Developing highly ordered and conductive phosphorous-based materials and identifying their active sites are critical to improve the catalytic performance for oxygen evolution reactions (OERs). Herein, we report a template-free and rapid high-pressure synthesis protocol to fabricate irregular CoMoP₂ nanoparticles for OER catalysts. Pure CoMoP₂ electrocatalysts show a reduced overpotential of 270 mV at 10 mA cm⁻², improved kinetics and long-term stability. XAS, XPS and DFT calculations reveal that the reorganization induces highly active Co sites with a Co(OH)₂ layer on the surface, while Mo atoms regulate electronic conductivity towards OER reduction potential and maintain the structural integrity of CoMoP₂. This work not only provides an identified activation mechanism for bimetallic catalysts, but also highlights the high-pressure synthesis as one of the alternative approaches for developing OER catalysts.