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Fundamental understanding of fabricating promoted bi-functional electrocatalyst to achieve fast charge-transfer and smooth mass-transport in oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) through the rational management of catalyst composition and ingenious design of nanostructure is highly desired but still a formidable challenge. Herein, an advanced carved particle-in-box nanoreactor, composed of small Fe-Co-Ni tri-metallic alloy nanoparticles confined in porous nitrogen-doped carbon nanocage, was developed through a spatially-confined pyrolysis strategy. Tri-metal alloy could optimize the electronic structure of the catalyst, thus inducing the charge redistribution, and then regulating the adsorption and desorption energy barriers of intermediates in electrochemical reactions. Unique nano-hole design provided convenient and efficient channels for mass transfer during ORR and OER processes. Thanks to these attributes, the hybrid electrocatalyst delivered decent reversible oxygen catalytic activities, evidenced by a high half-wave potential of 0.850 V towards ORR and a low overpotential of 355 mV at 10 mA/cm² for OER both in alkaline electrolyte. As a proof-of-concept, this as-developed carved particle-in-box nanoreactor enabled the assembled Zn-air battery to deliver a narrow potential gap of 0.735 V, a decent power density of 315 mW/cm², a notable specific capacity of 754 mAh/g_Zn and excellent durability up to 165 h of continuous charge and discharge operations, thus implying the potential applications of this sophisticated catalyst model for promising energy conversion.