Modified morphology and restrained overpotential of manganese dioxide by iron doping for boosting aqueous zinc storage

Aqueous zinc-ion hybrid capacitors (ZIHCs) based on a multivalent ion-storage mechanism are attracting increasing attention owing to their inherent safety and low-cost. However, their unsatisfactory energy density and durability have so far limited their practical application. Herein, iron-doped α-manganese dioxide was grown on carbon cloth (FMO/CC) via a facile method to obtaied an aqueous ZIHC cathode. The important role of the iron dopant in modulating the microstructure and assistingg ion diffusion as well as suppressing the overpotential for the hydrogen evolution reaction at the FMO/CC cathode was demonstrated by experimental results and theoretical calculations. Moreover, characterization by ex situ XPS revealed that the Mn4+/Mn3+ and Fe3+/Fe2+ redox couples were involved in the Zn2+ storage mechanism. As a result, the FMO/CC cathode displayed electrochemical performance with a capacity of 288 mAh g−1 at a current density of 1 A g−1, an increased operating voltage range of 1.4 V, and cycling stability with only 15 % capacity loss over 10,000 cycles at 10 A g−1. Moreover, the obtained ZIHC based on an FMO/CC cathode and an activated carbon anode exhibited an energy density of 47 Wh kg−1 and a power density of 995 W kg−1, as well as 72 % capacity retention after 5000 cycles. The excellent electrochemical performances of the FMO/CC cathode demonstrate great potential applications in Zn2+ energy storage devices.