This invention upcycles end-of-life LiFePO4-based lithium-ion battery (LIB) cathode into a single-atom electrocatalyst for oxygen reduction reaction (ORR) using a simple partial etching strategy. The LiFePO4/carbon was converted into Fe single atom-embedded hollow carbon spheres containing minor FeOx nanoclusters and FePO4 nanoparticles. The etching strategy breaks a long-standing stereotype by innovatively constructing atomic catalytic sites using a top-down approach. The resulting material exhibits excellent ORR activity/stability in an alkaline medium as demonstrated by the high Eonset of 0.97 V and a slight current decline of 9.5% after 16 hours of testing. Furthermore, a membrane electrode fabricated with this single atom-based catalyst demonstrated great potential value in two practical energy conversion devices: an ammonia fuel cell (FC) and a Zn-air battery (ZAB), building a bridge across energy applications.