Compared with traditional lithium-ion systems, solid-state batteries could achieve high safety and energy density. Although great improvements have been made, especially in solid-state electrolytes, fundamental challenges still remain for the solid-state systems in terms of chemistry and mechanics. This review summarizes the fundamental issues in solid-state batteries with a focus on three critical phenomena: (i) the principles of developing high ionic conductors, (ii) structural evolution at chemically unstable electrolyte-electrode interfaces, and (iii) the effects of manufacturing solid-state batteries, including electrode, and electrolyte design. The future perspectives are also outlined to guide the development of solid-state batteries.

The development of efficient catalysts for the oxygen reduction reaction (ORR) is crucial for a number of emerging technologies, to counter energy and environment crises. Herein, we report an alkyne metathesis polymerization protocol to synthesize a conjugated microporous metalloporphyrin-based framework containing interconnected ORR catalytic centers. A simple composite of the framework and carbon black shows excellent ORR electrocatalytic activity and specificity through a four-electron reduction mechanism under both acidic and alkaline conditions. The pyrolysis of the catalyst, which is commonly involved in the preparation of ORR catalytic systems, is not necessary. Compared to monomeric metalloporphyrins, the framework shows enhanced ORR catalytic activity, presumably due to the porous and conjugated nature of the framework structure, which allows better exposure of the catalytically active sites, and efficient electron/mass transport. More importantly, the composite electrocatalyst exhibits superior durability and methanol tolerance over commercial Pt/C and metalloporphyrin monomers. Given the highly structural tunability of conjugated microporous polymers, it is conceivable that such a non-pyrolytic approach could enable the systematic exploration of the structure-activity relationship of organic framework-based ORR catalysts and eventually lead to the development of cost-effective replacements for Pt/C.

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Developing efficient, readily available, and sustainable electrocatalysts for oxygen reduction reaction (ORR) in neutral medium is of great importance to practical applications of microbial fuel cells (MFCs). Herein, a porous nitrogen-doped carbon material with encapsulated Fe-based nanoparticles (Fe-N x /C) has been developed and utilized as an efficient ORR catalyst in MFCs. The material was obtained through pyrolysis of a highly porous organic polymer containing iron(II) porphyrins. The characterizations of morphology, crystalline structure and elemental composition reveal that Fe-N x /C consists of well-dispersed Fe-based nanoparticles coated by Ndoped graphitic carbon layer. ORR catalytic performance of Fe-N x /C has been evaluated through cyclic voltammetry and rotating ring-disk electrode measurements, and its application as a cathode electrocatalyst in an air-cathode single-chamber MFC has been investigated. Fe-N x /C exhibits comparable or better performance in MFCs than 20% Pt/C, displaying higher cell voltage (601 mV vs. 591 mV), maximum power density (1227 mW m-2 vs. 1031 mW m-2) and Coulombic efficiency (50% vs. 31%). These findings indicate that Fe-N x /C is more tolerant and durable than Pt/C in a system with bacteria metabolism and thus holds great potential for practical MFC

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The Fenton‐like reaction has great potential in water treatment. Herein, an efficient and reusable catalytic system is developed based on atomically dispersed Fe catalyst by anchoring Fe atoms on nitrogen‐doped porous carbon (Fe SA/NPCs). The catalyst of Fe SA/NPCs exhibits enhanced performance in activating peroxymonosulfate (PMS) for organic pollutant degradation and bacterial inactivation. The Fe SA/NPCs + PMS system demonstrates a high turnover frequency of 39.31 min−1 in Rhodamine B (RhB) degradation as well as a strong bactericidal activity that can completely sterilize an Escherichia coli culture within 5 min. Meanwhile, the degradation activity of RhB by Fe SA/NPCs is improved up to 28 to 371‐fold in comparison with the controls. Complete degradation of RhB can be achieved in 30 s by the Fe SA/NPCs + PMS system, demonstrating an efficiency much higher than most traditional Fenton‐like processes. Experiments with different radical scavengers and density functional theory calculations have revealed that singlet oxygen (1O2) generated on the N‐coordinated single Fe atom (Fe‐N4) sites is the key reactive species for the effective and rapid pollutant degradation and bacterial inactivation. This work innovatively affords a promising single‐Fe‐atom catalyst/PMS system for applying Fenton‐like reactions in water treatment.

A highly stable composite electrolyte was developed in this research to address the performance decline over time in a solid lithium ion battery (SLIB). It involved the synthesis of bifunctional MOF material (MOF-2) from two different functionalized UiO-66 materials containing carboxyl groups and amine groups, respectively, and the subsequent blending of PEO (polyethylene oxide) with the MOF-2 to form the novel composite solid electrolyte (PEO-MOF-2). The composite electrolytes showed higher ionic conductivity (5.20 × 10–4 S/cm) than that of pristine PEO. The LiFePO4||Li cells constructed with PEO-MOF-2 exhibited 98.45% capacity retention with 149.92 mA h/g after 100 cycles operation at 1.0 C, which was higher than those cells prepared with pristine PEO electrolyte or with PEO-based electrolytes that were only doped by aminated MOF or carboxylated MOF. Furthermore, our experiments showed that there was about a 40% increase in the potential window (from 3.5 to 5.0 V) and 80% increase in the lithium ion transfer number (from 0.20 to 0.36 at 60 °C) as a result of replacing pristine PEO electrolyte with PEO-MOF-2.

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