Investigation of La1−xSrxCrO3−∂ (x ~ 0.1) as Membrane for Hydrogen Production

Abstract

Various inorganic membranes have demonstrated good capability to separate hydrogen from other gases at elevated temperatures. Hydrogen-permeable, dense, mixed proton-electron conducting ceramic oxides offer superior selectivity and thermal stability, but chemically robust candidates with higher ambipolar protonic and electronic conductivity are needed. In this work, we present for the first time the results of various investigations of La1−xSrxCrO3−∂ membranes for hydrogen production. We aim in particular to elucidate the material’s complex transport properties, involving co-ionic transport of oxide ions and protons, in addition to electron holes. This opens some new possibilities for efficient heat and mass transfer management in the production of hydrogen. Conductivity measurements as a function of pH2 at constant pO2 exhibit changes that reveal a significant hydration and presence of protons. The flux and production of hydrogen have been measured under different chemical gradients. In particular, the effect of water vapor in the feed and permeate gas stream sides was investigated with the aim of quantifying the ratio of hydrogen production by hydrogen flux from feed to permeate and oxygen flux the opposite way (“water splitting”). Deuterium labeling was used to unambiguously prove flux of hydrogen species.

Hydrogen flux in La0.87Sr0.13CrO3–δ

“…Powders of La 0.87 Sr 0.13 CrO 3-δ were prepared by spray pyrolysis and sintered with sintering aids at 1600 1C in reducing atmospheres. For a more detailed description of the synthesis route, the reader is referred to [17]. SEM-analyses (FEI Quanta 200 F) showed that the samples had sintered dense.…”

“…Under reducing conditions, oxygen vacancies form and gradually take over as the major charge compensating defect [16]. Consequently, the p-type conductivity decreases to the order of 1 S cm À 1 at 1000 1C and 0.1 S cm À 1 at 300 1C in reducing atmospheres (pO 2 $ 10 -21 and $ 10 -42 , respectively) [7,17].…”

“…The material is patented as a high temperature membrane for use in a natural gas power cycle [18], and recently, details regarding the hydrogen flux in acceptor-doped LaCrO 3 were published [17]. Electrical conductivity measurements showed that the total conductivity decreases with increasing water vapor partial pressure.…”

“…[17], the ambipolar proton electron hole conductivity, presented in Fig. 6, can be estimated from the flux measurements.…”

“…Effect of Pt-coating on the apparent hydrogen flux To elucidate whether surface kinetics may limit the hydrogen flux for La 0.87 Sr 0.13 CrO 3-δ [17], sample 1 was coated with Pt on both surfaces. Fig.…”