Negative thermal expansion coefficient materials: From basics to applications, recent advances in solid oxide cells and future perspectives

Negative thermal expansion has always interested scientists as an extraordinary physical property. Understanding this specific phenomenon allows to design and synthesize materials with abnormal, anisotropic, near-zero, or negative expansion. In effect, these materials find applications in many branches of science like mechanics, optics, micro- and nanoelectronics, magnetics, and medical and chemical applications. Since the great majority of these materials are electrical insulators, they did not find practical applications in electrochemistry. However, recently a new group of perovskite-based materials was discovered which gave vast opportunities to utilize such materials in fuel cell technology giving outstanding possibilities to improve and enhance their electrical, thermomechanical, and electrochemical properties. Therefore, the most limiting factor, which is the long-term stability, may be mitigated leading to improved electrolyte/electrode durability which enables future perspectives possibly allowing for faster commercialization of the technology. In this review article, we present a general insight into thermal expansion and its physical explanation along with many examples of materials with negative expansion, exhibiting different crystal structures. Experimental techniques for thermal expansion coefficient evaluation are summarized and widely discussed. In the main part of the article, many applications of materials with negative expansion are presented, focusing on recent advances in electrochemistry, mainly as composite electrodes with negative thermal expansion materials addition, which improves the electrochemical performance of solid oxide cells. In the summary, we present drawn conclusions and discuss future perspectives as a widely and rapidly developing branch of electrochemistry.