Oxygen deficient Ruddlesden-Popper type lanthanum strontium

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Oxygen deficient Ruddlesden-Popper type lanthanum strontium cuprate doped with bismuth as cathode for solid oxide fuel cell Xueyu Hu, Mei Li, Yun Xie, Yi Yang, Xiaojun Wu, and Changrong Xia ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b05445 • Publication Date (Web): 31 May 2019 Downloaded from http://pubs.acs.org on May 31, 2019

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ACS Applied Materials & Interfaces

Oxygen Deficient Ruddlesden-Popper Type Lanthanum Strontium Cuprate Doped with Bismuth as Cathode for Solid Oxide Fuel Cell

Xueyu Hu, † Mei Li, † Yun Xie, † Yi Yang, † Xiaojun Wu,†,‡,* and Changrong Xia†, * †

CAS Key Laboratory of Materials for Energy Conversion, Department of Materials Science

and Engineering, University of Science and Technology of China, Hefei, Anhui 230026, P.R. China ‡

Hefei National Laboratory of Physical Science at the Microscale, University of Science and

Technology of China, Hefei, Anhui 230026, P.R. China

KEYWORDS: Solid oxide fuel cell, cathode, Ruddlesden-Popper type material, lanthanum strontium cuprate, bismuth doping, oxygen reduction reaction

ABSTRACT: Ruddlesden-Popper type strontium doped lanthanum cuprates are unique in oxygen defects due to the oxygen deficient composition. This work increases the oxygen vacancy concentration through bismuth doping and thus promotes the electrochemical performance for oxygen reduction reaction in solid oxide fuel cell. X-ray diffraction shows that up to 10% A-site

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elements can be doped with bismuth. The doping improves the catalytic activity through 1) increasing oxygen vacancy concentration by 87.5% and 65.5% at room temperature and 800 C, respectively, as demonstrated by iodometric titration and thermogravimetric analysis, 2) greatly reducing the energy for oxygen vacancy formation as shown by DFT calculation, 3) forming additional reactive oxygen species at the near surface region as suggested with X-ray photoelectron spectroscopy, and 4) enhancing the oxygen transport properties as exhibited with electrical conductivity relaxation. In addition, bismuth doping reduces the thermal expansion coefficient to a level that could exactly match the thermal expansion behavior to the electrolytes. Consequently, the interfacial polarization resistance for oxygen reduction reaction is decreased by 43% at 800C for the cuprate based composite electrodes. The decrease is greatly attributed to the enhancement in the charge transfer process, the rate limiting step. Further, the peak power density for a model cell is increased from 530 mW·cm-2 to 630 mW·cm-2 at 800C. Bismuth doping is a promise strategy to modify the catalytic properties of the unique cuprates towards oxygen reduction reaction.

INTRODUCTION Recent years have witnessed the great progress in the research of solid oxide fuel cells (SOFCs) ranging from the development of new material to the special design of their configurations

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. The Ruddlesden-Popper (R-P) oxides An+1BnO3n+1, especially the first series

A2BO4, have attracted great attention as the electrocatalyst for the oxygen reduction reaction (ORR) that takes place at the cathode and is responsible for the major loss of cell performance 8. Different from the perovskite oxides (ABO3), which are the state-of-the-art cathode materials


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being oxygen-deficient such as La0.6Sr0.4Co0.2Fe0.8O3-δ, typical R-P oxides, for example La2NiO4+δ, are often oxygen excess. The oxygen-excess structure has relatively large oxygen nonstoichiometry number δ, exhibiting excellent oxygen transport performance along a-b planes, the rock-salt layers where the perovskite layers are sandwiched. The oxygen-excess composition has an interstitial transport process that the apical oxygen transfers to the interstitial oxygen site while the formed oxygen vacancy is filled by another nearby interstitial oxygen. The interstitial transport is anisotropic and has significantly low activation energy owing to the great quantity of interstitial oxygen incorporated in A2O22+ layers 9. Therefore, compared with the perovskite oxides, the R-P oxides have relatively higher oxygen surface exchange and oxygen bulk diffusion coefficients 10-13, which are the key parameters determining ORR kinetics. Large oxygen nonstoichiometry δ is found with the B-site elements of Mn, Fe, Co and Ni. These oxides are oxygen-excess even the A-site is doped with strontium. When Cu is used as the B-site element, the oxygen nonstoichiometry is relatively small, δ = 0.01 for La2CuO4+δ. The small  value is expected with poor oxygen transport properties. However, the small value makes it possible to transfer the oxygen nonstoichiometry from oxygen-excess to oxygen-deficiency by doping the A-site with a lower valence element such as bivalent strontium. This has been achieved by Opila et al. who found that a slight amount of strontium introduced to the A-site can drive lanthanum cuprate from oxygen-excess La2CuO4+δ into oxygen-deficient La2-xSrxCuO4-δ 14. When it becomes oxygen-deficient, the R-P oxides are completely different in oxygen transport since the deficient oxygen nonstoichiometry arises from oxygen vacancies. The oxygen migration mechanism in oxygen-excess or oxygen-deficient A2BO4 is usually related to the performance of two types of oxygen species, “apical” and “equatorial” oxygen (shown in Supplementary Figure S1). The oxygen vacancies can be located at either apical or equatorial positions as illustrated with


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in situ neutron diffraction method 15. The oxygen-deficient oxides are demonstrated to have good properties in oxygen transport. J. L. Routbort et al. characterized the transport properties of La1.9Sr0.1CuO4-δ via isotopic exchange depth profiling method and found a pretty low oxygen migration energy of 0.80 eV, which is even lower than 0.87 eV for the oxygen-excess R-P oxide La2NiO4+δ 16, 17. In addition, elevated electrical conductivities was found by Jean-Claude Grenier et al. for a series of strontium doped compositions La2-xSrxCuO4-δ (x=0.1, 0.3, and 0.5), in which La1.9Sr0.1CuO4-δ possesses the highest electrical conductivity, 140 S·cm-1 (800 C in air) that is an order of magnitude higher than the undoped La2CuO4 and about twice as La2NiO4+

18, 19

. The

oxygen deficiency character together with good oxygen transport properties make strontium doped lanthanum cuprate a unique R-P oxide for application as ORR electrocatalyst in SOFCs. This work reports the improvement in electrochemical performance through bismuth doping to La1.9Sr0.1CuO4-δ. The equal-valence doping does not generate additional oxygen vacancies according to the electroneutral principle. However, this work finds that bismuth doping can generate additional oxygen vacancies. It is noted that the lone pair in Bi3+ could result in improved properties in oxygen transport, which have been demonstrated with the perovskite oxide SrFeO3-δ and La2Cu0.5Mn1.5O6 and oxygen excess R-P oxide La1.75Sr0.25NiO4+δ 20-22. EXPERIMENTAL SECTION Powder synthesis. The La1.9-xBixSr0.1CuO4-δ (LBSC, x = 0, 0.1, 0.2, 0.3, and 0.4) powders were synthesized using the citrate combustion method. The composition is further abbreviated to show the doping content, such as LBSC1 for x=0.1 and LBSC0 for x=0. The cation precursors were Bi(NO3)3 ·5H2O (99.0%), Sr(NO3)2 (99.5%), Cu(NO3)2 ·3H2O (99.0%), and La(NO3)3 (99.9%). Stoichiometric amount of the nitrate precursors was added to proper amount of distilled water according to the order of solubility from difficulty to easy. Then, the combustion agents


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were subsequently added to the nitrate solution with a molar ratio of 1:1:2 for the total metal ions, EDTA (99.5%), and citric acid (99.5%), respectively. Next, use aqueous ammonia to adjust the pH to about 6.0, stir the solution at 300 r·min-1 for about 3 h and heat the mixed solution on a hot plate until self-combustion occurred. And finally, the as-prepared black ash was collected and heated at 800 C for 3 h to form the LBSC powders. Sm0.2Ce0.8O1.9 (SDC) powder was prepared with the carbonate co-precipitation method using Sm(NO3)3 (99.95%) and Ce(NO3)3 (99%) as the cation sources and ammonia carbonate (99.7%) as the precipitant. The SDC solution, which was 0.1 M, was dropped to 0.1 M ammonia carbonate solution at room temperature. The white precipitate was then collected, dried at 90 C and calcined at 600 C for 2 h to obtain SDC powder with the fluorite structure as confirmed by X-ray diffraction measurement (XRD). All chemicals were from Sinopharm Chemical Reagent Co. Ltd. Characterization. The LBSC crystalline structures and the compatibility between LBSC and SDC were investigated by X-ray powder diffraction on Rigaku TTR-III diffractometer using Cu-Kα radiation, operated at 40 kV and 150 mA, with a step size of 0.02° and a scan speed of 1 °min-1. The microstructure was examined with scanning electron microscopy (SEM, JSM-6700F). The oxygen nonstoichiometry δ value was determined with iodometric titration and the thermogravimetric analysis (TG) using LBSC powders preheated at 800 C for 30 min to exclude the water interference. δ value at room temperature was derived from iodometric titration results, the details are mentioned in the previous literature 23. δ value at high temperature up to 900 C was determined with TG analysis, which was carried out with TG-DTA6300 in air at a heating rate of 10C·min-1. To make the element composition clear, X-ray photoelectron spectroscopy (XPS) measurements were performed with LBSC powders using an ESCALAB 250, equipped with a monochromatic Al Lα X-ray source.


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Dense strip samples were prepared to determine the conductivity (), thermal expansion coefficient (CTE) and oxygen transport properties. LBSC powders were uniaxially dry pressed at 300 MPa to strip green samples and subsequently sintered in air at high temperature (900~1000 C) for 3 h to obtain dense strips with a size of about 12.05.00.5 mm3. The sintering temperature was 1000 C for LBSC0, 975 C for LBSC1, 900 C for LBSC2 and the relative density was higher than 97% as determined with Archimedes method. The conductivity measurements were performed in air and in the temperature range from 550 to 800 C, using a DC four-probe technique (Keithley, 2001-785D). The average CTE of the strip sample was investigated in air using a standard pushrod dilatometer (NETZSCH DIL402C) at a heating rate of 5 C min-1. The thermal expansion behaviors were further investigated with high temperature XRD using Rigaku-smartlab at a heating rate of 3 C min-1 and a scan speed of 6°min-1. The oxygen transport properties were determined using electrical conductivity relaxation (ECR) method, whose detailed introduction is given in Supplementary information. The LBSC strip samples were placed in a quartz tube, heated to the target temperature to ensure full equilibration with the surrounding air. Then, the atmosphere was rapidly changed to 100% oxygen, and the gas flow rate was fixed at 200 mL min-1 throughout the experiment. The transient change of conductivity with increase of oxygen partial pressure was recorded, and fitted to a solution of Fick’s second law to obtain chemical surface exchange coefficient (kchem) and the chemical oxygen bulk diffusion coefficient (Dchem). The experiment temperature was in the range from 650 to 800 C, and the more specific descriptions of ECR technique are given before 24. Electrochemical test. The electrochemical performance for ORR was investigated in air using symmetrical cells consisting of SDC electrolytes and LBSC electrodes. To prepare the electrolyte, SDC powders were uniaxially pressed at 250 MPa into green pellets and then sintered


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at 1400 C for 5 h to form dense electrolyte substrates. The diameter was 1.05 cm and thickness 0.40 mm. The electrode was deposited onto the electrolyte surface using screen-printing technique with a slurry consisting of LBSC, SDC and α-terpineol (6% ethyl cellulose) with a weight ratio of about 1:1:3. The slurry was printed on both sides of the electrolyte, dried at 80 C for 30 min, and calcined at 900 C for 2 h in air to form porous LBSC-SDC electrodes. The silver wires were attached to both sides of the symmetrical cells with silver paste for current collection. The measurement of the AC impedance spectroscopy was tested at temperature from 600 to 800 C with GAMRY Interface 5000 in the frequency ranges from 0.01 Hz to 1 MHz using an excitation voltage of 10 mV. The effect of oxygen partial pressure on the ORR performance was conducted in N2-O2 atmospheres (≥99.999%, Nanjing special gas Factory Co., Ltd.). The impedance spectrum was analyzed with the distribution of relaxation times (DRT) method using Matlab 25. For the integral button cell performance test conducted in the temperature ranging from 600 to 800 C, yttria-stabilized zirconia (YSZ) was used as the electrolyte material. Considering the fact that the reaction between YSZ and LBSC can bring in non-conductive La2Zr2O7, the build of a SDC interlayer is necessary. Finally, the single cell had a configuration of a Ni-YSZ anode support, a thin layer of YSZ electrolyte, a thin SDC interlayer, and a LBSC-SDC cathode. Fine NiO powders were prepared by glycine-nitrate combustion method using Ni(NO3)2·6H2O (98.0%) and glycine (99.5%) as the precursors. Mixture of NiO, YSZ (8% yttria-stabilized zirconia, fuel cell materials) and PMMA (polymethyl methacrylate, 99%, M = 100) with a weight ratio of 6:4:1.5 was fully ground, and pressed into pellets. After been heated at 1000 C for 2 h, it gained the mechanical strength as an anode support. The YSZ electrolyte layer was prepared via dip-coating method. With YSZ suspension (alcohol: YSZ: dispersant=20:2:1) dropped at the surface and sintered at 1400 C for 5 h, a dense electrolyte thin layer was formed. The SDC interlayer was


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prepared by coating the SDC solution to the electrolyte surface. After sintered at 1200 C for 2 h, a pretty thin SDC interlayer was formed. The cathode was prepared using the same method as the symmetrical cell, and the silver wire was attached to the cathode side with silver paste for current collection. The single cell was sealed onto the top of a ceramic tube with the cathode side exposing in ambient air and the anode side flowing with humidified (∼3% H2O) hydrogen at 50 mL min-1. The measurement of the AC impedance spectroscopy and current-voltage response was also tested with GAMRY Interface 5000. Computational Details. All spin-polarized calculations were carried out using the Vienna ab initio simulation package (VASP) based on density functional theory (DFT) 26, 27. To solve the ion-electron interactions in a periodic system, the projector augmented wave (PAW) method with O (2s22p4), Cu (3d104s1), La (5d16s2), and Bi (5s26p3) was applied. The generalized gradient approximation (GGA) with Perdew-Burke-Ernzerhof (PBE) functional was used to take into consideration the exchange-correlation interactions in the Kohn-Sham equations

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. To describe

the correlated electrons of the Cu 3d-orbital, GGA + U with Ueff = 4.0 eV was used in the calculations

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. The energy cutoff was set to 425 eV and the convergence criteria was 10 -5 eV.

Structure optimization was carried out till the force on each atom was less than 0.02 eV Å-1. The electronic and ionic optimizations were performed using the RMM-DⅡS algorithm and the Conjugate-gradient algorithm, respectively. We focus on the effect of the substitution of lanthanum with bismuth on the adjacent oxygen. Hence, to simplify the calculation process, a ruddlesden-popper lanthanum cuprate (La2CuO4) structure with supercell sizes of 2a×2a×c was modeled, where a and c are the lattice vectors parallel and perpendicular to the rock salt layers, including 16 La, 8 Cu, and 32 O atoms. One eighth of La atoms were substituted by Bi atoms with the composition of La1.875Bi0.125CuO4


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to represent Bi doped La2CuO4. The Brillouin zone integration was sampled with a 4×4×2 Γcentered k-point grid. And the bulk oxygen vacancy formation energy is defined as Evac = E(bulkdefect) +0.5 × E(O2) – E(bulkperfect), where E(bulkdefect) and E(bulkperfect) are the total energy of the defected supercell La2-xBixCuO4-δ and pristine La2-xBixCuO4, respectively, while E(O2) = -8.50 eV/O2 is the corrected O2 molecule total energy according to Ref. 30.

RESULTS AND DISCUSSION Bi doping effect on phase structure. Figure 1A shows the room temperature x-ray diffraction (XRD) of the as-prepared La1.9-xBixSr0.1CuO4-δ (x=0, 0.1, 0.2, 0.3, and 0.4) powders. Pure phase materials with the first-series R-P structure are obtained for x = 0, 0.1 and 0.2, indicating successfully bismuth doping. Calculated by Pauling’s second law, the cation coordination number of the complicated R-P phase is 9 for A-site and 6 for B-site element. Since the radius of Bi3+(Ⅸ) (1.24 Å) is similar with La3+(Ⅸ) (1.22 Å) while Bi3+(Ⅵ) (1.03 Å) differs a lot with Cu2+(Ⅵ) (0.73 Å)

31, 32

, Bi3+ ions are considered to exclusively occupy A-site. Rietveld

refinements were further conducted to simulate the diffraction patterns. The fitted parameters are listed in Table 1 and the refined XRD profiles are shown in Supplementary Figure S2. The bismuth doping causes tiny increases in the lattice parameters without changing the tetragonal symmetry, the I4/mmm space group. However, the appearance of impurity phases for x = 0.3 and 0.4 (Figure 1A) demonstrates the solubility limit must be less than x = 0.3. The thermal stability was investigated with LBSC1 (x = 0.1) as a representative. Hightemperature XRD patterns are shown in Figure 1B. As it increases from room temperature to 800 C, LBSC1 keeps the R-P structure, with slight deviation in the peak position to lower angle. After the temperature returns back, the deviation disappears. So, Figure 1B demonstrates good thermal


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stability for application in intermediate-temperature SOFCs, which is operated below 800 C. The chemical compatibility with doped ceria electrolytes was investigated by heating a LBSC1-SDC composite at 900 C for 2h, and the room temperature XRD pattern is shown in Figure 1C. Every peak in the pattern can be attributed to either SDC or LBSC1 and not any impurity phases are observed, indicating great chemical compatible between SDC and LBSC1, which also give a specific guidance in the build of symmetry cells and single cells.


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Figure 1. X-ray diffraction analysis, (A) room-temperature XRD patterns for LBSC powders with different Bi contents, (B) high-temperature XRD patterns for LBSC1, and (C) room-temperature XRD pattern for LBSC1-SDC composite with equal weight ratio and heated at 900 C for 2h.

Table 1. Lattice parameters for LBSC obtained by fitting the XRD pattern using Rietveld refinement method LBSC0

LBSC1

LBSC2

Space group

I4/mmm

I4/mmm

I4/mmm

a/Å

3.78339

3.78830

3.78897

c/Å

13.21527

13.22591

13.22351

Rwp/%

8.54

8.22

11.5

Rp/%

6.34

6.54

8.24

Bi doping effect on valence state. To get a clear information of the chemical state of the variable metal (Cu) and the oxygen species in the near-surface region, the XPS analysis was carried out at full survey spectra, and the peak images of each element are given in Supplementary Figure S3. Peaks corresponding to lanthanum (La 3d), strontium (Sr 3d), copper (Cu 2p), and oxygen (O 1s) can be detected clearly. And the peak of bismuth (Bi 4f) is also detected for LBSC1 and LBSC2, which further demonstrates the effective doping of bismuth element. It is clear that Bi doping does not change the valence of La and Sr. Meanwhile, changes in Cu and O are noticed. The response of Cu 2p3/2 is shown in Figure 2A, which is divided into three parts with the peak fitting method. The binding energy of 932.5 eV, 934 eV and 935 eV corresponding to Cu+, Cu2+ and Cu3+, respectively 33, 34. The proportion of Cu+ is obviously increased by bismuth doping,


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from 38.15% for the parent phase to 47.48% for LBSC2, while the content of Cu2+ and Cu3+ are reduced. The reduction of the average valence with introduction of bismuth should be coupled with the increase in oxygen vacancy concentration [𝑉𝑂∙∙ ], according to the principle of electrical neutrality, which can be described as Equation 1 and 2 with the Kröger-Vink notations for the transfer of Cu2+→ Cu+ and Cu3+→ Cu2+, respectively. 1

(1)

1

(2)

× ′ 2𝐶𝑢𝐶𝑢 + 𝑂𝑂× = 2𝐶𝑢𝐶𝑢 + 𝑉𝑂∙∙ + 2 𝑂2 ↑ ∙ × 2𝐶𝑢𝐶𝑢 + 𝑂𝑂× = 2𝐶𝑢𝐶𝑢 + 𝑉𝑂∙∙ + 2 𝑂2 ↑

Thus, bismuth doping increases the oxygen vacancy concentration in the near-surface region, which is critical for the cathode-gas interface reaction, and the reaction is expressed with Equation 3 for a p-type electronic conducting electrocatalyst. 1 2

𝑂2 + 𝑉𝑂∙∙ = 2ℎ∙ + 𝑂𝑂×

(3)

The response of O 1s expresses a combination of four different oxygen related species (Figure 2B), with the binding energy of 529, 530.5, 531.5 and 532.5eV, ascribed to the contribution of lattice oxygen (O2 － ), reactive oxygen species (O22- and O-), surface adsorbed oxygen and hydroxyl groups (O2 and –OH), and adsorbed molecular water or carbonates (H2O or CO32-), respectively 35-37. The reactive oxygen species are considered to be essential intermediates for the cathode reaction. Compared with the parent phase LBSC0, more reactive oxygen species are detected associated with bismuth doping. So, the presence of bismuth can provide much more active sites for oxygen surface exchanges, thus could accelerate the cathode reaction rate.


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Figure 2. X-ray photon spectroscopy (XPS) spectra and the fitting profiles for (A) Cu 2p 3/2 and (B) O 1s. Bi doping effect on oxygen nonstoichiometry. The varying oxygen content manifests the abilities to store and transport lattice oxygen in an oxygen-ion conducting material. The room temperature oxygen nonstoichiometry  in La1.9-xBixSr0.1CuO4-δ (x=0, 0.1, and 0.2) was determined by iodometric titration with the assumption of no valence state change in La, Sr, Bi, and O elements, Figure 3. The parent phase fabricated by the combustion process shows the oxygen-deficiency stoichiometry, δ>0. Bismuth doping increases  from 0.16 for LBSC0 to 0.24 for LBSC1 and 0.30 for LBSC2. And the calculated relative error according to the error transfer formula is only 0.33%. The release of lattice oxygen with increasing temperature was investigated with thermogravimetric analysis, Supplementary Figure S4. After eliminating the effects of combined water, the weight loss can only be attributed to the escape of lattice oxygen, and the calculated  at 800 C is also shown in Figure 3. It is 0.29 for the parent phase, increases with Bi doping to 0.41 and 0.48 for x = 0.1 and 0.2, respectively. Thus, Bi doping increases the oxygen vacancy concentration by 87.5% and 65.5% at room temperature and 800 C, respectively. The oxygen nonstoichiometry value is


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a metric for the oxygen ion transport properties that a larger oxygen vacancy concentration usually leads to a greater oxygen-ion conductivity. And the significant increase in oxygen vacancy concentration is bound to bring improvement in the performance as a cathode electrocatalyst 8, 38, 39

. The doping effect on oxygen vacancy formation is further revealed with DFT calculation.

The optimized structure of La2CuO4 and La1.875Bi0.125CuO4 are shown in Supplementary Figure S5. There are two inequivalent oxygen sites, situated in the apical and equatorial position in the CuO6 octahedra. The oxygen vacancy formation energy in both sites are calculated, which is 4.48 eV (apical) and 3.02 eV (equatorial) for La2CuO4 while 3.86 eV and 2.39 eV for La1.875Bi0.125CuO4 (shown in Figure 3). From a thermodynamic point of view, bismuth facilitates the formation of vacancy in the adjacent oxygen position (both apical and equatorial), and a large oxygen nonstoichiometry value δ can be expected.


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Figure 3. Bi doping effects on the oxygen nonstoichiometry δ at room temperature and 800 C, and the oxygen vacancy formation energy of apical and equatorial position, respectively.

Bi doping effect on transport property. Figure 4A compares the temperature dependence of electrical conductivity obtained with dense bar samples. In the tested temperature range from 550 to 800 C, the electrical conductivity increases with the decrease of temperature and the fitted slop is almost equal for every line, suggesting the doped material has the same conductivity mechanism with the parent cuprate. In addition to temperature, the conductivity is affected by the atmosphere, Figure 4B. The conductivity measured in air is lower than in oxygen, demonstrating the dominated charge carrier is electron hole, Equation 3. The Arrhenius plots of the conductivity is shown in Figure 4C, from which the cuprate with different bismuth contents possess similar


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activation energy, suggesting a consistent conductive mechanism for both doped and un-doped materials. However, Bi doping reduces the electrical conductivity, Figure 4A. The conductivity of LBSC0 at 800 C is 158.2 S·cm-1, which is in good consistent with the previous report, about 140 S·cm-1

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. It is reduced to 129.8 S·cm-1 for LBSC1 and further to 75.2 S·cm-1 for LBSC2. As

demonstrated with the iodometric titration and TG analysis, bismuth doping increases the oxygen nonstoichiometry , which means generating additional oxygen vacancies meanwhile consuming the charge carriers of electron holes as shown in Equation 3 and thus reducing the electrical conductivity. Although the conductivity is reduced, LBSC1 still has conductivities higher than 100 S·cm-1, which is comparable with typical R-P structured electrode materials such as Ln2-xNiO4+δ (Ln = La, Pr, Nd) 17. It has been found that bismuth doping has different effects on the conductivity of cathode materials such as reducing the conductivity of La1-xSrxFeO3-δ while increasing that of La1.75Sr0.25NiO4+δ 22, 40, 41.


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Figure 4. Bi doping effects on the electrical conductivity, (A) the conductivity measured in air from 550 to 800 C, (B) comparison of conductivity measured in air and oxygen at 600, 700, and 800 C, and (C) temperature dependence of the conductivity in air. The oxygen transport properties were explored with electrical conductivity relaxation (ECR) technique for bismuth doped materials. The properties for LBSC0 were not measured due to its low sensitivity to oxygen partial pressure as shown in Figure 4B. Figure 5A shows the normalized conductivities for LBSC2 as a function of the relaxation time at temperatures from 650 to 800 C. The oxygen transport properties, including the chemical oxygen surface exchange coefficient kChem and chemical oxygen diffusion coefficient DChem, are obtained by fitting the normalized conductivities to Fick’s second law. The fitting curve of LBSC2 at 800 C is shown in Supplementary Figure S6 as an example while the results and the standard deviation between measurement curve and fitting curve are listed in Supplementary Table S1. The Arrhenius plots for kChem and DChem are shown in Figure 5B and 5C, respectively. It is clear that LBSC2 has much high kChem and DChem compared with LBSC1. For example, at 800 C, kChem for LBSC2 is 7.7 × 10-4 cm s-1, about 15% higher than LBSC1, while DChem is 1.5 × 10-5 cm2 s-1, twice as that for LBSC1. The enhancement could be caused by the increased concentrations in oxygen vacancies and active oxygen species as a results of bismuth doping, which have been experimentally demonstrated with iodometric titration, thermogravimetric measurement and XPS analysis. The kChem for bismuth doped La1.9Sr0.1CuO4-δ is higher than while DChem is comparable with those reported R-P oxides of La1.75Sr0.25NiO4+δ and Pr2NiO4+δ 22 42.


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Figure 5. Oxygen transport properties obtained by ECR measurements, (A) normalized conductivities for LBSC2 as a function of time at temperatures from 650 to 800 C, (B) and (C) temperature dependence of kChem and DChem, data for La1.75Sr0.25NiO4+δ by ECR from Zhesheng Zhu et al.

22

and for Pr2CuO4+δ by weight relaxation from Kun Zheng et al.

42

is also shown for

comparison.

Thermal expansion properties. The Bi doping effects on thermal expansion behaviors were investigated with dilatometry. The strip LBSC0 and LBSC1 samples have similar microstructures, which are dense with average grain size of less than 1 m (Supplementary Figure S7). Figure 6A shows the thermal expansion curves between 200 and 800 C. The average thermal expansion coefficient (CTE) of LBSC0 is 13.3 × 10-6 K-1, consistent with 14.0 × 10-6 K-1 reported for the strontium doped cuprate with the composition of La1.7Sr0.3CuO4-δ

43

. Bismuth doping

reduces CTE to 9.2 × 10-6 K-1 for LBSC1. The CTE is lower than those for typical electrolytes, such as 12.2 × 10-6 K-1 for SDC and 10.5 × 10-6 K-1 for YSZ 44, 45. It is noted that the cathode materials usually have CTE higher than the electrolytes. Bismuth doping to R-P cuprates can reduce CTE from above to below those of the electrolytes, thus makes it possible to exactly match the thermal expansion behavior. High temperature XRD measurements allow to calculate the linear CTE along a specific axis as shown by Equation 4: ∆𝜆

𝐶𝑇𝐸 = 𝜆

0 ∆𝑇

=𝜆

𝜆−𝜆0

0 (𝑇−𝑇0 )

(4)

where 𝜆 is the lattice parameter at temperature 𝑇 and 𝜆0 is that at 𝑇0 , the reference state. The lattice parameters are derived from the XRD information at different temperature. Since LBSC is a Ruddlesden-Popper material with a ＝ b ≠ c, 𝐶𝑇𝐸 are calculated for a and c by linear fitting the


20

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temperature dependence parameter curves shown in Figure 6B. For LBSC0, 𝐶𝑇𝐸,𝑎 is 9.9  10-6 K1

while 𝐶𝑇𝐸,𝑐 is 8.5  10-6 K-1, suggesting anisotropic thermal expansion behaviors for the Sr-doped

lanthanum cuprates. The bismuth doped material also shows the anisotropic characters. Doping 5% bismuth to the A site reduces 𝐶𝑇𝐸,𝑎 by 18%, from 9.9  10-6 K-1 to 8.1  10-6 K-1 while 𝐶𝑇𝐸,𝑐 by 16%, from 8.5  10-6 K-1 to 7.1  10-6 K-1. Figure 6C shows the lattice volume as a function of temperature, which can be used to derive the volumetric thermal expansion coefficient 𝐶𝑇𝐸,𝑉 . The average linear expansion coefficient 𝐶𝑇𝐸 can be calculated with 𝐶𝑇𝐸,𝑉 = 3𝐶𝑇𝐸 , which is 9.5  106

K-1 for LBSC0 and 7.8  10-6 K-1 for LBSC1. The difference in 𝐶𝑇𝐸 obtained with dilatometry

and XRD could be ascribed to the diversity of the measuring method. The thermal expansion of a mixed conducting electrode material comes from the lattice vibration and chemical expansion, i.e. the changes in chemical composition such as oxygen vacancy concentration associated with heating. Usually, the lattice vibration of materials with same structure and close elemental composition shares a similar contribution to the thermal expansion. Since LSBC0 and LSBC1 have the same crystalline structure and close composition, their lattice vibration contributions should be very similar. The different in 𝐶𝑇𝐸 must be caused by the variation in chemical expansion associated with oxygen nonstoichiometry. Usually, high oxygen vacancy concentration, which means high oxygen nonstiochiometry such as  in the La1xSrxCoO3-

perovskite, corresponds to high 𝐶𝑇𝐸 . However, a recent study has shown that a gain of

either apical or equatorial oxygen vacancies for La1.85Sr0.15CuO4 results in lattice contraction rather than expansion 46. This suggests 𝐶𝑇𝐸 for the R-P structured strontium doped lanthanum cuprates decrease with the increasing in oxygen nonstoichiometry. Thus, the reduced 𝐶𝑇𝐸 value associated with bismuth doping is consistent with the increase in  value (Figure 3A), specifically, the weight


21


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loss from room temperature to 800 C determined by the TG analysis was increased from 0.523% for LBSC0 to 0.674% for LBSC1.


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Figure 6. Thermal expansion behaviors for LBSC0 and LBSC1, (A) thermal expansion curves determined with dilatometry, (B) lattice parameters a and c as a function of temperature, and (C) lattice volume as a function of temperature.

Bi doping effect on ORR. The Bi doping effects on the electrochemical performance for oxygen reduction reaction were investigated by measuring the AC impedance spectrum of symmetrical cells using LBSC-SDC composite electrodes and SDC electrolyte substrates. By adding SDC to form the composite electrode, the area specific interfacial polarization (Rp) can be obviously reduced (Supplementary Figure S8). Figure 7A shows the typical impedance spectrum tested at 800 C where the original data is normalized to area and divided by 2 due to the symmetrical structure and the resistance from the electrolyte and lead-wires is eliminated for clear comparison. Rp is 0.28 cm2 for LBSC0-SDC, smaller than that (0.37 cm2 at 800 C) reported for the composite electrode based on typical R-P material La1.8Sr0.2NiO4+δ

47

. It is clear that

bismuth doping can effectively improve the ORR activity, reducing Rp from 0.28 cm2 to 0.23 cm2 for x=0.1 and further to 0.16 cm2 for x=0.2. The doped electrocatalysts are superior in the investigated temperature range from 600 to 800 C, Figure 7B. The Arrhenius plots indicate that the activation energy is slightly reduced by Bi doping, from 1.43 eV to 1.36 eV. In the purpose of shedding light on the contribution of each sub-step to the total processes, the impedance spectra were analyzed by the distribution of relaxation time (DRT) method to separate different sub-step with its own characteristic relaxation time (Figure 7C). Each plot contains two distinguished peaks, the high-frequency peak P1 and low-frequency peak P2. The frequency of the peak point represents the sub-step characteristic frequency, while the integral of the peak area represents the polarization resistance of the corresponding sub-step. Based on the


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DRT analysis, the impedance spectra were fitted using the equivalent circuit 𝐿-𝑅𝑠 -(𝑅1 𝐶𝑃𝐸1 )(𝑅2 𝐶𝑃𝐸2 ), shown in the Figure 7A. And the detailed fitting results are listed in Supplementary Table S2. The calculated 𝑅2 is similar for the three cells. However, 𝑅1 , which accounts for the major part of the polarization resistance, decreases obviously with the bismuth content. A further EIS experiment was implemented with the LBSC1-SDC electrode at different oxygen partial pressure ranging from 0.21 to 1 atm and the DRT plots are shown in Figure 7D, expecting to have a clear information of the rate-determining step for the oxygen reduction reaction. With single rate-determining step assumption, the polarization resistance can be written as 𝑅𝑝 = 𝑘𝑃𝑂𝑛2 and the calculated n for 𝑅1 is -0.390 (Figure 7E), demonstrating that P1 represents charge transfer process as shown by Equation 5, which corresponds to 𝑛 = −0.375. The value for 𝑅2 is 0.018 (Figure 7F), suggesting that P2 is associated with the oxygen ions transportation at the electrolyte-electrode interface as shown with Equation 6, where n is characterized by 0 48, 49. − 𝑂𝑎𝑑 + 𝑒 − ↔ 𝑂𝑎𝑑

(5)

2− ∙∙ × 𝑂𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑑𝑒 + 𝑉𝑂,𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑙𝑦𝑡𝑒 ↔ 𝑂𝑂,𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑙𝑦𝑡𝑒

(6)

So far, it is clear that the electrode performance is enhanced with the improvement of the charge transfer step, which contributes more than 90% of the electrode resistance. Bi doping increases the content of active oxygen species including 𝑂𝑎𝑑 , thus improves the reaction rate of the charge transfer reaction.


25


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Figure 7. Electrochemical performance for composite LSBC-SDC electrodes using symmetric cells with SDC electrolyte substrates, (A) Impedance spectra measured at 800 C in air, (B) The


26

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Arrhenius plots of Rp, (C) DRT analysis of the impedance spectra shown in (A), (D) DRT analysis of the impedance spectra for LBSC1-SDC electrodes at different oxygen partial pressure, (E) and (F) Linear fitting results of logarithmic P1 and P2 sub-step polarization resistance as a function of logarithmic oxygen partial pressure.

Button cell performance enhanced with Bi doping. The integral button cell was fabricated to further investigate Bi doping effect on ORR, and the schematic of it is shown in Supplementary Figure S9, which is comprised of 500-μm thick porous Ni-YSZ anode, 16-μm thick dense YSZ electrolyte, thin SDC interlayer and 30-μm thick porous LBSC-SDC composite cathode. The cell voltage and power density change as a function of current density and operational temperature when humidified H2 was used as the fuel and ambient air as the oxidant. The observed peak power density of 530 mW cm-2 at 800 C (Figure 8A) for LBSC0 has great superiority compared with those for copper based R-P materials such as La1.5Sr0.5CuO4

50

(150 mW cm-2 at

800 C) and Pr2CuO4 42 (120 mW cm-2 at 800 C), demonstrating that the button cells were well formed. Bi doping promotes the power density, from 530 to 610 mW cm-2 for LBSC1 and 630 mW cm-2 for LBSC2, Figure 8B and 8C. The enhanced power density must be attributed to the improvement in the cathode performance associated with the introduction of bismuth since the three cells have the same electrolyte and anode. And a pretty low single cell polarization resistance of 0.2 Ω cm2 obtained for LBSC2 at 800 C (Supplementary Figure S10) demonstrated that LBSC2 is an excellent copper based R-P cathode material. Short-term durability test shows no apparent decrease in current density (Figure 8D). The cross-section morphology of the button cell LBSC2 after the 50 h durability test is presented in Figure 8E. The porous MIEC cathode without obvious agglomeration indicates good stability. Further zoomed fracture section of LBSC2/SDC/YSZ is


27


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shown in Figure 8F. The thin SDC interlayer, effectively blocks the reaction between the cathode and YSZ electrolyte while minimizing the impact on overall button cell performance.

Figure 8. Cell voltage and power density as a function of current density for button cells incorporation (A) LBSC0-SDC, (B) LBSC1-SDC, and (C) LBSC2-SDC cathodes. (D) short-term


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durability test at 700 C with constant current discharge for a cell with LBSC2-SDC cathode, (E) SEM graph for the cross-sectional structure of the tested single cell, (F) zoomed fracture section of LBSC2/SDC/YSZ triple layer structure. The button cell performance was tested with humidified hydrogen as the fuel and ambient air as the oxidant.

CONCLUSIONS Bismuth was successfully doped to the oxygen deficient R-P type La1.9Sr0.1CuO4-δ at a concentration up to 10% of the A-site. The doping has several effects on the physical-chemistry properties of the cuprate, including 1) reducing the average valence state of the B-site element Cu, 2) producing additional oxygen reactive species, which could accelerate the cathode reaction rate, 3) generating extra oxygen vacancies, especially at high temperatures and the vacancies are favorable for oxygen transportation, 4) reducing the thermal expansion coefficient from above to below those of typical electrolytes, thus making it possible to exactly matching the thermal expansion behavior to the electrolyte, 5) increasing the chemical oxygen surface exchange coefficient and oxygen bulk diffusion coefficient, and 6) decreasing the electronic conductivity as a result of generating extra oxygen vacancy. Meanwhile, the doping promotes the electrochemical performance by reducing the interfacial polarization resistance at 800C from 0.28 Ωcm2 to 0.16 Ωcm2 for LBSC-SDC composite electrodes on doped ceria electrolytes. The promotion is mainly caused by accelerating the charge transfer process, the rate limiting step for oxygen reduction reaction on the cuprate electrocatalyst. As a result, peak power density is increased from 530 mW·cm-2 to 630 mW·cm-2 at 800 C for single cells based on YSZ electrolytes.


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Supporting Information

Characterization methods, established model, calculation details, and additional experimental results.

Corresponding Authors * E-mail address: [email protected]

* E-mail address: [email protected]

ORCID Xiaojun Wu: 0000-0003-3606-1211 Changrong Xia: 0000-0002-4254-1425

Notes The authors declare no competing financial interest.

ACKONWLEDGMENTS This work was supported by the National Natural Science Foundation of China (91645101) and Anhui Estone Material Technology Co., Ltd (2016340022003195). We acknowledge the


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Supercomputing Center of University Science and Technology of China for providing computational resources. Figures with geometry are based on VESTA.

REFERENCES 1. Sun, Y. F.; Li, J. H.; Zeng, Y. M.; Amirkhiz, B. S.; Wang, M. N.; Behnamian, Y.; Luo, J. L., A-site deficient perovskite: the parent for in situ exsolution of highly active, regenerable nano-particles as SOFC anodes (vol 3, pg 11048, 2015). J Mater Chem A 2017, 5 (2), 852-853. 2. Zhang, Y. P.; Yu, F. Y.; Wang, X. Q.; Zhou, Q.; Liu, J.; Liu, M. L., Direct operation of Ag-based anode solid oxide fuel cells on propane. J Power Sources 2017, 366, 56-64. 3. Chen, G.; Zhou, W.; Guan, D. Q.; Sunarso, J.; Zhu, Y. P.; Hu, X. F.; Zhang, W.; Shao, Z. P., Two orders of magnitude enhancement in oxygen evolution reactivity on amorphous Ba0.5Sr0.5Co0.8Fe0.2O3-(delta) nanofilms with tunable oxidation state. Sci Adv 2017, 3 (6). 4. Li, M.; Chen, K. F.; Hua, B.; Luo, J. L.; Rickard, W. D. A.; Li, J.; Irvine, J. T. S.; Jiang, S. P., Smart utilization of cobaltite-based double perovskite cathodes on barrier-layer-free zirconia electrolyte of solid oxide fuel cells. J Mater Chem A 2016, 4 (48), 19019-19025. 5. Li, M.; Hua, B.; Luo, J. L.; Jiang, S. P.; Pu, J.; Chi, B.; Li, J., Enhancing Sulfur Tolerance of Ni-Based Cermet Anodes of Solid Oxide Fuel Cells by Ytterbium-Doped Barium Cerate Infiltration. Acs Appl Mater Inter 2016, 8 (16), 10293-10301. 6. Wang, W. Y.; Zhu, C. L.; Xie, K.; Gan, L. Z., High performance, coking-resistant and sulfur-tolerant anode for solid oxide fuel cell. J Power Sources 2018, 406, 1-6. 7. Bian, L. Z.; Duan, C. C.; Wang, L. J.; Zhu, L. Z.; O'Hayre, R.; Chou, K. C., Electrochemical performance and stability of La0.5Sr0.5Fe0.9Nb0.1O3-delta symmetric electrode for solid oxide fuel cells. J Power Sources 2018, 399, 398-405. 8. Zhang, Y.; Knibbe, R.; Sunarso, J.; Zhong, Y. J.; Zhou, W.; Shao, Z. P.; Zhu, Z. H., Recent Progress on Advanced Materials for Solid-Oxide Fuel Cells Operating Below 500 degrees C. Adv Mater 2017, 29 (48). 9. Lee, D.; Lee, H. N., Controlling Oxygen Mobility in Ruddlesden-Popper Oxides. Materials 2017, 10 (4). 10. Gu, X. K.; Nikolla, E., Design of Ruddlesden-Popper Oxides with Optimal Surface Oxygen Exchange Properties for Oxygen Reduction and Evolution. Acs Catal 2017, 7 (9), 59125920. 11. Laguna-Bercero, M. A.; Monzon, H.; Larrea, A.; Orera, V. M., Improved stability of reversible solid oxide cells with a nickelate-based oxygen electrode. J Mater Chem A 2016, 4 (4), 1446-1453. 12. Lee, Y. L.; Lee, D.; Wang, X. R.; Lee, H. N.; Morgan, D.; Shao-Horn, Y., Kinetics of Oxygen Surface Exchange on Epitaxial Ruddlesden-Popper Phases and Correlations to FirstPrinciples Descriptors. J Phys Chem Lett 2016, 7 (2), 244-249. 13. Guan, B.; Li, W. Y.; Zhang, H.; Liu, X. B., Oxygen Reduction Reaction Kinetics in SrDoped La2NiO4+delta Ruddlesden-Popper Phase as Cathode for Solid Oxide Fuel Cells. J Electrochem Soc 2015, 162 (7), F707-F712.


31


Page 32 of 35

14. Opila, E. J.; Tuller, H. L.; Wuensch, B. J.; Maier, J., Oxygen Tracer Diffusion in La2Xsrxcuo4-Y Single-Crystals. J Am Ceram Soc 1993, 76 (9), 2363-2369. 15. Tomkiewicz, A. C.; Tamimi, M.; Huq, A.; McIntosh, S., Oxygen transport pathways in Ruddlesden-Popper structured oxides revealed via in situ neutron diffraction. J Mater Chem A 2015, 3 (43), 21864-21874. 16. Routbort, J. L.; Rothman, S. J.; Flandermeyer, B. K.; Nowicki, L. J.; Baker, J. E., Oxygen Diffusion in La2-Xsrx Cuo4-Y. J Mater Res 1988, 3 (1), 116-121. 17. Boehm, E.; Bassat, J. M.; Dordor, P.; Mauvy, F.; Grenier, J. C.; Stevens, P., Oxygen diffusion and transport properties in non-stoichiometric Ln(2-x)NiO(4+delta) oxides. Solid State Ionics 2005, 176 (37-38), 2717-2725. 18. Aguadero, A.; Alonso, J. A.; Martinez-Lope, M. J.; Fernandez-Diaz, M. T.; Escudero, M. J.; Daza, L., In situ high temperature neutron powder diffraction study of oxygen-rich La2NiO4+delta in air: correlation with the electrical behaviour. J Mater Chem 2006, 16 (33), 3402-3408. 19. Li, Q.; Zhao, H.; Huo, L. H.; Sun, L. P.; Cheng, X. L.; Grenier, J. C., Electrode properties of Sr doped La2CuO4 as new cathode material for intermediate-temperature SOFCs. Electrochem Commun 2007, 9 (7), 1508-1512. 20. Wedig, A.; Merkle, R.; Maier, J., Oxygen Exchange Kinetics of (Bi,Sr)(Co,Fe)O3-delta Thin-Film Microelectrodes. J Electrochem Soc 2014, 161 (1), F23-F32. 21. Yao, C. G.; Meng, J. L.; Liu, X. J.; Zhang, X.; Meng, F. Z.; Wu, X. J.; Meng, J., Effects of Bi doping on the microstructure, electrical and electrochemical properties of La2xBixCu0.5Mn1.5O6 (x=0, 0.1 and 0.2) perovskites as novel cathodes for solid oxide fuel cells. Electrochim Acta 2017, 229, 429-437. 22. Zhu, Z. S.; Li, M.; Xia, C. R.; Bouwmeester, H. J. M., Bismuth-doped La1.75Sr0.25NiO4+delta as a novel cathode material for solid oxide fuel cells. J Mater Chem A 2017, 5 (27), 14012-14019. 23. Wang, Y. P.; Xu, Q.; Huang, D. P.; Zhao, K.; Chen, M.; Kim, B. H., Diagnosis on improved electrocatalytic activity of La2Ni0.8Cu0.2O4+delta electrodes towards oxygen reduction reaction. Appl Surf Sci 2017, 423, 995-1002. 24. Hu, B. B.; Xia, C. R., Factors influencing the measured surface reaction kinetics parameters. Asia-Pac J Chem Eng 2016, 11 (3), 327-337. 25. Zhang, Y. X.; Chen, Y.; Yan, M. F.; Chen, F. L., Reconstruction of relaxation time distribution from linear electrochemical impedance spectroscopy. J Power Sources 2015, 283, 464-477. 26. Blochl, P. E., Projector Augmented-Wave Method. Phys Rev B 1994, 50 (24), 1795317979. 27. Kresse, G.; Furthmuller, J., Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set. Comp Mater Sci 1996, 6 (1), 15-50. 28. Perdew, J. P.; Burke, K.; Ernzerhof, M., Generalized gradient approximation made simple. Phys Rev Lett 1996, 77 (18), 3865-3868. 29. Xie, W.; Lee, Y. L.; Shao-Horn, Y.; Morgan, D., Oxygen Point Defect Chemistry in Ruddlesden-Popper Oxides (La1-xSrx)(2)MO4 +/-delta (M = Co, Ni, Cu). J Phys Chem Lett 2016, 7 (10), 1939-1944. 30. Lee, Y. L.; Kleis, J.; Rossmeisl, J.; Morgan, D., Ab initio energetics of LaBO3(001) (B=Mn, Fe, Co, and Ni) for solid oxide fuel cell cathodes. Phys Rev B 2009, 80 (22).


32

Page 33 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


31. Shannon, R. D., Revised Effective Ionic-Radii and Systematic Studies of Interatomic Distances in Halides and Chalcogenides. Acta Crystallogr A 1976, 32 (Sep1), 751-767. 32. Ok, K. M.; Ohishi, Y.; Mitazono, Y.; Muta, H.; Kurosaki, K.; Yamanaka, S., Bi-doped lanthanum molybdate: Enhancing the anharmonicity and reducing the thermal conductivity using Bi3+ with lone pair electrons. Ceram Int 2018, 44 (13), 15833-15838. 33. Gao, L.; Zhu, M. Z.; Li, Q.; Sun, L. P.; Zhao, H.; Grenier, J. C., Electrode properties of Cu-doped Bi0.5Sr0.5FeO3-delta cobalt-free perovskite as cathode for intermediate-temperature solid oxide fuel cells. J Alloy Compd 2017, 700, 29-36. 34. Tahir, D.; Tougaard, S., Electronic and optical properties of Cu, CuO and Cu2O studied by electron spectroscopy. J Phys-Condens Mat 2012, 24 (17). 35. Zhang, Z. B.; Zhu, Y. L.; Zhong, Y. J.; Zhou, W.; Shao, Z. P., Anion Doping: A New Strategy for Developing High-Performance Perovskite-Type Cathode Materials of Solid Oxide Fuel Cells. Adv Energy Mater 2017, 7 (17). 36. Zhu, Y. L.; Zhou, W.; Sunarso, J.; Zhong, Y. J.; Shao, Z. P., Phosphorus-Doped Perovskite Oxide as Highly Efficient Water Oxidation Electrocatalyst in Alkaline Solution. Adv Funct Mater 2016, 26 (32), 5862-5872. 37. Meng, Q. J.; Wang, W. L.; Weng, X. L.; Liu, Y.; Wang, H. Q.; Wu, Z. B., Active Oxygen Species in Lan+1NinO3n+1 Layered Perovskites for Catalytic Oxidation of Toluene and Methane. J Phys Chem C 2016, 120 (6), 3259-3266. 38. Chen, H. J.; Guo, Z.; Zhang, L. A.; Li, Y. F.; Li, F.; Zhang, Y. P.; Chen, Y.; Wang, X. W.; Yu, B.; Shi, J. M.; Liu, J.; Yang, C. H.; Cheng, S.; Chen, Y.; Liu, M. L., Improving the Electrocatalytic Activity and Durability of the La0.6Sr0.4Co0.2Fe0.8O3-delta Cathode by Surface Modification. Acs Appl Mater Inter 2018, 10 (46), 39785-39793. 39. Zhang, X. M.; Song, Y. F.; Guan, F.; Zhou, Y. J.; Lv, H. F.; Liu, Q. X.; Wang, G. X.; Bao, X. H., (La0.75Sr0.25)(0.95)(Cr0.5Mn0.5)O3-delta-Ce0.8Gd0.2O1.9 scaffolded composite cathode for high temperature CO2 electroreduction in solid oxide electrolysis cell. J Power Sources 2018, 400, 104-113. 40. Niu, Y. J.; Sunarso, J.; Liang, F. L.; Zhou, W.; Zhu, Z. H.; Shao, Z. P., A Comparative Study of Oxygen Reduction Reaction on Bi- and La-Doped SrFeO3-delta Perovskite Cathodes. J Electrochem Soc 2011, 158 (2), B132-B138. 41. Li, M.; Wang, Y.; Wang, Y. L.; Chen, F. L.; Xia, C. R., Bismuth Doped Lanthanum Ferrite Perovskites as Novel Cathodes for Intermediate-Temperature Solid Oxide Fuel Cells. Acs Appl Mater Inter 2014, 6 (14), 11286-11294. 42. Zheng, K.; Gorzkowska-Sobas, A.; Swierczek, K., Evaluation of Ln(2)CuO(4) (Ln:La, Pr, Nd) oxides as cathode materials for IT-SOFCs. Mater Res Bull 2012, 47 (12), 4089-4095. 43. Ding, X. F.; Kong, X.; Wang, X. O.; Jiang, J. G.; Cui, C., Characterization and optimization of Ln(1.7)Sr(0.3)CuO(4) (Ln = La, Nd)-based cathodes for intermediate temperature solid oxide fuel cells. J Alloy Compd 2010, 502 (2), 472-476. 44. Eguchi, K.; Setoguchi, T.; Inoue, T.; Arai, H., Electrical-Properties of Ceria-Based Oxides and Their Application to Solid Oxide Fuel-Cells. Solid State Ionics 1992, 52 (1-3), 165172. 45. Yamamoto, O., Solid oxide fuel cells: fundamental aspects and prospects. Electrochim Acta 2000, 45 (15-16), 2423-2435. 46. Meyer, T. L.; Jacobs, R.; Lee, D.; Jiang, L.; Freeland, J. W.; Sohn, C.; Egami, T.; Morgan, D.; Lee, H. N., Strain control of oxygen kinetics in the Ruddlesden-Popper oxide La1.85Sr0.15CuO4. Nat Commun 2018, 9.


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47. Wang, Y. P.; Xu, Q.; Huang, D. P.; Zhao, K.; Chen, M.; Kim, B. H., Evaluation of La1.8Sr0.2NiO4+delta as cathode for intermediate temperature solid oxide fuel cells. Int J Hydrogen Energ 2016, 41 (15), 6476-6485. 48. Wang, Y. L.; Zhang, L.; Chen, F. L.; Xia, C. R., Effects of doped ceria conductivity on the performance of La0.6Sr0.4Co0.2Fe0.8O3-delta cathode for solid oxide fuel cell. Int J Hydrogen Energ 2012, 37 (10), 8582-8591. 49. Kenney, B.; Karan, K., Impact of nonuniform potential in SOFC composite cathodes on the determination of electrochemical kinetic parameters - A numerical analysis. J Electrochem Soc 2006, 153 (6), A1172-A1180. 50. Niemczyk, A.; Olszewska, A.; Du, Z. H.; Zhang, Z. J.; Swierczek, K.; Zhao, H. L., Assessment of layered La2-x(Sr,Ba)(x)CuO4-delta oxides as potential cathode materials for SOFCs. Int J Hydrogen Energ 2018, 43 (32), 15492-15504.


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Oxygen deficient Ruddlesden-Popper type lanthanum strontium

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