C. Paoletti

Molten carbonate fuel cells fed with biogas: Combating H2S

The use of biomass and waste to produce alternative fuels, due to environmental and energy security reasons, is a high-quality solution especially when integrated with high efficiency fuel cell applications. In this article we look into the coupling of an anaerobic digestion process of organic residues to electrochemical conversion to electricity and heat through a molten carbonate fuel cell (MCFC). In particular the pathway of the exceedingly harmful compound hydrogen sulphide (H(2)S) in these phases is analysed. Hydrogen sulphide production in the biogas is strongly interrelated with methane and/or hydrogen yield, as well as with operating conditions like temperature and pH. When present in the produced biogas, this compound has multiple negative effects on the performance and durability of an MCFC. Therefore, there are important issues of integration to be solved. Three general approaches to solve the sulphur problem in the MCFC are possible. The first is to prevent the formation of hydrogen sulphide at the source: favouring conditions that inhibit its production during fermentation. Secondly, to identify the sulphur tolerance levels of the fuel cell components currently in use and develop sulphur-tolerant components that show long-term electrochemical performance and corrosion stability. The third approach is to remove the generated sulphur species to very low levels before the gas enters the fuel cell.

Characterization of Gas Diffusion Electrodes for Polymer Electrolyte Fuel Cells

Gas diffusion electrodes (GDEs), applied in polymer electrolyte fuel cells, are composed of a multilayer structure containing porous carbon materials and noble metal catalyst. Gas diffusion layer (GDL), a GDE component, consists of a thin layer of carbon black mixed with an organic binder, frequently polytetrafluoroethylene, which is coated onto a sheet of macroporous carbon backing cloth or paper. GDL serves as a current collector that allows ready access of fuel and oxidant to the anode and the cathode catalyst surfaces, respectively. In this work, a complete GDL state-of-the-art is first presented. Then, the effects of different fabrication methods and composition of gas diffusion layer are investigated and discussed in the light of gas permeability, thermal analysis, morphology, and electrical resistance. Besides, performances in H2/air fed cell at 50°C in different humidity conditions were discussed, and a comparison with own products and commercial GDLs was carried out. It was found that the different preparation methods influence the GDL properties, allowing the most suitable choice depending on the cell humidity conditions.

Performance Study of Nickel Covered by Lithium Cobaltite Cathode for Molten Carbonate Fuel Cells: A Comparison in Li/K and Li/Na Carbonate Melts

The slow dissolution of the lithiated NiO cathode represents one of the main causes of performance degradation in molten carbonate fuel cells. Two main approaches are usually investigated to overcome this problem: modifying the electrolyte composition and studying innovative cathode. In this work, the production of an alternative material as well as a study in different carbonate melt mixtures (62/38 mol % Li/K and 52/48 mol % Li/Na) of this innovative cathode have been taken into account. The issue of cathode surface protection was attained covering a nickel substrate with a thin layer of lithium cobaltite doped with magnesium (LiMg 0.05 Co 0 . 95 O 2 ); a sol impregnation technique was used to deposit gel precursors on the porous surface of the substrate. Chemical analysis, electrical conductivity measurements and scanning electron microscopy were used to characterize the cathodes before and after in-cell tests. The cathodic performance was tested in two 3 cm 2 area cells assembled with the following electrolyte compositions: Li/K=62/38 mol % and Li/Na =52/48 mol % in order to investigate the cathode behavior in different carbonate melt environments. Polarization curves and electrochemical impedance spectroscopy measurements were carried out during cell lifetime (about 850 h). Finally, different compositions of the cathodic gas were used to study the influence of oxygen and carbon dioxide on the electrode kinetics.

PEFC electrodes based on carbon black supporting electrocrystallised nanostructured Pt particles

This work is focused on the study of electro-crystallisation of Pt nanostructured particles used as catalyst on carbon black support for polymer electrolyte fuel cells electrodes. Electrochemical single and multiple pulse galvanostatic depositions have been applied defining the best operational parameters leading to a highly nanostructured electro-catalysts morphology. Electrochemical measurements such as cyclic voltammetries have been carried out in order to determine the electrochemical active surface together with morphological analysis by means of scanning electron microscopy. The influence of electro-deposition parameters on the Pt loading have been studied and optimised. The investigated materials have been then characterised by means of polarisation curves. The electrodeposited catalyst cathodes present performances and maximum specific power density values similar or better than those of standard E-TEK electrode, prepared by conventional powder-type technique. These results strongly encourage the implementation of cathodes obtained by electro-deposition in a real-world device.