Vertically aligned carbon nanotubes coated with manganese dioxide as cathode material for microbial fuel cells Roger Amade • Maria Vila-Costa • Shahzad Hussain • Emilio O. Casamayor • Enric Bertran Received: 20 June 2014 / Accepted: 20 October 2014 Ó Springer Science+Business Media New York 2014 Abstract To date different electrode materials have been used to improve the performance and reduce the costs of microbial fuel cells (MFCs). Particularly, there is a need to avoid the use of expensive Pt-based cathode materials. Here, we explored the use of vertically aligned carbon nanotubes (CNTs) deposited by plasma-enhanced chemical vapor deposition as cathode material in single chamber MFCs. In order to improve cell performance and lower the oxygen reduction reaction resistance at the cathode side, MnO 2 catalyst was electrochemically deposited on the CNTs. Results show an increase in the output voltage and power density by two orders of magnitude when compared to plain stainless-steel electrodes, with a maximum power density of 24 mW m -2 . Furthermore, the influence of medium solution in the electrolyte was also examined. Results demonstrate that microbial communities developed as biofilm in the anode were limited by substrate metabolic liability. The presence of a labile organic source (acetate) promoted an increase of one order of magnitude in cell performance. Overall, this study shows the potential of aligned CNTs to increase yield of MFCs. Introduction Microbial fuel cells (MFCs) convert chemical energy into electrical energy by the catalytic activity of microorgan- isms [1]. MFC technology represents a novel approach of using bacteria for generation of bioelectricity by oxidation of waste organic matter and renewable biomass [2, 3]. MFCs present several operational and functional advanta- ges such as the use of waste organic matter as fuels and readily available microbes as catalysts. Furthermore, MFCs do not require highly regulated distribution systems like the ones needed for Hydrogen Fuel Cells and have high con- version efficiency as compared to Enzymatic Fuel Cells, harvesting up to 90 % of the electrons from the bacterial electron transport system. Despite the growing interest on MFCs’ development in biotechnology and the exponential increase of publications focused on the efficiency and design of existing models, current key constraints are the economic cost of electrode materials, current collectors, and membranes, among oth- ers. Next-step improvements need of interdisciplinary approaches including recent developments in the fields of material science, microbial ecology, and nanotechnology to substantially decrease the cost per electron produced [4]. Recently, it has been proved that carbon nanotubes (CNTs) used as electrode material show greater electro- chemical performance as well as higher power density in MFCs than former materials [5, 6]. The 3-D structure of the nanotubes improves both the surface area and reaction kinetics of the electrodes, in comparison with current 2-D carbon cloth electrodes. CNTs on electrodes can be found R. Amade (&) Á S. Hussain Á E. Bertran FEMAN Group, IN2UB, Departament Fı ´sica Aplicada i O ` ptica, Universitat de Barcelona, Martı ´ i Franque `s 1, E-08028 Barcelona, Catalonia, Spain e-mail: r.amade@ub.edu M. Vila-Costa Department of Ecology, University of Barcelona, Av. Diagonal 643, 08028 Barcelona, Spain M. Vila-Costa Department of Environmental Chemistry, IDAEA-CSIC, Barcelona, Catalonia, Spain E. O. Casamayor Biogeodynamics&Biodiversity Group (B&B), Centre for Advanced Studies of Blanes, CEAB-CSIC, Blanes, Spain 123 J Mater Sci DOI 10.1007/s10853-014-8677-2