Water adlayers bridging metal spillover to boost catalytic activity.

Hydrogen spillover has been extensively studied in heterogeneous catalysis, whereas the analogous migration of metal species remains largely underexplored. Here, we report a spillover phenomenon for metal species, exemplified by copper, which spontaneously migrates across physically contacted hydrophilic supports under humid ambient conditions. This process is facilitated by water adlayers on support surfaces, which act as molecular bridges to enable surface and interfacial migration of cooper species via hydroxylated intermediates. The phenomenon is universal across diverse supports, including oxides, carbides, and sulfides, and extends to metals such as ruthenium, cobalt, and nickel. Remarkably, catalysts prepared via this spillover approach exhibit substantially enhanced low-temperature activity in reactions including carbon monoxide oxidation, reverse water-gas shift, selective catalyst reduction with ammonia, and hydrogen cyanide oxidation, outperforming counterparts prepared by conventional impregnation. This work redefines the spillover phenomenon by extending it to metal species through water adlayer-mediated migration, opening new avenues for the design of dynamic catalysts.