Modelling oxidation kinetics of half-Heusler thermoelectric materials and the role of protective coatings

Thermoelectric (TE) materials are increasingly utilised for electricity generation by harvesting waste heat in various practical applications. When deployed in high-temperature environments, their long-term thermal stability is crucial for ensuring high reliability and minimised mechanical degradation. While state-of-the-art experimental studies have highlighted the potential of half-Heusler TE materials in energy harvesting, experimental testing durations are often limited, leaving long-term performance uncertain. This paper addresses these gaps through finite element-based oxidation modelling, which explicitly accounts for the influence of protective coatings. Oxygen diffusion is modelled with a 1D Fick’s equation solved with FEniCSx, with a time-decaying diffusivity in both the substrate and coating domains. The model is calibrated against 50 h mass-gain data for uncoated and CrSi-coated half-Heusler TE materials. With the calibrated parameters, the framework is used to extrapolate mass gain and oxide-scale growth, and can serve as a tool for estimating the long-term thermal stability of TE materials protected by oxidation-resistant coatings.