In situ and ex situ spectroelectrochemical and X-ray absorption studies on rechargeable, chemically-modified and other MnO(sub 2) materials.

摘要

A combined series of in situ and ex situ UV spectroelectrochemical and X-ray absorption studies have been made on MnO(sub 2), chemically-modified by small amounts of Bi(III), and comparatively on other MnO(sub 2) materials such as a blank (Bi-free) and (gamma)-MnO(sub 2). These procedures are applied in order to follow the oxidation-states of Bi and of Mn during the course of discharge and recharge of MnO(sub 2) as a battery cathode material, and the extents of rechargeability that can be achieved with such materials. Presence of Bi appears to provide a preferred ''heterogeneous'' discharge/recharge pathway involving a soluble Mn(III) intermediate, over the alternative ''electron-proton'' hopping, solid-state mechanism. From XAS results, it is concluded that presence of Bi, although not affecting the O-coordination, does influence the Mn-Mn coordination, determining the way the MnO(sub 2) coordination octahedra are connected.