Sivaprakash Sengodan

Highly efficient and robust cathode materials for low-temperature solid oxide fuel cells: PrBa0.5Sr0.5Co2−xFexO5+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, PrBa0.5Sr0.5Co2−xFexO5+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.

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) .

A robust symmetrical electrode with layered perovskite structure for direct hydrocarbon solid oxide fuel cells: PrBa0.8Ca0.2Mn2O5+δ

Symmetrical solid oxide fuel cells (SOFCs), where the same material is used as both the anode and the cathode, have gained increasing attention due to a number of attractive benefits compared to the conventional SOFC such as a simplified fabrication procedure, reduced processing costs, minimized compatibility issues, as well as enhanced stability and reliability. Since the anode is in a reducing environment while the cathode is in an oxidizing environment, the symmetrical SOFC electrode should be chemically and structurally stable in both environments. Herein, we propose a highly stable symmetrical SOFC electrode, a layered perovskite Ca doped PrBaMn2O5+δ (PBCMO). The electrical conductivity of this electrode is very high in a reducing atmosphere and suitable in an oxidizing atmosphere. Furthermore, the PBCMO symmetrical electrode demonstrates excellent electrochemical performance and durability in various hydrocarbon fuels as well as hydrogen.

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−1and 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.

Self-assembled alloy nanoparticles in a layered double perovskite as a fuel oxidation catalyst for solid oxide fuel cells

In situ exsolved nanoparticles on metal oxide materials have received much attention in catalysis due to their well socketed structure and high catalytic activity. Recently, the demand for active nanoparticles with multiple functionalities in catalysis has increased, so exsolutions of intermetallic nanoparticles could be an effective strategy to meet the requirements. Herein, for the first time, we report exsolved Co–Ni alloy nanoparticles and their Gibbs free energy of alloy formation in a PrBaMn1.7Co0.1Ni0.2O5+δ layered double perovskite. These exsolved alloy nanoparticles have a high catalytic performance for fuel oxidation in fuel cells and in the dry reforming of methane. Furthermore, we probed the mechanism of the alloy formation in the exsolution using density functional theory (DFT). The theoretical calculations reveal that the Gibbs free energy of the surface alloy formation (ΔGaggr_surface) is more favorable than that of the bulk alloy formation (ΔGaggr_bulk), indicating that Co and Ni are exsolved separately from the bulk, and then aggregate to form a Co–Ni alloy on the surface.