ABSTRACTSubstituting the sluggish oxygen evolution reaction with a more thermodynamically favorable ethanol oxidation reaction (EOR) offers an opportunity to circumvent the efficiency loss in water splitting and metal‐air batteries. However, the effect of the dynamic surface evolution of the catalyst in operating conditions on the activity of EOR lacks comprehensive understanding. Herein, we demonstrate a tunable operational catalyst activity through the modulated redox property of nickel oxalate (NCO) by establishing a relation between the oxidation behavior of Ni, surface reconstruction, and catalyst activity. We propose a repeated chemical–electrochemical reaction mechanism of EOR on NCO, which is rigorously investigated through a combination of operando Raman and nuclear magnetic resonance. The modulation of the oxidation trend of Ni by doping heteroatoms stimulates the electrochemical oxidation of the catalyst surface to NiOOH, which alters the catalyst activity for EOR. Assembled ethanol‐assisted water electrolysis cell exhibits a reduced operating voltage for hydrogen production by 200 mV with a ~100% Faradaic efficiency, and zinc–ethanol–air battery showed a 287 mV decreased charge–discharge voltage window and enhanced stability for over 500 h.