The effect of aging temperature on oxygen storage materials (OSM) substantially free from platinum group (PGM) and rare earth (RE) metals is disclosed. Samples of ZPGM-ZRE metals OSM, hydrothermally aged at a plurality of high temperatures are found to have significantly high oxygen storage capacity (OSC) and phase stability than conventional PGM catalysts with Ce-based OSM. ZPGM-ZRE metals OSM includes a formulation of Cu—Mn stoichiometric spinel structure deposited on Nb—Zr oxide support and may be converted into powder to be used as OSM application or coated onto catalyst substrate. ZPGM-ZRE metals OSM, after aging condition, presents enhanced level of thermal stability and OSC property which shows improved catalytic activity than conventional PGM catalysts including Ce-based OSM. ZPGM-ZRE metals OSM may be suitable for a vast number of applications, and more particularly in underfloor catalyst systems.