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Advanced neutron technologies galvanise research into advanced polymer electrolyte membranes

Schematic, cross-sectional view of a PEM fuel cell. Hydrogen fuel is channelled to the anode, while oxygen from air is channelled to the cathode. At the anode, hydrogen is split into protons (H+) and electrons (e-). The PEM allows the protons to cross to the cathode, while the electrons travel via an external circuit, generating current. At the cathode, the electrons and protons combine with oxygen to form water, which is removed from the cell. Image copyright S Chapman.

In a joint publication, scientists from University College London, CEA/University Grenoble Alpes, ISIS Neutron and Muon Source, Institut Laue-Langevin (ILL) and Laboratoire Léon Brillouin (LLB), explain how innovations in neutron scattering are enabling researchers to create and test new Polymer Electrolyte Membrane (PEM) formulations for clean-energy applications.

With climate change and pollution placing increasing strain on the environment, scientists are working to develop sustainable energy solutions that reduce our dependency on fossil fuels. Among the most prominent clean-energy technologies are batteries, fuel cells and electrolysers, which exploit chemical processes to store and release electrical energy. These devices have several components in common, one of which is the Polymer Electrolyte Membrane (PEM) – a semi-permeable material that acts as both an electrolyte (selectively conducting charged particles) and a separator (preventing undesirable side-reactions and short circuits).

As key constituent of many clean-energy devices, PEMs are the focus of research to address critical issues around durability, performance and production cost. In an article for the Journal of Physics: Condensed Matter, Foglia et al. explain how neutron techniques (such as neutron reflectivity, QENS,[1] SANS[2] and WANS[3]) are providing insights into the complex structures and ion-transport mechanisms within PEMs, enabling scientists to design new and improved formulations.

The neutron is a powerful probe to study the structure and dynamics of PEMs over a range of length- and time-scales. As well as being non-destructive, neutrons can penetrate metallic and ceramic containers so that PEMs can be studied in their operating environment. Neutrons are also particularly sensitive to hydrogen (an element that is integral to the function of PEMs), with isotopic contrast experiments providing scope to deconvolute complex processes occurring within the membrane.

The properties of the neutron have been widely exploited in PEM research, for example in the optimisation of water distribution in fuel cells. Water is crucial to the performance of fuel cells, but its distribution must be carefully controlled. If water content is too low, ion exchange within the PEM is curtailed, yet excess water can cause the membrane to swell, undermining performance and stability. Neutron scattering techniques are enabling scientists to study the hydration-dependent structure and dynamics within PEMs, and to monitor changes under operational conditions. Such information is invaluable in the design of advanced functional membranes with enhanced conductivity and lifetime.

Whilst the intrinsic complexity of functional membranes poses a challenge for predicting and optimising PEMs, with new instrumentation, brighter neutron sources, and innovative experiments (including complementary and simultaneous studies), neutron scattering is emerging as a powerful research tool for the development of clean-energy devices.

Read the paper: Foglia, F., Lyonnard, S., Sakai, V.G., Berrod, Q., Zanotti, J.M., Gebel, G., Clancy, A.J. and McMillan, P.F., 2021. Progress in neutron techniques: towards improved polymer electrolyte membranes for energy devices. Journal of Physics: Condensed Matter33(26), p.264005.

Find out more about how neutron methods are being used in fuel cell research...

[1] Quasi-elastic neutron scattering

[2] Small-angle neutron scattering

[3] Wide-angle neutron scattering