Fuel cells are like batteries, but the electricity is instead generated by supplying the cell with a fuel mixture, such as hydrogen and oxygen. Materials which conduct a flow of protons underpin the operation of many common types of fuel cells. Understanding and optimising proton conduction is therefore an important aspect of fuel cell development. Proton conduction in fuel cells typically involves the use of water, but a common problem in fuel cells is that they cannot tolerate getting hot – they dry out. Molten salt 'ionic liquid' electrolytes have been proposed as an alternative. In these electrolytes however, there remains much to learn about the molecular mechanisms of proton conduction which may help realise better fuel cells.

To learn more, researchers at CLF's Ultra facility and the University of Pittsburgh used a molecule called a 'photoacid' to generate protons in an electrolyte solution under a pulse of visible light. Photoacids have proven useful for determining proton conduction mechanisms in liquid water. The CLF-Pittsburgh team instead added a photoacid to an ionic liquid electrolyte solution. The journey of the light-generated protons was deciphered from changes in the infrared absorption spectrum of the photoacid and the ionic liquid. The team were able to uncover in detail the journey of the proton from the photoacid to the electrolyte and back over an unprecedented time range of femtoseconds to microseconds and are hoping to apply the technique to ionic liquids predicted to have better proton transport properties. 

This work was published in The Journal of Physical Chemistry Letters here.​