Performance of non-compartmentalized enzymatic biofuel cell based on buckypaper cathode and ferrocene-containing redox polymer anode Christine Bunte a, 1 , Laith Hussein b, c, * , 1 , 2 , Gerald A. Urban b, c a Department of Microsystems Engineering (IMTEK), Laboratory for Chemistry and Physics of Interfaces, University of Freiburg, Freiburg, Germany b Freiburg Materials Research Centre (FMF), University of Freiburg, Freiburg, Germany c Department of Microsystems Engineering (IMTEK), Laboratory for Sensors, University of Freiburg, Freiburg, Germany highlights  Enzymatic single compartment glucose/O 2 fuel cells were developed.  Buckypaper-based cathode and ferrocene-containing redox polymer-based anode were employed.  The resulting biofuel cell generates an open circuit voltage of approximately 0.550 V.  The peak power density in quiescent buffer containing 5 mM glucose approaches 26 mW cm 2 . article info Article history: Received 15 May 2013 Received in revised form 26 July 2013 Accepted 20 August 2013 Available online 11 September 2013 Keywords: Biofuel cell Glucose Buckypaper Redox polymer Mediated electron transfer Implantable power abstract Novel single compartment Glucose/O 2 biofuel cells (BFCs) were developed using immobilized enzymes and the mediated electron transfer (MET) approach. The bioanode was prepared through a ferrocene- containing redox polymer crosslinked in the presence of a biocatalyst on a glassy carbon support. Here, the redox polymer can physically entrap the enzyme and prevent it from leaching. Additionally it provides a biocompatible microenvironment and thus could extend the life time of enzyme. On the other side, the mediated biocathode was prepared based on bilirubin oxidase and 2,2 0 -azinobis(3- ethylbenzothiazoline-6-sulfonate) diammonium salt (ABTS 2 ) system which has been physically entrapped in Nafion matrix and then adsorbed directly on a highly porous, conductive and functionalized buckypaper (fBP). Both electrodes were characterized physically and electrochemically. Employing these electrodes, the resulting BFC generates an open circuit voltage (V oc ) of approximately 0.550 V and a peak power density of 26 mW cm 2 at 0.2 V at 37  C in quiescent O 2 -saturated physiological buffer containing 5 mM glucose. The cell sustains a load up to 225 mA cm 2 . Moreover, a high short circuit current (I sc ) of 300 mA cm 2 is approached. This BFC can operate in mild conditions without using any toxic materials which makes it attractive for implantable devices. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Many efforts have been devoted recently to enzymatic biofuel cells (BFCs) which convert available chemical free energy of bio- fuels (e.g. glucose or organic acids) directly into electrical energy. This process is coupled with the reduction of molecular oxygen by means of inexpensive enzymatic catalysts for at least one of these two reactions. It has been shown that certain enzymes possess highly favorable catalytic properties in comparison to inorganic catalysts. For example, Heller et al. have proposed that the multi- copper oxidases, e.g. laccase and bilirubin oxidase (BOD), are more efficient electrocatalysts than Pt for the four-electron oxygen * Corresponding author. Department of Microsystems Engineering (IMTEK), Laboratory for Sensors, University of Freiburg, Freiburg, Germany. Fax: þ49 7612 037262. E-mail addresses: laith.hussein@fmf.uni-freiburg.de, hussein@ac.chemie.tu- darmstadt.de (L. Hussein). 1 Both authors made equal contribution to this work and thus the order of au- thors is ranked alphabetically. 2 Current address: Eduard-Zintl-Institute of Inorganic and Physical Chemistry, Darmstadt University of Technology, Darmstadt, Germany. Fax: þ49 (0) 6151/163470. Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour 0378-7753/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jpowsour.2013.08.077 Journal of Power Sources 247 (2014) 579e586