Tri-Doped BaCeO₃–BaZrO₃ as a Chemically Stable Electrolyte with High Proton-Conductivity for Intermediate Temperature Solid Oxide Electrolysis Cells (SOECs)

Abstract

Solid oxide electrolysis cells (SOECs) are devices that enable economically viable production of clean fuel such as hydrogen gas, which can be used in many industrial applications and serving as an energy carrier for renewable energy sources. Operation of SOEC at intermediate temperature (IT) range (400 to 600 °C) is highly attractive because many unexploited heat sources from industries can be utilized. Proton conducting SOECs based on barium− zirconium−cerate electrolytes show great potential for operating at this temperature range due to their high proton conductivity at reduced temperatures. In this study, a new tridoped BaCe 0.5 Zr 0.2 Y 0.1 Yb 0.1 Gd 0.1 O 3−δ (BCZYYbGd) electrolyte with very high chemical stability and proton conductivity is coupled with a PrNi 0.5 Co 0.5 O 3−δ steam electrode and a Ni-BCYYbGd hydrogen electrode for IT-SOEC operation. The dopants of the electrolyte were carefully designed to obtain the optimum stability and conductivity for IT-SOEC. The BCYYbGd electrolyte was stable over 200 h at 50 vol % steam in argon and at 600 °C, and a very high electrolysis current density of 2.405 A cm −2 was obtained at 600 °C and 1.6 V at 20 vol % of steam in argon. This system was also found to be highly reversible, exhibiting very high performance in SOFC mode and suggesting a potential candidate for next generation proton conducting electrolyte.

Degradation issues and stabilization strategies of protonic ceramic electrolysis cells for steam electrolysis

“…For example, Rajendran et al reported a tri-doped BaCeO 3 -BaZrO 3 by partially substituting Zr with Y, Yb, and gadolinium (Gd), forming BaCe 0.5 Zr 0.2 Y 0.1 Yb 0.1 Gd 0.1 O 3−δ (BCZYYbGd). 44 XRD spectra showed that the BCZYYbGd electrolyte was stable over 200 hours at 50 vol % steam in argon and 600°C (Figure 5D). This was attributed to the higher electronegativity value of Gd (1.20) compared to that of the host Ce (1.12), which stabilizes the crystal structure and minimizes the dopant−hydroxyl interaction.…”

“…(D) XRD patterns of the BCZYYbGd film before and after exposure to 50 vol.% steam in argon at 600°C for 200 h. Reprinted with permission from Ref. 44 Copyright 2020 American Chemical Society. (E) The current density of the BCZYYC2 cell as a function of time tested at 700°C with a pulse voltage.…”

“…Copyright 2020 John Wiley and Sons. (D) XRD patterns of the BCZYYbGd film before and after exposure to 50 vol.% steam in argon at 600°C for 200 h. Reprinted with permission from Ref 44 . Copyright 2020 American Chemical Society.…”

“…Partial substitution of B‐site ions of proton conductors with acceptor dopants can decrease the basicity for increasing tolerance factor and thus improve their stability. For example, Rajendran et al reported a tri‐doped BaCeO 3 ‐BaZrO 3 by partially substituting Zr with Y, Yb, and gadolinium (Gd), forming BaCe 0.5 Zr 0.2 Y 0.1 Yb 0.1 Gd 0.1 O 3−δ (BCZYYbGd) 44 . XRD spectra showed that the BCZYYbGd electrolyte was stable over 200 hours at 50 vol % steam in argon and 600°C (Figure 5D).…”

Toward Durable Protonic Ceramic Cells: Hydration-Induced Chemical Expansion Correlates with Symmetry in the Y-Doped BaZrO3–BaCeO3 Solid Solution

“…To operate solid oxide cells at intermediate temperatures, materials with high ionic conductivity and low electronic conductivity are needed for the electrolyte layer. Certain proton-conducting oxides offer higher ionic conductivity − than the best oxide ion conductors (acceptor-stabilized ZrO 2 , acceptor-doped CeO 2 , and Sr- and Mg-codoped LaGaO 3 ) and so can operate at lower temperatures with the same Ohmic resistance for an equivalent electrolyte geometry. Additionally, electrolysis cells using proton-conducting electrolytes generate H 2 at the fuel electrode that is undiluted with H 2 O, and proton conductors are also under development for gas separation and electrochemical reactors. − Among proton conductors, the Y-doped BaZrO 3 –BaCeO 3 solid solution has received significant attention.…”