Robust bifunctional buckypapers from carbon nanotubes and polynorbornene copolymers for flexible engineering of enzymatic bioelectrodes

Enzymatic biofuel cells offer the exciting prospect of clean energy production for implantable devices, but such devices are still exotic and require improvements in electrode design and performance. Here a global strategy to prepare robust and versatile buckypaper bioelectrodes for advancing biofuel cell applications is presented. The fabrication method is based on a combination of original bifunctional polynorbornene copolymers with carbon nanotubes. Use of copolymers containing both pyrene and activated ester groups for cross-linking and tethering, respectively, increases the mechanical and electrochemical performance compared to buckypaper prepared without polymer or with the pyrene homopolymer. The amount of polymer used is an important parameter and was optimized to improve mechanical performance. High surface concentrations of reactive ester functionalities were obtained using long-chain polymers and exhibited high selectivity for attachment of aminoanthraquinone and the enzyme laccase. High performance biocathodes for direct oxygen reduction were constructed by immobilization of laccase on unmodified and anthraquinone-modified buckypapers. Anthraquinone-modified electrodes gave increased current densities due to improved electrical wiring of laccase via the hydrophobic pocket near the laccase T1 site. Biocathode stability over one month was excellent (53% current density after 24 days) and thus a new class of practical carbon-based enzymatic biofuels is envisioned.