Manganese dioxides (MnO₂s) exhibit rich and diverse crystallographic structures (polymorphs). MnO₂ polymorphs comprise one-dimensional (1D) tunnels and two-dimensional (2D) layers which allow fast and highly reversible ion-exchange properties. MnO₂s have widely been studied as cathodes in aqueous rechargeable batteries due to their large tunnel and layer openings and reversible 3+/4+ Mn redox couple. Here, we are reporting high temperature (240^oC) hydrothermal syntheses of two tunnel-structured MnO₂s with 0.46 nm x 0.46 nm and 0.46 nm x 0.92 nm dimensions and a layered MnO₂ with an interlayer spacing of 0.46 nm. MnO₂ materials are fully characterized using PXRD, SEM/EDX, TEM, and N₂-sorption. Synthesized MnO₂ materials are tested as cathodes in rechargeable zinc ion batteries (ZIB) in two electrode cells and using Zn metal anode. Cyclic voltammetry, rate capability, and galvanostatic cycling performances are evaluated in two different aqueous Zn²⁺ electrolytes (ZnSO₄ and ZnTFSI) to disclose the mechanistic changes of reversible Zn²⁺ storage and the relationship between storage, tunnel and layer dimensions, and electrolyte. During the CV tests, all three materials showed similar redox potentials in ZnSO₄, whereas in ZnTFSI, layered and 0.46 nm x 0.92nm tunnel sized MnO₂s showed significantly different redox potentials along with an additional oxidation peak. These MnO₂s also showed better capacity retention in ZnTFSI than in ZnSO_4. These MnO₂ materials have similar crystallite sizes and surface areas (25-55 m²/g), differing only in the dimensions of their openings (layer or tunnel sizes). This allows us to directly evaluate the effect of the structural openings and electrolyte in functional electrochemistry by minimizing the effects of other physicochemical properties.