Disruption of extended defects in solid oxide fuel cell anodes for methane oxidation

Abstract

Point defects largely govern the electrochemical properties of oxides: at low defect concentrations, conductivity increases with concentration; however, at higher concentrations, defect-defect interactions start to dominate. Thus, in searching for electrochemically active materials for fuel cell anodes, high defect concentration is generally avoided. Here we describe an oxide anode formed from lanthanum-substituted strontium titanate (La-SrTiO3) in which we control the oxygen stoichiometry in order to break down the extended defect intergrowth regions and create phases with considerable disordered oxygen defects. We substitute Ti in these phases with Ga and Mn to induce redox activity and allow more flexible coordination. The material demonstrates impressive fuel cell performance using wet hydrogen at 950 degrees C. It is also important for fuel cell technology to achieve efficient electrode operation with different hydrocarbon fuels, although such fuels are more demanding than pure hydrogen. The best anode materials to date--Ni-YSZ (yttria-stabilized zirconia) cermets--suffer some disadvantages related to low tolerance to sulphur, carbon build-up when using hydrocarbon fuels (though device modifications and lower temperature operation can avoid this) and volume instability on redox cycling. Our anode material is very active for methane oxidation at high temperatures, with open circuit voltages in excess of 1.2 V. The materials design concept that we use here could lead to devices that enable more-efficient energy extraction from fossil fuels and carbon-neutral fuels.

What Can Electron Microscopy Tell Us Beyond Crystal Structures?

“…Randomly distributed dark spots are also visible but no local lattice distortion is observed. [19] Excess [55] The arrows indicate some dark spots, which are the locations of excess oxygen anions. The inset shows an enlarged image of a dark spot.…”

“…Figure 6 (a) shows a typical HRTEM image of La 4 Sr 8 Ti 12 O 38 in a perovskite structure with excess oxygen, with which a high anion conductivity was achieved. [55] Since there is not a large enough space for guest atoms in a perfect perovskite crystal with a formula of ABO 3 , the excess oxygen atoms must go to interstitial sites and build up local lattice strain. The resolution of the electron microscope (JEOL JEM-2010) used is not high enough to image randomly located individual oxygen atoms.…”

A Ceramic-Anode Supported Low Temperature Solid Oxide Fuel Cell

“…4 To overcome these issues, nickel-free metal oxide anode materials have been investigated, such as La 0.75 Sr 0.25 Cr 0.5 Mn 0.5 O 3−δ (LSCM), 5 Sr 2 Mg 1−x Mn x MoO 6−δ (x = 0 to 1), 6 and doped (La, Sr)(Ti)O 3 . 7,8 Experimental results have demonstrated that such anode materials are effective in inhibiting carbon deposition or sulfur poisoning. [9][10][11] So far the cell designs are exclusively electrolyte-supported when metal oxide anodes are employed.…”

Effect of oxygen vacancy distribution on the thermoelectric properties of La-doped SrTiO3 epitaxial thin films

“…INTRODUCTION SrTiO 3 (STO) exhibits a host of interesting phenomena ranging from being a quantum paraelectric insulator 1 to a ferroelectric under strain 2 and a metal 3 or superconductor 4 when doped and hence has been one of most extensively studied perovskite oxides. These diverse properties make it an attractive choice for many applications such as oxidebased electronics, 5 photocatalysis, and as electrodes 6 in solid oxide fuel cells. Recently, the presence of a two-dimensional electron gas at the bare surface of STO 7 and at the interface of the polar STO with non-polar LaAlO 3 (LAO) has been demonstrated, 8 triggering intense research from both fundamental and applications points of view.…”