The development of flexible zinc‐air batteries (FZABs) has attracted broad attention in the field of wearable electronic devices. Gel electrolyte is one of the most important components in FZABs, which is urgent to be optimized to match with Zn anode and adapt to severe climates. In this work, a polarized gel electrolyte of polyacrylamide‐sodium citric (PAM‐SC) is designed for FZABs, in which the SC molecules contain large amount of polarized −COO− functional groups. The polarized −COO− groups can form an electrical field between gel electrolyte and Zn anode to suppress Zn dendrite growth. Besides, the −COO− groups in PAM‐SC can fix H2O molecules, which prevents water from freezing and evaporating. The polarized PAM‐SC hydrogel delivers a high ionic conductivity of 324.68 mS cm−1 and water retention of 96.85 % after being exposed for 96 h. FZABs with the PAM‐SC gel electrolyte exhibit long cycling life of 700 cycles at −40 °C, showing the application prospect under extreme conditions.

Although one of the most promising aqueous batteries, all Zn‐Mn systems suffer from Zn dendrites and the low‐capacity Mn4+/Mn3+ process (readily leading to the occurrence of Jahn–Teller distortion, which in turn causes structural collapse and voltage/capacity fading). Here, the Mn3+ reconstruction and disproportionation are exploited to prepare the stable, Mn2+‐rich manganese oxides on carbon‐cloth (CMOs) in a discharged state through an inverted design, which promotes reversible Mn2+/Mn4+ kinetics and mitigates oxygen‐related redox activity. Such a 1.65 V Mn2+‐rich cathode enable constructing a 2.2 V Zn‐Mn battery, providing a high area capacity of 4.16 mA h cm–2 (25 mA h cm–2 for 10 mL electrolyte) and superior 4000‐cycle stability. Moreover, a flexible hybrid 2.7 V Zn‐Mn battery is constructed using 2‐pH hydrogel electrolytes to demonstrate excellent practicality and stability. A further insight has been gained to the commercial application of aqueous energy storage devices toward low‐cost, high safety, and excellent energy density.

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Hydrogels construct 3D ion channels in water-in-salt electrolytes to fully integrate ionic conductivity, rate performance, capacity, safety and multifunctionality.

The recycling of spent lithium-ion batteries (LIBs) has become a necessity for recovering valuable resources and protecting the environment to support sustainable development. We report the design of a highly efficient CoFe/C catalyst by combining the Co and Fe wastes from spent LIBs with sawdust-derived carbon, which were cathode materials in zinc− air batteries (ZABs). As a result of the electrostatic attraction between the Co 3+ /Fe 3+ cations and the hydroxyl groups in sawdust, CoFe nanoparticles are uniformly dispersed in the CoFe/C catalyst after annealing. The Fe atoms in the CoFe nanoparticles are all isolated into single sites by the Co atoms, which redistribute the electrons in the CoFe/C catalyst. The catalyst produced a Pt-like dissociative mechanism, contributing to an excellent oxygen reduction reaction performance. After assembly in ZABs, the CoFe/C catalyst cathode exhibits a long cycling stability of 350 h and an impressive power density of 199.2 mW cm −2 . The CoFe/C catalyst cathode has also been used in flexible ZABs to power LEDs or charge a mobile phone. The work combines spent LIBs with sawdust to fabricate highperformance catalysts, which could reduce environmental pollution and realize high economic value.

Transparent hydrogels are key materials for many applications, such as contact lens, imperceptible soft robotics and invisible wearable devices. Introducing large and engineerable optical anisotropy offers great prospect for endowing them with extra birefringence-based functions and exploiting their applications in see-through flexible polarization optics. However, existing transparent hydrogels suffer from limitation of low and/or non-fine engineerable birefringence. Here, we invent a transparent magneto-birefringence hydrogel with large and finely engineerable optical anisotropy. The large optical anisotropy factor of the embedded magnetic two-dimensional material gives rise to the large magneto-birefringence of the hydrogel in the transparent condition of ultra-low concentration, which is several orders of magnitude larger than usual transparent magnetic hydrogels. High transparency, large and tunable optical anisotropy cooperatively permit the magnetic patterning of interference colours in the hydrogel. The hydrogel also shows mechanochromic and thermochromic property. Our finding provides an entry point for applying hydrogel in optical anisotropy and colour centred fields, with several proof-of-concept applications been demonstrated.

chemical properties, 2D materials have long been the forefront of fundamental research and applications in optics and many other fields. [1][2][3][4] For instance, many efforts have been devoted to explore physical paradigms under 2D limit and enable novel optical devices, such as exciton-resonance-enabled lens, [5,6] wideband tunable mode lockers, [7,8] as well as photodetectors and harmonic generators in terahertz regime. [2,9] Noteworthy, together with recently reported 2D ferromagnets, [10][11][12] 2D materials based magneto-optics have attracted great attentions nowadays. Categorized by the interaction between material and incident light under magnetic field, four main magnetooptical effects are investigated commonly, namely the Zeeman effect, Faraday effect, magneto-optical Kerr effect, and Cotton-Mouton effect, in which 2D materials are recognized as promising matters. [13] Among these four magneto-optical effects, the Cotton-Mouton effect is of great benefits for transmitted light modulation in a see-through manner, with the potential applications ranging from sub-micron-scale dynamic light modulators to meter-scale displayable windows in future society. [14,15] The current electro-optical technologies based on liquid crystals face Liquid crystal devices using organic molecules are nowadays widely used to modulate transmitted light, but this technology still suffers from relatively weak response, high cost, toxicity and environmental concerns, and cannot fully meet the demand of future sustainable society. Here, an alternative approach to color-tunable optical devices, which is based on sustainable inorganic liquid crystals derived from 2D mineral materials abundant in nature, is described. The prototypical 2D mineral of vermiculite is massively produced by a green method, possessing size-to-thickness aspect ratios of >10 3 , inplane magnetization of >10 emu g −1 , and an optical bandgap of >3 eV. These characteristics endow 2D vermiculite with sensitive magneto-birefringence response, been several orders of magnitude larger than organic counterparts, as well as capability of broad-spectrum modulation. The finding consequently permits the fabrication of various magnetochromic or mechanochromic devices with low or even zero-energy consumption during operation. This work creates opportunities for the application of sustainable materials in advanced optics.

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