High proton conduction in grain-boundary-free yttrium-doped barium zirconate films grown by pulsed laser deposition

Abstract

Reducing the operating temperature in the 500-750 • C, is one of the major targets in present SOFC research 1,2 , and it is also a requisite for the development of miniaturized SOFCs for portable power supply 3,4 . Improving the electrolyte performance for intermediate-temperature operation can be achieved by reducing the electrolyte thickness 5,6 , and by using alternative materials to yttria-stabilized zirconia with a larger ionic conductivity in the intermediate temperature range 7 . With respect to the oxygen-ion conductors conventionally used in SOFCs, electrolytes based on high-temperature proton conductors (HTPCs) take advantage of their lower activation energy for charge transport 8 and of water formation at the cathode side 9,10 , thereby resulting in suitable conductivity in the intermediate temperature range and avoiding fuel dilution with water.Among HTPCs, Y-doped barium cerate (BCY) electrolytes have shown rather high protonic conductivity (10 −2 S cm −1 at 600 • C; ref. 11), although BCY strongly reacts with CO 2 (ref. 12) and water vapour 13 , hindering technological applications. On the other hand, despite a very good chemical stability of Y-doped barium zirconate (BZY) under fuel-cell operating environments, the total proton conductivity of BZY sintered pellets is generally significantly lower (about 10 −3 S cm −1 at 600 ; refs 14,15). This is due to the poor sinterability of BZY (ref. 16), together with the poor conducting properties of BZY grain boundary regions 17 . Scattered conductivity values for BZY samples are reported in the literature, and mostly depend on the processing parameters (see Supplementary Fig. S1).However, about a decade ago electrochemical impedance spectroscopy (EIS) measurements at temperatures below 200• C, that is, in the temperature range where impedance spectra allowed separation of the bulk and the grain boundary contribution,

Research Update: Fast and tunable nanoionics in vertically aligned nanostructured films

“…These are known to hinder oxygen ionic transport. 86,87 On the other hand, in VAN films comprising ionically conducting SDC nanopillars, the crystallinity of the SDC phase is much enhanced. 50,56 The reason for the enhanced crystallinity in VAN films is related to the large area vertical heteroepitaxy along many interfaces, 73 contrasting with the single interface formed in a planar film.…”

Ab initioinvestigation of defect formation at ZrO2-CeO2interfaces

“…[1][2][3][4] Yttria-stabilized zirconia (YSZ) and doped cerium oxide are the most established electrolyte materials for SOFCs, since they show a significant thermally activated oxygen mobility when they crystallize in a fluorite structure. 5,6 Another way to reduce the operating temperature is the fabrication of electrolytes in film form to reduce their ohmic resistance.…”

Tailoring phase stability and electrical conductivity of Sr0.02La0.98Nb1–xTaxO4 for intermediate temperature fuel cell proton conducting electrolytes

“…The overall total conductivity of several ion conducting oxides is strongly affected by the grain size, and thus the grain boundary density, since grain boundaries can act as a barrier for ion transport [9,[13][14][15][16]. For SLNT pellets, the correlation between conductivity and grain size was investigated by comparing the statistical descriptors (average, mode, median and standard deviation) with the conductivity at 500°C.…”

“…This value can be reached at 600°C for the SLNT sample with 20 mol% Ta using a film having a thickness of about 50 nm. Though not trivial, this target is indeed plausible to be reached using pulsed laser deposition as the fabrication method to grow films [13], making foreseeable the practical use as a stable proton conducting electrolyte of the SLNT material in thin-film form. which is undermined by phase transitions.…”