For the first time, scientists have mapped the movement of electrical charge through a material known as a metal organic framework or ‘MOF’, designed to host charge in future vehicle fuel cells which offer a greener alternative to traditional combustion engines. By using a combination of X-ray and neutron techniques, scientists now have a better understanding of the flow of charge in the material, and can begin to design more efficient fuel cells in pursuit of cleaner energy.
Fuel cells convert the chemical energy of a fuel into electricity by means of a chemical reaction, and there are a variety of fuel cells available, with polymer electrolyte membrane fuel cells currently used most widely. However, the performance of a fuel cell depends on the electrolyte, the porous material at the centre of the cell which controls the flow of charge – to boost its efficiency, scientists are developing smart membranes with new materials which produce more charge.
A team from The University of Manchester linked up with others, including the University of Nottingham, have mapped the atomic structure and workings of the metal organic framework using intense X-rays at the UK’s Diamond Light Source ‘super-microscope’. They then used neutrons to map the flow of charge, known as proton conduction, in the material for the first time. The results, published in the Journal of the American Chemical Society, found that the protons move freely within a sphere, rather than the more common ‘jump diffusion between sites’ mechanism. This new knowledge will enable the design of improved proton conducting materials by optimising the pathway that the protons take.
The success of this work will not only create new knowledge on metal organic frameworks, but also enable the building of next generation fuel cells that operate at a wider temperature range and with higher efficiency. This will help to turn this technology into a reality.
Drs Sihai Yang and Martin Schröder, group leaders
Dr Claire Murray from Diamond Light Source said: “This represents really beautiful chemistry in a new and exciting area of research. Up until now, metal organic frameworks have been mainly used for gas absorption, but scientists hope to be able to exploit proton conductivity for the production of green energy fuel cells that can operate at high temperatures and in dry conditions. Because the X-rays we generate are so intense, researchers can reveal the structure of materials in very fine detail, enabling the detection of tiny changes that could impact on their performance.”
Now the team have cracked the mechanism behind proton conductivity in the material, they have returned to the laboratory to use this information to design and study new materials with increased conductivity.