Electrochemical properties of hydrogenase on glass carbon electrodes modified with carbon nanotubes

Hydrogenase (H₂ ase) purified from phototropic bacteriumThiocapsa roseopersicina was coassembled with carbon nanotubes (CNTs) on glass carbon electrodes. Both oxidized CNTs and Nafion-CNT composites were used to modify the electrodes. The pure H₂ are formed dot-like domains, while the oxidized CNT-H₂ ase and Nafion-CNT-H₂ ase composites formed wire-like and large closely packed aggregates, respectively. The reductive potentials for the 4Fe-4S]^2+/1+ clusters of H₂ase were at about −500, −650, and −700 mV (vs Ag/AgCl) for the electrodes modified with pure H₂ase, Nafion-SWNT-H₂ase, and Nafion-MWNT-H₂ase composites, respectively. Potential step chronocoulometry measurements indicated a larger charge-transfer diffusion coefficient between the H₂ase and electrodes when the CNTs were co-assembled with H₂ase, suggesting that the CNTs can not only act as a supporting layer to immobilize enzymes, but also act as a highly conductive wire throughout the films.