With an aim of decreasing the temperature (T-gamma) at which metallic Y reacts with H-2 to form the semiconductor phase YH3-delta, we employed Pd and Ni co-capping layers as catalysts, and compared the result with those obtained when employing Pd or Ni single-capping layers. These Y films capped with three types of catalytic layers were deposited by electron beam evaporation, and subsequently hydrogenated at a H-2 partial pressure of approximately 3 x 10(3) Pa while varying the H-2 reaction temperature (T-H2) from 20 degrees C to 500 degrees C. Pd/Ni co-capping materials exhibited a T-gamma of similar or equal to 50 degrees C which is approximately 40 degrees C lower than that of Ni capped materials. With regard to Pd-capped material, the metal-dihydride phase YH2 +/-delta prevailed for all investigated T-H2. Quantitative studies in terms of the Gibbs free energy were conducted by assessing the molar concentrations of the YH delta<0.21, YH2 +/-delta, and YH3-delta phases from corresponding X-ray diffraction intensities. (C) 2017 Elsevier B.V. All rights reserved.