Reversible phase transition of indium hydroxide for giant mechanical energy storage

Amorphization of cubic In(OH)3 nanocrystals with a bulk modulus of ~183 ( ± 27) GPa is observed in situ through the utilization of both synchrotron powder X-ray diffraction and Raman scattering techniques as they are subjected to the pressure of up to ~50 GPa. In further combination with ex situ microscopic structural analysis from transmission electron microscopy, ab initio density functional theory calculations and molecular dynamic simulations, it becomes apparent that the amorphization reaction initiates at two surfaces and subsequently propagates into the interior via surmounting an energy barrier of ~19 eV per unit cell. Amorphous In(OH)3 spontaneously reverts to its original cubic crystal structure at room temperature and ambient pressure. This reversion process, however, requires a recovery period of about 20 days. Such a long crystallization time and the reversible phase transition behaviors between crystalline and non-crystalline states make In(OH)3 a promising candidate for highly efficient mechanical energy storage with a gravimetric energy density of up to 2.04 ( ± 0.09) MJ/kg. Indium hydroxide has emerged as a promising material for mechanical energy conversion and storage, owing to its exceptionally high energy storage density. Here, the authors present fundamental insights into recent innovations and breakthroughs of conventional materials.