Structure-Function Relationship of Highly Reactive CuO_x/Co₃O₄ Heterostructures Towards Superior Formaldehyde Sensing Performance

Structural control over nano-sized heterostructures enables selective molecular interactions in low-temperature catalysis and chemical sensing.¹ Yet, finding effective material combinations and identifying the reactive site remains challenging and an obstacle for rational catalyst/sensor design. Here,² the low-temperature oxidation of formaldehyde with CuO_x clusters on Co₃O₄ nanoparticles is demonstrated yielding an excellent sensor for this critical air pollutant. When fabricated by flame-aerosol technology,³ such CuO_x 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 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. With selectivity against other aldehydes, ketones and alcohols, such CuO_x/Co₃O₄ heterostructures are promising for personal exposure tracking and occupational safety.

References
[1] X. Yang, Y. Deng, H. Yang, Y. Liao, X. Cheng, Y. Zou, L. Wu and Y. Deng. Advanced Science 2023, 10, 2204810.
[2] M. D’Andria, F. Krumeich, Z. Yao, F.R. Wang and A.T. Güntner. Advanced Science 2024, 11, 2308224
[3] A.T. Güntner, N.J. Pineau and S.E. Pratsinis. Progress in Energy and Combustion Science 2022, 90, 100992