Superblackbody Metasurface Activates CO₂ Vibrational Mode for Enhanced Selectivity in CO₂ Reduction.

Abstract

Thermal activation of reactants is a key initial step in catalysis, which can occur either by temperature-driven activation of surface adsorbates or by radiation-driven excitation above the surface. Here, two configurations of five-bilayer Ni/SiO₂ thermal metasurfaces are engineered to provide superblackbody near-field emission within the CO₂ asymmetric stretching band of 4.3 μm wavelength, with broadband and narrowband absorption, respectively. Thermal dipole simulations show that the broadly absorbing cylindrical array drives edge-guided resonances with a near-uniform rim field, whereas the narrowly emitting cuboid array with higher absorptivity shows corner field localization due to higher field interior confinement. Both metasurfaces have high near-field intensities in excess of blackbody radiation by up to ×2. Experimentally, the wideband metasurface achieves a higher CO production rate and >50% higher CO/CH₄ selectivity. In situ-diffused reflectance Fourier transform spectroscopy indicates reduced buildup of carbonate intermediates and adsorbed CO on the wideband metasurface relative to the narrowband metasurface, indicating faster CO desorption and suppressed methanation. Density functional theory simulations support the observation by showing that gas CO₂ bond stretching can eliminate the kinetic energy barrier to CO₂ chemisorption and promote CO₂ dissociation toward CO formation. Minimizing CO adsorbate stretching suppresses hydrogenation pathways that proceed through formate intermediate and subsequent methanation. Overall, the engineering of the metasurface thermal dipole-induced field coupling with confinement or radiative channels, modulated by emission spatial distribution, can independently activate reactant molecules above the surface while favoring the surface for desorption of products. This shows a physically driven approach to catalysis by decoupling the surface activation and desorption counteractions.