Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour Hydrophilic microporous layer coatings for polymer electrolyte membrane fuel cells operating without anode humidifcation Pranay Shrestha, Rupak Banerjee, Jongmin Lee, Nan Ge, Daniel Muirhead, Hang Liu, Andrew Kai Cheung Wong, David Ouellette, Benzhong Zhao, Aimy Bazylak ∗ Thermofluids for Energy and Advanced Materials Laboratory, Department of Mechanical & Industrial Engineering, Institute for Sustainable Energy, Faculty of Applied Science and Engineering, University of Toronto, Toronto, Ontario, Canada HIGHLIGHTS • A hydrophilic MPL coating was ap- plied to a commercial hydrophobic GDL. • Membrane resistance decreased for the fuel cell without anode humidif- cation. • Liquid water retention increased at the catalyst layer-MPL interfaces. • Liquid water accumulation within the cathode GDL increased at high current densities. • Oxygen transport resistances in- creased at high current densities. GRAPHICALABSTRACT ARTICLEINFO Keywords: Polymer electrolyte membrane fuel cell Gas difusion layer Microporous layer Hydrophilic coating Synchrotron X-ray radiographic imaging No external humidifer ABSTRACT In this study, a hydrophilic microporous layer (MPL) coating was applied to a commercial hydrophobic bi-layer gas difusion layer (GDL). We investigated the efect of the hydrophilic MPL coating on membrane hydration and liquid water distribution within the GDLs during fuel cell operation without anode humidifcation, using fuel cell performance monitoring and simultaneous synchrotron X-ray visualization. The application of the hydrophilic coating was found to enhance performance of the fuel cell. Specifcally, the application of the hydrophilic MPL coating led to an increase in cell potential of up to 14% (0.07 V at 1.5 A/cm 2 ) and a decrease in fuel cell membrane resistance. The decrease in membrane resistance was attributed to improved membrane hydration. This improvement in membrane hydration was caused by the increase in liquid water retention at the catalyst layer-MPL interfaces. At high current densities, the application of the hydrophilic MPL coating led to increased liquid water accumulation within the cathode GDL, which subsequently led to increased oxygen transport re- sistance. Our study demonstrates that the wettability of the GDL can be tailored to enhance fuel cell performance for a desired range of operating conditions by balancing membrane hydration and oxygen transport. https://doi.org/10.1016/j.jpowsour.2018.08.062 Received 17 May 2018; Received in revised form 8 August 2018; Accepted 21 August 2018 Abbreviations: CCM, Catalyst coated membrane; Cryo-SEM, Cryo-scanning electron microscopy; EIS, Electrochemical impedance spectroscopy; GDL, Gas difusion layer; MEA, Membrane electrode assembly; Micro-CT, Micro-computed tomography; MPL, Microporous layer; PEM, Polymer electrolyte membrane; RH, Relative humidity; Wt., Weight ∗ Corresponding author. Mechanical & Industrial Engineering, Faculty of Applied Science & Engineering, University of Toronto, 5 King's College Road, Toronto, ON, M5S 3G8, Canada. E-mail address: abazylak@mie.utoronto.ca (A. Bazylak). Journal of Power Sources 402 (2018) 468–482 0378-7753/ © 2018 Elsevier B.V. All rights reserved. T