Direct, electrocatalytic oxygen reduction by laccase on anthracene-2-methanethiol-modified gold

Laccase, a multicopper oxidase, catalyzes the four-electron reduction of oxygen to water. Upon adsorption to an electrode surface, laccase is known to reduce oxygen at overpotentials lower than the best noble metal electrocatalysts usually employed. Whereas the electrocatalytic activity of laccase is well established on carbon electrodes, laccase does not typically adsorb to better defined noble metal surfaces in an orientation that allows for efficient electrocatalysis. In this work, we utilized anthracene-2-methanethiol (AMT) to modify the surface of Au electrodes and examined the electrocatalytic activity of adsorbed laccase. AMT facilitated the adsorption of laccase, and the onset of electrocatalytic oxygen reduction was observed as high as 1.13V_RHE. We observed linear Tafel behavior with a 144 mV/dec slope, consistent with an outer sphere single electron transfer from the electrode to a Cu site in the enzyme as the rate-determining step of the oxygen reduction mechanism.