Topics in Number 49 include: • In-depth review of the durability issues in PEFCs • Understanding and mitigation of degradation in the polymer membrane and electrocatalyst • Summary of experimental diagnostics and modeling studies of cold start • Methods for distributed diagnostics of species, temperature and current in PEFCs • The operational principles of neutron radiography for in-situ visualization of liquid water distribution • Magnetic resonance imaging (MRI) technique for visualization of water in PEFCs and tunable diode laser absorption spectroscopy (TDLAS) for measurement of water vapor concentration • Liquid water transport in porous DM due to capillarity • Meso-scale modeling of two-phase transport • The atomistic simulations of electrochemical reactions on ectrocatalysts and the transport of protons through the polymer electrolyte From reviews of previous volumes: “This long-standing series continues its tradition of offering high quality reviews of established and emerging subject areas, together with the less common aspects of electrochemical science... [and]... deserves a place in electrochemistry libraries and should prove useful to electrochemists and related workers.” —Chemistry and Industry “Continues the valuable service that has been rendered by the Modern Aspects series.” —Journal of Electroanalytical Chemistry “Will definitely be of much use to researchers in the field of electrochemistry. . . . The editors of this well-produced volume deserve all appreciation for maintaining the excellent standard of the series.” —Bulletin of Electrochemistry “Extremely well-referenced and very readable.... Maintains the overall high standards of the series.” —Journal of the American Chemical Society