Oxygen Is Electroreduced to Water on a “Wired” Enzyme Electrode at a Lesser Overpotential than on Platinum

Abstract

The first enzyme-based catalyst that is superior to platinum in the four-electron electroreduction of oxygen to water is reported. The smooth Pt cathode reached half and 90% of the mass transport-limited current density at respective overpotentials of −0.4 and −0.58 V in 0.5 M sulfuric acid, and only at even higher overpotentials in pH 7.2 phosphate buffer. In contrast, the smooth “wired” bilirubin oxidase cathode reached half and 90% of the mass transport-limited current density at respective overpotentials as low as −0.2 and −0.25 V. The mass transport-limited current density for the smooth “wired” enzyme cathode in PBS was twice that with smooth Pt in 0.5 M sulfuric acid. Under 1 atm O₂ pressure, O₂ was electroreduced to water on a polished carbon cathode, coated with the “wired” BOD film, in pH 7.2 saline buffer (PBS) at an overpotential of −0.31 V at a current density of 9.5 mA cm^-2. At the same overpotential, the current density of the polished platinum cathode in 0.5 M H₂SO₄ was 16-fold lower, only 0.6 mA cm^-2.