Wu, Y.; Meyer, Q.; Liu, F.; Rasha, L.; Cho, J.I.S.; Neville, T.P.; Millichamp, J.; Ziesche, R.; Kardjilov, N.; Boillat, P.; Markötter, H.; Manke, I.; Cochet, M.; Shearing, P.; Brett, D.J.L.: Investigation of water generation and accumulation in polymer electrolyte fuel cells using hydro-electrochemical impedance Imaging. Journal of Power Sources 414 (2019), p. 272-277

In-depth understanding of water management is essential for the optimization of the performance and durability of polymer electrolyte fuel cells (PEFCs). Neutron imaging of liquid water has proven to be a powerful diagnostic technique, but it cannot distinguish between ‘legacy’ water that has accumulated in the system over time and ‘nascent’ water recently generated by reaction. Here, a novel technique is introduced to investigate the spatially resolved water exchange characteristics inside PEFCs. Hydro-electrochemical impedance imaging (HECII) involves making a small AC-sinusoidal perturbation to a cell and measuring the consequential water generated, using neutron radiographs, associated with the stimulus frequency. Subsequently, a least-squares estimation (LSE) analysis is applied to derive the spatial amplitude ratio and phase shift. This technique provides a complementary view to conventional neutron imaging and provides information on the source and ‘history’ of water in the system. By selecting a suitable perturbation frequency, HECII can be used to achieve an alternative image ‘contrast’ and identify different features involved in the water dynamics of operational fuel cells.