Single Cu Atom Sites on Co ₃ O ₄ Activate Interfacial Oxygen for Enhanced Reactivity and Selective Gas Sensing at Low Temperature

Controlling the redox landscape of transition metal oxides is central to advancing their reactivity for heterogeneous catalysis or high-performance gas sensing. Here, we report single Cu atom sites (1.42 wt.%) anchored on Co₃O₄ nanoparticles (Cu₁-Co₃O₄) that dramatically enhance reactivity and molecular sensing properties of the support at low temperature. The Cu₁ are identified by x-ray absorption near edge structure and feature metal-support interaction between the atomically dispersed Cu (mostly in 2+ oxidation state) and Co₃O₄, as revealed by x-ray photoelectron spectroscopy. The ability of Cu₁ to form interfacial Cu-O-Co linkages strongly reduces the temperature of lattice oxygen activation compared to CuO nanoparticles on Co₃O₄ (CuONP-Co₃O₄), as demonstrated by temperature-programmed reduction and desorption analyses, in agreement with density functional theory calculations. To demonstrate practical impact, we deploy Cu₁-Co₃O₄ nanoparticles as a chemoresistive sensor for formaldehyde that yields more than an order of magnitude higher response than CuONP-Co₃O₄ and consistently outperforms state-of-the-art sensors. Formaldehyde is detected down to 5 parts-per-billion at 50% relative humidity and 75°C with excellent selectivity over critical interferents. These results establish a strategy for activating redox-active supports using single-atom isolates of non-noble nature, yielding drastically enhanced and well-defined reactivity to promote low-temperature oxidation reactions and selective analyte sensing.