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It is still an urgent but challenging task to rational design metal organic frameworks (MOFs)-derived architectures with decent oxygen bifunctionality and durability on substrates for the development of flexible Zn-air batteries (ZABs). Herein, unique yolk-shelled microcages with Co-Nx-C decorations (Co-Nx-YSC) are designed and fabricated on carbon cloth (CC) through a proposed self-assembly strategy. Prior to assembly on carbon-based substrates pretreated with negative charge, the cationic modified colloidal MOFs with controllable morphology and composition were synthesized. After calcination of the obtained ZIF-67/CC under 600 °C, the flexible electrode Co-Nx-YSC-600/CC is obtained, which exhibits excellent oxygen bifunctionality, good cycling stability (400 cycles at 10 mA cm−2) and outstanding flexibility when directly employed as air electrode in flexible ZABs. Such yolk-shelled architecture not only optimizes the reactants availability towards active sites, but also provides capacious spaces for oxygen reactions and the corresponding mass transportation. Besides, the interconnected carbon nanotube frameworks can further ensure fast charge transfer and serve as the robust host for Co-Nx-C active sites. With these structural merits, Co-Nx-YSC-600/CC showcases its promises as air electrode for flexible ZABs.

Dual ion batteries are one of the emerging substitutes for lithium ion batteries with high operating voltages and energy density, but their recent advancements have been limited by unsatisfactory cathode stability in the form of irreversible exfoliation. To address this bottleneck, a strategy to selectively incorporate carboxylic anhydride functionality between graphite layers is developed to enforce a stabilizing effect to the crystal structure, which allows for effective performance optimization through particles downsizing and interlayer distance tuning without the compromises of intercalation site disruption and voltage deduction. The resulting graphite cathode experienced significant capacity, rate capability and stability improvements, achieving a highly reversible capacity of 91.2 mAh g−1 at 2 C, which then cycled consistently for over 1,000 cycles. Overall, this work removes a major handicap that has limited the development of dual ion batteries and demonstrates a design pathway for high performance graphite intercalation cathode suitable for anion intercalation with both enhanced stability and discharge capacity.

Desirable sulfur electrochemistry strongly relies on host-guest interactions, which calls for rational designs on the surface fine structure of sulfur reservoir materials. Herein, we for the first time, explore the coordinative unsaturation in ferric hexacyanoferrate (FeHCF) for sulfur immobilization and catalyzation towards improved lithium-sulfur (Li–S) batteries. A simple ammonia etching treatment is implemented to selectively remove FeIII–H2O moieties, leaving vast coordinatively unsaturated Fe sites with a simultaneous establishment of considerable mesoporosity in the activated matrix (denoted as FeHCF-A). As a sulfur-host, the massive meso-scale channels endow FeHCF-A with abundant active interfaces and ion/mass transfer pathways, while more importantly, the coordinatively unsaturated Fe sites are revealed with higher adsorbability and conversion catalytic activity to polysulfides. Attributed to theses chemical and structural superiorities, the as-developed FeHCF-A enables a fast, stable, and efficient sulfur electrochemistry, e.g., good rate capability up to 5C and excellent cyclability with an ultralow decay rate of 0.024% per cycle over 500 cycles, as well as a commendable areal capacity of 4.5 mAh cm−2 under high sulfur loading. This work affords a new and insightful perspective of coordinative chemistry for material engineering in Li–S batteries as well as other related fields.

It’s well known that ion-doping could modify the crystal structure and adjust the corresponding performance of cathode, but how the doped ions affect the structure formations during high-temperature calcination still remains a daunting challenge, which is critical for the ideal controlled synthesis. In our pervious study, we have found that the cationic ion doping can both tune the single phase structure and adjust the phase ratio in layer-tunnel Na0.6MnO2. And in the present study, we furtherly try to track the influence of varied Fe3+ and Ti4+ on the formation process of layer-tunnel hybrid structures and focus on the thermal behavior, structure evolution and morphology change. The kinetics-preferred layered structure can be detected at the initial stage and transfer to the thermodynamic-stable tunnel structure at increased temperature. The Fe3+ can stabilize the formed layer structure while the Ti4+ promote the latter transformation. More interesting, the Ti4+ plays a dominant role when Fe3+/Ti4+ were co-doped. The impressive results can be related with the more orderly structure of layer phase and distorted coordination in tunnel phase. This research correlates the synthesis process and the final structure, as well as the ultimate electrochemical performance, which shed new light on the development of advanced oxides cathode.

Zn-air batteries (ZABs) represent promising candidates for the next generation energy conversion and storage systems based on their superior features to those of lithium-ion batteries, including high theoretical energy density, low cost, and high safety. However, their further development and application is severely lagged due to the lack of high efficient and durable bifunctional oxygen electrocatalysts. The widely applied carbon-based catalysts are thermodynamically instable during battery charging. Herein, TiC supported amorphous MnOx (a-MnOx/TiC) is reported for the first time as electrocatalyst for the corrosion resistant oxygen electrodes of ZABs. A-MnOx/TiC delivers a remarkable activity and stability toward both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with a high half-wave potential (0.8 V) for ORR and a low potential (1.56 V) at 10 mA cm−2 for OER, which far outperforms the state of the art ORR catalyst (Pt/C) and OER catalyst (IrO2), as well as the Pt/C-IrO2 and a-MnOx/C bifunctional catalysts. The excellent bifunctional activity of a-MnOx/TiC can be attributed to the efficient synergistic effect between the active amorphous MnOx catalyst and the highly conductive and stable TiC support. More impressively, a-MnOx/TiC demonstrates an outstanding electrochemical stability in strong alkaline electrolyte under OER condition in contrast to the readily oxidized carbon-based a-MnOx/C catalysts. ZAB with a-MnOx/TiC delivers a greater discharge performance with a peak power density of 217.1 mW cm−2 than that of Pt/C-based ZAB, and a surpassing discharge and charge cycling performance and stability to ZABs with Pt/C-IrO2 and a-MnOx/C. Furthermore, a-MnOx/TiC can be applied for solid-state ZABs which exhibit excellent mechanical flexibility and cycle stability under their flat and bent states. The a-MnOx/TiC bifunctional electrocatalyst with extraordinarily high activity and electrochemical stability provides a promising approach for exploring corrosion resistant electrocatalysts for Zn-air batteries with high efficiency and long-term cycling stability.

Exceptional and durable catalysts for Zinc-air batteries are plagued by nanoparticle agglomeration. As a proof-of-concept, we designed carbon-pore-sheathed cobalt nanoseeds by loading cobalt nanoparticles into N-doped defective carbon pores. Introduced N-doping, Co–N–C bond and graphitic/graphenic carbon defects endow the catalyst with exceptional catalytic activity. Most importantly, the design of Co confined within carbon pores effectively solved the dilemma of nanomaterial stability. By balancing the high catalytic activity and stable cyclability, this unique catalyst is among the outstanding bifunctional catalysts, with a high ORR half-wave potential of 0.847 V and a low OER potential at 10 mA/cm2 of 1.593 V. As demonstrated in the full cell, a peak power density of 135 mW/cm2 at a current density of 200 mA/cm2 and 450 h of stable cycling performance without fading at a current density of 30 mA/cm2 was delivered.