel way for creating an active nanocomposite catalyst for OER in alkaline media. [ABSTRACT FROM AUTHOR]

The development of efficient and low‐cost bifunctional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is imperative but remains challenging in rechargeable zinc–air batteries. Herein, a metal oxidation‐assisted approach is developed for the facile synthesis of a highly efficient bifunctional catalyst (Co@NC@LDHs) which is composed of layered double hydroxides (LDHs) nanosheets in situ vertically grown on the surface of hollow carbon nanoframes encapsulating Co nanoparticles (Co@NC). Specifically, the vertical LDHs distributing on the carbon surface ensure the maximized number of accessible active sites and the interaction between LDHs with the carbon matrix. The hierarchically structured bifunctional Co@NC@LDHs display an overpotential of 0.33 V at 10 mA cm−2 for OER and a half‐wave potential of 0.88 V for ORR. The potential gap (ΔE) of Co@NC@LDHs is calculated to be 0.68 V, outperforming the mixed Pt/C + RuO2 catalysts (ΔE = 0.77 V), manifesting its superior bifunctional electrocatalysis performance. Moreover, the Zn–air batteries based on Co@NC@LDHs electrocatalyst exhibit a high peak power density (185.2 mW cm−2) and excellent durability (5.0 mA cm−2 over 500 h). This work may provide a facile strategy for the fabrication of LDHs on carbon substrate, acting as efficient catalysts for broad energy‐related applications. [ABSTRACT FROM AUTHOR]

The rapid developments of the Internet of Things (IoT) and portable electronic devices have created a growing demand for flexible electrochemical energy storage (EES) devices. Nevertheless, these flexible devices suffer from poor flexibility, low energy density, and poor dynamic stability of power output during deformation, limiting their practical applications. Carbon nanofibers (CNFs) with high conductivity, good flexibility, and large‐scale preparation are regarded as promising electrodes for flexible EES devices. Based on the issues of current flexible EES devices, this review presents various strategies from the design of CNFs‐based electrodes to the fabrication of devices and overviews their applications in various flexible metal ion/air batteries (Li/Na/K‐ion batteries, Li‐S batteries, metal–air batteries, and other novel secondary batteries) and supercapacitors. Finally, the remaining challenges and perspectives on the CNFs‐based flexible EES devices are proposed to provide guidance for the researchers concentrating on high‐performance flexible EES devices. [ABSTRACT FROM AUTHOR]

Developing efficient and affordable electrocatalysts for the sluggish oxygen evolution reaction (OER) remains a significant barrier that needs to be overcome for the practical applications of hydrogen production via water electrolysis, transforming CO2 to value‐added chemicals, and metal‐air batteries. Recently, hydroxides have shown promise as electrocatalysts for OER. In situ or operando techniques are particularly indispensable for monitoring the key intermediates together with understanding the reaction process, which is extremely important for revealing the formation/OER catalytic mechanism of hydroxides and preparing cost‐effective electrocatalysts for OER. However, there is a lack of comprehensive discussion on the current status and challenges of studying these mechanisms using in situ or operando techniques, which hinders our ability to identify and address the obstacles present in this field. This review offers an overview of in situ or operando techniques, outlining their capabilities, advantages, and disadvantages. Recent findings related to the formation mechanism and OER catalytic mechanism of hydroxides revealed by in situ or operando techniques are also discussed in detail. Additionally, some current challenges in this field are concluded and appropriate solution strategies are provided. [ABSTRACT FROM AUTHOR]

Due to the depletion of fossil fuels, the demand for renewable energy has increased, thus stimulating the development of novel materials for energy conversion devices such as fuel cells. In this work, nickel nanoparticles loaded on reduced graphene oxide (Ni/rGO) with small size and good dispersibility were successfully prepared by controlling the pyrolysis temperature of the precursor at 450 °C, assisted by a microwave-assisted hydrothermal method, and exhibited enhanced electrocatalytic activity towards oxygen reduction reaction (ORR). Additionally, the electron enrichment on Ni NPs was due to charge transfer from the rGO support to metal nickel, as evidenced by both experimental and theoretical studies. Metal–support interactions between nickel and the rGO support also facilitated charge transfer, contributing to the enhanced ORR performance of the composite material. DFT calculations revealed that the first step (from O2 to HOO*) was the rate-determining step with an RDS energy barrier lower than that of the Pt(111), indicating favorable ORR kinetics. The HOO* intermediates can be transferred onto rGO by the solid-phase spillover effect, which reduces the chemical adsorption on the nickel surface, thereby allowing continuous regeneration of active nickel sites. The HO2− intermediates generated on the surface of rGO by 2e− reduction can also efficiently diffuse towards the nearby Ni surface or the interface of Ni/rGO, where they can be further rapidly reduced to OH−. This mechanism acts as the pseudo-four-electron path on the RRDE. Furthermore, Ni/rGO-450 demonstrated superior stability, methanol tolerance, and durability compared to a 20 wt% Pt/C catalyst, making it a cost-effective alternative to conventional noble metal ORR catalysts for fuel cells or metal–air batteries. [ABSTRACT FROM AUTHOR]

Metal–air batteries have emerged as a promising solution for large-scale energy storage and conversion, thanks to their higher energy density than lithium-ion batteries. However, their commercialization as a secondary battery is challenging due to limitations imposed by the properties of individual components. The air cathode, in particular, requires advanced catalyst materials to enhance its performance. This study explores using carbon nanomaterials as a cathode component in metal–air batteries due to their exceptional electrical conductivity and physical/chemical stability. To synthesize heteroatom-containing carbon nanosheets, we employed the solution plasma process (SPP), a non-equilibrium cold plasma technique at atmospheric pressure and room temperature. Our research successfully produced sulfur-containing carbon nanosheets through the SPP and conducted preliminary investigations to evaluate their electrocatalytic activity for both the oxygen reduction reaction and oxygen evolution reaction. These findings contribute to the advancement of metal–air battery technology and bring us closer to overcoming the challenges associated with commercializing this promising energy storage system. [ABSTRACT FROM AUTHOR]

The oxygen evolution reaction (OER) plays a pivotal role in diverse electrochemical conversion applications, such as water splitting and metal–air batteries. Nevertheless, the formation of several active sites in catalysts made of non-noble metals continues to encounter notable obstacles. To tackle this challenge, a 2D heterostructure catalyst composed of Fe2P–CoP2/MoOx nanosheets was designed. The cobalt molybdate (CoMoO4) nanosheets and their supported FeOOH nanoflakes were in situ transformed into 2D heterostructure Fe2P–CoP2/MoOx nanosheets via a simple hydrothermal and phosphorization process. Note that the 2D MoOx nanosheets significantly enhance the electrochemically active surface area (ECSA), and there is a synergistic effect between cobalt phosphide (CoP2) and iron phosphide (Fe2P) nanoparticles, improving the OER reaction activity. When the electrocatalyst was employed for the OER, the Fe2P–CoP2/MoOx nanosheets exhibit remarkable OER efficiency, reducing overpotentials to as low as 235 mV at a current density of 50 mA cm−2, accompanied by a Tafel slope of 33.32 mV dec−1, along with exceptional enduring stability. The synthesis of the 2D heterostructure Fe2P–CoP2–MoOx nanosheets and their remarkable OER performance represent substantial advancements in developing electrocatalysts that are productive and stable in sustainable energy conversion and storage applications. [ABSTRACT FROM AUTHOR]

The use of platinum-free (Pt) cathode electrocatalysts for oxygen reduction reactions (ORRs) has been significantly studied over the past decade, improving slow reaction mechanisms. For many significant energy conversion and storage technologies, including fuel cells and metal–air batteries, the ORR is a crucial process. These have motivated the development of highly active and long-lasting platinum-free electrocatalysts, which cost less than proton exchange membrane fuel cells (PEMFCs). Researchers have identified a novel, non-precious carbon-based electrocatalyst material as the most effective substitute for platinum (Pt) electrocatalysts. Rich sources, outstanding electrical conductivity, adaptable molecular structures, and environmental compatibility are just a few of its benefits. Additionally, the increased surface area and the simplicity of regulating its structure can significantly improve the electrocatalyst's reactive sites and mass transport. Other benefits include the use of heteroatoms and single or multiple metal atoms, which are capable of acting as extremely effective ORR electrocatalysts. The rapid innovations in non-precious carbon-based nanomaterials in the ORR electrocatalyst field are the main topics of this review. As a result, this review provides an overview of the basic ORR reaction and the mechanism of the active sites in non-precious carbon-based electrocatalysts. Further analysis of the development, performance, and evaluation of these systems is provided in more detail. Furthermore, the significance of doping is highlighted and discussed, which shows how researchers can enhance the properties of electrocatalysts. Finally, this review discusses the existing challenges and expectations for the development of highly efficient and inexpensive electrocatalysts that are linked to crucial technologies in this expanding field. [ABSTRACT FROM AUTHOR]

[Display omitted] The development of highly active and durable nonprecious metal-based bifunctional electrocatalysts for oxygen reduction/evolution reaction (ORR/OER) is important for rechargeable zinc-air batteries. Herein, a three-dimensional conductive niobium-doped TiO-TiO 2 heterostructure supported ZIF-67-derived Co-NC bifunctional catalyst was fabricated. In the Co-NC@Nb-TiO x catalyst, the Nb doping promoted the formation of TiO-TiO 2 heterojunction support, enhanced its conductivity and stability and provided strong electron metal-support interaction between Co-NC and Nb-TiO x. Also, the supported Co-NC nanoparticles provided abundant active sites with excellent ORR/OER activity. Experimental analysis reveals that the high OER activity of Co-NC@Nb-TiO x can be attributed to the in-situ generated CoOOH species. It exhibits excellent ORR activity, as shown by its onset potential (0.95 V vs. RHE) and half-wave potential (0.86 V vs. RHE). Its OER overpotential at 10 mA cm−2 is 480 mV. The zinc-air battery realizes outstanding cycling stability over 225 h cycles tested at 10 mA cm−2. This work demonstrates the importance of designing highly stable metal oxide-supported catalysts in electrochemical energy conversion devices. [ABSTRACT FROM AUTHOR]

One type of MOF-derived porous N -doped carbon anchoring iron phthalocyanines has been obtained. Owing to abundant Fe-N4 active centers, FePc@NC-1000 exhibits excellent ORR activity, and its assembled zinc-air batteries also show favorable performance and durability. [Display omitted] • One Zn-based pillar-layer MOF nanosheet is easily achieved by its restricted axial growth. • Iron phthalocyanines could be firmly immobilized into MOF-derived porous Ndoped carbons. • The optimal catalyst of FePc@NC-1000 shows high oxygen reduction activity and durability. Functional carbon nanomaterials play a crucial role in the cathodic oxygen reduction reaction (ORR) for sustainable fuel cells and metal-air batteries. In this study, we propose an effective approach to immobilize iron phthalocyanines (FePc) by employing a porous N -doped carbon material, denoted as NC-1000 , derived from a sheet-shaped coordination polymer. The resulting NC-1000 possesses substantial porosity and abundant pore defects. The nitrogen sites within NC-1000 not only facilitate FePc adsorption but also optimize the electron distribution at the Fe-N site. The FePc@NC-1000 composite material exhibits a significant number of active centers in the form of Fe-N 4 moieties, showcasing satisfactory ORR activity. Specifically, it demonstrates an onset potential of 0.99 V, a positive half-wave potential of 0.86 V, a large limiting current of 5.96 mA cm−2, and a small Tafel slope of 44.41 mV dec-1. Additionally, theoretical calculations and experimental results confirm the favorable performance and durability of zinc-air batteries assembled using FePc@NC-1000 , thereby highlighting their considerable potential for practical applications. Overall, this study provides a comprehensive exploration of the enhanced catalytic performance and increased stability of metal–organic framework-derived functional carbon nanomaterials as cost-effective, efficient, and stable catalysts for the ORR. [ABSTRACT FROM AUTHOR]

Single‐atomic transition metal–nitrogen–carbon (M–N–C) structures are promising alternatives toward noble‐metal‐based catalysts for oxygen reduction reaction (ORR) catalysis involved in sustainable energy devices. The symmetrical electronic density distribution of the M─N4 moieties, however, leads to unfavorable intermediate adsorption and sluggish kinetics. Herein, a Fe–N–C catalyst with electronic asymmetry induced by one nearest carbon vacancy adjacent to Fe─N4 is conceptually produced, which induces an optimized d‐band center, lowered free energy barrier, and thus superior ORR activity with a half‐wave potential (E1/2) of 0.934 V in a challenging acidic solution and 0.901 V in an alkaline solution. When assembled as the cathode of a Zinc–air battery (ZAB), a peak power density of 218 mW cm−2 and long‐term durability up to 200 h are recorded, 1.5 times higher than the noble metal‐based Pt/C+RuO2 catalyst. This work provides a new strategy on developing efficient M–N–C catalysts and offers an opportunity for the real‐world application of fuel cells and metal–air batteries. [ABSTRACT FROM AUTHOR]