Chemical looping technology has been demonstrated to be one of the most promising and versatile technologies in the clean energy industry. Oxygen carrier, also known as the redox catalyst is the cornerstone for the successful implementation of chemical looping conversions. During reduction, the oxygen carrier donates the required amount of oxygen ions for fuels conversion in a reducer. In the oxidation step, the oxygen-depleted oxygen carrier is replenished with molecular oxygen from combust air in an oxidizer where heat is released. A tremendous change occurs in the morphology of the oxygen carrier particles due to the ionic diffusion and oxygen vacancies formation both in the bulk and on the surface of the oxygen carriers thereby generating evolution of local chemical environment of the lattice oxygen and/or oxygen vacancies which are regarded as active sites during chemical looping reactions. In recent years, great significant research on improving the performance of the oxygen carriers by modulating their component design, structural construction, and modification for various chemical looping conversions has been conducted. However, limited attentions have paid to the evolution of the microstructure and the local chemical environment of the lattice oxygen and/or oxygen vacancies of the oxygen carriers, including lattice distortion, site symmetry, Me-O bond strength, and crystal lattice tilting etc. This review discusses the state-of-the-art advancements in ions diffusion regulation, phase segregation, and modulating the local chemical environment of lattice oxygen and/or oxygen vacancies in oxygen carriers. These progresses will facilitate the research and development of oxygen carriers for high efficient chemical looping processes.

oxygen carrier, lattice oxygen, local chemical environment, review