Designing a highly efficient electrocatalyst to realize overall water splitting is vital, yet identifying the active site remains an ongoing challenge. Herein, the electrochemical in situ surface activation of P@Co/Se₂-NW/CC was investigated to understand the enhanced OER activity of P@Co/Se₂-NW/CC. The incorporation of phosphorus is thought to increase the vacancies surrounding the Co cations in the initial Co/Se₂ and speed up the structural change into "active species" like cobalt oxide/oxyhydroxide. The as-synthesized P@Co/Se₂-NW/CC required a low overpotential for OER (η₁₀₀ = 230 and 280 mV) and HER (η₁₀₀ = 111 and 132 mV), respectively, in alkaline water and alkaline seawater media. In-situ infrared reflection-absorption spectroscopy (IRRAS) and Post characterization unraveled the existence of surface-bounded Co oxide species on P@Co/Se₂-NW/CC after OER catalysis, which is responsible for the enhanced electrocatalytic activity. This study offers a valuable strategy for developing noble-metal-free bifunctional catalysts for efficient hydrogen generation from alkaline seawater and alkaline water electrolysis.