Non-selective synthesis and controllable transformation of parallel MnO2 with hydrogen ions

Abstract

Acids play a vital role in the controlled synthesis of parallel MnO₂; the appropriate acid groups with highest oxidation state have no effect on the parallel structure, but acid groups with reducibility can promote its formation. Importantly, excess H⁺ also can serve as a medium for the transformation of parallel δ-MnO₂ to needle-like α-MnO₂. However, this process can be hindered by adding K⁺. Besides, the increased Mn₃O₄ from the pre-calcined templates can give rise to a selective growth of parallel δ-MnO₂ and exhibit good cycle stability with 114% retention of initial specific capacitance after 10 000 cycles.