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Abstract The utilization of redox‐active gas as cathode materials has been proposed as a promising approach to meet the demand for next‐generation battery technologies. Toward this end, nitrogen oxides (NO_x)—inexpensive, abundant gases readily produced from ammonia on an industrial scale—is a promising energy storage media; however, its utilization as cathode material has not been achieved. In this work, the cage effect of NO and NO₂radicals are utilized to stabilize the charge product of Li‐NO_xcell as N₂O₃. This cell operates via reversible redox of LiNO₃to N₂O₃, achieving a specific capacity of 1,570 mA h g_carbon⁻¹or 25 mA h cm_electrode⁻² at a full cell voltage of 3.85 V with an average energy efficiency of 89% at a current density up to 2 mA cm_electrode⁻². These metrics represent one of the highest areal capacity, current density, cell voltage, and energy efficiency reported for a metal‐gas cells. 

One-pot reaction of tris(2-aminoethyl)amine (TREN), [Cu I (MeCN) 4 ]PF 6 , and paraformaldehyde affords a mixed-valent [ TREN4 Cu II Cu I Cu I (μ 3 -OH)](PF 6 ) 3 complex. The macrocyclic azacryptand TREN4 contains four TREN motifs, three of which provide a bowl-shape binding pocket for the [Cu 3 (μ 3 -OH)] 3+ core. The fourth TREN caps on top of the tricopper cluster to form a cryptand, imposing conformational constraints and preventing solvent interaction. Contrasting the limited redox capability of synthetic tricopper complexes reported so far, [ TREN4 Cu II Cu I Cu I (μ 3 -OH)](PF 6 ) 3 exhibits several reversible single-electron redox events. The distinct electrochemical behaviors of [ TREN4 Cu II Cu I Cu I (μ 3 -OH)](PF 6 ) 3 and its solvent-exposed analog [ TREN3 Cu II Cu II Cu II (μ 3 -O)](PF 6 ) 4 suggest that isolation of tricopper core in a cryptand enables facile electron transfer, allowing potential application of synthetic tricopper complexes as redox catalysts. Indeed, the fully reduced [ TREN4 Cu I Cu I Cu I (μ 3 -OH)](PF 6 ) 2 can reduce O 2 under acidic conditions. The geometric constraints provided by the cryptand are reminiscent of Nature's multicopper oxidases (MCOs). For the first time, a synthetic tricopper cluster was isolated and fully characterized at Cu I Cu I Cu I ( 4a ), Cu II Cu I Cu I ( 4b ), and Cu II Cu II Cu I ( 4c ) states, providing structural and spectroscopic models for many intermediates in MCOs. Fast electron transfer rates (10 5 to 10 6 M −1 s −1 ) were observed for both Cu I Cu I Cu I /Cu II Cu I Cu I and Cu II Cu I Cu I /Cu II Cu II Cu I redox couples, approaching the rapid electron transfer rates of copper sites in MCO. 

Abstract There is a strong interest in finding highly soluble redox compounds to improve the energy density of redox flow batteries (RFBs). However, the performance of electrolytes is often negatively influenced by high solute concentration. Herein, we designed a high‐potential (0.5 V vs. Ag/Ag⁺) catholyte for RFBs, where the charged and discharged species are both gaseous nitrogen oxides (NO_x). These species can be liberated from the liquid electrolyte and stored in a separate gas container, allowing scale‐up of storage capacity without increasing the concentration and volume of the electrolyte. The oxidation of NO in the presence of NO₃⁻affords N₂O₃, and the reduction of N₂O₃regenerates NO and NO₃⁻, together affording the electrochemical reaction: NO₃⁻+3 NO⇌2 N₂O₃+e⁻with a low mass/charge ratio of 152 grams per mole of stored electron. A proof‐of‐concept NO_xsymmetric H‐cell shows 200 stable cycles over 400 hours with >97 % Coulombic efficiency and negligible capacity decay.