Mixed‐Conducting Perovskites as Cathode Materials for Protonic Ceramic Fuel Cells: Understanding the Trends in Proton Uptake

Abstract

The proton uptake of 18 compositions in the perovskite family (Ba,Sr,La)(Fe,Co,Zn,Y)O 3-δ , perovskites, which are potential cathode materials for protonic ceramic fuel cells (PCFCs), is investigated by thermogravimetry. Hydration enthalpies and entropies are derived, and the doping trends are explored. The uptake is found to be largely determined by the basicity of the oxide ions. Partial substitution of Zn on the B-site strongly enhances proton uptake, while Co substitution has the opposite effect. The proton concentration in Ba 0.95 La 0.05 Fe 0.8 Zn 0.2 O 3-δ is found to be 10% per formula unit at 250 °C, 5.5% at 400 °C, and 2.3% at 500 °C, which are the highest values reported so far for a mixed-conducting perovskite exhibiting hole, proton, and oxygen vacancy transport. A comprehensive set of thermodynamic data for proton uptake in (Ba,Sr,La)(Fe,Co,Zn,Y)O 3-δ is determined. Defect interactions between protons and holes partially delocalized from the B-site transition metal to the adjacent oxide ions decrease the proton uptake. From these results, guidelines for the optimization of PCFC cathode materials are derived.

Gas Humidification Impact on the Properties and Performance of Perovskite‐Type Functional Materials in Proton‐Conducting Solid Oxide Cells

“…The recently published work of Zohourian et al demonstrated some directly opposite results . The authors studied the proton uptake capability of ≈20 simple perovskite oxides belonging to ferrite or cobaltite family ( Figure ) . They found that the hydration content was determined by the basicity of cations in ABO 3 and covalent character of BO bonds, reaching the highest values for barium ferrites doped with lanthanum and zinc, respectively.…”

“…The recently published work of Zohourian et al demonstrated some directly opposite results . The authors studied the proton uptake capability of ≈20 simple perovskite oxides belonging to ferrite or cobaltite family ( Figure ) .…”

“…b) Effect of Zn and Co substitution on the B‐site. All panels reproduced with permission . Copyright 2018, WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim.…”

Robust catalytically-activated LSM-BCZY-based composite steam electrodes for proton ceramic electrolysis cells

“…Proton conducting ceramics have attracted much attention due to their applications in energy conversion, hydrogen sensing and separation, and chemical synthesis. [1][2][3][4][5][6][7][8][9][10][11][12] For proton ceramic fuel cells (PCFCs), the cathode is a challenge, because it is difficult to nd suitable materials with good mixed p-type electronic and protonic conductivity. 13,14 Recent work on PCFC cathode performance has shown that the use of a ceramic-ceramic (cer-cer) composite having a proton conducting phase (electrolyte) and an electronically conducting phase with respect to the cathode material, enables major improvement of the electrochemical performance, ascribed to extension of the three phase boundary (TPB) area from the electrode-electrolyte interface to the whole cathode thickness.…”

Microstructural and compositional optimization of La0.5Ba0.5CoO3−δ—BaZr1−zYzO3−δ (z = 0, 0.05 and 0.1) nanocomposite cathodes for protonic ceramic fuel cells

“…With only mixed oxygen ion and electronic conduction in the cathode materials, the reaction sites are restricted to the electrolyte/ cathode interface. Therefore, the introduction of proton conductivity in the cathode is necessary in order to activate the whole cathode [18]. Ceramic-ceramic composite cathodes consisting of the La 0.5 Ba 0.5 CoO 3−δ oxygen ion and electronic conductor and the BaZrO 3 -based protonic conductor would therefore potentially increase the performance of the fuel cell.…”