Co　core@Co　oxide　shell　(Co@CoOx)　catalysts　represent　a　large　family　with　promising　oxygen　reduction　reaction　(ORR)　catalytic　activity.　However,　inadequate　understanding　of　Co@CoOx　synergy　prohibits　further　pursuit　of　catalytic　performance　enhancement.　Herein,　a　Co　zeolitic-imidazolate　framework　was　converted　into　metallic　Co,　followed　by　controlled　air　treatment　to　form　Co@CoOx.　The　composition　and　structure　evolution　as　a　function　of　air　treatment　temperature　were　studied　thoroughly　through　conventional　and　synchrotron　(both　ex-situ　and　in-situ)　characterizations,　confirming　the　coexistence　of　CoO　and　Co3O4　in　the　shell.　The　optimal　catalyst　showed　an　ORR　half-wave　potential　of　0.87　V　(vs.　RHE)　in　an　alkaline　half-cell　and　delivered　high　discharge　capacity　in　an　aprotic　Li-O-2　battery　(7,124　mAh　g(Cat+C)(-1))　and　an　aqueous　Zn-air　battery　(694　mAh　g(Zn)(-1))　with　good　performance　retention　after　durability　test.　Modeling　simulation　and　density　functional　theory　calculation　confirmed　the　charge　donation　from　metal　core　to　oxide　shell　and　shed　light　on　new　insights　of　how　metal@metal　oxide　synergy　impacted　the　ORR　via　tuning　the　charge　conductivity,　oxygen　affinity　and　intermediate　transfer　pathway.　This　work　opens　up　a　venue　to　boost　ORR　catalytic　activity　from　an　interfacial　synergy　perspective.