Production of hydrogen (H₂) from H₂ storage materials is very attractive as a source of sustainable energy. We report that AuNi@ZIF-8 alloys are very efficient nanocatalysts for H₂ evolution upon ammonia borane hydrolysis under visible-light illumination with turnover frequency 3.4 times higher than with the monometallic Ni catalyst in the dark. This improvement is attributed to dramatic volcano-type positive synergy optimized in Au_0.5Ni_0.5 @ZIF-8, for which ZIF-8 is by far the superior support, as well as to the localized surface plasmon resonance induced between 450 and 620 nm. Infrared spectra analysis and tandem reaction confirm the origin of the hydrogen atoms, reveal the reaction mechanism, and suggest how the cleavage of the B–H and O–H bonds proceeds in this reaction. Deuteration experiments with D₂O including primary kinetic isotope effects and density functional theory calculation under both dark and visible light conditions show that activation of H₂O always is the rate-determining step.