This review has highlighted the recent advances in the development of nonstoichiometric oxides, ranging from simple oxide, perovskite, layered perovskite, and pyrochlore, for ORR and OER in MABs and LTFCs. These catalysts are characterized to be low cost and earth-abundant, as well as possess relatively high activity and stability under operation conditions. It is expected that these catalysts will be essential to the future development of multiple technologies. For practical large-scale commercialization, the development of even more active and stable oxygen catalysts is essential and will be the central topic of advanced research. It is expected that the development of nonstoichiometric oxides, with the mutual development of system components, will lead to highly stable and efficient MABs and LTFCs in practical applications in the near future.

http://pubs.acs.org/doi/full/10.1021/acs.chemrev.5b00073