Electrokinetic Proton Transport in Triple (H+ /O2- /e- ) Conducting Oxides as a Key Descriptor for Highly Efficient Protonic Ceramic Fuel Cells.

Recently, triple (H+ /O2- /e- ) conducting oxides (TCOs) have shown tremendous potential to improve the performance of various types of energy conversion and storage applications. The systematic understanding of the TCO is limited by the difficulty of properly identifying the proton movement in the TCO. Herein, the isotope exchange diffusion profile (IEDP) method is employed via time-of-flight secondary ion mass spectrometry to evaluate kinetic properties of proton in the layered perovskite-type TCOs, PrBa0.5 Sr0.5 Co1.5 Fe0.5 O5+ δ (PBSCF).Within the strategy, the PBSCF shows two orders of magnitude higher proton tracer diffusion coefficient (D* H , 1.04 × 10-6  cm2 s-1 at 550 °C) than its oxygen tracer diffusion coefficient at even higher temperature range (D* O, 1.9 × 10-8  cm2 s-1 at 590 °C). Also, the surface exchange coefficient of a proton (k*H ) is successfully obtained in the value of 2.60 × 10-7  cm s-1 at 550 °C. In this research, an innovative way is provided to quantify the proton kinetic properties (D* H and k*H ) of TCOs being a crucial indicator for characterizing the electrochemical behavior of proton and the mechanism of electrode reactions.

Cation-swapped homogeneous nanoparticles in perovskite oxides for high power density.

Exsolution has been intensively studied in the fields of energy conversion and storage as a method for the preparation of catalytically active and durable metal nanoparticles. Under typical conditions, however, only a limited number of nanoparticles can be exsolved from the host oxides. Herein, we report the preparation of catalytic nanoparticles by selective exsolution through topotactic ion exchange, where deposited Fe guest cations can be exchanged with Co host cations in PrBaMn1.7Co0.3O5+δ. Interestingly, this phenomenon spontaneously yields the host PrBaMn1.7Fe0.3O5+δ, liberating all the Co cations from the host owing to the favorable incorporation energy of Fe into the lattice of the parent host (ΔEincorporation = -0.41 eV) and the cation exchange energy (ΔEexchange = -0.34 eV). Remarkably, the increase in the number of exsolved nanoparticles leads to their improved catalytic activity as a solid oxide fuel cell electrode and in the dry reforming of methane.

Exsolution trends and co-segregation aspects of self-grown catalyst nanoparticles in perovskites.

In perovskites, exsolution of transition metals has been proposed as a smart catalyst design for energy applications. Although there exist transition metals with superior catalytic activity, they are limited by their ability to exsolve under a reducing environment. When a doping element is present in the perovskite, it is often observed that the surface segregation of the doping element is changed by oxygen vacancies. However, the mechanism of co-segregation of doping element with oxygen vacancies is still an open question. Here we report trends in the exsolution of transition metal (Mn, Co, Ni and Fe) on the PrBaMn2O5+δ layered perovskite oxide related to the co-segregation energy. Transmission electron microscopic observations show that easily reducible cations (Mn, Co and Ni) are exsolved from the perovskite depending on the transition metal-perovskite reducibility. In addition, using density functional calculations we reveal that co-segregation of B-site dopant and oxygen vacancies plays a central role in the exsolution.

A perovskite oxide with high conductivities in both air and reducing atmosphere for use as electrode for solid oxide fuel cells.

Electrode materials which exhibit high conductivities in both oxidising and reducing atmospheres are in high demand for solid oxide fuel cells (SOFCs) and solid oxide electrolytic cells (SOECs). In this paper, we investigated Cu-doped SrFe0.9Nb0.1O3-δ finding that the primitive perovskite oxide SrFe0.8Cu0.1Nb0.1O3-δ (SFCN) exhibits a conductivity of 63 Scm(-1)and 60 Scm(-1) at 415 °C in air and 5%H2/Ar respectively. It is believed that the high conductivity in 5%H2/Ar is related to the exsolved Fe (or FeCu alloy) on exposure to a reducing atmosphere. To the best of our knowledge, the conductivity of SrFe0.8Cu0.1Nb0.1O3-δ in a reducing atmosphere is the highest of all reported oxides which also exhibit a high conductivity in air. Fuel cell performance using SrFe0.8Cu0.1Nb0.1O3-δ as the anode, (Y2O3)0.08(ZrO2)0.92 as the electrolyte and La0.8Sr0.2FeO3-δ as the cathode achieved a power density of 423 mWcm(-2) at 700 °C indicating that SFCN is a promising anode for SOFCs.

Layered oxygen-deficient double perovskite as an efficient and stable anode for direct hydrocarbon solid oxide fuel cells.

Different layered perovskite-related oxides are known to exhibit important electronic, magnetic and electrochemical properties. Owing to their excellent mixed-ionic and electronic conductivity and fast oxygen kinetics, cation layered double perovskite oxides such as PrBaCo2O5 in particular have exhibited excellent properties as solid oxide fuel cell oxygen electrodes. Here, we show for the first time that related layered materials can be used as high-performance fuel electrodes. Good redox stability with tolerance to coking and sulphur contamination from hydrocarbon fuels is demonstrated for the layered perovskite anode PrBaMn2O5+δ (PBMO). The PBMO anode is fabricated by in situ annealing of Pr0.5Ba0.5MnO3-δ in fuel conditions and actual fuel cell operation is demonstrated. At 800 °C, layered PBMO shows high electrical conductivity of 8.16 S cm(-1) in 5% H2 and demonstrates peak power densities of 1.7 and 1.3 W cm(-2) at 850 °C using humidified hydrogen and propane fuels, respectively.

Triple-conducting layered perovskites as cathode materials for proton-conducting solid oxide fuel cells.

We report on an excellent anode-supported H(+) -SOFC material system using a triple conducting (H(+) /O(2-) /e(-) ) oxide (TCO) as a cathode material for H(+) -SOFCs. Generally, mixed ionic (O(2-) ) and electronic conductors (MIECs) have been selected as the cathode material of H(+) -SOFCs. In an H(+) -SOFC system, however, MIEC cathodes limit the electrochemically active sites to the interface between the proton conducting electrolyte and the cathode. New approaches to the tailoring of cathode materials for H(+) -SOFCs should therefore be considered. TCOs can effectively extend the electrochemically active sites from the interface between the cathode and the electrolyte to the entire surface of the cathode. The electrochemical performance of NBSCF/BZCYYb/BZCYYb-NiO shows excellent long term stability for 500 h at 1023 K with high power density of 1.61 W cm(-2) .

Highly efficient and robust cathode materials for low-temperature solid oxide fuel cells: PrBa0.5Sr0.5Co(2-x)Fe(x)O(5+δ).

Solid oxide fuel cells (SOFC) are the cleanest, most efficient, and cost-effective option for direct conversion to electricity of a wide variety of fuels. While significant progress has been made in anode materials with enhanced tolerance to coking and contaminant poisoning, cathodic polarization still contributes considerably to energy loss, more so at lower operating temperatures. Here we report a synergistic effect of co-doping in a cation-ordered double-perovskite material, PrBa0.5Sr0.5Co(2-x)Fe(x)O(5+δ), which has created pore channels that dramatically enhance oxygen ion diffusion and surface oxygen exchange while maintaining excellent compatibility and stability under operating conditions. Test cells based on these cathode materials demonstrate peak power densities ~2.2 W cm(-2) at 600°C, representing an important step toward commercially viable SOFC technologies.