Fast and Stable Proton Conduction in Heavily Scandium‐Doped Polycrystalline Barium Zirconate at Intermediate Temperatures

Abstract

The environmental benefits of fuel cells and electrolyzers have become increasingly recognized in recent years. Fuel cells and electrolyzers that can operate at intermediate temperatures (300–450 °C) require, in principle, neither the precious metal catalysts that are typically used in polymer‐electrolyte‐membrane systems nor the costly heat‐resistant alloys used in balance‐of‐plant components of high‐temperature solid oxide electrochemical cells. These devices require an electrolyte with high ionic conductivity, typically more than 0.01 S cm−1, and high chemical stability. To date, however, high ionic conductivities have been found in chemically unstable materials such as CsH2PO4, In‐doped SnP2O7, BaH2, and LaH3−2xOx. Here, fast and stable proton conduction in 60‐at% Sc‐doped barium zirconate polycrystal, with a total conductivity of 0.01 S cm−1 at 396 °C for 200 h is demonstrated. Heavy doping of Sc in barium zirconate simultaneously enhances the proton concentration, bulk proton diffusivity, specific grain boundary conductivity, and grain growth. An accelerated stability test under a highly concentrated and humidified CO2 stream using in situ X‐ray diffraction shows that the perovskite phase is stable over 240 h at 400 °C under 0.98 atm of CO2. These results show great promises as an electrolyte in solid‐state electrochemical devices operated at intermediate temperatures.

High proton conductivity of NaMg1−xLixHx (PO3)3·yH2O with a three-dimensional open framework in the intermediate temperature range

“…Perovskites with rigid frameworks formed by only ionic/covalent bonds show excellent thermal stability and exhibit high proton conductivity at around 400°C by the material design based on the point defects chemistry. However, an achievement of fast proton diffusion via the Grotthouss mechanism below 300°C is still difficult due to the high charge density on the surface of protons [5][6]. [20][21].…”

“…Proton conduction is a common phenomenon observed in various materials, including liquid and organic and inorganic solids [1][2][3][4][5][6], and is essential for the metabolism of biological systems [7][8][9] and the operation of fuel cells [10][11][12]. In particular, proton conductors are important for practical applications as electrolytes that determine the operating temperature of fuel cells.…”

“…In-doped SnP 2 O 7 exhibits high proton conductivity up to 350°C [4,11]. Perovskites exhibit excellent thermal stability and high proton conductivity above 300°C [5][6][18][19]. Although all of them are excellent proton conductors, they have a common issue in that they exhibit high proton conductivity at a limited temperature.…”

Structure–property correlation in oxide-ion and proton conductors for clean energy applications: recent experimental and computational advancements

“…However, Hyodo and co-workers were able to introduce up to 60 wt% of Sc in BaZrO 3 by chemical solution and sintering at 1600 C, providing dense pellets of a single-phase cubic perovskite material. 76 Importantly, this high doping level resulted in a proton concentration close to 0.55 mol per formula unit leading to a total proton conductivity, reecting both the bulk and grain boundary resistivities in the polycrystalline pellet, exceeding 0.01 S cm À1 between 396 and 534 C under a water partial pressure of 0.02 atm. 76 Finally, this composition resulted also to be stable against CO 2 as determined by an accelerated test at 400 C. Clearly this work highlights some further potential of cerates and zirconates event though the well-known high temperature sintering issues still represent a practical problem to be overcome.…”

Metal/Oxide Heterojunction Boosts Fuel Cell Cathode Reaction at Low Temperatures

“…[ 28,29 ] The σ of Sc50‐cell is apparently greater than that of the Sc20‐cell at all temperatures, with a value of 10 −3 S cm −1 at 400 °C, deviating downward above 400 °C, which can be attributed to the decline of protonic carriers because of dehydration at elevated temperatures. [ 30 ]…”