Fuel Cells. PEMFCs

 

The research activities of GREENMat point toward toward new-generation PEMFCs, based on polybenzimidazole membranes working at low H3PO4 doping level, under low RH conditions at or above 120°C for both stationary and transport applications. The development of membranes based on H3PO4-doped polybenzimidazole (PBI) has several benefits. However, they still suffer of some instability problems, such as leaching of the doping acid causing drops in conductivity, membrane degradation and stack durability.

In the recent years, GREENMat has gained a wide experience in the synthesis of PBIs and in the preparation of membranes for HT-PEMFCs. Particular interest has been devoted to the optimization of these systems, in order to offer a practical alternative to Nafion in cells operating at temperatures higher than 120°C and low relative humidity. A deep interest has been therefore focused on overcoming the abovementioned technological limits. Our actual challenge is the achievement of a proper compromise between H3PO4 doping level and membrane stability. The strategy that we are following is the proper monomer designs, which can lead to more performing cells, in terms of long-term durability, acid leaching and electrodes safety.

To this aim, we proceeded through three main approaches: i) structural modulation of the monomer unit exploiting the rich chemistry of the benzimidazole group, by means of the addition of Nitrogen-based units (so as to increase the basicity of the system and consequently the acid retention capacity), or of aryloxy- and fluoroaryloxy-bridges (so as to improve the oxidative as well as mechanical stability of the system), ii) proper sulfonation of PBIs to enhance the proton transport at low doping levels; iii) use of inorganic fillers, nanometric and/or mesoporous, possibly functionalized in a proper manner.

 

Fuel Cells. SOFCs

 

In the SOFCs field, we mainly work on the development and optimization of novel ionic conductors. We focus on the investigation of structure-properties relations, with particular attention to the role of point defects in tailoring material properties.

We have been studying both electrolyte and electrode materials for SOFC applications, often combining computational and experimental work. Indeed, in this field we range from structural studies based on powder diffraction (X-ray and neutron) to investigate, for example, phase transitions or oxygen content variations as a function of temperature, to thin film depositions of functional layers and chemical compatibility studies between potential electrodes and electrolyte materials. Atomistic modelling of defects, dopants and transport is aimed at elucidating the mechanistic features of ionic conduction and its relations to structural parameters.  In this regard, we are interested in investigating the effects of lattice strain as an effective way to modulate functional properties in ionic conductors.    

Oxide ion conducting materials recently investigated include melilite-type electrolytes and K2NiF4-type cathodes.  

We are currently involved in the “FIRB2012-Futuro in ricerca” project INCYPIT devoted to materials and devices based on proton conducting electrolytes for intermediate temperature SOFCs.