Gas-Diffusion Cathodes Integrating Carbon Nanotube Modified-Toray Paper and Bilirubin Oxidase.

This research introduces the design of a gas-diffusional cathode employing bilirubin oxidase (BOx) immobilized on a complex matrix composed of carbon nanotube (CNT) modified Toray paper (TP) and, encapsulated in silica-gel. The developed enzymatic cathode consists of two layers. One is the hydrophobic gas-diffusional layer (GDL) and the other a hydrophilic catalytic layer (CL) which were combined by pressing at 1000 psi for five minutes. The GDL (35% weight teflonized Vulcan carbon powder (XC35)) that is exposed to air has hydrophobic and porous properties that facilitate oxygen diffusion. The CL consists of a thin, high surface area, 3D CNT/silica-gel matrix where the 3D-enzymatic structure is immobilized and preserved. The nanostructured architecture of the CL was designed to improve conductivity and surface area. Such a design was achieved by modifying the TP surface with CNTs. CNTs are grown on TP by chemical vapor deposition which is possible by electrodepositing Ni seeds via pulse chronoamperometry. Entrapment of BOx was achieved by using tetramethyl orthosilicate (TMOS), a highly volatile compound that results in a polymeric condensation reaction with H₂O at room temperature. TMOS polymerization of the cathode surface was performed in a chemical vapor deposition process to form a silica-gel matrix. The gas diffusional cathode was assembled to a capillary driven microfluidic system to be electrochemically characterized. The characterization was performed from electrolyte pH 5 to pH 8 with increments 0.5 in pH. The best performance was observed at pH 5.5 showing a current output of 655.07 ± 146.18 µA.cm^-2 and 345.36 ± 30.04 µA.cm^-2 at 0 V and 0.3 V, respectively. At a pH of 7.5 the current generated was 287.05 ± 20.37 µA.cm^-2 and 205.37 ± 1.57 µA.cm^-2 at 0 V and 0.3 V, respectively. The results show the stability of the enzymatic structure, subject to various pH, is maintained within the 3D-CNT silica-gel matrix for pH lower than 8. Future work will focus on storage life and stability over time. [ABSTRACT FROM AUTHOR]