Dynamic behavior of impurities and native components in model LSM microelectrodes on YSZ

Energy conversion materials exhibit complex dynamic behavior when subjected to elevated temperatures and polarization.</p

High-temperature thermoelectric properties of Na- and W-Doped Ca₃Co₄O₉ system

The detailed crystal structures and high temperature thermoelectric properties of polycrystalline Ca(3−2x)Na(2x)Co(4−x)W(x)O(9) (0 ≤ x ≤ 0.075) samples have been investigated. Powder X-ray diffraction data show that all samples are phase pure, with no detectable traces of impurity. The diffraction peaks shift to lower angle values with increase in doping (x), which is consistent with larger ionic radii of Na(+) and W(6+) ions. X-ray photoelectron spectroscopy data reveal that a mixture of Co(2+), Co(3+) and Co(4+) valence states are present in all samples. It has been observed that electrical resistivity (ρ), Seebeck coefficient (S) and thermal conductivity (κ) are all improved with dual doping of Na and W in Ca(3)Co(4)O(9) system. A maximum power factor (PF) of 2.71 × 10(−4) W m(−1) K(−2) has been obtained for x = 0.025 sample at 1000 K. The corresponding thermoelectric figure of merit (zT) for x = 0.025 sample is calculated to be 0.21 at 1000 K, which is ∼2.3 times higher than zT value of the undoped sample. These results suggest that Na and W dual doping is a promising approach for improving thermoelectric properties of Ca(3)Co(4)O(9) system

Oxygen Electrode Kinetics and Surface Composition of Dense (La_0.75Sr_0.25)_0.95MnO₃ on YSZ

Lanthanum strontium manganate (LSM) micro-electrodes with the nominal composition of (La0.75Sr0.25)0.95MnO3 were deposited on yttria stabilized zirconia (YSZ). The diameter varied from 20 – 100 μm and the thickness was kept constant at ca. 0.5 μm. Electrochemical characterization was carried out in situ at temperatures from 660 to 860 °C using controlled atmosphere high temperature scanning probe microscope (CAHT-SPM) set-up for measurements of impedance spectroscopy and potential sweep. The oxygen partial pressure, pO2, was varied. Further, ex situ surface analysis by time of flight secondary mass spectrometry (TOF-SIMS) and structure examination by scanning electron microscopy (SEM) were performed. Segregation of Sr and La oxides to LSM surfaces and Mn rich oxide to the three phase boundary (TPB) was observed. YSZ and LSM attract different oxides/impurities. The oxygen electrode kinetics are discussed in light of the surface compositions and compared with the literature on microelectrode and composite LSM-YSZ electrode kinetics.</jats:p