Tritium Conductivity and Isotope Effect in Proton‐Conducting Perovskites

Abstract

High temperature protonic-conducting oxides based on the perovskite structure have been studied extensively since their discovery in 1981. 1 The hydrogen and deuterium isotope conductivities in these oxides have been evaluated 2,3 recently, and their potential application as hydrogen separation membranes has been discussed. 4 However, there are no reported studies on the tritium ion-conduction in these perovskites. In this paper, we report the hydrogen (H), deuterium (D), and tritium (T) conductivities of three protonic conducting perovskites, viz. SrZr 0.9 Yb 0.1 O 2.95 , BaCe 0.9 Yb 0.1 O 2.95 , and SrCe 0.95 Yb 0.05 O 2.975 . The conductivity of tritium ions through these perovskites not only gives fundamental information regarding the hydrogen transport in these perovskites, but also allows for the exciting possibility of tritium separation using these oxides as an electrochemical membrane.The proton-conducting compounds that were investigated in this study were selected for the following reasons. (1) The strontium zirconates are known to have the best chemical stability in CO 2 containing atmospheres (stable in 20 vol % CO 2 at 700ЊC). 5 (2) The barium cerates have one of the highest magnitudes of protonic conductivity. 6 (3) The strontium cerates, having a high protonic transference number, are the most extensively studied proton-conducting perovskites. [7][8][9] Although a H/D isotope effect has been shown in proton-conducting perovskites, the data in the literature is neither extensive nor consistent enough to clearly establish a model for protonic conduction in these perovskites. 2 The measured difference in activation energies for the H-and D-ion conduction has eliminated the possibility of proton hopping governed by a classical theory and has given support to a semiclassical approach. This approach takes into consideration the difference in zero point energies between the ground state of H and D, given by Eq. 1 10where E H and E D are the activation energies for the H-and D-ion conduction, respectively, and H and D are the OH and OD stretching frequencies. However the pre-exponential factors presented in the literature do not obey the predictions of the semiclassical theory given by Eq. 2, c eff -concentration of mobile protons, and v ϭ unit cell volume.In this paper, we present the H-, D-, and T-ion conductivities of SrZr 0.9 Yb 0.1 O 2.95 and BaCe 0.9 Yb 0.1 O 2.95 , and attempt to explain the various factors that need to be addressed in order to unambiguously determine the conduction mechanism in these perovskites. ExperimentalSingle-phase perovskite samples of SrZr 0.9 Yb 0.1 O 2.95 , BaCe 0.9 Yb 0.1 O 2.95 , and SrCe 0.95 Yb 0.05 O 2.975 were prepared using standard solid-state methods by heating appropriate stoichiometric mixtures of BaCO 3 , SrCO 3 , CeO 2 , ZrO 2 , and Yb 2 O 3 at 1773 K for 20 h with two intermediate ballmilling steps. The formation of a single-phase orthorhombic perovskite was confirmed by powder X-ray diffraction using a Siemens D 5000 diffractometer. Dense ceramic samples (...

H/D isotope effects in high temperature proton conductors

“…3 Arrhenius conductivity parameters in HTPCs exchanged with the three isotopes of hydrogen, based on data in ref. [21]. The activation energies increase with isotope mass, except for one point for BaCe 0.9 Yb 0.1 O 2.95 , while the pre-exponentials decrease, contrary to expectations from ref.…”

Prospect of hydrogen technology using proton-conducting ceramics

“…M. Kato et al at JAERI and Matuzaki at RIKEN [44] designed a compact enrichment system of hydrogen isotopes using a ceramic hydrogen pump. R. Mkundan et al [45] at Los Alamos National Laboratory are intending tritium recovery using hydrogen pump and studied on deuteron and triton transports in socalled proton-conducting ceramics.…”

Tritium recovery from blanket sweep gas via ceramic proton conductor membrane

“…It is close to the reciprocal of the square root of the mass number. Mukundan et al have reported about isotopic effect on bulk conductivity of several proton conductor ceramics, and have concluded that it is consistent with semi-classical theory [8]. So, this suggests that the contribution of bulk diffusion (ceramic lattice) process to the hydrogen transportation process through proton conductor membrane is comparatively large.…”