This report quantifies hydrogen permeation through dense 50/50 wt.-% BaCe0.8Y0.2O3-delta - Ce0.8Y0.2O2-delta membranes in which BaCe0.8Y0.2O3-delta serves as a proton conductor and Ce0.8Y0.2O2-delta serves as an electron conductor. A maximum hydrogen flux of 0.0744 mL cm(-2) min(-1) (5.54 x 10(-4) mol m(-2) s(-1)) at 900 degrees C is observed through a 1.44-mm thick membrane with a 0.5 atm hydrogen partial pressure gradient. This results in a permeability of 0.0107 mL cm(-1) min(-1) when normalized by thickness. This is one of the highest permeabilities reported to date for proton-conducting ceramic membranes. While permeation rates through BaCe0.8Y0.2O3-delta - Ce0.8Y0.2O2-delta membranes are promising, membrane performance is found to degrade over time. The source of degradation is hypothesized to be the formation of a dopant-deficient phase on the feed-side membrane surface which creates an increased inter-granular contact resistance. Additionally, Ni metal particles are observed inside of internal pores, and at grain boundaries between BaCe0.8Y0.2O3-delta and Ce0.8Y0.2O2-delta grains, indicating the reduction of the NiO used in solid-state reactive sintering during device operation. These particles may contribute to increased mechanical stresses between grains and subsequent membrane fracture. While the permeation demonstrated by these composite membranes is encouraging, further development is needed before these novel materials can be used in commercial applications. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.