Tailoring hydroxyl groups of organic phenazine anodes for high-performance and stable alkaline batteries

Alkaline-based aqueous batteries have attracted intensive research interests due to their high voltage, low cost, and high safety. However, metal anodes in alkaline electrolytes usually possess poor stability and severe side reactions. Organics are potential alternatives to address these problems, but they are typically not negative enough as anodes. Herein, a group of organic phenazine derivatives including phenazine (PZ), 2-hydroxyphenazine (PZ-OH), and 1,2-dihydroxyphenazine (PZ-2OH) are developed as anode materials for alkaline-based batteries. It is revealed that introducing hydroxyl groups can lower the redox potential by 0.4 V, and fast ion transport channels formed by intramolecular hydrogen bonds can remarkably improve redox kinetics. The optimized PZ-2OH||Ni (OH)2 batteries deliver a high capacity of 208 mA h g-1anode, a high energy density of 247 W h kg-1anode, and ultra-stable cyclability up to 9000 cycles with a low-capacity decay rate (approximately 0.075 parts per thousand capacity decay rate per cycle). Meanwhile, we also demonstrate an alkaline PZ-2OH||air cell, further proving the applicability of PZ-2OH under alkaline conditions. This work not only explores the effect of hydroxyl substituents on the electrochemical potential and reaction kinetics but also opens up the door to stable anodes for alkaline-based batteries. With the aid of a hydroxyl group as an electron-donating group, the redox potential of phenazine derivatives is reduced, and the rate performance increases due to the hydrogen bonds between hydroxyl molecules.