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Latest biomaterials offer fuel cell hope
06 August 2007
Carbon nanotube scaffolds that can support bacterial cells could be used as electrodes in microbial fuel cells.
Francisco del Monte and María Ferrer at the Madrid institute of materials science (ICMM*), Spain, and colleagues at the national centre for biotechnology (CNB*), also in Madrid, made multi-wall carbon nanotube scaffolds with a micro-channel structure in which bacteria can grow.
'Proteins and enzymes immobilized on carbon nanotubes (CNTs) have been used as biosensors and in methanol fuel cells. Given that CNTs are also suitable supports for cell growth, one could also use them as CNT-based electrodes in microbial fuel cells,' said del Monte.
Microbial fuel cells work on the basis that bacteria can produce either hydrogen or electrons by oxidising compounds from, for example, waste water, thus generating electricity using a cathode-anode system.
Del Monte's team tried to grow bacteria on the scaffolds by two different means
'Efficient electron transfer between the bacteria and the anode (for example, via a biofilm on the nanotubes) seems to play a major role in the performance of the fuel cell. To further enlarge the electrode surface exposed to the bacterial medium - and, hence, the energy conversion - the preparation of three-dimensional architectures through which bacteria can grow and proliferate will further improve the performance of this sort of device,' explained del Monte.
Del Monte's team tried to grow bacteria on the scaffolds by two different means: by direct soaking in a bacterial culture medium and by the immobilisation of nutrient-containing beads prior to scaffold preparation.
The former approach provided a higher bacteria population, but only in a few layers at the surface of the scaffold, while the latter colonized the whole of the nanostructure. 'Given that full colonisation is highly desirable,' del Monte maintained, 'we are currently focused on the improvement of bacterial viability during the scaffold formation process.'
'The efficient proliferation of hydrogen-producing bacteria throughout an electron-conducting scaffold like ours can form the basis for their potential application as anodes in microbial fuel cells,' added del Monte. This is the goal of a joint project formed by these and other researchers, and financed by the Spanish national research council (CSIC).
Claudio Della Volpe, a physical chemist from the University of Trento, Italy, said the strengths of del Monte's approach lie in its simplicity and the speed and efficiency of the encapsulation of the bacteria in a three-dimensional structure. 'However,' he added, 'the structure does not possess an active transfer mechanism for the processing of material and relies on diffusion, which is intrinsically slow.'
*The Madrid institute of materials science (Instituto de Ciencia de Materiales de Madrid - ICMM) and the national centre for biotechnology (Centro Nacional de Biotecnología - CNB) are institutes of the Spanish national research council (Consejo Superior de Investigaciones Cientificas - CSIC)
Link to journal article
Biocompatible MWCNT scaffolds for immobilization and proliferation of E. coli
María C. Gutiérrez, Zaira Y. García-Carvajal, María J. Hortigüela, Luis Yuste, Fernando Rojo, María L. Ferrer and Francisco del Monte, J. Mater. Chem., 2007, 17, 2992