Electrolytic water splitting using surplus electricity represents one of the most cost-effective and promising strategies for hydrogen production. The high overpotential of the oxygen-evolution reaction (OER) caused by the multi-electron transfer process with a high chemical energy barrier, however, limits its competitiveness. Here, a highly active and stable OER electrocatalyst was designed through a cobalt-induced intrastructural enhancement strategy combined with suitable electronic structure modulation. A carved carbon nanobox was embedded with tri-metal phosphide from a uniform Ni-Co-Fe Prussian blue analogue (PBA) nanocube by sequential NH3 center dot H2O etching and thermal phosphorization. The sample exhibited an OER activity in an alkaline medium, reaching a current density of 10 mA cm(-2) at an overpotential of 182 mV and displayed a small Tafel slope of 47 mV dec(-1), superior to the most recently reported OER electrocatalysts. Moreover, it showed impressive electrocatalytic durability, increasing by approximately 2.7 % of operating voltage after 24 h of continuous testing. The excellent OER activity and stability are ascribed to a favorable transfer of mass and charge provided by the porous carbon shell, synergistic catalysis between the three-component metal phosphides originating from appropriate electronic structure modulation, more exposed catalytic sites on the hollow structure, and chainmail catalysis resulting from the carbon protective layer. It is foreseen that this successfully demonstrated design concept can be easily extended to other heterogeneous catalyst designs.