Electro-precipitation via oxygen reduction: a new technique for thin film manganese oxide deposition

Abstract

Manganese oxide was deposited from a non-aqueous solution, dimethyl sulfoxide (DMSO), via the reduction of dissolved oxygen. The formed superoxide radical ion (O₂⁻˙) reacts rapidly with the manganese ions forming a smooth and thin film (80 nm) of manganese oxide. From an in situ EQCM study, it could be concluded that MnO₂ was the most probable oxide which was deposited at an average growth rate of 0.049 μg s⁻¹ or 0.077 nm s⁻¹. Since the direct deposition of a phase pure MnO₂ layer was not confirmed by XRD, it is more likely that a variety of manganese oxides has been deposited during the electro-precipitation reaction and thus further optimization or post-treatments are required to obtain an active manganese oxide layer for thin film deposits. The key property of this new deposition technique is the self-limiting behavior, proven by rotating ring-disk electrode experiments. This is crucial to electrodeposit thin films conformally on high aspect ratio structures for 3D all-solid-state lithium-ion batteries or supercapacitors.