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Abstract:

Fuel cells, also known as flow batteries, hold great promise for generation of electricity in previously unimaginable ways, but rely upon platinum catalysts to do so.  Biological fuel cells (BFCs) use organic catalysts and fuels and are able to derive electricity from nearly any biological process.  Power density and longevity limitations of BFCs have prevented their widespread adoption.  A novel BFC design incorporating bioregenerative microorganism(s) is currently undergoing testing.  Applications include a suite of self-powered implantable medical devices, wastewater treatment plants, and biosensors as well as low-cost remote power generation from waste materials.  

Intro:

Fuel cells are much like traditional batteries in that the energy in chemical bonds is liberated to produce electricity, but differ significantly in that they are open flow systems, facilitating extended run times on the order of decades.  Traditional fuel cells use precious metals, most commonly platinum, to catalyze reduction and oxidation (REDOX) reactions at the electron generating anode and the electron receiving cathode.  Traditional fuel cells are very promising for their abilities to convert previously unusable feedstocks into electricity at high efficiencies in remote and biological applications, but suffer from two major draw backs intrinsic to their basic design: the first is a high cost due to the precious metal catalysts, and the second is the reliance on pure fuels, which can be impossible to obtain in the envisioned applications. 

To address these issues, researchers have turned to biological fuel cells (BFCs) which utilize biological components to catalyze the REDOX reactions; BFCs are significantly more cost effective and can utilize a wider array of impure feed stocks including waste water and solid agricultural wastes. Biofuel cells have been limited by the selection of cathode catalysts, and their low power output; recently however, Sane et al. have reported that crude laccase from Trametes versicolor can be used to construct a BFC cathode with a higher open circuit potential (OCP), and longer run time than comparable platinum cathodes. 

The present research focuses on creating a practical laccase-based cathode that can outperform a platinum-based cathode in both OCP and longevity.  Two strategies were adopted to this end: producing the laccase in different fermentation styles and incorporating a laccase producing organism into a BFC cathode chamber.  These designs serve respectively as a practical cathode design for the four electron reduction of oxygen to water, as well as a model for a new class of

Results:

Methods:

20X100mm carbon rods were purchased from hBarScientific, yeast extract was purchased from Difco, laccase (13.6U/mg) was purchased from MyBioSource.com (L3030862).  Polyvinylidene fluoride (PVDF), ABTS, catalase, succinic acid, and glucose were purchased from Sigma Aldrich.  Carbon nanotubes (CNTs) were obtained from MER corporation.

Electrodes were prepared by dip-coating acetone cleaned carbon rods into a mixture of 10% PVDF in acetone with a CNT loading of 2mg/mL and allowing them to dry at 4C overnight. 

Laccase was produced by growing fungi directly in GYE media (LSF) or on substrate soaked in GYE media (SSF), for 10 days.  A crude enzyme supernatant was prepared by filtering the growth medium through a sterile 0.45um cellulose filter.  Pre-prepared electrodes were then immersed in filtrate for 12 hours to adsorb laccase to the CNTs to facilitate direct electron transfer (DET).  

Discussion:

Three dimensional electrodes utilizing biocompatible TiO2-based binders are currently being optimized to prevent mycelial interference at the cathode surface and facilitate the implementation of the new cathode into existing fuel cells and biomedical devices including: waste water treatment facilities, stand-alone fuel cell generators, implantable glucose sensors, and lab-on-a-chip diagnostic arrays.  Future work will include vertical integration of electricity production with waste treatment, and production of food and building materials.  

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