CHAPTER 4: Redox Oxides for Thermochemical Energy Storage

Solar energy presents enormous potential to spearhead the fight against climate change. However, due to its intrinsic intermittent character it requires an energy storage media for fully exploiting its potential. Although there are several competing and partially complementary technologies for achieving that goal, thermochemical processes are becoming relevant in concentrating solar power plants for energy storage. Among the systems used for those applications, redox metal oxides stand out as very flexible and robust materials for either direct heat storage, or CO₂ and H₂O splitting in thermochemical cycles for solar fuel production. Furthermore, methane chemical looping reforming coupled with CO₂ valorisation and/or H₂O dissociation is an incompletely decarbonised route that can also take advantage of these materials. This alternative strategy compensates sustainability losses by increasing the overall efficiency. All these processes operate at high temperatures swinging from an oxidised to a reduced state, and this fact imposes harsh conditions to the stability of the solids acting as oxygen carriers. The latest developments in this area are described in detail here, paying attention to the relevance of structural and morphological changes, as well as to the role of thermodynamics and kinetics aspects on the performance of these redox transformations in the solid–gas interphase.