To synthesize nanocomposites (NCs) comprising two different materials, a multi-step synthetic method is generally required. In this work, we report the synthesis of a heterometallic nanostructure that can be synthesized using a simple antisolvent crystallization-based method. Cu/CoO NCs composed of Cu nanoparticles and CoO nanosheets were formed by reducing mixed salt particles containing both Cu and Co precursors. The synthesized Cu/CoO NCs exhibit higher sensitivity and increased stability compared to conventional catalysts when used for the electrochemical detection of hydrogen peroxide (H2O2).