CuOx – enriched Co3O4 surfaces enable selective formaldehyde sensing at low temperature

Designing highly reactive surface clusters at the nanoscale on metal-oxide supports enables selective molecular interactions in low-temperature catalysis and chemical sensing. Yet, finding effective material combinations and identifying the reactive site remains challenging and a key obstacle for rational catalyst/sensor design. Here, we demonstrate the low-temperature oxidation of formaldehyde with CuOx clusters on Co3O4 nanoparticles yielding an excellent sensor for this critical air pollutant. When fabricated by flame-aerosol technology, such CuOx clusters are finely dispersed onto the surface, while some Cu ions are incorporated into the Co3O4 lattice enhancing thermal stability. Most importantly, infrared spectroscopy of adsorbed CO and temperature-programmed reduction in H2 identified Cuδ+ species in these clusters as active sites. In fact, its surface concentration correlated with the apparent activation energy of formaldehyde oxidation (Spearman’s coefficient ρ = 0.89) and sensor response (0.96). At optimal composition, such sensors detected even the lowest formaldehyde levels of 3 parts-per-billion at 75 °C, superior to the state-of-the-art sensors. Also, selectivity to other aldehydes, ketones, alcohols, and inorganic compounds, robustness to relevant humidity levels and stable performance over 4 weeks were achieved, rendering such sensors promising as low-power gas detectors in air and food quality control as well as in health monitoring.