Reducing the Charging Voltage of a Zn–Air Battery to 1.6 V Enabled by Redox Radical-Mediated Biomass Oxidation

Zn–air batteries (ZABs) are one of the promising candidates of future energy storage technology owing to their advantages of high theoretical energy density, high safety, and low cost. However, high voltage polarization and low energy efficiency hinder their practical applications. Herein, we show that the charging voltage of a ZAB can be reduced to ∼1.6 V with a high energy efficiency of ∼70% by adding a redox radical, 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO), and a biomass, glucose, into the electrolyte. Upon charging, the oxidation of TEMPO forming the oxoammonium cation at the cathode catalyzes the oxidation of glucose to generate value-added derivatives. Operando differential electrochemical mass spectrometry, first principle calculations, and ex situ spectroscopic characterizations demonstrate the significant effects of TEMPO and glucose on inhibiting side reactions and dendrite growth of the Zn anode, which endow the TEMPO-mediated ZABs with long-term charging/discharging cycles over 400 h.