Rechargeable Zn-air Batteries Research Articles

Facile hydrothermal synthesis of NiMoO4·xH2O nanorods-like structures as bifunctional oxygen electrocatalysts for rechargeable zinc-air batteries

Developing highly active and low-cost bifunctional catalyst materials to replace precious metal species is of utmost importance for the commercialization of clean and sustainable energy systems. In this report, homogenous NiMoO4·xH2O nanorods (NRs)-like structured materials were synthesized by an annealing-free hydrothermal method. The synthesized electrode electrochemical properties were determined by linear sweep voltammetry using a rotating ring disk electrode to determine the characteristics of oxygen reduction reaction in an O2-saturated electrolyte solution. For the oxygen evolution reaction, the NiMoO4·xH2O NRs electrocatalyst showed lower overpotential of 185 mV to obtain 10 mA cm−2. Furthermore, the NiMoO4·xH2O NRs electrocatalyst-based zinc (Zn)-air battery exhibited lower voltage gaps and smaller electrochemical impedance spectroscopy values than the Pt/C catalyst. Importantly, the NiMoO4·xH2O NRs-based battery (60 cycles (∼1100 min)) revealed excellent cycling stability results when compared with the Pt/C-based battery (30 cycles (∼550 min)). The NR structured electrode provided good steady potential after being subjected to a fixed current density of 10 mA cm−2 for 100 h. Therefore, these results demonstrate that the synthesized NiMoO4·xH2O NRs material is promising as a bifunctional electrocatalyst for rechargeable Zn-air batteries.

Supporting Critical Raw Material Circularity – Graphite from Waste LIBS to Zn-Air Batteries

The use of Li-ion batteries (LIBs) in electrical vehicles and consumer electronics is continuously on the rise which means that the amount of spent LIB (SLIB) is on the rise as well. The sustainable recycling of SLIB for production of secondary resources will prevent the loss of valuable materials and ensures safe and economical management of used batteries. During industrial black mass recycling process only Co and Ni from SLIBs is currently recycled, though LIBs contain many other valuable materials too. Graphite, which is used as an anode active material in LIBs, is discarded as a waste during industrial recycling process. Repurposing inexpensive waste graphite has a huge potential to be alternative for pristine graphite.In this research a novel way to prepare bifunctional oxygen electrocatalyst from industrially produced and hydrometallurgically leached black mass leach residue is shown. The recycling leach residue is utilized as a valuable raw material, graphite and transition metal (Co, Mn, Ni) source, with N-precursor for the synthesis of N-Me-C graphite-based electrocatalyst. For the first time the battery metal residues, left into SLIBs recycling waste, are strategically exploited to achieve metal co-doping of graphite-based material. Battery derived electrocatalysts demonstrated promising electrocatalytic activity towards ORR and OER in alkaline media. Moreover, the novel bifunctional oxygen electrocatalysts were used in a rechargeable Zn-air battery as an air cathode catalyst and achieved a high-power density of 104 mW·cm-2 (Figure 1). The advantageous electrochemical activity of the catalyst materials was linked with its surface morphology, structure, porosity, and elemental composition.This research shows the great potential of SLIBs black mass leach residue as a resource for the more sustainable production of high performance and low-cost bifunctional oxygen electrocatalyst appliable in Zn-air battery. Figure 1

Ni-Fe-S Supported on Mo-Based Mxene (Mo2CTx) As a High-Performance Bifunctional Electrocatalyst for Rechargeable Zinc–Air Batteries

Rechargeable Zn-air batteries are a promising alternative to lithium-ion batteries due to their high theoretical energy density (1350 Wh kg−1), low cost, and environmental benefits. To meet the growing demand on renewable power for electric vehicles and sustainable goals, inexpensive and efficient bifunctional catalysts with both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities have recently garnered a great interest in energy conversion fields. MXene, a rising family of two-dimensional (2D) materials, particularly Mo2CTx, has been identified as a promising electrocatalyst supporter. The tunable surface chemistry, atomic thickness, and high surface area of the MXene architecture reduce the reaction barrier by enhancing the conductivity, exposing active sites and increasing the reaction rate in charge transfer and gas/ion diffusion process. Therefore, with coexistence of MXene platform, favorable reaction conditions can be created to facilitate the catalyst's performance.In this study, a novel bifunctional electrocatalyst of Ni-Fe sulfide uniformly embedded in a Mo-based MXene (Mo2CTx) sheet structure is designed for Zn-air battery applicaiton. Surface characterization shows that 2-D Mo2CTx nanosheets can be successfully fabricated by hydrothermal etching method. The deposition of Ni-Fe sulfide nanocatalysts onto Mo2CTx MXene nanosheets exhibits excellent electrochemical performance, which is attributed to the enhanced intrinsic activity due to rapid electron transfer from MXene, abundant functional groups on the surface to lower the reaction activity energy. In addition, the architecture of MXene support provides a large specific surface area, high porosity, good conductivity and highly exposed active sites. When using MXene supported Ni-Fe-S nanocatalysts as the electrode materials for Zn-air battery application, a high peak power density at 107.24 mW cm−2 with superior cycle stability within 200h is obtained. Moreover, the possible mechanisms on energy storage is also proposed. These results clearly indicates the successfully development of an exciting bifunctional electrocatalyst for electrochemical energy conversion applications.

Longevous Cycling of Rechargeable Zn-Air Battery Enabled by "Raisin-Bread" Cobalt Oxynitride/Porous Carbon Hybrid Electrocatalysts.

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-Nx -C sites as the active sites, resulting from a strong coupling between CoOx Ny 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 0.65V and a battery lifetime exceeding 1350 h, which sets a new record for rechargeable Zn-air battery reported so far.

Fe-Nx sites coupled with core-shell FeS@C nanoparticles to boost the oxygen catalysis for rechargeable Zn-air batteries

The development of efficient single-atom catalysts (SACs) for the oxygen reduction reaction (ORR) remains a formidable challenge, primarily due to the symmetric charge distribution of metal single-atom sites (M-N4). To address such issue, herein, Fe-Nx sites coupled synergistic catalysts fabrication strategy is presented to break the uniform electronic distribution, thus enhancing the intrinsic catalytic activity. Precisely, atomically dispersed Fe-Nx sites supported on N/S-doped mesoporous carbon (NSC) coupled with FeS@C core-shell nanoparticles (FAS-NSC@950) is synthesized by a facile hydrothermal reaction and subsequent pyrolysis. Due to the presence of an in situ-grown conductive graphitic layer (shell), the FeS nanoparticles (core) effectively adjust the electronic structure of single-atom Fe sites and facilitate the ORR kinetics via short/long-range coupling interactions. Consequently, FAS-NSC@950 displays a more positive half-wave potential (E1/2) of 0.871 V with a significantly boosted ORR kinetics (Tafel slope = 52.2 mV dec−1), outpacing the commercial Pt/C (E1/2 = 0.84 V and Tafel slope = 54.6 mV dec−1). As a bifunctional electrocatalyst, it displays a smaller bifunctional activity parameter (ΔE) of 0.673 V, surpassing the Pt/C-RuO2 combination (ΔE = 0.724 V). Besides, the FAS-NSC@950-based zinc-air battery (ZAB) displays superior power density, specific capacity, and long-term cycling performance to the Pt/C-Ir/C-based ZAB. This work significantly contributes to the field by offering a promising strategy to enhance the catalytic activity of SACs for ORR, with potential implications for energy conversion and storage technologies.

Ru doping induced interface engineering in flower-liked CoMoO4-RuO2 boosts oxygen electrocatalysis for rechargeable Zn-air battery

Constructing heterogeneous catalysts can significantly boost the electrocatalytic activity due to the improved intrinsic catalytic activity induced by tailored electronic structure and optimized chemisorption to the reaction intermediates. RuO2 based electrocatalysts are especially attractive due to the high catalytic activity of RuO2. To reduce the usage of noble metal and improve the catalytic activity of catalyst, CoMoO4-RuO2 micro-flower was synthesized using a facile hydrothermal-calcination method in this work. CoMoO4-RuO2 exhibits a low overpotential of 177 mV at 10 mA cm−2 for oxygen evolution reaction (OER) and a high half-wave potential of 0.858 V for oxygen reduction reaction (ORR). Moreover, the Zn-air battery assembled using CoMoO4-RuO2 exhibit shows a high maximum discharge power density of 149 mW cm−2 and a large open circuit voltage of 1.38 V. The good performance can be attributed to the incorporation of RuO2, which not only induces extra catalytic active sites, but also forms heterojunction with CoMoO4 to optimize the electronic structure of CoMoO4-RuO2, thereby achieving a better equilibrium of absorption and desorption of intermediates. The work provides insights into designing RuO2 based electrocatalysts for advanced electrocatalysis.

Engineering Electronic Structure of Nitrogen‐Carbon Sites by sp3‐Hybridized Carbon and Incorporating Chlorine to Boost Oxygen Reduction Activity

AbstractDevelopment of efficient and easy‐to‐prepare low‐cost oxygen reaction electrocatalysts is essential for widespread application of rechargeable Zn‐air batteries (ZABs). Herein, we mixed NaCl and ZIF‐8 by simple physical milling and pyrolysis to obtain a metal‐free porous electrocatalyst doped with Cl (mf‐pClNC). The mf‐pClNC electrocatalyst exhibits a good oxygen reduction reaction (ORR) activity (E1/2=0.91 V vs. RHE) and high stability in alkaline electrolyte, exceeding most of the reported transition metal carbon‐based electrocatalysts and being comparable to commercial Pt/C electrocatalysts. Likewise, the mf‐pClNC electrocatalyst also shows state‐of‐the‐art ORR activity and stability in acidic electrolyte. From experimental and theoretical calculations, the better ORR activity is most likely originated from the fact that the introduced Cl promotes the increase of sp3‐hybridized carbon, while the sp3‐hybridized carbon and Cl together modify the electronic structure of the N‐adjacent carbons, as the active sites, while NaCl molten‐salt etching provides abundant paths for the transport of electrons/protons. Furthermore, the liquid rechargeable ZAB using the mf‐pClNC electrocatalyst as the cathode shows a fulfilling performance with a peak power density of 276.88 mW cm−2. Flexible quasi‐solid‐state rechargeable ZAB constructed with the mf‐pClNC electrocatalyst as the cathode exhibits an exciting performance both at low, high and room temperatures.

Engineering Electronic Structure of Nitrogen-Carbon Sites by sp3 -Hybridized Carbon and Incorporating Chlorine to Boost Oxygen Reduction Activity.

Development of efficient and easy-to-prepare low-cost oxygen reaction electrocatalysts is essential for widespread application of rechargeable Zn-air batteries (ZABs). Herein, we mixed NaCl and ZIF-8 by simple physical milling and pyrolysis to obtain a metal-free porous electrocatalyst doped with Cl (mf-pClNC). The mf-pClNC electrocatalyst exhibits a good oxygen reduction reaction (ORR) activity (E1/2 =0.91 V vs. RHE) and high stability in alkaline electrolyte, exceeding most of the reported transition metal carbon-based electrocatalysts and being comparable to commercial Pt/C electrocatalysts. Likewise, the mf-pClNC electrocatalyst also shows state-of-the-art ORR activity and stability in acidic electrolyte. From experimental and theoretical calculations, the better ORR activity is most likely originated from the fact that the introduced Cl promotes the increase of sp3 -hybridized carbon, while the sp3 -hybridized carbon and Cl together modify the electronic structure of the N-adjacent carbons, as the active sites, while NaCl molten-salt etching provides abundant paths for the transport of electrons/protons. Furthermore, the liquid rechargeable ZAB using the mf-pClNC electrocatalyst as the cathode shows a fulfilling performance with a peak power density of 276.88 mW cm-2 . Flexible quasi-solid-state rechargeable ZAB constructed with the mf-pClNC electrocatalyst as the cathode exhibits an exciting performance both at low, high and room temperatures.

In Situ Construction of Zinc-Mediated Fe, N-Codoped Hollow Carbon Nanocages with Boosted Oxygen Reduction for Zn-Air Batteries.

The rational design of bifunctional oxygen electrocatalysts with unique morphology and luxuriant porous structure is significant but challenging for accelerating the reaction kinetics of rechargeable Zn-air batteries (ZABs). Herein, zinc-mediated Fe, N-codoped carbon nanocages (Zn-FeNCNs) are synthesized by pyrolyzing the polymerized iron-doped polydopamine on the surface of the ZIF-8 crystal polyhedron. The formation of the chelate between polydopamine and Fe serves as the covering layer to prevent the porous carbon nanocages from collapsing and boosts enough exposure and utilization of metal-based active species during carbonization. Furthermore, both the theoretical calculation and experimental results show that the strong interaction between polyhedron and polydopamine facilitates the evolution of high-activity zinc-modulated FeNx sites and electron transportation and then stimulates the excellent bifunctional catalytic activity for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). As expected, the Zn-air battery with Zn-FeNCNs as an air cathode displays a superior power density (256mW cm-2) and a high specific capacity (813.3mA h gZn-1), as well as long-term stability over 1000h. Besides, when this catalyst is applied to the solid-state battery, the device exhibited outstanding mechanical stability and a high round-trip efficiency under different bending angles.

Achieving High Energy Efficiency: Recent Advances in Zn‐Air‐Based Hybrid Battery Systems

Rechargeable Zn‐air batteries (ZABs) are regarded as an attractive green energy storage technology, featured with large theoretical energy densities and intrinsic high safety factors. However, hindered by the sluggish kinetics of both oxygen reduction reaction and oxygen evolution reaction, rechargeable ZABs are confronted with some critical challenges such as low operating voltage, poor energy efficiency, and limited cycle life. Zn‐air‐based hybrid batteries (ZAHBs), integrating the advantages of a conventional ZAB with supplementary redox reactions, have emerged as a promising solution to address those challenges. Based on working principles, the hybrid batteries can be categorized into two groups: Zn‐M/air hybrid batteries (M = Ni, Co, Ag, Cu, and Mn) and Zn‐X/air hybrid batteries (X = KI, ethanol, and urea), which can achieve improved energy efficiency and density by optimizing charge–discharge voltage. Herein, a comprehensive overview of ZAHBs is provided, including the classification, latest progress, and electrochemical properties, as well as detailed discussion of relevant mechanisms. Moreover, the perspectives and opportunities for future research in the field of hybrid battery systems are also outlined. This review shall give helpful guidance on the design and application of ZAHBs, and provide important insights into the development of new electrochemical energy storage systems.

Heteroatom-doped carbon attached to ultra-fine Fe-NiCoP as high-performance oxygen electrocatalyst for Zn-air batteries

The construction of efficient and durable electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) remains a challenge for rechargeable Zn-air batteries (ZABs). Bimetallic phosphide (NiCoP) holds considerable promise as a bifunctional catalyst. Here, an efficient NiCoP-based bifunctional electrocatalyst was fabricated using PCN-222-assembled organophosphorus complexes, specifically 1,1-bis(diphenylphosphine)ferrocene (DPPF). These DPPF complexes serve as sources of phosphorus and metals, undergoing in-situ conversion into Fe-doped NiCoP nanoparticles (Fe-NiCoP) while simultaneously constructing a heteroatom-doped carbon matrix (NPC). The final catalytic structure, composed of ultra-fine Fe-NiCoP nanoparticles confined within the NPC, exhibits superior bifunctional electrocatalytic activity (with a ΔEgap of 0.69 V between OER and ORR) and exceptional stability. In-situ Raman spectroscopy and DFT calculations reveal that the high performance arises from the synergistic effect of Fe-NiCoP and NPC, where Fe-NiCoP triggers the catalytic activity of the attached NPC. The calculated active site is identified as the C atom near the N atom on the NPC, lowering the potential barrier for O-containing intermediate compounds and enhancing the catalytic performance. In addition, NPC protects the Fe-NiCoP core from oxidation during battery cycles, allowing ZABs equipped with this catalyst to achieve high power density and long-term cycling performance.

Controlled three-dimensional leaf-like NiCoO2@NiCo layered double hydroxide heterostructures for oxygen evolution electrocatalysts in rechargeable Zn–air batteries

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, NiCoO2 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 NiCoO2@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 NiCoO2@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.

Atomic regulation strategies of dual-metal single-atom catalytic sites supported on 3D N-doped carbon nanotube aerogels for boosting oxygen reduction and zinc-air battery

Dual-metal single-atom catalysts (DSAs) exhibit excellent electrocatalytic properties, holding great promise in energy conversion and storage fields. Their rational design and synthesis are realized by optimizing the types of supporting substrate or regulating the coordination microenvironment. Herein, FeCo DSAs supported on N-doped carbon nanotube aerogels (FeCo DSAs/N-CNAs) were facilely fabricated by a glucose-assisted atomic regulation pyrolysis approach. The morphology and structure were characterized by a series of techniques. The influences of the pyrolysis temperature and types of the metal precursors were carefully investigated, coupled by elaborating the formation mechanism. The resulting FeCo DSAs/N-CNAs catalyst shows a positive onset potential (Eonset = 1.075 V) and half-wave potential (E1/2 = 0.907 V) for oxygen reduction reaction (ORR) in a 0.1 M KOH solution, outperforming those of commercial Pt/C. The obtained catalyst is further exploited for establishing rechargeable Zn-air battery, which shows a larger peak power density of 86.7 mW cm−2 and a longer cycle stability over 144 h. These findings identify low-cost FeCo DSAs/N-CNAs as promising electrocatalysts for advanced rechargeable Zn-air batteries.

Bamboo-Modulated Helical Carbon Nanotubes for Rechargeable Zn-Air Battery.

The high-performance and sustainable electrocatalysts toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are essential for rechargeable Zn-air batteries (ZABs). In this paper, a natural all-components bamboo is provided as the carbon source, and melamine and cobalt chloride are provided as the nitrogen and cobalt sources, respectively. As a result, the unique helical carbon nanotubes (HCNTs) encapsulated cobalt nanoparticles are prepared, which are acted as ORR/OER electrocatalysts to improve ZABs performance. The resultant HCNTs contribute to high ORR/OER activities via exposing more Co─N sites, providing excellent electron conductivity, and facilitating mass transfer of the reactant. The HCNTs assembled rechargeable liquid ZABs showed a maximum output power density of 226mWcm-2 and a low voltage gap of 0.85V for 330h cycles. The flexible all-solid-state ZABs achieved the maximum power density with 59.4mWcm-2 and charge-discharge cycles over 25h. The density functional theory (DFT) calculations reveal that the increase of Co─N at HCNTs effectively regulates the electronic structure of Co, optimizing the binding affinity of oxygen intermediates and resulting in the low ORR/OER overpotentials. This work paves the way for transforming renewable bamboo biomass into versatile electrocatalysts, which boosts the development of next-generation energy storage and conversion devices.

Facile synthesis of the multidimensional oxygen redox electrocatalysts by anion-mediated self-template one-step in situ assembly

The exploration of a non-precious metal bifunctional electrocatalyst with novel structures for the efficient oxygen reduction reaction (ORR) and oxygen evolution reactions (OER) remains a great challenge. Multidimensional assembled nanostructures with nitrogen-doped carbon matrix inlaid with transition-metal (M-N-C) can be used as efficient electrocatalysts due to its large surface area and highly revealed active sites. Herein, we report an anion-mediated self-template one-step in situ transformation into multidimensional hierarchical nano-assembled M-N-C catalysts, which is assembled from 0D cobalt nanoparticles terminally inlaid in 1D carbon nanotubes growing on a honeycomb-like ultrathin 3D carbon network (denoted as Co@N-CNTs/CS). By further synthetic process characterization, the nitrate-mediated structural evolution during rising thermal stages is disclosed. Thanks to the fully exposed surfaces and highly accessible active sites in the unique multidimensional structure, our developed catalyst exhibits a large surface area and enhanced performance in bifunctional oxygen redox in alkaline media, which further endows potentials in rechargeable Zn-air batteries, surpassing the typical benchmark catalysts Pt/C + Ir/C. Our study affords a fresh path to facile fabrication of M-N-C electrocatalysts.

The chemical state of iron species influence on the performance of Fe–N–C bifunctional electrocatalyst for Zn–air batteries

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.

Engineering of heterointerface of ultrathin carbon nanosheet-supported CoN/MnO enhances oxygen electrocatalysis for rechargeable Zn–air batteries

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 + RuO2 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.

Metal-organic framework derived porous N, P co-doping carbon microcubes toward aqueous and flexible quasi-solid-state rechargeable Zn-air batteries

The sluggish kinetics of oxygen reduction and/or evolution reactions in air cathodes of Zn-air batteries (ZABs) limits their practical applications. Herein, a facile strategy of phosphating metal-organic framework is developed to fabricate porous defect-enriched nitrogen and phosphorus co-doing carbon microcubes (NPC) both toward efficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), as a cost-efficiency bi-functional electrocatalyst. With detailed regulation in annealing temperatures, the optimized NPC sample (NPC-10) with nitrogen (N, 1.0 at.%) and phosphorus (P, 1.6 at.%) co-doping possesses bi-model micro-/meso-pores, and large specific surface area of 1627.1 m2 g−1. Thanks to unique structural merits and N/P synergetic contribution, the NPC-10 is endowed with abundant active sur-/interfaces and rapid kinetics for efficient ORR (limited ORR current density of 5.4 mA cm−2, half-wave potential of 0.89 V at 10 mA cm−2, Tafel slope of 141.6 mV dec−1 and a four-electron selectivity of >94.7 %) and OER (overpotential of 220 mV at 10 mA cm−2 and Tafel slope of 57.3 mV dec−1). More encouragingly, the NPC-10 assembled aqueous and flexible quasi-solid-state (QSS) rechargeable ZABs both deliver high power density and long-cycle stability. The work provides highly efficient, durable, and low-cost ORR/OER electrocatalysts toward rechargeable aqueous and/or QSS ZABs.

A facile and green strategy for mass production of dispersive FeCo-rich phosphides@N,P-doped carbon electrocatalysts toward efficient and stable rechargeable Zn-air battery and water splitting

One key step for advancing the widespread practical application of rechargeable metal-air batteries and water electrolysis fundamentally relies on the development of cost-effective multifunctional electrocatalysts toward oxygen and hydrogen-involving reactions. The present work initiates a tofu-derived one-pot strategy for green, facile, and mass production of highly active and stable catalyst toward oxygen reduction/evolution and hydrogen evolution reactions, through the preparation of Fe/Co cross-linked tofu gel and the subsequent pyrolysis. Despite the free use of additional N/P precursors or pore-forming agents, the as-prepared materials comprise highly dispersive FeCo-rich phosphides nanoparticles and porous N,P co-doped carbon network inherited from the tofu skeleton. The resultant catalysts exhibit remarkably enhanced trifunctional activities as compared to the Fe2P and Co2P counterparts, along with better long-term stabilities than the benchmark RuO2 and Pt/C catalysts. Accordingly, the as-assembled Zn-air battery delivers a large power density (174 mW cm−2) with excellent cycle stability (the gap of charge/discharge voltage@10 mA cm−2 increases by 0.01 V after 720 h of operation, vs. 0.16 V of Pt/C-RuO2 based battery after 378 h). Furthermore, the as-constructed alkaline electrolyzer just requires a small voltage of 1.55 V@10 mA cm−2, which outperforms nearly all of those of biomass-derived electrocatalysts ever reported, and that of noble metal catalysts-based electrolyzers (1.72 V@10 mA cm−2 for Pt/C-RuO2), underscoring their bright future toward commercial applications in green energy conversion devices.

CoFe Alloys Dispersed on Se, N Co-Doped Graphitic Carbon as Efficient Bifunctional Catalysts for Zn-Air Batteries.

The development of a stable and efficient non-noble metal catalyst with both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is paramount to achieving the widespread application of Zn-air batteries (ZABs) but remains a great challenge. Herein, a novel Co3 Fe7 alloy nanoparticle dispersed on Se, N co-doped graphitic carbon (denoted as CoFe/Se@CN) was prepared through a facile hydrothermal and pyrolysis process. The synthesized CoFe/Se@CN exhibits outstanding ORR and OER properties with an ultralow potential gap of 0.625 V, which is mainly attributed to the abundant porous structure, the rich structural defects formed by doping Se atoms, and the strong synergistic effects between the CoFe alloys and graphitic carbon nanosheet. Furthermore, the ZAB fabricated by CoFe/Se@CN shows a high peak power density of 160 mW cm-2 and a large specific capacity of 802 mA h g-1 with favorable cycling stability, outperforming that of Pt/C+RuO2 . Our study offers a plausible strategy to explore bifunctional carbon-based materials with efficient electrocatalytic properties for rechargeable ZABs.