Effect of hydrothermal time on Zn2+ transport channel in manganese dioxide

Abstract

Manganese dioxide is an environmentally friendly, low-cost zinc-based energy storage electrode material. However, its practical application is easily hindered by slow diffusion kinetics and low specific capacity. During the preparation of manganese dioxide by hydrothermal method, we observed that the hydrothermal time had a significant effect on the zinc-ion transport channels in MnO₂, which was manifested as a shift from 1 × 1 tunnel structure (MnO₂-24h, hydrothermal for 24h) to 2 × 2 tunnel structure (MnO₂-8h, hydrothermal for 8h). MnO₂-8h sample achieves a faster Zn²⁺ migration rate due to the widening of ion channels and the microporous structure formed by the aggregation of nanowire morphology. At the same time, the sample demonstrated excellent specific capacity and stability. At a current density of 0.2 A g⁻¹, the specific capacity is as high as 256.9 mA h g⁻¹, which is much higher than that of the MnO₂-24h sample. It also has excellent durability of 71.7% after 1000 cycles at 1 A g⁻¹. In addition, the dynamic behavior shows that capacitive control is dominant, with the pseudo-capacitance of the MnO₂-8h sample contributing up to 79% at 0.4 mV s⁻¹.