is of interest as a cathode material for 3 V lithium batteries and as an electrode/electrocatalyst for higher energy, hybrid Li-ion/Li−O 2 systems. It has a structure with large tunnels that contain stabilizing cations such as Ba 2+ , K + , NH 4 + , and H 3 O + (or water, H 2 O). When stabilized by H 3 O + /H 2 O, the protons can be ion-exchanged with lithium to produce a Li 2 O-stabilized α-MnO 2 structure. It has been speculated that the electrocatalytic process in Li−O 2 cells may be linked to the removal of lithium and oxygen from the host α-MnO 2 structure during charge, and their reintroduction during discharge. In this investigation, hydrated α-MnO 2 was used, as a first step, to study the release and uptake of oxygen in α-MnO 2 . Temperature-resolved in situ synchrotron X-ray diffraction (XRD) revealed a nonlinear, two-stage, volume change profile, which with the aide of X-ray absorption near-edge spectroscopy (XANES), redox titration, and density functional theory (DFT) calculations, is interpreted as the release of water from the α-MnO 2 tunnels. The two stages correspond to H 2 O release from intercalated H 2 O species at lower temperatures and H 3 O + species at higher temperature. Thermogravimetric analysis confirmed the release of oxygen from α-MnO 2 in several stages during heating−including surface water, occluded water, and structural oxygen−and in situ UV resonance Raman spectroscopy corroborated the uptake and release of tunnel water by revealing small shifts in frequencies during the heating and cooling of α-MnO 2 . Finally, DFT calculations revealed the likelihood of disordered water species in binding sites in α-MnO 2 tunnels and a facile diffusion process.