# Imaging Liquid Water in a Polymer Electrolyte Fuel Cell with High-Energy X-ray Compton Scattering  
[PERSON]  
1 Japan Synchrotron Radiation Research Institute (JASRI), Sayo 679-5198, Hyogo, Japan; [EMAIL_ADDRESS] (T.M. ); ntsuji@spring8.orj (N.T. ); [EMAIL_ADDRESS] (D.F. ); [EMAIL_ADDRESS] (T.K. ); [EMAIL_ADDRESS] (Y.M.) [PERSON]  
1 Japan Synchrotron Radiation Research Institute (JASRI), Sayo 679-5198, Hyogo, Japan; [EMAIL_ADDRESS] (T.M. ); ntsuji@spring8.orj (N.T. ); frijoka@spring8.orjp (D.F. ); [EMAIL_ADDRESS] (T.K. ); [EMAIL_ADDRESS] (Y.M.) [PERSON]  
1 Japan Synchrotron Radiation Research Institute (JASRI), Sayo 679-5198, Hyogo, Japan; [EMAIL_ADDRESS] (T.M. ); [EMAIL_ADDRESS] (N.T. ); frijoka@spring8.orjp (D.F. ); [EMAIL_ADDRESS] (T.K. ); [EMAIL_ADDRESS] (Y.M.) [PERSON]  
1 Japan Synchrotron Radiation Research Institute (JASRI), Sayo 679-5198, Hyogo, Japan; [EMAIL_ADDRESS] (T.M. ); [EMAIL_ADDRESS] (N.T. ); frijoka@spring8.orjp (D.F. ); tkaneko@spring8.orjp (T.K. ); [EMAIL_ADDRESS] (Y.M.) [PERSON]  
1 Japan Synchrotron Radiation Research Institute (JASRI), Sayo 679-5198, Hyogo, Japan; [EMAIL_ADDRESS] (T.M. ); [EMAIL_ADDRESS] (N.T. ); [EMAIL_ADDRESS] (D.F. ); tkaneko@spring8.orjp (T.K. ); [EMAIL_ADDRESS] (Y.M.) [PERSON]  
2 Graduate School of Human and Environmental Studies, Kyoto University, Kyoto 606-9501, Japan 2  
the water content, and excessive water disturbs the chemical reaction at the catalyst site. In addition, liquid water existing in the cathode GDL blocks up the oxygen flow [3]. Therefore, water control in PEFCs is crucially important [4; 5; 6]. Water generation and its transport are inhomogeneous and random since the materials are porous and complex. Under an operating condition, water transport is governed the complex two-phase flow with an evaporation and condensation process, which depends on the local humidity and temperature in a PEFC [6; 7]. In order to understand the water behaviors in an operating PEFC and then optimize the design for an improved performance, direct experimental information is indispensable for the simulation and modeling of PEFCs. A number of experimental studies have been carried out using X-ray computed tomography (CT) [3; 8; 9; 10; 11; 12], or neutron radiography and CT [13; 14; 15; 16; 17; 18; 19]. These studies have non-destructively visualized the liquid water distributions in PEFCs under operating conditions. Neutron radiography has been used for the observation of PEFCs, but three-dimensional information, such as a cross-sectional image, inside the PEFCs is difficult to obtain. X-ray CT has been employed for obtaining three-dimensional information, but the targets are limited to model cells since the X-ray CT requires sample rotations. In addition, in conventional X-ray CT it is difficult to probe the liquid water in the vicinity of a catalyst layer because of large X-ray absorption by platinum, except for the use of high energy X-rays around 30 keV or higher. Until now, the application of X-ray CT techniques has been limited to the water behavior in GDLs. The distribution of water in an operating PEFC has been studied using a combination of small-angle neutron scattering and neutron imaging techniques [20]. The neutron imaging experiment shows that liquid water tends to accumulate around the channel and rib interface in the GDL and the channel, while the small-angle neutron scattering reveals a smooth distribution of water in the PEM. Due to the lack of one-on-one correlation in the water distribution between the GDL and the PEM, the two-phase flow model with water evaporation and condensation is proposed. The combined techniques, however, are unable to reveal the water content and distribution in the CLs because of the limited spatial resolution. Observing the water behavior throughout the PEM, CLs, GDLs, and channel is crucially important to build a water flow model, associated with water flooding in CLs. Compton scattering imaging (CSI) has been developed as a non-destructive cross-sectional imaging technique.