Structure‐Function Relationship of Highly Reactive CuO<sub>x</sub> Clusters on Co<sub>3</sub>O<sub>4</sub> for Selective Formaldehyde Sensing at Low Temperatures
Matteo D’Andria, Frank Krumeich, Zhangyi Yao, Feng Ryan Wang, Andreas T. Güntner
Abstract
Abstract Designing 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 CuO x clusters on Co 3 O 4 nanoparticles is demonstrated yielding an excellent sensor for this critical air pollutant. When fabricated by flame‐aerosol technology, such CuO x clusters are finely dispersed, while some Cu ions are incorporated into the Co 3 O 4 lattice enhancing thermal stability. Importantly, infrared spectroscopy of adsorbed CO, near edge X‐ray absorption fine structure spectroscopy and temperature‐programmed reduction in H 2 identified Cu + and Cu 2+ 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.