Highly efficient non-noble metal electrocatalysts are vital for metal-air batteries and fuel cells. Herein, a noble-metal-free single-atom Fe-N x -C electrocatalyst is synthesized by incorporating Fe-Phen complexes into the nanocages in situ during the growth of ZIF-8, followed by pyrolysis at 900 °C under inert atmosphere. Fe-Phen species provide both Fe 2+ and the organic ligand (Phen) simultaneously, which play significant roles in preparing singleatom catalysts. The obtained Fe-N x -C exhibits a half-wave potential of 0.91 V for the oxygen reduction reaction, higher than that of commercial Pt/C (0.82 V). As a cathode catalyst for primary zinc-air batteries (ZABs), the battery shows excellent electrochemical performances in terms of the high opencircuit voltage (OCV) of 1.51 V and a high power density of 96.4 mW cm −2 . The rechargeable ZAB with Fe-N x -C catalyst and the alkaline electrolyte shows a remarkable cycling performance for 300 h with an initial round-trip efficiency of 59.6%. Furthermore, the rechargeable all-solid-state ZABs with the Fe-N x -C catalyst show high OCV of 1.49 V, long cycle life for 120 h, and foldability. The single-atom Fe-N x -C electrocatalyst may function as a promising catalyst for various metal-air batteries and fuel cells.

SSEs can effectively avoid short circuit caused by sodium dendrites. [2] Among these SSEs, the Na 3 Zr 2 Si 2 PO 12 (NZSP)type materials meet most of the requirements as promising candidates. Compared with other common sodium ion conductors, such as β-Al 2 O 3 , borate and chalcogenide-based electrolytes, the NZSP shows intermediate densification temperature, wide electrochemical stable windows, high hardness, and high ionic transference number. [3] While, ongoing extensive researches on the NZSP electrolyte-based SSSBs, the low ionic conductivity, and large interfacial resistances between electrodes and electrolytes are the major bottlenecks for their industrial application. After high temperature sintering, the NZSP electrolyte materials always coexist with impurity phase of ZrO 2 and show high grain boundary resistance. [4] The ZrO 2 impurity phase leads to the enrichment of Si and Na elements with generating glassy impurity phase at grain boundary, which shows much lower sodium ionic conductivity, and evidently increases the grain boundary resistance. [5] Thus, it is important to prepare a pure phase NZSP electrolyte with high conductivity (>10 −3 S cm −1 ) to satisfy the requirements of SSSBs.Another challenge hindering the application of SSSBs is the large interfacial resistance between NZSP electrolytes and sodium metal anodes. [6] Sodium metal was proposed to be melted on planar NZSP pellets. However, due to the high surface tension of NZSP ceramics, the melting sodium metal exhibits poor wettability on surface and cannot form a good contact with the electrolyte that results in large interfacial resistances of SSSBs. [7] Additionally, the typical planar SSEs with simple flat surface have limited contact area with sodium metal anodes, and the drastic volume changes of sodium metal anodes during plating and striping would further deteriorate the interface contact. [8] So, the poor solid interface contact, simple interface geometry, and volume change of sodium metal anodes during cycling significantly restrict the application of ceramic electrolytes with sodium metal anodes.To overcome the above-mentioned obstacles, a monolithic all SSSB based on 3D high ion-conductive NZSP-type electrolytes was designed. First, a ZrO 2 -free Ca 2+ doped NZSP electrolyte material was successfully prepared by a sol-gel method. Proper doping strategy with divalent elements at the Zr site of NZSP materials can modulate the lattice parameters, charge carrier Solid-state sodium batteries (SSSBs) are promising electrochemical energy storage devices due to their high energy density, high safety, and abundant resource of sodium. However, low conductivity of solid electrolyte as well as high interfacial resistance between electrolyte and electrodes are two main challenges for practical application. To address these issues, pure phase Na 3 Zr 2 Si 2 PO 12 (NZSP) materials with Ca 2+ substitution for Zr 4+ are synthesized by a sol-gel method. It shows a high ionic conductivity of more than 10 −3 S cm −1 at 25 °C. Moreover, a robus...

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To improve the energy density of supercapacitors, a new type of electrode material with high electrochemical activity and favorable morphology is extremely desired.

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Developing nonprecious electrocatalysts with superior activity and durability for electrochemical water splitting is of great interest but challenging due to the large overpotential required above the thermodynamic standard potential of water splitting (1.23 V). Here, in situ growth of Fe2+‐doped layered double (Ni, Fe) hydroxide (NiFe(II,III)‐LDH) on nickel foam with well‐defined hexagonal morphology and high crystallinity by a redox reaction between Fe3+ and nickel foam under hydrothermal conditions is reported. Benefiting from tuning the local atomic structure by self‐doping Fe2+, the NiFe(II,III)‐LDH catalyst with higher amounts of Fe2+ exhibits high activity toward oxygen evolution reaction (OER) as well as hydrogen evolution reaction (HER) activity. Moreover, the optimized NiFe(II,III)‐LDH catalyst for OER (O‐NiFe(II,III)‐LDH) and catalyst for HER (H‐NiFe(II,III)‐LDH) show overpotentials of 140 and 113 mV, respectively, at a current density of 10 mA cm−2 in 1 m KOH aqueous electrolyte. Using the catalysts for overall water splitting in two‐electrode configuration, a low overpotential of just 1.54 V is required at a benchmark current density of 10 mA cm−2. Furthermore, it is demonstrated that electrolysis of the water device can be drived by a self‐powered system through integrating a triboelectric nanogenerator and battery, showing a promising way to realize self‐powered electrochemical systems.

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Graphene hydrogels (GHs) and their composites have attracted wide attention because of the special structure of graphene assembly and exceptional electrochemical performance as electrodes for energy storage devices. Here, we report a GH with three-dimensional architecture prepared by a hydrothermal method via a self-assembled process in glucose and ammonia system as well as subsequent freeze-drying. The δ-MnO/GH composite was then obtained by immersing GH in KMnO solution with a certain concentration under heat treatment. The asymmetric supercapacitor MnO/GH//GH consisting of pseudocapacitive nanosheet-like δ-MnO/GH as the cathode and electric double-layer capacitive GH as the anode provides high energy density of 34.7 W h/kg at a power density of 1.0 kW/kg. Importantly, it is found that the pseudocapacitive behavior of MnO has great effects on the rate performance of the supercapacitor, which is identified by kinetic analysis.