Anodic protection enables moisture-stable Mg₃(Sb, Bi)₂ for thermoelectric cooling

Mg₃(Sb, Bi)₂ is the most promising candidate as a next-generation thermoelectric cooling material; however, its application is bottlenecked by poor moisture stability. We demonstrate a protection strategy for Mg₃(Sb, Bi)₂ by constructing anodic phases that are preferentially corroded to protect the cathodic material matrix, as enabled by the in situ formation of uniformly distributed multiscale anodic phases based on a large Pilling-Bedworth ratio, low equilibrium potential, high chemical inertness and rapid oxide/hydroxide coverage ability. Mg₁₇Al₁₂ preferentially corrodes and promotes the formation of a protective film, reducing the average corrosion rate of Mg₃(Sb, Bi)₂ by 92% to ~95 μm year^-1 in air and 86% to ~0.36 μm h^-1 in water, achieving excellent corrosion resistance. The cooling performance of the fabricated module is comparable with that of commercial bismuth telluride modules at 300 K, and exceeds them at 325 K and 350 K. Meanwhile, no performance degradation is observed after 28-day aging at 350 K and 70% relative humidity. Our study addresses the issues of moisture stability of Mg₃(Sb, Bi)₂ during storage, processing and application, and could be extended to other aqueous vapour-sensitive materials.