Year: 2026
Type: article
Abstract: The conversion between heat and electricity via the thermoelectric effect offers a promising pathway for solid-state cooling [1,2]. Among emerging materials, Mg3(Bi, Sb)2 has been regarded as a leading candidate to replace conventional Bi2Te3 owing to its low cost, light weight and excellent performance [3,4]. However, its practical application is critically hindered by its inherent stability issues, particularly its chemical instability under ambient conditions in Bi-rich compositions [5,6]. In atmospheric environments, nanoscale water films inevitably condense on material surfaces, triggering electrochemical reactions. For Mg3(Bi, Sb)2, its highly negative equilibrium potential (−0.8 to −0.9 V) will induce hydrogen evolution corrosion, producing porous MgO/Mg(OH)2 layers that cannot effectively passivate the surface and are continuously stripped by hydrogen bubbles. This issue is further exacerbated in thermoelectric cooling devices, where temperature gradients promote moisture condensation, leading to rapid degradation of thermoelectric performance [5–7]. Previous strategies have mainly relied on external coatings to block H2O and O2, which have proven to be effective in mitigating degradation [8–10]. In contrast, in a recent work published in Nature Materials, Yu et al. proposed a different strategy by introducing a sacrificial anodic second phase (Mg17Al12) into Mg3(Bi, Sb)2 to achieve cathodic protection (Fig. 1) [7]. The large potential difference between Mg17Al12 (−1.99 V) and Mg3(Bi, Sb)2 forms local galvanic couples, where Mg17Al12 preferentially corrodes and protects the matrix. The dissolution of the anodic phase produces Mg2⁺ and Al3⁺, which subsequently form dense Mg/Al hydroxide and oxide layers, providing an additional protective barrier. Anodic protection mechanism. Adapted with permission from Ref. [7]. Beyond this classical electrochemical mechanism, the authors further reveal an electronic effect: due to the higher work function of Mg3(Bi, Sb)2, electrons transfer from Mg₁₇Al₁₂ to the matrix, rendering Mg3(Bi, Sb)2 negatively charged and thermodynamically less susceptible to oxidation. Notably, the in situ formed protective layer exhibits self-healing behavior, ensuring sustained protection. This dual protection mechanism dramatically improves stability. The corrosion rate is reduced by 92% in air (∼95 μm year⁻1) and 86% in water (∼0.36 μm h⁻1). At the device level, modules incorporating Mg17Al12 show comparable performance to commercial Bi2Te3 at 300 K and superior performance at elevated temperatures, while maintaining stable operation after 28 days under harsh conditions (350 K, 70% relative humidity). This work shows a paradigm shift from passive barrier protection to active electrochemical design in thermoelectrics. By integrating sacrificial anodic phases, it provides a generalizable strategy to stabilize moisture-sensitive functional materials, as also verified in Mg2Sn and CaMg2Bi2 [7]. Future efforts might focus on optimizing phase distribution, minimizing electronic transport penalties and extending this concept to high-performance but environmentally unstable systems. Conflict of interest statement. None declared.
Source: National Science Review
DOI: 10.1093/nsr/nwag232
Authors: Xinzhi Wu, Longquan Wang, Gang Wu, Airan Li, Takao Mori
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,000
OpenAlex ID: W7154731548