AbstractWater electrolysis has been considered a promising technology for the conversion of renewables to hydrogen. However, preventing mixing of products (H₂ and O₂) and exploring cost‐efficient electrolysis components remains challenging for conventional water electrolyzers. Herein, we designed a membrane‐free decoupled water electrolysis system by using graphite felt supported nickel‐cobalt phosphate (GF@Ni_xCo_y‐P) material as a tri‐functional (redox mediator, hydrogen evolution reaction (HER), oxygen evolution reaction (OER)) electrode. The versatile GF@Ni₁Co₁‐P electrode obtained by a one‐step electrodeposition not only exhibits high specific capacity (176 mAh g⁻¹ at 0.5 A g⁻¹) and long cycle life (80 % capacity retention after 3000 cycles) as a redox mediator, but also has relatively outstanding catalytic activities for HER and OER. The excellent properties of the GF@Ni_xCo_y‐P electrode endow this decoupled system with more flexibility for H₂ production by fluctuating renewable energies. This work provides guidance for multifunctional applications of transition metal compounds between energy storage and electrocatalysis.