ORIGINAL PAPER Electrochemical reduction of oxygen with iron phthalocyanine in neutral media Eileen Hao Yu Æ Shaoan Cheng Æ Bruce E. Logan Æ Keith Scott Received: 10 September 2008 / Accepted: 29 October 2008 / Published online: 12 November 2008 Ó Springer Science+Business Media B.V. 2008 Abstract Recent interest in electricity production using microbial fuel cells makes it important to better understand O 2 reduction in neutral solutions with non-precious metal catalysts. Higher O 2 reduction activity was obtained using iron phthalocyanine supported on Ketjen black carbon (FePc-KJB) than with a platinum catalyst in neutral pH. At low overpotentials, a Tafel slope close to -0.06 V/dec in both acid and neutral pH suggested that the mechanism of O 2 reduction on FePc is not changed with the change of pH, and the reaction is mainly controlled by Fe II /Fe III redox couple. This behaviour gives us new insight into catalysis using FePc, and further supports the use of FePc as a promising catalyst for the oxygen reduction applications in neutral media. Keywords Microbial fuel cells  Oxygen reduction  Iron phthalocyanine  Redox couple  EIS 1 Introduction Renewable energy production and the use of biofuels are attracting more attention due to continuously increasing demands on energy and limited energy reserves. Research on biological fuel cells, either using living microorganisms (microbial fuel cells; MFCs) or enzymes (enzymatic bio- fuel cells) has been increasing [1–6]. The common point for all the biological systems is need for near-neutral operating conditions, especially when using bacteria. In MFCs, microbes are used as biocatalysts on the anode to oxidise the organic matter and produce electrons. However, platinum is still often used as a catalyst for oxygen reduction. The use of Pt is not cost effective, and the operational conditions of neutral pH and relatively low temperatures (compared to hydrogen fuel cells) cause poor kinetics of oxygen reduction and limit MFC performance. Transition metal macrocycles have been of great interest for electrochemical reduction of oxygen since the work of Jasinski on metal phthalocyanines in the 1960s [7]. The molecular structure of metal phthalocyanine is shown in Fig. 1. Extensive studies on metal macrocycles for oxygen reduction have been carried out in either strongly acidic or alkaline solutions [8–17]. These catalysts have shown highly selective catalytic activity for oxygen reduction in the presence of methanol and CO in direct methanol fuel cells (DMFC) and hydrogen fuel cells [18–26]. The chemical stability of these catalysts in acidic conditions is low due to the demetalisation of the macrocycle rings. However, metal macrocyclic catalysts are stable in neutral and alkaline media. This suggests their application in MFCs and other biological fuel cells operating at neutral pH will be more feasible than in these other fuel cells. Oxygen reduction proceeds through parallel two- and four-electron reaction pathways, which can be expressed as: O H O H O K K 2 3 2 2 2 2 K1 K4 E. H. Yu (&)  K. Scott School of Chemical Engineering and Advanced Materials, University of Newcastle upon Tyne, Newcastle upon Tyne NE1 7RU, UK e-mail: eileen.yu@ncl.ac.uk S. Cheng  B. E. Logan Department of Civil and Environmental Engineering, The Penn State Hydrogen Energy (H 2 E) Center, Penn State University, University Park, PA 16802, USA 123 J Appl Electrochem (2009) 39:705–711 DOI 10.1007/s10800-008-9712-2