Redox-Selective Control of Perylene Diimide Enables Fast, Durable Aqueous Sodium-Ion Storage

Confining the redox activity of perylenetetracarboxylic diimide (PTCDI) to the single-electron neutral/radical-anion couple enables ultrafast, durable aqueous sodium-ion storage. Differential electrochemical mass spectrometry and comparative OCP measurements identify hydrogen evolution and oxygen-associated reoxidation as self-discharge pathways of the dianion, motivating operation within a restricted potential window. XPS and EDX measurements support Na-ion coordination to reduced carbonyls as the principal charge-compensation mechanism. In a symmetric PTCDI cell, the selected redox couple retains 88% of its capacity after more than 19,000 cycles with near-unity coulombic efficiency. At nominal charge times of 60 and 2 s, the electrode retains 86 and 41% of its theoretical capacity, respectively, demonstrating ultrafast kinetics without sacrificing durability. These results establish redox-selective control as a design strategy for aqueous carbonyl electrodes whose deeper reduction approaches the stability limit of water.