Building a sustainable society requires efficient chemical storage of hydrogen and facile on-demand generation. In this work, hydrogen is spontaneous generated from reforming formaldehyde and water on bimetallic Ag/Cu NWs catalyst, which is synthesized by a simple wet etching method together with electrochemical reduction. The results indicate that O2 can effectively promote H2 generation by forming *OOH specie, and act as a medium for H atom transfer. The synergistic effect between Ag and Cu greatly improves the catalytic activity. Specifically, the adsorption of O2 on Cu sites promotes the dehydrogenation of formaldehyde and proton coupling on Ag sites. Consequently, the Ag/Cu catalyst expresses excellent hydrogen production from aqueous formaldehyde solution at a rate of 12.3 mmol/(gcat.∙min), which surpass the past record. This work clearly explains the synergistic effect mechanism on formaldehyde reforming from the atomic level, providing guidance for the design of highly efficient catalysts for aqueous-phase spontaneous hydrogen evolution reactions.