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Cost‐effective Fe‐based cathode materials have attracted significant attention. Recently, antifluorite‐type Li5FeO4 has been investigated as a high‐capacity cathode material owing to its high lithium content and solid‐state oxygen redox reactions. However, its reversible capacity is restricted to transition‐metal redox reactions because of its irreversible structural transformation and oxygen evolution. This study demonstrates the reversible oxygen redox reaction in metastable cubic antifluorite Li5FeO4 obtained by mechanochemical treatment. It exhibits a reversible capacity of more than 300 mAh g‐1, corresponding to an approximately 1.7‐electron reaction, without oxygen gas evolution. Combined analyses of X‐ray absorption spectroscopy (XAS) and theoretical calculations reveal that both Fe3+/Fe4+ and O2‐/O22‐ redox reactions proceed under semi‐coherent structural transformations between antifluorite and rocksalt, which differs from the known orthorhombic Li5FeO4 phase. Although the cyclability of oxygen redox is poor, its solid solution with Co2+ enhances cyclability by suppressing oxygen evolution. Tuning the structural symmetry and transition‐metal content can overcome the reversible capacity limit of antifluorite cathode materials, which is useful for the development of high‐energy cathode materials by the effective utilization of solid‐state oxygen redox reactions. [ABSTRACT FROM AUTHOR]

The electrochemical CO2 reduction reaction (CO2RR) activity of Ni2MnIn and Ni2MnSn Heusler alloys was investigated. Although pure In, Sn and Ni2MnIn generated formate as the major product, Ni2MnSn generated H2 as the major product. The CO2RR selectivity could be controlled by selecting the constituent elements of the intermetallic catalysts. [ABSTRACT FROM AUTHOR]

Electrochemical CO2 reduction (CO2RR) is a key technology to convert greenhouse gas CO2 to value‐added products, such as CO and formic acid (HCOOH). In the present study, two‐dimensional Cu‐ and Al‐based layered double hydroxides (Cu−Al/LDHs) were applied as CO2RR catalysts. The catalysts were synthesized using a simple co‐precipitation method employing sodium carbonate solutions with different pH and synthesis temperatures. The elemental ratio of Cu and Al, and sheet size were controlled. The most active Cu−Al/LDH showed a faradaic efficiency for CO generation of 42 % and one for formate generation of 22 % at the current density of 50 mA using a gas diffusion electrode system under galvanostatic conditions. Our result indicates that the sheet size of the LDH sheet is a critical parameter for determining CO2RR activity. [ABSTRACT FROM AUTHOR]

3D printing technologies have been adapted to enable the fabrication of lithium-ion batteries (LIBs), allowing flexible designs such as micro-scale 3D shapes. Here, we demonstrate 3D-printable gel electrolytes, printed at room temperature. The electrolyte gel solidified by UV irradiation maintains its structural integrity and high lithium-ion conductivity, enabling fully 3D-printed quasi-solid-state LIBs. [ABSTRACT FROM AUTHOR]

To enhance the oxygen evolution reaction mass activity of cobalt–manganese layered oxide (CMO), we develop a one-pot synthetic process to anchor CMO onto graphene sheets (CMO/G). Its mass activity is 66-fold higher than that of physically mixed bare CMO with graphene and even better than those of previously reported graphene-supported first-row transition metal oxide-based electrocatalysts. The remarkable mass activity is attributed to the excellent intrinsic activity of CMO, small and well-dispersed CMO nanosheets on graphene sheets and hydrophilized graphene due to the synthetic process. Furthermore, CMO/G exhibits excellent stability. [ABSTRACT FROM AUTHOR]

Zinc‐ion batteries (ZIBs) are promising grid‐scale energy storage devices owing to their low cost, high energy/power densities, high safety, benign environmental impact, etc. Among various cathode materials, ZnMn2O4 spinel has attracted attention because of its high theoretical capacity (448 mAh g−1) associated with the two‐electron redox reaction of Mn ions (2+/4+), a higher voltage (≈1.4 V vs Zn/Zn2+) than V2O5‐based cathodes (≈1.0 V), and better cyclability among manganese oxide‐based cathodes. However, so far only the one‐electron reaction of Mn ions is used with ZnMn2O4 spinel (≈224 mAh g−1), impairing its attractive features. In this study, the two‐electron reaction is successfully enabled by synthesizing ultrasmall ZnMn2O4 spinel nanoparticles (≈5 nm) composited with graphene (US‐ZMO/G) via a rapid room‐temperature alcohol reduction process, achieving the reversible capacity of 445 mAh g−1 at the second cycle. As far as it is known, the US‐ZMO/G composite achieves the highest gravimetric energy/power densities among cathodes for ZIBs. The combination of high capacity and high voltage enables an outstanding energy density approaching that of lithium‐ion batteries. [ABSTRACT FROM AUTHOR]

We report the synthesis, characterization, and electronic properties of the quinoid-based three-dimensional metal-organic framework [Fe 2 (dhbq) 3 ]. The MOF was synthesized without using cations as a template, unlike other reported X 2 dhbq 3 -based coordination polymers, and the crystal structure was determined by using single-crystal X-ray diffraction. The crystal structure was entirely different from the other reported [Fe 2 (X 2 dhbq 3 )] 2- ; three independent 3D polymers were interpenetrated to give the overall structure. The absence of cations led to a microporous structure, investigated by N 2 adsorption isotherms. Temperature dependence of electrical conductivity data revealed that it exhibited a relatively high electrical conductivity of 1.2 × 10 -2 S cm -1 ( E a = 212 meV) due to extended d-π conjugation in a three-dimensional network. Thermoelectromotive force measurement revealed that it is an n-type semiconductor with electrons as the majority of charge carriers. Structural characterization and spectroscopic analyses, including SXRD, Mössbauer, UV-vis-NIR, IR, and XANES measurements, evidenced the occurrence of no mixed valency based on the metal and the ligand. [Fe 2 (dhbq) 3 ] upon incorporating as a cathode material for lithium-ion batteries engendered an initial discharge capacity of 322 mAh/g.

Magnesium rechargeable batteries (MRBs) promise to be the next post lithium-ion batteries that can help meet the increasing demand for high-energy, cost-effective, high-safety energy storage devices. Early prototype MRBs that use molybdenum-sulfide cathodes have low terminal voltages, requiring the development of oxide-based cathodes capable of overcoming the sulfide's low Mg 2+ conductivity. Here, we fabricate an ultraporous (>500 m 2 g -1 ) and ultrasmall (<2.5 nm) cubic spinel MgMn 2 O 4 (MMO) by a freeze-dry assisted room-temperature alcohol reduction process. While the as-fabricated MMO exhibits a discharge capacity of 160 mAh g -1 , the removal of its surface hydroxy groups by heat-treatment activates it without structural change, improving its discharge capacity to 270 mAh g -1 ─the theoretical capacity at room temperature. These results are made possible by the ultraporous, ultrasmall particles that stabilize the metastable cubic spinel phase, promoting both the Mg 2+ insertion/deintercalation in the MMO and the reversible transformation between the cubic spinel and cubic rock-salt phases.

The electrochemical CO 2 reduction reaction (CO 2 RR) activity of Ni 2 MnIn and Ni 2 MnSn Heusler alloys was investigated. Although pure In, Sn and Ni 2 MnIn generated formate as the major product, Ni 2 MnSn generated H 2 as the major product. The CO 2 RR selectivity could be controlled by selecting the constituent elements of the intermetallic catalysts.

3D printing technologies have been adapted to enable the fabrication of lithium-ion batteries (LIBs), allowing flexible designs such as micro-scale 3D shapes. Here, we demonstrate 3D-printable gel electrolytes, printed at room temperature. The electrolyte gel solidified by UV irradiation maintains its structural integrity and high lithium-ion conductivity, enabling fully 3D-printed quasi-solid-state LIBs.