A synergic effect of Rh and Ni in the bimetallic Rh4Ni nanocatalyst (Rh/Ni ratio = 4:1) makes it possible to achieve a 100% selectivity for hydrogen generation by complete decomposition of hydrous hydrazine at room temperature. The Rh,Ni nanocatalysts with a particle size of similar to 3 nm were prepared by alloying Rh and Ni using a coreduction process in the presence of hexadecyltrimethyl ammonium bromide (CTAB).