Magneto-Plasmonic Coupling Enhances Hot Carrier Dynamics for CO2 Reduction over Black Gold

Plasmonic catalysis presents a promising approach for solar-to-chemical energy conversion by generating energetic hot carriers (electrons and holes) upon light excitation. However, their ultrafast relaxation and limited mobility remain major bottlenecks, limiting their effective involvement in surface reactions. In this study, we explore a magneto-plasmonic strategy to overcome these challenges, significantly boosting the photocatalytic CO2-to-CO conversion using a black gold-nickel catalyst. Under an external magnetic field, the CO production rate increased by 140%, from 5,109 to 12,245 μmol g-1 h-1 under simulated solar irradiation. This enhancement is attributed to improved charge separation through the Lorentz force, extended hot carrier lifetimes (possibly due to spin polarization), and negative magnetoresistance altering charge transport dynamics. Ultrafast transient absorption spectroscopy revealed faster decay dynamics of the plasmonic excited state, indicating accelerated hot electron transfer from Au to Ni under the influence of the magnetic field. While the in situ DRIFTS indicated that the CO2 reduction pathway remained unchanged, the light-induced CO desorption exhibited an increased desorption rate in the presence of a magnetic field, demonstrating that the magnetic field also modulates surface dynamics. In situ synchrotron X-ray absorption spectroscopy confirmed that Ni sites are dynamically reduced to the catalytically active Ni0 state under illumination, with H2 enabling reversible regeneration during CO2 reduction. Control experiments performed under a thermally driven reaction (on black gold-Ni) and a light-driven reaction on non-plasmonic black carbon-supported Ni show no magnetic-field-induced enhancement, establishing that plasmonic excitation and hot charge carriers are essential prerequisites for the observed effect. Temperature-dependent internal quantum efficiency and electron scavenging studies further confirmed that the magneto-plasmonic catalysis operates through a nonthermal, hot-electron-driven pathway. This work establishes magneto-plasmonics as a lever for controlling hot-carrier chemistry and advancing solar fuel catalysis.