A laccase-wiring redox hydrogel for efficient catalysis of O2 electroreduction

Laccase was earlier wired to yield an O2 electroreduction catalyst greatly outperforming platinum and its alloys. Here we describe the design, synthesis optimization of the composition, and characterization of the +0.55 V (AgAgCl) laccase-wiring redox hydrogel, with an apparent electron diffusion coefficient (D(app)) of 7.6 x 10(-7) cm2 s(-1). The high D(app) results in the tethering of redox centers to the polymer backbone through eight-atom-long spacer arms, which facilitate collisional electron transfer between proximal redox centers. The O2 flux-limited, true-area-based current density was increased from the earlier reported 560 to 860 microA cm(-2). When the O2 diffusion to the 7-microm-diameter carbon fiber cathode was cylindrical, half of the O2 flux-limited current was reached already at 0.62 V and 90% at 0.56 V vs Ag/AgCl, merely -0.08 and -0.14 V versus the 0.7 V (Ag/AgCl) reversible O2/H2O half-cell potential at pH 5.