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Compact direct (m)ethanol fuel cell for portable application (MOREPOWER)

Exploitable results

Anode: The use of methanol as a fuel requires the development of more effective catalytic materials for electro-oxidation for the anode. When ethanol is considered as a fuel the catalyst development is even more challenging due to the electrochemical dissociation of the carbon-carbon (C-C) bond at low temperatures. Johnson Matthey (JM) has compared non-supported and carbon-supported platinum-ruthenium (Pt-Ru) anode catalysts. In general, carbon supported catalysts were shown to offer higher methanol (MeOH) oxidation activity due to higher active metal area, although they suffered extra mass transport losses at higher currents due to thicker anode catalyst layers. In particular a 75% Pt-Ru/C2 catalyst was shown to give higher MeOH oxidation activity than the baseline 60% Pt-Ru/XC72R catalyst. Initial work on ethanol (EtOH) oxidation catalysts has shown that platinum-tin (Pt-Sn) formulations show better activity than Pt-Ru catalysts and is expected to be suitable to meet the final project activity target. At Istituto di Tecnologie Avanzate per l'Energia del Consiglio Nazionale delle Ricerche (CNR-ITAE) a colloidal preparation procedure has been developed for the preparation of the anode and cathode catalysts. In the latter case, the colloidal procedure was followed by an impregnation step. For the anode, 85% Pt-Ru (1:1)/C bifunctional catalysts were prepared and optimised in terms of morphological and physical-chemical properties. Cathode: Here the requirements are catalysts with alcohol tolerance higher than the platinum black materials currently used and enhanced oxygen reduction activity. At CNR-ITAE for the oxygen reduction process, 60% Pt- 5% Fe/C, 60% Pt- 5% Cu/C and 60% Pt- 5% Co/C catalysts were produced within the project with optimised morphological properties to mitigate the effects of methanol cross-over (mixed potential at the cathode). At 0.5 V a current density of 80 mAcm{-2} was reached with the platinum-iron (Pt-Fe) catalyst at the cathode in the presence of Nafion membrane under atmospheric pressure. In these conditions a maximum power density of 75 mWcm{-2} was achieved.
New low cost proton exchange membranes based on a proprietary radiochemical graft polymerisation developed by Solvay were under investigation. Membranes with high density of proton exchange sites near the surface (improved membrane-electrode contact) and a highly cross-linked core structure (cross-over reduction) were under evaluation. Further inorganic modification of membranes (Solvay grafting membranes and membranes based on sulfonated polyether ether ketone (SPEEK)) were performed by GKSS Forschungszentrum Geesthacht to reduce the permeability to alcohols while keeping high proton conductivity. Membrane electrode assemblies were manufactured and were under evaluation in micropilot scale for Direct methanol fuel cells (DMFCs) by Johnson Matthey (JM) and Istituto di Tecnologie Avanzate per l'Energia del Consiglio Nazionale delle Ricerche (CNR-ITAE). The first evaluations of the developed membranes at CNR-ITAE, using catalysts provided by JM, confirmed that a maximum power density of 85 mW cm{-2} could be obtained in the presence of a highly cross-linked membrane at 60° C provided by Solvay with 1 M methanol and air feed under atmospheric pressure and 100 mWcm{-2} with 2 Bar cathode pressure. Similar results were obtained with a modified SPEEK membrane produced by GKSS Forschungszentrum Geesthacht. These performances are comparable to the project target i.e. 100 mWcm{-2}. Yet, due to the more favorable scaling-up properties of Solvay membrane, this latter was selected for the realization of the large area MEAs for the prototype. A 25 cells DMFC stack was demonstrated by Nedstack using these MEAs with an average cell performance of 70 mW cm{-2}.The performance in the presence of ethanol feed at the anode was about 50 mWcm{-2} with 2 Bar air pressure at 80° C. The current status of the results regards the development of manufacturing processes at larger scale, and the validation of the components in laboratory scale prototypes.
A challenging issue is the optimisation of the cell design to provide the efficient transport of the reactants in very compact device. Politecnico di Torino (POLITO) and Centro Ricerche Fiat (CRF) were supplying system and detailed components modelling. Computational fluid dynamics (CFD) modelling of the flow fields allowed the Institut für Mikrotechnik Mainz GmbH (IMM) to make a selection of an adequate flow field, using micro channel plates. Channels were being manufactures via laser machining and milling. Interdigitated and serpentine designs were under consideration. IMM has designed, built and tested the devices making-up the liquid management system including the cold start heater, the humidity-heat exchanger, the gas-liquid separator, the radiator and the catalytic afterburner. An electrochemical amperometric sensor for alcohols was developed by CRF. The device is based on the electro-oxidation of methanol (ethanol) to carbon dioxide on platinum catalyst into a polymeric-membrane fuel cell operated as a galvanic cell.