Electrochimica Acta 80 (2012) 399–404 Contents lists available at SciVerse ScienceDirect Electrochimica Acta jou rn al hom epa ge: www.elsevier.com/locate/electacta Buckypaper as Pt-free cathode electrode in photoactivated fuel cells S. Sfaelou a , M. Antoniadou a , G. Trakakis b , V. Dracopoulos b , D. Tasis b , J. Parthenios b , C. Galiotis b,c , K. Papagelis b,c , P. Lianos a,b,∗ a Engineering Science Department, University of Patras, 26500 Patras, Greece b Foundation of Research and Technology Hellas, Institute of Chemical Engineering Sciences (FORTH/ICE-HT), P.O. Box 1414, GR-26504 Rio-Patras, Greece c Department of Materials Science, University of Patras, 26500 Patras, Greece a r t i c l e i n f o Article history: Received 3 July 2012 Received in revised form 12 July 2012 Accepted 13 July 2012 Available online 20 July 2012 Keywords: Photoactivated fuel cells Buckypaper NiO Pt-free cathode electrodes a b s t r a c t The possibility to substitute a standard Pt/carbon-black/carbon-cloth oxygen-reducing cathode by buck- ypaper has been studied in a photoactivated fuel cell. It was found that a buckypaper bearing NiO can very well compete with a standard cathode, thus offering a Pt-free alternative. The buckypaper was made through a process of epoxidation of multiwall carbon nanotubes while NiO was casted through a simple procedure employing surfactant templates. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction Photoactivated fuel cells (Photo-Fuel-Cells, PFCs) are devices, which can produce electricity by photocatalytic oxidation of organic fuels [1,2]. These cells comprise a photoanode electrode bearing a photocatalyst, typically, nanocrystalline titania, a cath- ode electrode bearing an oxygen reducing electrocatalyst and an electrolyte. Most efficient cells are divided into two compartments separated by an ion transfer membrane [2–5]. The fuel is introduced in the anode compartment. PFCs resemble alkaline fuel cells. Their major difference from the latter is that, instead of an electrocatalyst on the anode electrode, they utilize a photocatalyst that is activated by absorption of light. Since photocatalysts are not specific towards photodegradable fuels, PFCs may run with aqueous organic wastes as fuel [1,2,6] thus providing the double environmental benefit of producing renewable energy with water cleaning. We have been recently studying various aspects of PFCs focusing at the optimization of device functionality as well as the investiga- tion of new materials that may reduce device cost [2,7–11]. The major cost in the construction of a PFC is due to Pt utilized as elec- trocatalyst on the cathode electrode. It is then beneficial to examine alternative cost-effective materials. The reductive capacity of the cathode electrode is an issue that concerns not only PFCs but it ∗ Corresponding author at: Engineering Science Department, University of Patras, 26500 Patras, Greece. E-mail address: lianos@upatras.gr (P. Lianos). is equally important for other similar types of cells, namely, fuel cells, microbial fuel cells, etc. A typical cathode electrode, which may serve as gas diffusing electrode (GDE) in membrane–electrode assemblies (MEA) is a carbon cloth bearing a hydrophobic paste enriched with amorphous carbon (for example, carbon black) and Pt nanoparticles. In most cases, Pt loadings are rather high rang- ing from 0.1 to 1 mg cm -2 [12] thus precluding massive application due to the scarcity of this precious metal. In addition, loss of activity due to Pt aggregation as well as Pt passivation in aggressive envi- ronments makes the search for alternative electrocatalysts a very important issue. In the present paper, we propose the employment of buckypaper, i.e. a nanostructured porous sheet based on entan- gled ropes and bundles of multiwall carbon nanotubes (MWCNTs) [13–15], plain or enriched with NiO, as possible substitutes of stan- dard Pt on amorphous carbon electrodes. The cells we have employed to test the applicability of alterna- tive cathodes carry a photoanode bearing nanocrystalline titania (nc-TiO 2 ), photosensitized in the visible spectrum by ZnS–CdS quantum dots (QDs). Such combinations were previously shown to be effective in PFCs running with alkaline electrolyte and with ethanol as fuel [8]. Pure ethanol is, of course, not a waste but the PFC may well work with products of biomass, of which aqueous ethanol is a representative model appropriate for research purposes. The ZnS–CdS QDs comprised 75% Cd and 25% Zn, could absorb visible light up to about 500 nm and were more effective in PFC function than neat CdS. In the present work we used a PFC with the following configuration and geometry, also depicted in Fig. 1. The photoanode consisted of a transparent fluorine-doped tin oxide electrode (FTO) 0013-4686/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.electacta.2012.07.046