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

Laccase was earlier wired to yield an O-2 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 7.6x10(-7) cm(2) 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 O-2 flux-limited, true-area-based current density was increased from the earlier reported 560 to 860 mu A cm(-2). When the O-2 diffusion to the 7-mu m-diameter carbon fiber cathode was cylindrical, half of the O-2 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 O-2/H2O half-cell potential at pH 5.