Incorporation of Bulk Proton Carriers in Cubic Perovskite Manganite Driven by Interplays of Oxygen and Manganese Redox

Abstract

Mixed proton–electron conductors (MPECs) are indispensable for the efficient operation of proton conducting ceramic fuel cells and electrolyzer cells at intermediate temperatures (below 500 °C), but robust guidelines for their material design are still missing. Here, this study for the first time reports on the massive uptake of proton carriers in cubic perovskite type La0.7Sr0.3MnO3−δ at intermediate temperatures through the hydration reaction triggered by the coupled oxygen and manganese redox reaction. La0.7Sr0.3MnO3−δ undergoes decline of antibonding O 2p states hybridized with Mn 3d orbitals together with oxidation of Mn3+ to Mn4+ by hydration and thus retains bulk protons in the concentrations of 0.14 in wet air at around 420 °C, which is corresponding to the concentration of the well-known proton conductor BaZr x Ce0.8–x Y0.2O3−δ. The current results offer a general concept to design MPECs operating in air conditions, namely, that transition metal oxides possessing many oxygen vacancies and oxygen hole carriers could be promising candidates.

In Situ Activation of a Manganese Perovskite Oxygen Reduction Catalyst in Concentrated Alkaline Media

“…38 Hence, the pre-edge features are very sensitive to a change from a centrosymmetric to noncentrosymmetric coordination environment of Mn atoms by the creation of oxygen vacancies. 29,36,38,40 The pre-edge intensity increased remarkably with increasing cathodic polarization level (Figure 5c), which proved that oxygen vacancies were incorporated in the LSMN surface with the progress of the ORR in concentrated alkaline media.…”

“…The Mn K-edge XANES yielded a vertically rising main edge with a maximum peak at approximately 6550 eV, corresponding to an electron transition from the 1s to the 4p orbitals (Figure a). − Before the main adsorption peak, the spectra exhibited a pre-edge peak at approximately 6540 eV attributed to the electric-dipole-forbidden transition of a 1s electron to an unoccupied 3d orbital, which was partially allowed because of electric quadrupole coupling and/or 3d–4p orbital mixing arising from the noncentrosymmetric environment of the slightly distorted MnO 6 octahedral framework . Hence, the pre-edge features are very sensitive to a change from a centrosymmetric to noncentrosymmetric coordination environment of Mn atoms by the creation of oxygen vacancies. ,,, The pre-edge intensity increased remarkably with increasing cathodic polarization level (Figure c), which proved that oxygen vacancies were incorporated in the LSMN surface with the progress of the ORR in concentrated alkaline media.…”

La0.8Sr0.2Co1-xNixO3-δ as the Efficient Triple Conductor Air Electrode for Protonic Ceramic Cells

“…LSCN8210 exhibits the highest ΔW value of 0.57 wt % (Table 1) in wet air, which is higher than the corresponding value of the cubic perovskite type La 0.7 Sr 0.3 MnO 3 (C-LSM73; ΔW = 0.5 wt %) at the same temperature. 28 ΔW decreased as the Ni content (x) increased by 0.48, 0.31, and 0.24 wt % for x = 0.1, 0.2, and 0.3, respectively.…”

“…La 0.8 Sr 0.2 Co 1-x Ni x O 3-δ (LSCN; x = 0.0, 0.1, 0.2, 0.3) fine powders have been prepared by a citrate precursor process, the detail of which has been reported elsewhere. 28 In short, nitrate salts of lanthanum, strontium, cobalt, and nickel were dissolved in pure water with addition of a citric acid (CA; C 6 H 8 O 7 •H 2 O) chelating agent at a mole ratio of CA/LSCN = 2:1. The mixed solution was heated at 60 °C for drying and gelation.…”

Perspectives on Cathodes for Protonic Ceramic Fuel Cells

“…Hence, the first studies involving cathodes for H + -conducting solid oxide cells frequently employed perovskites with Fe and/or Co-containing B-site cations. Nevertheless, Wang et al recently demonstrated a high uptake of protons in La 0.7 Sr 0.3 MnO 3−δ by using XAFS, TG, and hydration experiments [38].…”