Structural and transport properties of Nd tungstates and their composites with Ni_0.5Cu_0.5O obtained by mechanical activation

Abstract

Nd tungstates and molybdates are promising materials for hydrogen separation membranes due to a high protonic conductivity. This work aims at elucidating structural, textural and oxygen transport features of Nd5.5WO11.25-δ,...

Design of Mixed Ionic-Electronic Materials for Permselective Membranes and Solid Oxide Fuel Cells Based on Their Oxygen and Hydrogen Mobility

“…The using of the isotope exchange with C 18 O 2 made it possible to confirm the high mobility of oxygen in these compounds in air, starting from 200 °C ( Figure 13 ) [ 212 ]. A high or at least intermediate oxygen mobility was demonstrated for other fluorites and bixbyites (in some cases due to defect features such as the effect of grain boundaries resulting in a fast oxygen diffusion along grain boundaries (2D diffusion)), while rhombohedral phases possess lower oxygen mobility ( Figure 13 ) [ 55 , 58 , 163 , 206 , 212 , 216 ].…”

“…A promising approach in the design of materials for SOFC and permselective membranes is the synthesis of composites comprising both an electronic-conductive or MIEC material and an ionic conductive material [ 55 , 58 , 91 , 216 , 248 , 269 , 315 ]. The ionic-conductive component applied can be fluorite [ 55 , 60 , 244 , 316 , 317 , 318 , 319 , 320 , 321 ], pyrochlore [ 55 , 60 , 69 ], spinel [ 55 , 322 ], etc.…”

“…Thus, for the composites based on Pr 1.9 NiO 4+δ and solid electrolytes (Ce 0.9 Gd 0.1 O 1.95 , Y 2 (Ti 0.8 Zr 0.2 ) 1.6 Mn 0.4 O 7−δ ) a decrease in the oxygen tracer diffusion coefficient values compared to the individual Pr 1.9 NiO 4+δ material was reported, which is probably explained by the incorporation of the cations from the electrolyte into the RP structure leading to hampering the cooperative mechanism of oxygen migration mentioned above [ 58 ]. For the composites (Nd,La) 5.5 (W,M)O 11.25−δ –Ni 0.5 Cu 0.5 O, a decrease in the oxygen tracer diffusion coefficient values compared to the individual defective fluorites was probably due to blocking the fluorite phase surface by Ni (II)–Cu (II) oxide nanoparticles possessing a low oxygen mobility, as well as the formation of admixture phases [ 216 ].…”

“…They possess absolute selectivity with respect to hydrogen; however, they are too expensive and have issues with stability under operating conditions [ 49 , 55 , 56 , 84 , 85 , 99 , 139 , 358 ]. As an alternative to precious metals, Ni and its alloys, being cheap but also possessing a high mixed protonic-electronic conductivity, can be used in hydrogen separation membranes in an individual form or as a component of cermet composites [ 55 , 56 , 132 , 216 , 359 , 360 ]. V and its alloys with Ni, Cu, V, Nb, Ta and other metals are promising materials showing high hydrogen permeation fluxes exceeding those for Pd-based membranes and having a lower cost [ 55 , 359 , 360 , 361 ].…”

“…Copyright 2019 American Chemical Society. ( b ) Arrhenius plots of oxygen tracer diffusion coefficients for Nd 5.5 WO 11.25−δ (1) [ 216 ] and Nd 10 Mo 2 O 21 (2) [ 163 ].…”