Development of Bio-Functional Molecule-Modified Nano-Carbon Electrode for Fast Catalytic Oxygen Reduction with Highly Electrode Potential

Abstract

Fast oxygen (O₂) reduction at high positive potential is essential to obtain effective green energy conversion systems. Here, in an attempt to develop a desirable O₂ reduction biocathode for fuel cells using laccase (Lac), we modify the surface of single-walled carbon nanotubes (SWCNTs) with various biosurfactants (SC: sodium cholate, SD: sodium deoxycholate, CHAPS: 3-[(3-cholamidopropyl)dimethylammonio]propanesulfonate, BIGCHAP: N,N-bis(3-D-gluconamidopropyl)cholamide) to obtain fast direct electron transfer from the SWCNTs to Lac, resulting in O₂ reduction starting from a potential close to the redox equilibrium potential of the oxygen/water couple. Heterogeneous direct electron transfer reaction was reached to 3000 s^–1 of the T1 Cu site of Lac with a SC-SWCNT interface, and that the electron transfer rate is very sensitive to the side-chain structure of the steroid-type biosurfactant. The k^o of Lac adsorbed on SC-SWCNTs is more than 10 times larger than that on SD-SWCNTs. The investigation using CHAPS- and BIGCHAP-SWCNT electrodes also indicated that the side chain has an important role in directing Lac molecular orientation, which influences direct electron transfer of Lac with SWCNTs.