Structure‐Function Relationship of Highly Reactive CuOx Clusters on Co3O4 for Selective Formaldehyde Sensing at Low Temperatures

Abstract

AbstractDesigning 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 an obstacle for rational catalyst/sensor design. Here, the low‐temperature oxidation of formaldehyde with CuOx clusters on Co3O4 nanoparticles is demonstrated yielding an excellent sensor for this critical air pollutant. When fabricated by flame‐aerosol technology, such CuOx clusters are finely dispersed, while some Cu ions are incorporated into the Co3O4 lattice enhancing thermal stability. Importantly, infrared spectroscopy of adsorbed CO, near edge X‐ray absorption fine structure spectroscopy and temperature‐programmed reduction in H2 identified Cu+ and Cu2+ species in these clusters as active sites. Remarkably, the Cu+ surface concentration correlated with the apparent activation energy of formaldehyde oxidation (Spearman's coefficient ρ = 0.89) and sensor response (0.96), rendering it a performance descriptor. At optimal composition, such sensors detected even the lowest formaldehyde levels of 3 parts‐per‐billion (ppb) at 75°C, superior to state‐of‐the‐art sensors. Also, selectivity to other aldehydes, ketones, alcohols, and inorganic compounds, robustness to humidity and stable performance over 4 weeks are achieved, rendering such sensors promising as gas detectors in health monitoring, air and food quality control.