Preface to the JPCM special issue on physical and chemical properties of reducible oxides

The development of efficient functional materials for solar and chemical energy conversion and storage is extremely relevant to face the challenges posed by the environment and climate emergency. Reducible oxides are a class of compounds in which the cations can quickly and reversibly change their oxidation state, driving interesting physical and chemical properties, such as a remarkable activity for oxidation and reduction reactions, a high oxygen-ion conductivity and a high oxygen storage capacity. The electronic properties of these materials can be largely modified by, for example, defect engineering, playing with dimensionality and shape or coupling with metal atoms or nanoparticles, which lead to efficient electron transfer processes, and in turn to changes in oxygen vacancy formation energies and derived functionalities. Intensive research is being recently oriented towards investigating and tailoring the properties of such materials via an accurate atomic scale understanding, using advanced experimental and theoretical methods, which can drive a knowledge-based optimization of the functionalities. The special issue on ‘Physical and Chemical Properties of Reducible Oxides’ collects studies of systems based on reducible oxides in different forms, which point out the present experimental and theoretical challenges for the development and application of such materials. The most widely investigated reducible oxides are titanium (titania, TiO2) and cerium oxide (ceria, CeO2). Moreover, other transition metal oxides also in the form of more complex ternary oxides are a further subject of intense research in the field.