Incorporation and Conduction of Protons in Ca, Sr, Ba-Doped BaLaInO4 with Ruddlesden-Popper Structure

Abstract

The new phases BaLa0.9M0.1InO3.95 (M = Ca2+, Sr2+, Ba2+) with a Ruddlesden-Popper structure were obtained. It was established that all investigated samples were capable for the water uptake from the gas phase. The ability of water incorporation was due to not only by the presence of oxygen vacancies, but also due to the presence of La-O blocks in the structure. The degree of hydration of the samples was much higher than the concentration of oxygen vacancies and the composition of the samples appear to be BaLaInO3.42(OH)1.16, BaLa0.9Ca0.1InO3.25(OH)1.4, BaLa0.9Sr0.1InO3.03(OH)1.84, BaLa0.9Ba0.1InO2.9(OH)2.1. The degree of hydration increased with an increase in the size of the dopant, i.e., with an increase in the size of the salt blocks. It was proven that doping led to the increase in the oxygen ionic conductivity. The conductivities for doped samples BaLa0.9M0.1InO3.95 were higher than for undoped composition BaLaInO4 at ~1.5 order of magnitude. The increase in the conductivity was mainly attributed to the increase of the carrier concentration as a result of the formation of oxygen vacancies during doping. The proton conductivities of doped samples increased in the order Ca2+–Sr2+–Ba2+ due to an increase in the concentration of protons. It was established that all doped samples demonstrated the dominant proton transport below 450 °C.

Effect of doping on the local structure of new block‐layered proton conductors based on BaLaInO4

“…The obtained lattice parameters were in good agreement with previously reported data. [ 12–14 ] Both types of doping (acceptor and donor) leads to the increase in the unit cell volume compared with undoped composition BaLaInO 4 (Table 1).…”

“…It can be assumed that observable decrease of crystal lattice distortion can lead to facilitated oxygen‐ion and protonic transport. Table 4 represents the values of oxygen‐ionic and protonic conductivity at 400°C [ 12,13 ] for investigated samples. As can be seen, the increase in the conductivity values is well correlated with decrease in the tilt angle of [InO 6 ] octahedra and the approaching of the tolerance factor to 1 (Table 3).…”

“…Recently, compounds based on AA′BO 4 (BaLaInO 4 ) with block‐layered Ruddlesden–Popper (RP) structure were described as proton conductors. [ 12,13 ] The phase BaLaInO 4 consists of alternative stacking of the [Ba,LaO] oxide layer and [Ba ¾ La ¼ InO 3 ] perovskite layer with the [InO 6 ] edge‐facing [Ba,La–O] layers. [ 14 ] It was shown that the composition BaLaInO 4 is capable for water uptake (0.62 mol water per formula unit), although the phase does not contain oxygen vacancies in the structure.…”

“…The improving ionic (oxygen‐ionic and protonic) conductivity (up to ~1.5 order of magnitude) can be achieved by the acceptor (M = Sr 2+ , Ba 2+ ) (Equation ) or by the donor (Equations and ) doping: of cationic sublattices (La 3+ , In 3+ ) of BaLaInO 4 . It was shown [ 12,13 ] that water uptake for doped compounds is achieved up to ~1.5 mol water per formula unit. The ability to incorporate water for these phases (with RP structure) is determined by the size of the [Ba,La–O] oxide layers and not by the nature of the defects (oxygen vacancy and oxygen interstitial).…”

One-Step Fabrication of Protonic Ceramic Fuel Cells Using a Convenient Tape Calendering Method

“…Protonic ceramic fuel cells (PCFCs) form a class of fuel cells (FCs) providing highly efficient and economically advantageous chemical-to-electrical energy conversion at elevated temperatures [1][2][3][4][5]. A proton-conducting electrolyte membrane as a PCFC's heart transports proton charge carriers with high levels of ionic conductivity compared with those of oxygen-ionic electrolytes of the traditional solid oxide fuel cells (SOFCs), owing to the corresponding high mobility/concentration of protons [6][7][8][9]. This allows the operational temperatures of the FCs to be decreased by~100-300 • C to reach low-(300-500 • C) and intermediate-temperature (500-700 • C) ranges [10][11][12][13].…”