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

Abstract

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 H 2 O 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. Interest in biofuel cells has increased in the past decade in pursue of self energetically-sustained biomedical devices and also small, portable electrical devices capable of work by harvesting energy from natural fuel sources. Such interests exist due to the low temperature and neutral pH operating range of biofuel cells.1-3 Depending on the mechanism of the enzyme, either direct or mediated electron transfer (DET and MET, respectively) reflects the electron transfer distance between enzyme active site and electrode interface. One must couple mediators/cofactors for the latter in order to have electrons transferred to the electrode and further to an external circuit therefore subjecting electrons to a diffusion distance.2,4-13 On the other hand DET works under an electron tunneling distance. Further design considerations are centered on the three main regions of inherent energetic losses in fuel cells known as kinetic, ohmic and mass transfer limits. Although there are many different ways to design an enzymat...

O2Reduction in Enzymatic Biofuel Cells

“…Design of experiments have been used to optimize such interface. 714 DET and MET based air-breathing electrodes have been reported with BODs, 368,466,712,715 laccases 708,709,716 and CueO. 706 For example, Atanassov et al reported a DET-based laccase-modified gas-diffusion electrode with a current density 0.5 mA.cm -2 .…”

“…However, designing a gas-diffusion cathode is not trivial. The gas-diffusion cathode usually consists of two layers: a gas-diffusion layer made of hydrophobized carbon black , or Ketjen black, ,, which has to be permeable to gas; a hydrophilic catalytic layer made with carbon black, carbon cloth, CNTs, − or carbon felt and containing the MCO. These first two layers may also be added on top of a third layer providing for mechanical stability.…”

“…Design of experiments has been used to optimize such an interface . DET and MET based air-breathing electrodes have been reported with BODs, ,,, laccases, ,, and CueO . For example, Atanassov et al.…”

Graphene oxide as a protein matrix: influence on protein biophysical properties

“…1 ). BOD is a multi-copper oxidase that has been used in several biotechnological applications, such as, biosensors [ 29 , 30 ], biofuel cells [ 31 – 33 ], and other environmental and industrial applications [ 34 , 35 ]. Due to the wide range of biotechnological applications, BOD was selected as our model enzyme.…”

Spectroelectrochemical studies of structural changes during reduction of oxygen catalyzed by laccase adsorbed on modified carbon nanotubes

“…Cerrena unicolor laccase molecules adsorbed on carbon electrodes catalyze oxygen reduction at potential very close to formal potential of T1 site, 750 mV vs. NHE [23]. The structure of a surface has a great impact as well [23,24]. The catalytic current on highly ordered pyrolytic graphite (HOPG) has a low value, which is probably caused by relatively flat surface favouring low surface concentration [25].…”