Light tuning CO/H2 composition on Ag: unraveling CO2 mass transfer and electron-phonon coupling in plasmon-enhanced electrocatalysis

Plasmon-enhanced electrocatalysis (PEEC) is an emerging approach to mitigate CO2 emissions. The mechanisms behind CO2 adsorption and reduction at the catalyst–electrolyte interface in PEEC still need to be further explored. Herein, we employ a well-defined Ag nanostructure to elucidate these pivotal issues. By shining light with wavelengths of 625, 525, 405 nm on Ag, an adjustable CO/H2 ratio from 35 to 1 can be obtained. The reaction pathway changing under plasmonic excitation does not originate from the lowered CO2 mass transfer in the vicinity of Ag, as the electrochemical quartz crystal microbalance results unravel that a slightly elevated temperature in bulk electrolyte caused by light irradiation cannot weaken the CO2 adsorption at the Ag catalyst–electrolyte interface. Theoretical calculations reveal that optical excitation towards shorter wavelengths leads to a progressive lowered energy barrier for H2 formation together with an enhanced energy barrier for *COOH formation. Although thermodynamically suppressed, CO2 reduction can still be improved kinetically by optimizing the excitation wavelength and intensity, being accompanied with the enhanced photocurrent. Transient absorption spectroscopy results further correlate the higher photocurrent with a prolonged electron-phonon coupling time, verifying that the improvement of CO2 reduction kinetics in PEEC can be realized by hot electron harnessing.

Subjects

CO/H2 ratio

electron-phonon coupling

hot electron generation

photoelectrochemical CO2 reduction

plasmonic catalysis

thermal effect

DDC Class

600: Technology

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Light tuning CO/H2 composition on Ag: unraveling CO2 mass transfer and electron-phonon coupling in plasmon-enhanced electrocatalysis