The tunnel-type MnO₂ structure is regarded as one of the most promising cathode materials for aqueous zinc-ion batteries due to its high theoretical specific capacity and excellent rate capability. In this study, α-MnO₂ nanorods (MnO₂-r) and nanotubes (MnO₂-t) were synthesized by reacting KMnO₄ with different reducing agents, namely Cr(NO₃)₃ and hydrochloric acid. Their molecular formulas were determined using various techniques as K_0.8Mn₈O₁₆·1.44H₂O and K_0.8Mn₈O₁₆·0.80 H₂O, respectively. By taking advantage of the charge screening effect induced by the higher crystal water content including enhanced Zn²⁺ diffusion kinetics, the zinc-ion storage capacity of MnO₂-r is significantly improved. This results in a consistently increasing specific capacity of 372 mAh·g⁻¹ on the 50th cycle at 0.1 A·g⁻¹, excellent cycle stability over 1600 cycles at 1.0 A·g⁻¹ and superior rate performance. Moreover, a two-stage process involving the insertion/extraction of H⁺ and Zn²⁺ accompanied by precipitation/dissolution of ZnSO₄ [Zn (OH)₂]₃·3H₂O (ZHS) on the electrode surface was tentatively proposed as the mechanism for Zn²⁺ storage in two electrode materials.