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[Display omitted] Balancing the bicatalytic activities and stabilities between oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is a critical yet challenging task for exploring advanced rechargeable Zinc–air batteries (ZABs). Herein, a hybrid nanosheet catalyst with highly dispersed and densified metallic species is developed to boost the kinetics and stabilities of both ORR and OER concurrently. Through a progressive coordination and pyrolysis approach, we directly prepared highly conductive onion-like carbon (OLC) accommodating dense ORR-active Co N C species and enveloping high-loading OER-active CoNi-synergic structures within a porous lamellar architecture. The resultant CoNi/OLC nanosheet catalyst delivers better ORR and OER activities showcasing a smaller reversible oxygen electrode index (Δ E = E j10 − E 1/2) of 0.71 V, compared to state-of-the-art Pt/C-RuO 2 catalysts (0.75 V), Co/amorphous carbon polyhedrons (0.80 V), NiO nanoparticles with higher Ni loading (1.00 V), and most CoNi-based bifunctional catalysts reported so far. The rechargeable ZAB assembled with the developed catalyst achieves a remarkable peak power density of 270.3 mW cm−2 (172 % of that achieved by Pt/C + RuO 2) and ultrahigh cycling stability with a negligible increase in voltage gap after 800 h (110 mV increase after 200 h for a Pt/C + RuO 2 -based battery), standing the top level of those ever reported. [ABSTRACT FROM AUTHOR]

[Display omitted] • The catalyst was in-situ constructed via a facile molten salt-assisted pyrolysis route. • The Co/Co 2 P heterojunction plays predominant catalysis for OER. • Co/Co 2 P@NPCNS shows excellent bifunctional activity with a Δ E = 0.66 V. • The battery performs high peak power density of 187 mW cm−2. Transition metal phosphides (TMPs) with high electrocatalytic activity for the oxygen evolution reaction (OER) are reckoned as a substitution of precious group metals catalysts in rechargeable Zn-air battery. In this work, Co/Co 2 P heterojunction nanoparticles supported N,P-doped carbon nanosheets (Co/Co 2 P@NPCNS) were designed and prepared via a facile one-step molten salt-assisted pyrolysis process. Density function theory calculations reveal that the heterogeneous interactions of Co/Co 2 P effectively enhance the bifunctional electrocatalytic activity for oxygen reduction reaction (ORR) and OER. The synergistic interaction between the Co/Co 2 P heterojunction nanoparticles with highly exposed active sites and excellent catalytic activity and the two-dimensional doped carbon nanosheets with high conductivity contributes to Co/Co 2 P@NPCNS exhibiting preeminent bifunctional ORR/OER activity and stability with a high half-wave potential for ORR (0.87 V), a low overpotential for OER (302 mV at 10 mA cm−2) and a low potential gap (0.66 V). The homemade rechargeable Zn-air battery performs high peak power density (187 mW cm−2) and exceptional endurance. This heterogeneous interface tactic of integrating TMPs with heteroatom-doped carbon materials may shed light on the research and development of non-precious metal electrocatalysts. [ABSTRACT FROM AUTHOR]

The oxygen evolution reaction (OER) is central to energy conversion technologies, but the high cost and scarcity of commercial noble metal catalysts limit their widespread application. Natural products exhibit great potential in preparing high‐performance electrocatalysts due to their cost‐effectiveness and sustainability. Here, a kind of 1D polymers [M‐EA (M═Co, Cu, Ni)] for oxygen evolution reaction via the complexation of ellagic acid (EA) with metal ions are reported. It is found that Ni‐EA displays a low overpotential (190 mV at 10 mA cm−2) and an ultralow Tafel slope (28 mV dec−1), with a production cost of only 3.6 × 10−2% of IrO2. Density functional theory investigations reveal the electrocatalytic mechanism of the OER. A rechargeable Zn‐Air battery using Ni‐EA+Pt/C as the air electrode shows a lower charging potential and better cycling stability than the IrO2+Pt/C‐based battery. This work provides a train for the development of state‐of‐the‐art OER catalysts. [ABSTRACT FROM AUTHOR]

Herein, we successfully construct bifunctional electrocatalysts by synthesizing atomically dispersed Fe−Se atom pairs supported on N‐doped carbon (Fe−Se/NC). The obtained Fe−Se/NC shows a noteworthy bifunctional oxygen catalytic performance with a low potential difference of 0.698 V, far superior to that of reported Fe‐based single‐atom catalysts. The theoretical calculations reveal that p‐d orbital hybridization around the Fe−Se atom pairs leads to remarkably asymmetrical polarized charge distributions. Fe−Se/NC based solid‐state rechargeable Zn‐air batteries (ZABs−Fe−Se/NC) present stable charge/discharge of 200 h (1090 cycles) at 20 mA cm−2 at 25 °C, which is 6.9 times of ZABs−Pt/C+Ir/C. At extremely low temperature of −40 °C, ZABs−Fe−Se/NC displays an ultra‐robust cycling performance of 741 h (4041 cycles) at 1 mA cm−2, which is about 11.7 times of ZABs−Pt/C+Ir/C. More importantly, ZABs−Fe−Se/NC could be operated for 133 h (725 cycles) even at 5 mA cm−2 at −40 °C. [ABSTRACT FROM AUTHOR]

[Display omitted] • A facile compression-pyrolysis route to obtain mesoporous waffle-like carbon. • Waffle-like carbon is built up of interwoven N -doped CNTs and graphene nanosheets. • Co@pNC has excellent bifunctional activity with ultralow potential gap of 0.70 V. • Assembled battery shows energy density of 928 Wh kg Zn -1, close to theoretical value. Rational design and facile preparation of high-performance carbon-based eletrocatalysts for both oxygen reduction and evolution reactions (ORR and OER) is crucial for practical applications of rechargeable zinc-air batteries. Inspired by the fact that the metallic Co catalysis on the formation of carbon nanotubes (CNTs), this work develops a facial compression-pyrolysis route to synthesize a mesoporous waffle-like N -doped carbon framework with embedded Co nanoparticles (Co@pNC) using a Co metal–organic framework and melamine as precursors. The unique porous waffle-like carbon framework is built up of interwoven N -doped CNTs and graphene nanosheets, which offers abundant catalytic-active sites and rapid diffusion channels for intermediates and electrolyte. The optimized Co@pNC shows excellent bifunctional ORR/OER electrocatalytic activity in alkaline media with a half-wave potential (E 1/2) of 0.85 V for ORR and a small potential gap of 0.70 V between ORR E 1/2 and OER potential at 10 mA cm−2. Its assembled battery exhibits a peak power density up to 150.3 mW cm−2, an energy density of 928 Wh kg Zn -1 and superb rate capability. It highlights a facile component and architecture strategy to design high-performance carbon-based eletrocatalysts. [ABSTRACT FROM AUTHOR]

Integrating components for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) while optimizing their electronic structure is an effective strategy for developing excellent bifunctional catalysts for rechargeable zinc-air batteries (ZABs). In this study, we successfully fabricated Mn 0.3 Ru 0.7 O 2 nanosheets based on a solid solution oxide using a simple molten salt method. The Mn 0.3 Ru 0.7 O 2 nanosheets exhibits abundant Ru and Mn sites through the Ru-O-Mn structure, which serve as excellent OER and ORR active centers. Experimental and theoretical studies validate the coccurrence of charge transefer between the Ru-O-Mn bond, modulating the valence state and d-band center of the Mn and Ru, thereby subsequently improving their ORR/OER intrinsic activity. Remarkably, the Mn 0.3 Ru 0.7 O 2 nanosheets displays superior electropcatalytic performance with a charge/discharge voltage gap (ΔE) of only 0.59 V, which is the best among all reported counterpart catalysts. A rechargeable ZAB utilizing Mn 0.3 Ru 0.7 O 2 nanosheets achieved a power density of 154 mW cm−2 and a specific capacity of 821 mA h g−1, surpassing that of the commercial Pt/C + RuO 2 mixing catalyst. This study offers a new strategy for preparing highly active and durable bifunctional catalysts for rechargeable ZABs. [Display omitted] • Mn 0.3 Ru 0.7 O 2 nanosheets is fabricated using a molten salt method. • Charge transfer within Ru-O-Mn optimizes the electronic structure of active sites. • Mn 0.3 Ru 0.7 O 2 allows an ultralow charge/discharge potential gap of 0.59 V. • A rechargeable Zn-air battery with Mn 0.3 Ru 0.7 O 2 shows excellent performance. [ABSTRACT FROM AUTHOR]

The construction of suitable heterostructures in materials can tune the Fermi energy levels and electron transport rates of materials to achieve attractive oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) properties. In this study, a catalyst anchored in nitrogen-doped carbon nanowires (NCNW) with a heterogeneous interface of Co and CoSe is constructed to realize high-performance ORR and OER bifunctional catalysis. These Co and CoSe heterostructure interfaces can optimize the adsorption of intermediates. The Co/CoSe@NCNW catalyst performs excellent ORR catalytic activity (E 1/2 = 0.89 V), and good OER activity (potential at 10 mA/cm2, E j = 10 = 1.55 V). More importantly, the material shows excellent performance in rechargeable zinc-air batteries (ZABs). The open-circuit voltages of 1.47 and 1.50 V and the peak power densities of 122.56 and 74.49 mW/cm2 in liquid and solid electrolytes, respectively, are superior to those of the ZABs prepared from noble metals. Consequently, the construction of heterogeneous structures can convincingly boost the commercialization of rechargeable ZABs, and be extended to other fields involving ORR and OER. • Co/CoSe heterostructure catalyst is successfully prepared. • Co/CoSe@NCNW has excellent ORR and OER electrocatalytic properties. • Co/CoSe@NCNW applies to liquid and flexible solid-state Zn-air batteries. [ABSTRACT FROM AUTHOR]

• A bifunctional m-CoS x @NSC catalyst with dual electric field effects was fabricated. • The interfacial micro-electric field improves the intrinsic activity and stability. • The tentacle-induced local electric field boosts the catalytic reaction kinetics. • The m-CoS x @NSC exhibits excellent OER/ORR electrocatalytic activities. • The assembled m-CoS x @NSC-based ZAB presents outstanding performance. Regulation of the surface microenvironment is crucial for the development of highly active and durable OER/ORR bifunctional catalysts. In this study, a bifunctional m-CoS x @NSC electrocatalyst with dual electric field effects was designed and fabricated by synchronous pyrolysis of organic sulfur-rich cobalt compounds (Co-DC) and melem. The introduction of nitrogen-rich melem effectively induced the conversion of Co-DC and the growth of tentacles to form a hierarchical carbon skeleton. The interfacial micro-electric field between the carbon layer and CoS x active species improves the intrinsic activity and stability of m-CoS x @NSC. Finite element method simulation and in-situ measurements proved that the tentacle-induced external local electric field promotes the formation of Co(OH) 2 /CoOOH intermediates and mass transfer, thus accelerating the catalytic reaction kinetics. Through the synergistic effect of dual electric fields, the m-CoS x @NSC catalyst demonstrated a low overpotential of 340 mV for OER and a high half-wave potential of 0.85 V for ORR. Furthermore, the m-CoS x @NSC-based ZAB exhibited an open-circuit voltage of 1.42 V, a maximum power density of 87.38 mW cm−2, a specific capacity of 876.17 mAh g Zn −1, and a cycling performance of 700 cycles. The synergistic regulation of the internal and external microenvironments provides a novel insight to improve the catalytic reaction kinetics of OER/ORR. [ABSTRACT FROM AUTHOR]

[Display omitted] • The bio-derived FeNi@NCSs were synthesized by a one-step pyrolysis. • The unique structure offers enlarged specific active area and improved stability. • Multi-component synergetic effect brings out bifunctional catalytic activities. • The catalyst exhibits efficient oxygen electrocatalysis for Zn–air battery. It is imperative to design and manufacture electrocatalysts towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) for popularization of rechargeable Zn–air batteries. Herein, FeNi alloy confined in N-doped carbon nanosheets (FeNi@NCSs) was harvested via a facile complexation-pyrolysis strategy from the mixture of guanine and metal chlorides. After strictly exploring the pyrolysis temperature and metal types, the resulted FeNi@NCSs showed greatly improved performances on both the ORR (onset potential of 0.93 V and half-wave potential of 0.84 V) and OER (overpotential of 318 mV at 10 mA cm−2 and 379 mV at 100 mA cm−2). Further, the FeNi@NCSs based Zn–air battery exhibited a higher open circuit voltage (1.496 V), a larger power density (128.8 mW cm−2), and prominent durability (360 cycles, 120 h). This study provides an appealing approach to utilize biomass for synthesis of low-cost and high-efficiency electrocatalysts in energy associated systems. [ABSTRACT FROM AUTHOR]

Bidirectional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalysts are key for molecular oxygen-centric renewable energy transduction via metal-air batteries. Here, a molecular cobalt complex is covalently tethered on a strategically functionalized silica surface that displayed both ORR and OER in alkaline media. The detailed X-ray absorbance spectroscopy (XAS) studies indicate that this catalyst retains its intrinsic molecular features while playing a central role during bidirectional electrocatalysis and demonstrating a relatively lower energy gap between O 2 /H 2 O interconversions. This robust molecular catalyst-silica composite (deposited on a porous carbon paper) is assembled along with a zinc foil and polymeric gel membrane to devise an active single-stack quasi-solid zinc-air battery (ZAB) setup. This quasi-solid ZAB assembly displayed impressive power density (60 mW cm -2 @100 mA cm -2 ), specific capacity (818 mAh g -1 @ 5mA cm -2 ), energy density (757 Whkg -1 @5mA cm -2 ), and elongated charging/discharging life (28 h). An appropriate assembly of these ZAB units is able to power practical electronic appliances, requiring ≈1.6-6.0V potential requirements., (© 2024 Wiley‐VCH GmbH.)

A combined hydroxyl-functionalized and NH 4 Cl-assisted etching strategy is developed to effectively promote the yield of edge-hosted single-atomic Cu-N4 sites. The developed CuSAs@DCSs renders outstanding ORR activity (E onset =1.02 V, E 1/2 = 0.90 V), and excellent stability. CuSAs@DCSs-based Zn-air battery achieves ultralong cycle life and large power density. Rich edge-hosted active sites are responsible for the remarkable ORR performance. [Display omitted] • A hydroxyl-functionalized and NH 4 Cl-assisted etching strategy is developed to promote the yield of edge-hosted Cu-N4 sites. • Rich accessible edge-hosted Cu-N4 sites are responsible for the remarkable ORR performance. • CuSAs@DCSs exhibits extraordinarily ORR activity and excellent stability in both alkaline and acid solution. • CuSAs@DCSs exhibits superb performance when used as air cathode for Zn–air battery. • This strategy can be extended to fabricate other single atoms catalyst with controlled electronic structure. Single-atom electrocatalysts with metal-nitrogen-carbon (M N C SACs) moieties in carbon support display outstanding electrocatalytic performance towards oxygen reduction reaction (ORR) and have received widespread attentions. Only active sites on the edges of pores in carbon support are electrochemically accessible and contribute to ORR. Herein, we report a combined hydroxyl-functionalized and NH 4 Cl-assisted etching strategy to effectively promote the yield of edge-hosted Cu SAs. Thus, well-defined SAs with Cu-N 4 configuration are generated into the defect of carbonaceous nanospheres (CuSAs@DCSs). Impressively, the obtained SACs renders outstanding electrocatalytic ORR activity with onset, half-wave potentials of 1.02 V, 0.90 V, and extremely high stability, which transcends the noble-metals and most of the previously reported catalysts. When used in rechargeable Zn-air batteries, CuSAs@DCSs achieves ultralong cycle life at the large current density of 10 mA cm−2 (over 260 h) with low charge–discharge potential gap. Our study demonstrates that the creation of abundant micropores enriches the electrochemically accessible SAs, which locate at the edge-defects and are responsible for the remarkable ORR performance. This work sheds a facile strategy for designing and developing efficient electrocatalyst for various energy-related electrocatalytic reactions. [ABSTRACT FROM AUTHOR]

Due to the insufficient stability and expensive price of commercial precious metal catalysts like Pt/C and IrO2, it is critical to study efficiently, stable oxygen reduction reaction as well as oxygen evolution reaction (ORR/OER) electrocatalysts of rechargeable Zn-air batteries. PrBa0.5Sr0.5Co1.5Fe0.5O5 (PBSCF) double perovskite was adopted due to its flexible electronic structure as well as higher electro catalytic activity. In this study, PBSCF was prepared by the citrate-EDTA method and the optimized amount of PBSCF-Pt/C composite was used as a potential ORR/OER bifunctional electrocatalyst in 0.1 M KOH. The optimized composite exhibited excellent OER intrinsic activity with an onset potential of 1.6 V and Tafel slope of 76 mV/dec under O2-saturated 0.1 M KOH. It also exhibited relatively competitive ORR activity with an onset potential of 0.9 V and half-wave potential of 0.78 V. Additionally, Zn–air battery with PBSCF composite catalyst showed relatively good stability. All these results illustrate that PBSCF-Pt/C composite is a promising bifunctional electrocatalyst for rechargeable Zn-air batteries. [ABSTRACT FROM AUTHOR]

Zinc–air batteries are one of the most excellent of the next generation energy devices. However, their application is greatly hampered by the slow kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) of air electrode. It is of great importance to develop good oxygen electrocatalysts with long durability as well as low cost. Here, A-site deficient (SmSr)0.95Co0.9Pt0.1O3 perovskites have been studied as potential OER electrocatalysts prepared by EDTA–citrate acid complexing method. OER electrocatalytic performance of (SmSr)0.95Co0.9Pt0.1O3 was also evaluated. (SmSr)0.95Co0.9Pt0.1O3 electrocatalysts exhibited good OER activities in 0.1 M KOH with onset potential and Tafel slope of 1.50 V and 87 mV dec−1, similar to that of Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF-5582). Assembled rechargeable Zn–air batteries exhibited good discharge potential and charge potential with high stability, respectively. Overall, all results illustrated that (SmSr)0.95Co0.9Pt0.1O3 is an excellent OER electrocatalyst for zinc–air batteries. Additionally, this work opens a good way to synthesize highly efficient electrocatalysts from A-site deficient perovskites. [ABSTRACT FROM AUTHOR]

[Display omitted] • The petaloid CoP/FeP@PCN catalyst was synthesized with ZIF and melamine as templates. • CoP/FeP@PCN composite serves as a good bifunctional electrochemical oxygen catalyst. • The E 1/2 of ORR is 0.894 V and the potential gap between ORR and OER is 0.566 V. • CoP/FeP@PCN-based aqueous ZAB exhibits good performance and 579 h cycling stability. • CoP/FeP@PCN-based solid-state ZAB exhibits 100 h charge–discharge cycling stability. Exploring alternative energy sources and innovative energy storage and conversion technologies is essential for pursuing sustainable development in this global society. Metal-air batteries are considered as one of the most promising green energy sources due to their high energy density and environmentally benign, and the development of efficient cathodic catalysts for metal-air batteries is a critical topic in the energy field. In this work, a two-step high-temperature pyrolysis strategy is proposed to prepare to synthesize the petaloid CoP/FeP@PCN catalyst with tiny Co-ZIF and Fe-ZIF as templates, melamine/thiourea as the carbon framework sources, and (NH 4)H 2 PO 4 as the P-sources. Plentiful nanoparticles are homogeneously dispersed on the surface of the petaloid carbon layers. From the configuration perspective, this petaloid structure benefits the adsorption/desorption of the reactants/products and the mass transfer. The optimized CoP/FeP@PCN catalyst serves as a highly efficient bifunctional electrochemical oxygen catalyst, delivering excellent ORR and OER performance with the ORR half-wave potential of 0.894 V (0.1 M KOH) and the OER overpotential of 230 mV (1 M KOH), which is higher than the corresponding monometallic catalysts and most of the reported works. Moreover, the catalytic active site is investigated by DFT calculations. The CoP/FeP@PCN-based aqueous ZAB exhibits exceptional battery performance with high peak power density (175.4 mW·cm−2), large specific capacity (780 mAh·g−1@10 mA·cm−2), and long-term charge–discharge stability. The corresponding solid-state Zn-air battery also performs well with high specific capacity (750 mAh·g−1@5 mA·cm−2) and long-term charge–discharge stability. Both the liquid and solid-state ZABs perform better than the commercial Pt/C+RuO 2 -based ZAB. [ABSTRACT FROM AUTHOR]

Abstract As bifunctional oxygen evolution/reduction electrocatalysts, transition-metal-based single-atom-doped nitrogen–carbon (NC) matrices are promising successors of the corresponding noble-metal-based catalysts, offering the advantages of ultrahigh atom utilization efficiency and surface active energy. However, the fabrication of such matrices (e.g., well-dispersed single-atom-doped M-N4/NCs) often requires numerous steps and tedious processes. Herein, ultrasonic plasma engineering allows direct carbonization in a precursor solution containing metal phthalocyanine and aniline. When combining with the dispersion effect of ultrasonic waves, we successfully fabricated uniform single-atom M-N4 (M = Fe, Co) carbon catalysts with a production rate as high as 10 mg min−1. The Co-N4/NC presented a bifunctional potential drop of ΔE = 0.79 V, outperforming the benchmark Pt/C-Ru/C catalyst (ΔE = 0.88 V) at the same catalyst loading. Theoretical calculations revealed that Co-N4 was the major active site with superior O2 adsorption–desorption mechanisms. In a practical Zn–air battery test, the air electrode coated with Co-N4/NC exhibited a specific capacity (762.8 mAh g−1) and power density (101.62 mW cm−2), exceeding those of Pt/C-Ru/C (700.8 mAh g−1 and 89.16 mW cm−2, respectively) at the same catalyst loading. Moreover, for Co-N4/NC, the potential difference increased from 1.16 to 1.47 V after 100 charge–discharge cycles. The proposed innovative and scalable strategy was concluded to be well suited for the fabrication of single-atom-doped carbons as promising bifunctional oxygen evolution/reduction electrocatalysts for metal–air batteries.

Abstract Low cost and green fabrication of high-performance electrocatalysts with earth-abundant resources for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial for the large-scale application of rechargeable Zn–air batteries (ZABs). In this work, our density functional theory calculations on the electrocatalyst suggest that the rational construction of interfacial structure can induce local charge redistribution, improve the electronic conductivity and enhance the catalyst stability. In order to realize such a structure, we spatially immobilize heterogeneous CoS/CoO nanocrystals onto N-doped graphene to synthesize a bifunctional electrocatalyst (CoS/CoO@NGNs). The optimization of the composition, interfacial structure and conductivity of the electrocatalyst is conducted to achieve bifunctional catalytic activity and deliver outstanding efficiency and stability for both ORR and OER. The aqueous ZAB with the as-prepared CoS/CoO@NGNs cathode displays a high maximum power density of 137.8 mW cm−2, a specific capacity of 723.9 mAh g−1 and excellent cycling stability (continuous operating for 100 h) with a high round-trip efficiency. In addition, the assembled quasi-solid-state ZAB also exhibits outstanding mechanical flexibility besides high battery performances, showing great potential for applications in flexible and wearable electronic devices.

Highlights: Interface engineering of heterogeneous CoS/CoO nanocrystals and N-doped graphene composite facilitates high-performance oxygen reduction reaction and oxygen evolution reaction. Density functional theory calculations and experimental results confirm the enhanced electrocatalytic performances via the proposed interface engineering. The bifunctional oxygen electrocatalyst exhibits excellent performances in rechargeable Zn–air batteries. Low cost and green fabrication of high-performance electrocatalysts with earth-abundant resources for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial for the large-scale application of rechargeable Zn–air batteries (ZABs). In this work, our density functional theory calculations on the electrocatalyst suggest that the rational construction of interfacial structure can induce local charge redistribution, improve the electronic conductivity and enhance the catalyst stability. In order to realize such a structure, we spatially immobilize heterogeneous CoS/CoO nanocrystals onto N-doped graphene to synthesize a bifunctional electrocatalyst (CoS/CoO@NGNs). The optimization of the composition, interfacial structure and conductivity of the electrocatalyst is conducted to achieve bifunctional catalytic activity and deliver outstanding efficiency and stability for both ORR and OER. The aqueous ZAB with the as-prepared CoS/CoO@NGNs cathode displays a high maximum power density of 137.8 mW cm−2, a specific capacity of 723.9 mAh g−1 and excellent cycling stability (continuous operating for 100 h) with a high round-trip efficiency. In addition, the assembled quasi-solid-state ZAB also exhibits outstanding mechanical flexibility besides high battery performances, showing great potential for applications in flexible and wearable electronic devices. [ABSTRACT FROM AUTHOR]

Rational design and fabrication of optimal reversible oxygen electrocatalysts are essential yet still remain great challenges for rechargeable metal-air batteries. Supramolecular coordination polymer-derived strategy for transition metal–nitrogen–doped carbon (M–N/C, M = Co, Fe, etc.) composites catalysts has been deemed promising in preserving rich M–N x coordination modes and enhancing their intrinsic activities. However, the closely packed and nonporous characteristics of coordination polymer usually lead to the serious agglomeration of metallic nanoparticles and lack of porous channels after pyrolysis, impacting the abundance and accessibility of the exposed active sites during electrocatalysis. In this work, we put forward a new tactic to obtain ultra-small Co nanoparticles confined within N-doped carbon nanotubes grafted to reduced graphene oxide (Co/N-CNTs@rGO) through a coordination-driven in situ self-assembly approach followed by pyrolysis. The integration of high intrinsic activity, enhanced conductivity, populated and richly exposed active species throughout the laminated hierarchical composite structure endows Co/N-CNTs@rGO with appealing bifunctional oxygen electrocatalysis properties. Impressively, Co/N-CNTs@rGO was subsequently fabricated as the air electrode in a rechargeable Zn−air battery, and the device achieves a maximum power density of 168 mW cm−2, a large specific capacity of 765 mA h g−1 while maintaining satisfying cycling durability. This work may provide valuable insights in regulating the coordination polymer derivatives and bring new perspectives for future design of promising composites electrocatalysts for electrochemical conversions and energy storage technologies. [Display omitted] [ABSTRACT FROM AUTHOR]

Transition metal sulfide (TMS) promises an excellent prospect in electrocatalysis with high intrinsic activity but poor conductivity. In this work, a series of TMS wrapped by a thin carbon layer with enhanced conductivity have been developed by a facile and rapid strategy. Among them, the prepared CoSx compound exhibits the optimal ORR and OER performances because of the synergistic effect between the high intrinsic activity of CoSx and the desirable conductivity of carbon layer. More importantly, the CoSx‐based zinc‐air batteries (ZABs) exhibit a current density of 10 mA cm−2 with voltage gap of 0.8 V and remarkable cycling durability, which is comparable to those of the state‐of‐art noble Pt/C+IrO2 batteries. Therefore, this work introduces a facile route that opens up a new horizon and inspiration for the development of sulfide for energy conversion. [ABSTRACT FROM AUTHOR]

Significant advancements towards enhancing the catalytic activity of spinel ferrites in oxygen evolution reaction (OER) have been achieved, however, further studies are required on this regard. In this study, Cr-doped spinel ferrite (NiFe 2 O 4) embedded in N-doped C (Cr-NiFe 2 O 4 @NC) was synthesized via a high-temperature treatment using an NiFe Prussian blue analog as a precursor and K 2 Cr 2 O 7 as a Cr source. Owing to the strong octahedral site preference energy, Cr3+ ions were successfully doped into octahedral sites and tailored the electronic configuration of NiFe 2 O 4 , as confirmed by XPS. The Cr-substituted Cr-NiFe 2 O 4 @NC exhibited the overpotential of 241 mV at 10 mA cm−2, which was smaller than that of NiFe 2 O 4 @NC (266 mV) at the same current density. Meanwhile, the Tafel slope of Cr-NiFe 2 O 4 @NC (65.32 mV dec−1) was also lower than that of NiFe 2 O 4 @NC (86.96 mV dec−1). Therefore, the Cr substitution can improve the electrocatalytic OER performance of NiFe 2 O 4 @NC. In particular, an assembled rechargeable Zn-air battery using Cr-NiFe 2 O 4 @NC as the cathode catalyst afforded a high power density (61.1 mA cm−2) together with a high specific capacity (740 mA g−1). Amazingly, it could power light-emitting diodes, demonstrating its real-world application. Density functional theory calculations revealed that Cr ion doping led to electron transfer in NiFe 2 O 4 , resulting in a density of electronic states close to the Fermi level, which probably regulated the adsorption/desorption behaviors of oxygenate intermediates (*O and *OOH), thus promoting the reaction kinetics of the OER. This study provides a helpful basis for the development of spinel oxides with high electrocatalytic OER activity and durability via cation doping. [Display omitted] • Cr-NiFe 2 O 4 @NC was prepared from NiFe Prussian blue analogue (NiFePBA). • The Cr dopant regulated d-band center position of NiFe2O4 for improving electrocatalytic OER activity. • The connection between Cr doping and OER activity was clarified by DFT. [ABSTRACT FROM AUTHOR]

Abstract An in situ coupling strategy to prepare Co9S8/S and N dual-doped graphene composite (Co9S8/NSG) has been proposed. The key point of this strategy is the function-oriented design of organic compounds. Herein, cobalt porphyrin derivatives with sulfo groups are employed as not only the coupling agents to form and anchor Co9S8 on the graphene in situ, but also the heteroatom-doped agent to generate S and N dual-doped graphene. The tight coupling of multiple active sites endows the composite materials with fast electrochemical kinetics and excellent stability for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The obtained electrocatalyst exhibits better activity parameter (ΔE = 0.82 V) and smaller Tafel slope (47.7 mV dec−1 for ORR and 69.2 mV dec−1 for OER) than commercially available Pt/C and RuO2. Most importantly, as electrocatalyst for rechargeable Zn–air battery, Co9S8/NSG displays low charge–discharge voltage gap and outstanding long-term cycle stability over 138 h compared to Pt/C–RuO2. To further broaden its application scope, a homemade all-solid-state Zn–air battery is also prepared, which displays good charge–discharge performance and cycle performance. The function-oriented design of N4-metallomacrocycle derivatives might open new avenues to strategic construction of high-performance and long-life multifunctional electrocatalysts for wider electrochemical energy applications.

Abstract This work reports a novel approach for the synthesis of FeCo alloy nanoparticles (NPs) embedded in the N,P‐codoped carbon coated nitrogen‐doped carbon nanotubes (NPC/FeCo@NCNTs). Specifically, the synthesis of NCNT is achieved by the calcination of graphene oxide‐coated polystyrene spheres with Fe3+, Co2+ and melamine adsorbed, during which graphene oxide is transformed into carbon nanotubes and simultaneously nitrogen is doped into the graphitic structure. The NPC/FeCo@NCNT is demonstrated to be an efficient and durable bifunctional catalyst for oxygen evolution (OER) and oxygen reduction reaction (ORR). It only needs an overpotential of 339.5 mV to deliver 10 mA cm−2 for OER and an onset potential of 0.92 V to drive ORR. Its bifunctional catalytic activities outperform those of the composite catalyst Pt/C + RuO2 and most bifunctional catalysts reported. The experimental results and density functional theory calculations have demonstrated that the interplay between FeCo NPs and NCNT and the presence of N,P‐codoped carbon structure play important roles in increasing the catalytic activities of the NPC/FeCo@NCNT. More impressively, the NPC/FeCo@NCNT can be used as the air‐electrode catalyst, improving the performance of rechargeable liquid and flexible all‐solid‐state zinc–air batteries.

This work reports a novel approach for the synthesis of FeCo alloy nanoparticles (NPs) embedded in the N,P‐codoped carbon coated nitrogen‐doped carbon nanotubes (NPC/FeCo@NCNTs). Specifically, the synthesis of NCNT is achieved by the calcination of graphene oxide‐coated polystyrene spheres with Fe3+, Co2+ and melamine adsorbed, during which graphene oxide is transformed into carbon nanotubes and simultaneously nitrogen is doped into the graphitic structure. The NPC/FeCo@NCNT is demonstrated to be an efficient and durable bifunctional catalyst for oxygen evolution (OER) and oxygen reduction reaction (ORR). It only needs an overpotential of 339.5 mV to deliver 10 mA cm−2 for OER and an onset potential of 0.92 V to drive ORR. Its bifunctional catalytic activities outperform those of the composite catalyst Pt/C + RuO2 and most bifunctional catalysts reported. The experimental results and density functional theory calculations have demonstrated that the interplay between FeCo NPs and NCNT and the presence of N,P‐codoped carbon structure play important roles in increasing the catalytic activities of the NPC/FeCo@NCNT. More impressively, the NPC/FeCo@NCNT can be used as the air‐electrode catalyst, improving the performance of rechargeable liquid and flexible all‐solid‐state zinc–air batteries. [ABSTRACT FROM AUTHOR]

The CoC x /(Co 0.55 Fe 1.945) 2 P@C electrocatalyst developed through a phosphating strategy from covalent porphyrin polymer absorbed with Co 3 [Co(CN) 6 ] 2 and NaH 2 PO 2 precursors that displays superior electrocatalytic activity for ORR, OER and rechargeable zinc-air battery. • A phosphating strategy was developed for bimetallic phosphides modified carbon catalyst. • CoC x /(Co 0.55 Fe 1.945) 2 P@C displays improved ORR and OER bifunctional performances. • The introducing of P leading to a decreased energy gap of CoC x /(Co 0.55 Fe 1.945) 2 P@C. • Good stability and higher power density than Pt/C are revealed in zinc-air battery. It is very important, but also challenging to produce high-activity, high durability and affordable non-noble-metal-bifunctional-electrocatalysts for sustainable energy application. Here, one-pot synthesized iron covalent porphyrin polymers (FePor-CPP), with carefully placed Fe, N atoms, a regular porous structure, Co 3 [Co(CN) 6 ] 2 and NaH 2 PO 2 precursors were carbonized into N,P-doped carbon nanospheres with the active species of both bimetallic CoFe phosphides and CoC x nanoparticles (denoted as CoC x /(Co 0.55 Fe 1.945) 2 P@C). By employing the CoC x /(Co 0.55 Fe 1.945) 2 P@C as oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrode catalysts, superior catalytic activity is achieved with E 1/2 of 0.84 V for ORR, and overpotential of 0.39 V at 10 mA cm−2 for OER in an alkaline medium, respectively. Furthermore, CoC x /(Co 0.55 Fe 1.945) 2 P@C as air electrode for rechargeable Zn-air battery shows power density as high as 131 mW cm−2 and charge-discharge cycle stability, and this suggests the potential application of CoC x /(Co 0.55 Fe 1.945) 2 P@C in energy transformation systems. The high electrocatalytic performances are revealed to originate from the change of electronic structure of bimetallic (Co 0.55 Fe 1.945) 2 P via introducing P into the Co 0.55 Fe 1.945 alloy, resulting in a decreased energy gap of CoC x /(Co 0.55 Fe 1.945) 2 P@C relative to that of CoC x /Co 0.55 Fe 1.945 @C. This work proposes a versatile strategy to develop multifunctional non-precious catalysts for this kind of energy-related electrocatalytic reactions. [ABSTRACT FROM AUTHOR]

Developing non-noble oxygen electrocatalyst is of great importance in multiple energy conversion and storage technologies, for instance, metal-air battery, fuel cell and water electrolysis. Here, we report a bifunctional oxygen electrocatalyst derived from Ni–Fe dual-metal zeolitic imidazole frameworks, Ni 3 Fe nanoalloys embedded in N-doped carbon (Ni 3 Fe/N–C) containing carbon nanotube and porous carbon, which exhibits superior oxygen reduction and evolution reaction electrocatalytic performance. For oxygen reduction reaction, the onset potential and the half-wave potential of Ni 3 Fe/N–C are 0.92 V and 0.85 V, respectively, which are well consistent with those of commercial Pt/C. For oxygen evolution reaction, a low overpotential of 330 mV at 10 mA cm−2 is obtained for Ni 3 Fe/N–C, prominently better than that of commercial RuO 2 /C. Moreover, the oxygen reduction and evolution stability of Ni 3 Fe/N–C distinctly overmatches that of commercial Pt/C and RuO 2 /C. Benefiting from the favorable electrocatalytic activity and stability, the rechargeable Zn–air battery based on Ni 3 Fe/N–C exhibits smaller voltage gap (∼0.8 V) than the one based on commercial Pt/C and RuO 2 /C, and remarkable stability during 300-cycle discharge-charge test. The excellent performance can be attributed to the interaction between Ni 3 Fe nanoalloy and N-doped carbon, the unique nanostructure composed of carbon nanotube and porous carbons, and high graphitization degree. Ni 3 Fe nanoalloys embedded in nitrogen-doped carbon (Ni 3 Fe/N–C) containing carbon nanotube and porous carbon is derived from Ni–Fe dual-metal ZIFs. As the Ni 3 Fe/N–C is employed as the cathode electrocatalyst for Zn-air battery, excellent performance is achieved. Image 1 • Ni 3 Fe embedded in N-doped carbon (Ni 3 Fe/N–C) is derived from Ni–Fe dual-metal ZIFs. • In Ni 3 Fe/N–C, 1D CNT and 3D porous carbon are combined. • Interaction between Ni 3 Fe and N-doped carbon is crucial for the performance. • Zn-air battery assembled with Ni 3 Fe/N–C exhibits excellent electrochemical performance. [ABSTRACT FROM AUTHOR]

M –Nx–C (M =Fe, Co, etc.) substances received tremendous attention due to its outstanding performance for oxygen reduction reaction and oxygen evolution reaction. Usually, metal nanoparticles could form simultaneously during synthesis process, whereas these nanoparticles received very little attention since they were often removed by acid etching. Here, we designed and synthesized an active-N-dominated Co, N co-doped carbon layers supported Co nanoparticles material (denoted as CoNPs@CoNC) by annealing the composites of Co-Phen confined in porous carbon supports together with urea at 900∘C. Compared with the acid etching CoNC catalyst without the surface Co nanoparticles, CoNPs@CoNC catalyst exhibited a higher Co content and slightly positive shifting of the main peak of Co 2p3/2 that is closely associated with the tuned electronic structure. Additionally, the as-prepared CoNPs@CoNC catalyst provided a superior performance ( E j = 1 ∕ 2 = 0. 8 6 V versus RHE, η j = 1 0 = 0. 3 6 V) than that of CoNC catalyst ( E j = 1 ∕ 2 = 0. 8 1 V, η j = 1 0 = 0. 4 4 V), which led to a lower reversible overvoltage of 0.73 V for CoNPs@CoNC. Furthermore, the superior performance enabled the CoNPs@CoNC-based Zn–air battery catalyst with a more admirable charge-discharge performance in terms of open-circuit voltage, energy density and power density, unveiling its immense potential in realistic utilization. Boosting bifunctional electrocatalysis with surface/subsurface Co nanoparticles decorated Co, N co-doped defective graphene/carbon-tube hybrid catalysts for rechargeable Zn-air batteries. Surface/subsurface Co nanoparticles integrated Co, N co-doped carbon play a key role in promoting ORR/OER, and hybrid structural characteristics exhibit specific functionality in catalyzing electrochemical process. [ABSTRACT FROM AUTHOR]

Highlights: Single-atom M-N4/N-doped carbons (M = Fe, Co) prepared as OER/ORR catalysts. Ultrasonication-assisted plasma engineering used for catalyst synthesis. Co-N4/NC outperformed benchmark commercial catalysts in practical Zn–air battery test. DFT calculations provided insights into the origin of superior ORR/OER performance.As bifunctional oxygen evolution/reduction electrocatalysts, transition-metal-based single-atom-doped nitrogen–carbon (NC) matrices are promising successors of the corresponding noble-metal-based catalysts, offering the advantages of ultrahigh atom utilization efficiency and surface active energy. However, the fabrication of such matrices (e.g., well-dispersed single-atom-doped M-N4/NCs) often requires numerous steps and tedious processes. Herein, ultrasonic plasma engineering allows direct carbonization in a precursor solution containing metal phthalocyanine and aniline. When combining with the dispersion effect of ultrasonic waves, we successfully fabricated uniform single-atom M-N4 (M = Fe, Co) carbon catalysts with a production rate as high as 10 mg min−1. The Co-N4/NC presented a bifunctional potential drop of ΔE = 0.79 V, outperforming the benchmark Pt/C-Ru/C catalyst (ΔE = 0.88 V) at the same catalyst loading. Theoretical calculations revealed that Co-N4 was the major active site with superior O2 adsorption–desorption mechanisms. In a practical Zn–air battery test, the air electrode coated with Co-N4/NC exhibited a specific capacity (762.8 mAh g−1) and power density (101.62 mW cm−2), exceeding those of Pt/C-Ru/C (700.8 mAh g−1 and 89.16 mW cm−2, respectively) at the same catalyst loading. Moreover, for Co-N4/NC, the potential difference increased from 1.16 to 1.47 V after 100 charge–discharge cycles. The proposed innovative and scalable strategy was concluded to be well suited for the fabrication of single-atom-doped carbons as promising bifunctional oxygen evolution/reduction electrocatalysts for metal–air batteries. [ABSTRACT FROM AUTHOR]

The rational construction of highly active and durable oxygen-reactive electrocatalysts for oxygen reduction/evolution reaction (ORR/OER) plays a critical role in rechargeable metal-air batteries. It is pivotal to achieve optimal utilization of electrocatalytically active sites and valid control of the high specific internal surface area. Inspiration for designing electrocatalysts can come from nature, as it is full of precisely manipulated and highly efficient structures. Herein, inspired by earthworms fertilizing soil, a 3D carbon nanofibrous electrocatalyst with multiple interconnected nanoconfined channels, cobalt-based heterojunction active particles and enriched N, S heteroatoms (Co/Co 3 O 4 /CoF 2 @NSC with confined channels) is rationally designed, showing superior bifunctional electrocatalytic activity in alkaline electrolyte, even outperforming that of benchmark Pt/C-RuO 2 catalyst. This work demonstrates a new method for porous structural regulation, in which the internal confined channels within the nanofibers are controllably formed by the spontaneous migration of cobalt-based nanoparticles under a CO 2 atmosphere. Theoretical analysis reveals that constructing Co/Co 3 O 4 /CoF 2 @NSC electrocatalyst with confined channels can greatly adjust the electron distribution, effectively lower the reaction barrier of inter-mediate and reduce the OER/ORR overpotential. This work introduces a novel and nature-inspired strategy for designing efficient bifunctional electrocatalysts with well-designed architectures., (© 2024 Wiley‐VCH GmbH.)

Non-precious efficient bifunctional catalysts towards oxygen reduction/evolution reactions (ORR/OER) are highly desired to enable the widespread application of rechargeable Zn-air batteries (r-ZABs). Herein, Prussian blue analogues (PBA) anchored on CdS nanorods (CdS NRs) pre-coated with polydopamine (PDA) are utilized as precursors to prepare ultrafine Co 4 S 3 nanoparticles supported on N, S-codoped CNTs (Co 4 S 3 @N,S-CNT), where CdS NRs are served as sulfur sources and hard templates. After pyrolysis, the resulting Co 4 S 3 @N,S-CNT-800 shows a high specific surface area of 142.4 m2 g−1, together with merely 0.780 V difference between the OER potential at 10 mA cm−2 and the ORR potential at 3 mA cm−2. The Co 4 S 3 @N,S-CNT-800 based air cathode displays a higher discharge capacity of 787 mAh g Zn −1 at 10 mA cm−2, a higher output power density of 154 mW cm−2, better working stability, as well as a lower charge–discharge voltage gap than the Pt/C + RuO 2 based air electrode at various working current density. The remarkable oxygen reversible catalytic activities are mainly attributed to the presence of a thin layer of mesoporous carbon on partial sections of the open-end N,S-CNTs, which not only shortens the mass diffusion length but also prevents N,S-CNTs from excessively bundling to maximize the exposure of Co 4 S 3 nanocrystallites and graphitized carbon skeletons with N or S heteroatoms. [ABSTRACT FROM AUTHOR]

Developing the highly efficient and durable non-precious metal electrocatalysts by taking advantage of inexpensive and abundant resources is of paramount importance for the widespread application of energy conversion and storage techniques such as fuel cells and metal-air batteries. Herein, the sponge-like unadulterated carbontube-graphene complexes (D/G-CTs-1,000) with multifarious intrinsic defect active sites are fabricated by boric acid-hydrothermal and pyrolysis treatments. The close contact or juncture between open nanotubes and few-layer graphene in D/G-CTs-1,000 constructs the hierarchical networks with plentiful channels, the larger surface area and outstanding conductivity. As a result, the as-prepared D/G-CTs-1,000 electrocatalyst exhibits an excellent trifunctional electrocatalytic performance for oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The primary Zn-air batteries and overall water splitting system using D/G-CTs-1,000 as the electrode materials delivers higher power density outperforming the advanced Pt/C-based batteries and the overall water splitting performance comparable to those using the non-precious metal/carbon-based materials as electrode. This work provides a universal and efficient synthetic strategy to produce the unadulterated carbons with high activity and long-time durability as trifunctional electrocatalysts and promote the widespread applications of metal-free electrocatalysts in sustainable energy conversion technology. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are key electrochemical reactions for the development of rechargeable Zn-air batteries. However, due to the high cost of commercial noble metal-based catalysts and their limited bifunctionality, it is necessary the design of new electrocatalysts. In this study, stable electrocatalysts have been synthesized through a hydrothermal method and further low-temperature thermal treatment. The materials consist of La stabilized low crystallinity Mn and Co metal (hydro-)oxides. The electrocatalytic performance of these materials has been compared with counterparts calcined at higher temperatures. The findings demonstrate that materials synthesized at lower temperatures and with low crystallinity exhibit superior electrocatalytic activity for both ORR and OER. Moreover, the research highlights the favorable influence of the lanthanum cation, which enhances changes of surface morphology and oxidation states of other cations (Mn and Co). Additionally, the positive contribution of the carbon component to electrochemical activity and electrical conductivity has been elucidated. The best electrocatalyst was studied in a rechargeable Zn-air battery with a durability of up to 120 h. They exhibited better stability and performance than the commercial Pt/C + RuO 2 catalyst currently used. [Display omitted] [ABSTRACT FROM AUTHOR]

The development of efficient, stable and low-cost dual-function electrocatalysts and applicated it to Zn-air batteries are very important for the development of renewable energy storage and conversion technologies. Antiperovskite catalysts have attracted much attention recently due to their advantages of adjustable structure and high element selectivity. In this work, a flexible and adjustable antiperovskite catalyst ZnCCe 3−x Ni x (0 ≤ x ≤ 3) loaded on carbon fiber (ZnCCe 3−x Ni x /CNFs) was prepared by electrospinning technology and used as an air cathode catalyst for rechargeable Zn-air batteries. By doping the X-site with highly conductive transition metal Ni, the electronic structure of the catalyst ZnCCe 3−x Ni x /CNFs was optimized, and the catalytic activity of the antiperovskite bimetallic X-site was tuned to achieve an efficient and synergistic catalytic reaction. Among them, ZnCCe 2.7 Ni 0.3 /CNFs showed excellent OER/ORR bi-functional catalytic activity (Δ E = 0.82 V) and good stability. When ZnCCe 2.7 Ni 0.3 /CNFs is used as the cathode catalyst for rechargeable Zn-air batteries, it shows a power density of 117.99 mW cm−2, and the cycle stability can be maintained for up to 300 h, indicating its application potential in the field of Zn-air batteries. • Antiperovskite ZnCCe 3−x Ni x /CNFs were prepared by electrospinning method. • The OER/ORR bifunctional activity of ZnCCe 3−x Ni x /CNFs were optimized by doping Ni. • The power density of ZnCCe 2.7 Ni 0.3 /CNFs based zinc-air batteries was 117.99 mW cm−2. [ABSTRACT FROM AUTHOR]

Developing commercially viable electrocatalyst lies at the research hotspot of rechargeable Zn-air batteries, but it is still challenging to meet the requirements of energy efficiency and durability in realistic applications. Strategic material design is critical to addressing its drawbacks in terms of sluggish kinetics of oxygen reactions and limited battery lifespan. Herein, a "raisin-bread" architecture is designed for a hybrid catalyst constituting cobalt nitride as the core nanoparticle with thin oxidized coverings, which is further deposited within porous carbon aerogel. Based on synchrotron-based characterizations, this hybrid provides oxygen vacancies and Co-N x -C sites as the active sites, resulting from a strong coupling between CoO x N y nanoparticles and 3D conductive carbon scaffolds. Compared to the oxide reference, it performs enhanced stability in harsh electrocatalytic environments, highlighting the benefits of the oxynitride. Furthermore, the 3D conductive scaffolds improve charge/mass transportation and boost durability of these active sites. Density functional theory calculations reveal that the introduced N species into hybrid can synergistically tune the d-band center of cobalt and improve its bifunctional activity. As a result, the obtained air cathode exhibits bifunctional overpotential of 0.65 V and a battery lifetime exceeding 1350 h, which sets a new record for rechargeable Zn-air battery reported so far., (© 2023 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

• Dense silica nanoparticles on ZIF-67 serves as hard encapsulation layer. • Silica promotes the formation of N-rich mesoporous Co@NHCC after pyrolysis. • C3N4 helps dope more nitrogen into NHCC when decomposed at high temperature. • Co@NHCC-800 air electrode is highly efficient in ORR and OER electrocatalysis. • Rechargeable Zn-air battery with a power density of 248 mW cm-2. Integrating high electrocatalytic activities for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) into one nonprecious catalyst entity is highly desired for simplifying the fabrication, operation as well as lowering the production cost of rechargeable Zn-air batteries. Herein, zeolite imidazole framework-67 (ZIF-67) polyhedron nanocrystals are used as N-containing carbonaceous precursors to synthesize N-rich hollow carbon cage composites with Co nanoparticles (Co@NHCC) in the presence of silica nanoparticles and graphitic carbon nitride (g-C 3 N 4), an additional high-temperature decomposable nitrogen source. The assembly of dense silica nanoparticles on ZIF-67 surface may serve as hard encapsulation layers, which not only facilitates the incorporation of nitrogen atoms onto graphitized carbon skeletons, but also prevents the ZIF-67 polyhedrons from collapsing and effectively impedes the growth of carbon nanotubes during pyrolysis through surface confinement. Gasification in such an encapsulated environment concurrently generates abundant mesopores in the thin walls of carbonized ZIF-67 polyhedrons, which contributes to a high specific surface area of 910.71 m2 g−1 in the resulting Co@NHCC-800 sample, and hence endows an efficient bifunctional electrocatalyst, with a half-wave potential of +0.837 V for ORR in 0.1 M KOH aqueous solution and a required potential of only +1.512 V to reach 10 mA cm−2 in OER catalysis. When used as a breathable electrode for Zn-air batteries, Co@NHCC-800 shows a much higher open-circuit voltage of 1.490 V, a higher discharge power density of 248 mW cm−2 as well as a smaller increasement of only 0.100 V for the charge-discharge voltage gap after cycling for 12 h, as compared with commercial Pt/C catalyst. The results in present work pave a new avenue to the synthesis of sophisticated carbon nanomaterials for electrocatalysis. [ABSTRACT FROM AUTHOR]

The commercialization of oxygen-related energy storage/conversion devices, for instance metal-air batteries or fuel cells, is highly dependent on development of low-cost, high performance electrocatalysts for oxygen reduction/oxygen evolution reactions (ORR and OER). In the present study, we employed Co-ZIF-9 as a sacrificial precursor to synthesize highly efficient bifunctional ORR/OER electrocatalysts through tuning the pyrolysis temperature and Fe-doping of the zeolitic imidazolate framework. The synthesized samples were characterized extensively using X-ray photoelectron spectroscopy (XPS), X-ray diffraction, elemental CHN and ICP analyses, and Fourier transform infrared (FTIR) spectroscopy as well as scanning (SEM) and transmission (TEM) electron microscopies. It has been found that the Fe-doping can significantly affect the electrocatalytic activity of the product through improving the number of transferred electrons. The ZIF-9_Fe3_Pyrol exhibited excellent electrocatalytic activity towards ORR (E onset = 0.90 V vs. RHE) and OER (E onset = 1.55 V vs. RHE), much better than other evaluated catalysts and comparable to the commercial PtRuC bifunctional catalyst. Moreover, the ZIF-9_Fe3_Pyrol sample outperformed the precious PtRuC catalyst with very little decay in ORR and OER activity over long continuous operation. The ZIF-9_Fe3_Pyrol exhibited excellent performance as a cathode catalyst in rechargeable Zn-air batteries, superior to the one assembled with the state-of-the-art catalyst. Image 1 • Fe/Co-bimetal ZIF-9 as sacrificial precursor towards highly efficient ORR/OER electrocatalyst. • Fe-doping affects electrocatalytic activity and improves the number of transferred electrons. • ZIF-9_Fe3_Pyrol shows excellent performance in Zn-air batteries (815 mAh∙g−1, 1018 Wh∙kg Zn −1). [ABSTRACT FROM AUTHOR]

• Ultrathin 2D metal-organic frameworks decorated with Pt NPs have been fabricated using an ultrasonication-assisted method. • A "win-win" electron decoration effect has been evidenced on the active sites for both ORR and OER. • Remarkable bifunctional catalytic activity towards ORR and OER with ultralow overpotential gap of 665 mV has been demonstrated. • Excellent performance and durability is achieved in the rechargeable Zinc-air battery assembled with the bifunctional catalyst. To meet the increasing demands for highly active electrocatalysts towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), here in this work, a new strategy of synergistic nano-architecture design based on Platinum nanoparticles (Pt NPs) and ultrathin two-dimensional (2D) metal-organic frameworks (MOFs) is developed for bifunctional electrochemical catalysts. Compared with commercial Pt/C and RuO 2 catalysts, remarkable enhancements in activity and durability of both oxygen reduction and oxygen evolution reactions are achieved on our PtNPs@MOFs composite materials, with one of the lowest over-potential gaps (E gap) of 665 mV that has ever been reported. The tests on the assembled Zn-air batteries have revealed promising electrocatalytic performance and practical advantage of our new materials as air cathode catalyst. Both experimental results and theoretical study have confirmed the synergistic effect between Pt NPs and MOF nanosheets through a "win-win" electron structural modification, demonstrating the effectiveness of our strategy in developing effective bifunctional oxygen electrocatalysts for various types of electrochemical devices. [ABSTRACT FROM AUTHOR]

Abstract Highly efficient and low-cost bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are greatly desirable for rechargeable metal-air batteries. Herein, we propose a useful strategy of integrating a bimetallic nanoparticle into the N-doped porous carbon to synthesize highly active bifunctional oxygen catalyst (CoNi/NG). The bimetallic CoNi/NG catalyst exhibits a positive half-wave potential of 0.85 V (versus , RHE) for ORR, and a low operating potential of 1.6 V (versus , RHE) to achieve a 10 mA cm−2 current density for OER. The excellent bifunctional properties of CoNi/NG are attributed to the various active sites (i.e., Co-N-C, Ni-N-C moieties and N-C sites) and its 2D graphene-like ultrathin structure, as well as synergistic effect of CoNi alloys. Importantly, the liquid Zn-air battery with CoNi/NG as oxygen electrode presents not only excellent charging and discharging curves and maximal power density of 130.5 mW cm−2, but also robust durability with only 50 mV increase in the voltage gap (the voltage difference between the charging and discharging) after continuous 110 h cycle tests. This work provides a general design principle for development of bifunctional catalysts by integrating different bimetals responsible for different electrochemical reactions into the N-doped graphitic carbons. Graphical abstract We propose a universal design principle to develop bifunctional catalysts by integrating different metals beneficial for different electrochemical reactions into N-doped carbon nanosheets. The as-synthesized CoNi/NG-based Zn-air battery exhibits high power density and robust durability, which is greatly better than the Pt/C + IrO 2 -based counterpart. Image 1 [ABSTRACT FROM AUTHOR]

The traditional-type Co 3 O 4 air electrode was first prepared by spraying technology, and then the main OER catalyst layer (FeNi-LDH) was grown in-situ by electrochemical deposition, no further hydrophobic treatment was carried out. With a FeNi-LDH as main OER active site, assembled ZABs delivered an enhance cycle life of 38.1h, 3.15 times than initial Co 3 O 4 air electrode (12.1h). Using multiwalled carbon nanotubes (MWCNTs) with better oxidation resistance as the conductive carbon instead of Ketjen Black (KB), and increasing the mass loading of Co 3 O 4 air electrode from 2.0 to 4.0 mg cm−2, the FeNi-LDH layer can increase ZABs cycle life to 218.3h. [Display omitted] • A novel air electrode structure is proposed. • FeNi-LDH was electrodeposited on traditional-type Co 3 O 4 air electrode. • The reasons for battery failure during cycle tests were discussed. As a promising secondary battery, the short cycle life of Zn-air batteries (ZABs) severely limits their further application. The traditional air electrode could not maximize the OER activity of air electrode due to the existence of multiphase interface. In this work, FeNi layered double hydroxide (FeNi-LDH) without further hydrophobic treatment as main OER catalyst was in-situ grown on the initial Co 3 O 4 air electrode (Ketjen Black as conductive carbon) surface by electrochemical deposition method. With a FeNi-LDH as main OER active component, assembled ZABs delivered an enhance cycle life of 38.1 h, 3.15 times than initial Co 3 O 4 air electrode (12.1 h). The significant increase in cycle life is mainly due to the lower charging voltage caused by the FeNi-LDH layer with better OER catalytic activity than Co 3 O 4 , which reduces the ORR site inactivation and carbon oxidation rate. Therefore, after using multiwalled carbon nanotubes with better oxidation resistance as the conductive carbon instead of Ketjen Black and increasing the mass loading of Co 3 O 4 air electrode from 2.0 to 4.0 mg cm−2, the FeNi-LDH layer can increase ZABs cycle life from 61.4 to 218.3 h. The in-situ electrodeposition FeNi-LDH on traditional air electrode strategy provides a simple method for enhancing the cycle life of ZABs. [ABSTRACT FROM AUTHOR]

Developing bifunctional catalysts to oxygen reduction (ORR) and oxygen evolution reactions (OER) is of vital to the practical application of rechargeable Zn-air batteries. Herein, an N-doped carbon-based catalyst (FeCo-NC-St) was prepared by using starch as a basic material which was transferred to defective carbon particles. The fresh starch-derived carbon is favor of the doping of nitrogen atoms to form more N-related ORR active sites. The existence of cobalt further positively regulates the OER activity of FeCo-NC-St. Resultantly, FeCo-NC-St shows 0.837 V of ORR E 1/2 and 1.611 V of OER E 10 which is slightly lower than the 0.850 V of ORR E 1/2 for Pt/C but far better than the 1.723 V of OER E 10 for the benchmark RuO 2 , revealing the superior bifunctional activities of FeCo-NC-St. Practically, the Zn-air battery with FeCo-NC-St outputs 1.505 V of open circuit voltage, 1.15–1.25 V of working voltage and 937.51 mW h g−1 Zn of specific energy density at 10 mA cm−2. The Zn-air battery also exhibits remarkable rechargeability and long-term durability, demonstrating the promising potential to substitute the precious Pt/Ru-based catalysts in the practical applications. An N-doped carbon-based catalyst (FeCo-NC-St) was prepared by using starch as a basic material. The resultant catalyst exhibits superior bifunctional catalytic activity to ORR and OER. [Display omitted] • An N-doped carbon-based bifunctional catalyst was fabricated. • Starch was utilized as a sustainable material. • The starch-derived carbon was favor of the doping of nitrogen atoms. • OER performance was positively regulated by cobalt element. • The catalyst exhibits satisfactory activity to ORR and OER. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract We investigate the possibility of utilizing benzyl alcohol oxidation reaction to replace sluggish oxygen evolution reaction (OER) for the charging process in a rechargeable zinc-air battery, catalyzed by NiCo alloy nanoparticles supported on activated carbon (NiCo/AC) with the multifunctional electrocatalytic activities of the oxygen reduction, oxygen evolution and benzyl alcohol oxidation reactions. As an electrocatalyst for the oxygen reduction reaction (OER), NiCo/AC exhibits superior catalytic activity with an onset potential of 0.85 V (vs. RHE), a half-wave potential of 0.74 V (vs. RHE) and a large limiting current density of 4.65 mA cm−2 at 0.2 V (vs. RHE). Moreover, NiCo/AC also demonstrates the electrocatalytic oxidation activities toward water and benzyl alcohol, moreover, the benzyl alcohol oxidation reaction is more thermodynamically and kinetically favourable with 254 mV smaller overpotential than water oxidation at 10 mA cm−2. Owing to these advantages, NiCo/AC as air cathode material is assembled into a home-made rechargeable zinc-air battery, resulting an almost 200 mV lower charging voltage at the current density of 50 mA cm−2 in the presence of 0.1 M benzyl alcohol compared to the battery without benzyl alcohol, consequently obtaining 10.5% energy saving at the charging current density of 50 mA cm−2 with high durability. [ABSTRACT FROM AUTHOR]

Development of stable, high-performance and cost-effective bifunctional electrocatalysts that can replace baseline Pt- and Ir-based catalysts has been a central theme in metal-air batteries. Along this direction, transition metal-based oxides and nitrides have attracted attention due to their abundance, stability, and low cost. Here, Mn nitride, fabricated via annealing of Mn powder in N, is investigated for the first time as a candidate bifunctional electrode for rechargeable Zn-air batteries (ZABs). Three samples were prepared by nitridation of a Mn precursor, with particle size <100 μm, at 1100 °C for 4-30 h. The morphology and microstructure of the fabricated samples were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), secondary ion mass spectrometry (SIMS), and X-ray diffraction (XRD). Phase quantification for all samples was performed using Rietveld-based fitting. The samples treated for 4 and 10 h had the largest fraction (~75%) of nitride phases (MnN and MnN); the remaining material was primarily MnO. The nitride phases were not pure, but contained oxygen, resulting in the formation of pseudobinary phases. The oxygen reduction/evolution reaction (ORR/OER) performance of all samples was evaluated using rotating disk electrode (RDE) voltammetry in an alkaline electrolyte (0.1 M KOH). Among all the catalysts, the sample treated for 10 h exhibited the most positive ORR onset potential (−0.038 V vs. Hg/HgO) with good stability. The catalyst was incorporated into a practical ZAB and displayed a battery efficiency of 52.7% after 14 h of charge-discharge cycling (1 h/cycle) at a current density of 7.5 mA cm. Graphical abstract: [ABSTRACT FROM AUTHOR]

Rechargeable Zn-air batteries (ZABs) are regarded as promising energy storage devices due to their high energy and power density, high safety and cost-effectiveness. Nevertheless, the practical application has been hampered by the sluggish kinetics of the oxygen reaction during the discharge and charge processes, respectively. Herein, La 0.75 Sr 0.25 Fe 0.5 Mn 0.5 O 3 (LSFMO) nanoparticles with a modified coprecipitation method possess high intrinsic activities. More importantly, the synergic covalent coupling between N/S dual-doped reduced graphene (NS-RGO) and LSFMO greatly improves the ORR and OER capabilities of novel perovskite/dual-doped graphene hybrid material (LSFMO@NS-RGO). The oxygen reduction reaction (ORR) activity (E 1/2 of 0.806 V and n of 3.66) and oxygen evolution reaction (OER) activity (the E j=10 of 1.672 V and overpotential of 442 mV) of LSFMO@NS-RGO are equivalent to the advanced Pt/C catalyst and RuO 2 catalyst, respectively, thereby leading to excellent bifunctional property (ΔE = 0.86 V). Rechargeable ZABs deliver a fairly small charge-discharge voltage polarization (0.72 V). Besides, a rechargeable ZAB with flowing-electrolyte is constructed, which reveals considerably high reversibility and stability over 80 h, much improved over rechargeable ZAB in static electrolyte system. Such excellent results demonstrate that LSFMO@NS-RGO represents a new class of promising bifunctional catalysts for rechargeable ZABs. [Display omitted] • Synergic coupling effect between LSFMO and NS-RGO enhances oxygen electrocatalysis. • LSFMO@NS-RGO displays admirable bifunctional property (ΔE = 0.86 V). • Rechargeable ZABs deliver a small charge-discharge voltage polarization (0.72 V). • Rechargeable ZABs in flowing-electrolyte reveals high reversibility over 80 h. • Rechargeable ZAB for fluid systems is a great improvement over the static system. [ABSTRACT FROM AUTHOR]