Solid-state proton conductors operating at low temperature are particularly desirable for mobile instruments in the field of electrochemical devices including fuel cells, redox flow batteries, water electrolyzers or sensors. In this context, a variety of solid electrolytes have been explored, such as Nafion based polymers or more recently hybrid Metal-Organic Frameworks. Resulting from this systematic study, the key features that control the proton conduction are nowadays relatively well identified. This requires the presence of acidic protons within an appropriate topology of the solid that facilitates charge transport intrinsically through the material framework itself, and/or through some carrier-mediated pathway, such as water loaded into the pores. However, understanding the molecular mechanism and pathway of proton conduction and the sequential structure-property relationship is still needed for the design of new materials with improved performances. In this context, we screened the proton conducting performances of a range of porous Metal Organic Frameworks (MOFs) showing distinct features including (i) linkers grafted with acidic functions (-COOH) or hydrophobic (-CF3) groups (ii) water coordinated to metal centers and (iii) structural defects. For comparison, the three-dimensional open framework titanium phosphate [Ti(HPO4)2] was equally investigated. This work has been achieved using a subtle combination of Complex Impedance Spectroscopy, Quasi-Elastic Neutron Scattering, forcefield and quantum-based molecular simulations (Monte Carlo and Molecular Dynamics). This joint experimental-modelling approach was successfully employed to determine the proton conduction performances of this series of porous solids and to follow the mobility of both the water carriers and the proton excess for providing an unambiguous microscopic picture of the mechanism at the origin of the properties of these hybrid solids

Exploration of inorganic and hybrid porous materials as proton conductors

253rd National Meeting (2017)

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