Switchable mirrors based on nickel–magnesium films

TLDR

Thin, magnesium‑rich Ni–Mg films co‑sputtered onto glass are mirror‑like with low visible transmittance. Exposure to hydrogen gas or cathodic polarization in alkaline electrolyte causes the Ni–Mg films to absorb hydrogen, becoming transparent via reversible formation of Mg₂NiH₄ and MgH₂. The study reports an electrochromic Ni–Mg mirror electrode that reversibly switches between mirror and transparent states with hydrogen uptake and release, and a palladium overlayer improves insertion/extraction kinetics and protects against oxidation.

Abstract

An electrochromic mirror electrode based on reversible uptake of hydrogen in nickel magnesium alloy films is reported. Thin, magnesium-rich Ni–Mg films prepared on glass substrates by co-sputtering from Ni and Mg targets are mirror-like in appearance and have low visible transmittance. Upon exposure to hydrogen gas or on cathodic polarization in alkaline electrolyte, the films take up hydrogen and become transparent. When hydrogen is removed, the mirror properties are recovered. The transition is believed to result from reversible formation of Mg2NiH4 and MgH2. A thin overlayer of palladium was found to enhance the kinetics of hydrogen insertion and extraction, and to protect the metal surface against oxidation.