Enhancement of the Electron Conductivity ofLa₂₇(W_0.85Nb_0.15)₅O_{55.5 − δ}by Mo Doping for Hydrogen Permeation

Abstract

Lanthanum tungstates are a family of promising proton conductors for potential applications in fuel cells and in hydrogen permeation membranes. Single phase 15% and 30% Mo-doped La 27 (W 0.85 Nb 0.15 ) 5 O 55.5−δ were synthesized via a solid-state reaction route. The cell parameters of the cubic unit cell with space group F-43m increased from 11.181(7) Å to 11.186(5) Å when increasing the Mo content from 0% to 30%. The proton concentration in La 27 (W 0.55 Nb 0.15 Mo 0.30 ) 5 O 55.5−δ was similar to La 27 (W 0.85 Nb 0.15 ) 5 O 55.5−δ , and the influence of Mo doping on the total, proton and electron conductivity of La 27 (W 0.85 Nb 0.15 ) 5 O 55.5−δ was small in wet O 2 . The electron conductivity of 30% Mo-doped La 27 (W 0.85 Nb 0.15 ) 5 O 55.5−δ in wet 5% H 2 -Ar increased by more than one order of magnitude compared to the undoped material. The hydrogen flux increased from 4.96 × 10 −5 to 5.82 × 10 −4 ml cm −1 min −1 by 30% Mo doping of La 27 (W 0.85 Nb 0.15 ) 5 O 55.5−δ with dry Ar as the sweep gas and wet H 2 as the feed gas at 750 • C.