Proton exchange membrane fuel cells (PEMFCs) are a promising technology for powering hydrogen-based vehicles. Their delivery will require the development of materials that can move protons efficiently across the membrane.
The polymer Nafion is the most commonly used membrane material in PEMFCs, but the lack of long-range order in polymers makes them poor candidates for new materials with higher conductivity and a wider temperature range for operation.
Hybrid MOF (Metal-Organic Framework) materials are emerging as a potential new class of proton conductors. Including acidic groups such as –COOH, –PO3H2 and –SO3H can facilitate efficient proton transfer pathways. However, it is very challenging to synthesise MOFs with these acidic groups.
Recent research has shown quasi-elastic neutron scattering (QENS) to be a powerful technique for gaining insights into proton conduction in crystalline MOFs. In work published in Chemical Science, a team of researchers used QENS on IRIS to investigate new barium-based MOFs. They designed and synthesised three new MOFs (MFM-510, -511 and -512) from a family of organic ligands containing multiple carboxylic acid groups. Their results showed that MFM-512 (see image below) is a promising candidate compared to other low-temperature proton-conducting MOFs.
Related publication: “Modulating proton diffusion and conductivity in metal–organic frameworks by incorporation of accessible free carboxylic acid groups" Chem. Sci., 2019,10, 1492-1499, DOI: 10.1039/C8SC03022G
Authors: Peter Rought (University of Manchester), Christopher Marsh (University of Manchester), Simona Pili (University of Manchester), Ian P. Silverwood (ISIS), Victoria García Sakai (ISIS), Ming Li (University of Nottingham), Martyn S. Brown (University of Manchester), Stephen P. Argent (University of Warwick), Inigo Vitorica-Yrezabal (University of Manchester), George Whitehead (University of Manchester), Mark R. Warren (Diamond Light Source), Sihai Yang (University of Manchester) and Martin Schröder (University of Manchester)