Operando mu-Raman Measurement of Water Distribution Along and Across the Membrane in a Fuel Cell

To obtain a fundamental understanding of the transport regimes governing the electrochemical behavior of the polymer electrolyte membrane fuel cell, the measurement of the membrane water content, along both directions parallel and perpendicular to the surface, is essential. In this paper, operando mu-Raman spectroscopy is used to probe the water content of the Nafion (R) membrane in the fuel cell (OCV around 1 V) working at constant stoichiometry and low relative humidity (20%). Water concentration profiles crossing the membrane thickness are obtained with pm resolution at different locations of the active surface: at the middle and close to the inlets/outlets of the reactants, at the feed gas channel and under-lands areas. The influence of the operating temperature and of the current density delivered by the cell are investigated. Of particular interest for perspective fuel cells, the membrane inner water partition appears highly heterogeneous when operating at ambient conditions, and dependent on the delivered current. The increase of temperature decreases the membrane water content at all the probed positions and induces a less uneven water distribution. The membrane hydration appears to be a key parameter for understanding the water redistribution between cathode and anode with the change of the cell operating conditions. (C) 2022 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.