Plasmon-induced selective carbon dioxide conversion on earth-abundant aluminum-cuprous oxide antenna-reactor nanoparticles

Abstract

The rational combination of plasmonic nanoantennas with active transition metal-based catalysts, known as 'antenna-reactor' nanostructures, holds promise to expand the scope of chemical reactions possible with plasmonic photocatalysis. Here, we report earth-abundant embedded aluminum in cuprous oxide antenna-reactor heterostructures that operate more effectively and selectively for the reverse water-gas shift reaction under milder illumination than in conventional thermal conditions. Through rigorous comparison of the spatial temperature profile, optical absorption, and integrated electric field enhancement of the catalyst, we have been able to distinguish between competing photothermal and hot-carrier driven mechanistic pathways. The antenna-reactor geometry efficiently harnesses the plasmon resonance of aluminum to supply energetic hot-carriers and increases optical absorption in cuprous oxide for selective carbon dioxide conversion to carbon monoxide with visible light. The transition from noble metals to aluminum based antenna-reactor heterostructures in plasmonic photocatalysis provides a sustainable route to high-value chemicals and reaffirms the practical potential of plasmon-mediated chemical transformations.Plasmon-enhanced photocatalysis holds promise for the control of chemical reactions. Here the authors report an Al@Cu₂O heterostructure based on earth abundant materials to transform CO₂ into CO at significantly milder conditions.

Fig. 1

Characterization of plasmonic photocatalysts. a TEM image of the pristine Al NCs with nominal size before and b after growth of Cu₂O shell around Al core. The scale bars in a and b are 50 nm. c HRTEM image of Al/Al₂O₃/Cu₂O showing the Cu₂O layer is highly polycrystalline. The scale bar is 5 nm. d High-angle annular dark field scanning transmission electron micrograph (HAADF-STEM) of the Al@Cu₂O particles in low magnification and higher resolution (inset) indicating different Z-contrast for the core and the shell materials. The scale bars for low-resolution and inset images are 400, and 50 nm, respectively. e–h Energy-dispersive X-ray (EDX) mapping showing the distribution of Al e, Cu f and O g, and their overlay h

Fig. 2

Plasmon-enhanced rWGS. a The impact of visible light intensity on the rate of CO formation on photocatalysts prepared from Cu₂O, Al NCs and Al@Cu₂O. b The apparent external quantum efficiency (EQE) calculated from measured reaction rate in a and plotted against photon flux

Fig. 3

Light-driven vs. thermal-driven activity characterization for rWGS. a Spatial temperature mapping of the catalysts surface during illumination of Al NCs/γ-Al₂O₃ in air under visible light intensity of 10 W cm⁻². b Steady-state temperature monitoring for oxide supported plasmonic nanoparticles compared to pure oxide support with and without irradiation in air. c Typical gas chromatogram of the chamber output during light (7 W cm⁻²) and thermal driven (350 °C) rWGS on Al@Cu₂O. d The overall rate of products formation as a function of applied temperature in purely thermal-driven (light off) rWGS for oxide supported Al NCs and Al@Cu₂O (unfilled data points). For comparison, the reaction rates during the light-induced process (10 W cm⁻²) are shown at the corresponding recorded temperatures for oxide supported Al NCs and Al@Cu₂O (filled data points)

Fig. 4

Distinguishing between plasmon-induced carrier-assisted and photothermal heating for rWGS on Al@Cu₂O. a The measured EQE as a function of illumination wavelength for oxide-supported Al@Cu₂O compared to Al vs. illumination wavelength. b Numerically calculated local electric field strength |E(r)|² in Al core (left axis) and Cu₂O shell (right axis). c A simulated absorbed fraction in 100 nm diameter Al core, 15 nm thick Cu₂O shell and total structure placed on γ-Al₂O₃ in air. d Comparison between experimentally measured heat density and ensemble Monte-Carlo simulation vs. illumination wavelength for oxide-supported Al@Cu₂O nanoparticles in air. e, f The absorption efficiency of oxide-supported Al@Cu₂O nanoparticles at e 400 nm and f 800 nm obtained from ensemble Monte-Carlo calculation. The scales in e and f are based on the sample holder dimensions and volume of oxide-supported Al@Cu₂O nanoparticles loaded into the sample holder. The calculated heat density corresponding to 400 and 800 nm are assigned in d

Fig. 5

Structure and mechanism of plasmon-induced carrier-assisted rWGS on Al@Cu₂O. a Energy band diagram of Al@Cu₂O for plasmon-mediated carrier generation for injection into unoccupied state of CO₂ for C–O bond activation. b Schematic of plasmon-induced carrier-driven rWGS on Al@Cu₂O