An Optical Study of the Deposition, Discharge, and Recharge of Manganese Dioxide Films

Abstract

The galvanostatic electrodeposition of manganese dioxide films onto a platinum substrate is studied over a thickness range from 0 to 2000 nm. At the upper end of the thickness range, optical absorption causes the ellipsometer null settings to approach within 0.02° of the infinite thickness limit, at which the films are indistinguishable from substrates. The optical extinction coefficient increases with film thickness over the range 0–50 nm, but from 50 to 160 nm the films have optical constants which are independent of thickness but which depend on the deposition current density. Beyond 160 nm, the optical data become progressively more difficult to interpret in terms of uniform isotropic or anisotropic film models. When relatively thin films (50 nm) are transferred to alkaline electrolyte and are cycled galvanostatically, optical changes are observed which correlate well with the electrochemical behavior for both reversible partial discharge cycles and irreversible complete discharge cycles.