Infrared surface plasmons on a Au waveguide electrode open new redox channels associated with the transfer of...

Plasmonic catalysis holds promise for opening new reaction pathways inaccessible thermally or for improving the efficiency of chemical processes. We report a gold stripe waveguide along which infrared (λ₀ ~ 1350 nanometers) surface plasmon polaritons (SPPs) propagate, operating simultaneously as an electrochemical working electrode. Cyclic voltammograms obtained under SPP excitation enable oxidative processes involving energetic holes to be investigated separately from reductive processes involving energetic electrons. Under SPP excitation, redox currents increase by 10×, redox potentials decrease by ~2× and split in correlation with photon energy, and the charge transfer resistance drops by ~2× as measured using electrochemical impedance spectroscopy. The temperature of the working electrode was monitored in situ, ruling out thermal effects. Chronoamperometry measurements with SPPs modulated at 600 hertz yield a commensurately modulated current response, ruling out thermally enhanced mass transport. Our observations indicate opening of optically controlled nonequilibrium redox channels associated with energetic carrier transfer to the redox species.