Michael D. Gross

Redox Stability of SrNb x Ti1 − x O3 – YSZ for Use in SOFC Anodes

The conductive properties of bulk SrNb x Ti 1-x O 3 (SNT) and porous SrNb x Ti 1-x O 3 -yttria-stabilized zirconia (YSZ) composites for x = 0.01, 0.05, and 0.20 have been examined under relevant solid oxide fuel cell (SOFC) operating temperatures and redox cycling conditions. The porous composite conductivities were approximately 1 order of magnitude lower than the corresponding bulk material. In order to obtain reasonable conductivity levels for SOFCs, samples were prereduced at 1400°C in H 2 . The conductivity of prereduced samples increased with increasing Nb content when directly measured in humidified H 2 ; however, when considering the conductivities measured after redox cycling, there appears to be no benefit to using higher dopant levels. After redox cycling at 800°C, a composite conductivity of 1 S/cm at 800°C in humidified H 2 (3% H 2 O) was achieved for x = 0.01 and 0.05 and a composite conductivity of 0.5 S/cm was achieved for x = 0.20. Fuel cell power densities of 415 mW/cm 2 at 700°C and 640 mW/cm 2 at 800°C were achieved in humidified H 2 (3% H 2 O) with a porous SNT-YSZ anode infiltrated with 1 wt % Pd and 3 wt % CeO 2 , a 50 μm thick YSZ electrolyte, and an La 0.8 Sr 0.2 FeO 3 (LSF), LSF-YSZ cathode. The implications of these results for the development of redox-stable anodes are discussed.

SOFC Anodes Based on LST–YSZ Composites and on Y0.04Ce0.48Zr0.48O2

The properties of solid oxide fuel cell (SOFC) anode functional layers prepared by impregnation of 1 wt % Pd and 10 wt % ceria into porous scaffolds of either Y 0.04 Ce 0.48 Zr 0.48 O 2 (CZY) or composites of La 0.3 Sr 0.7 TiO 3 (LST) and yttria-stabilized zirconia (YSZ) were examined to determine whether these scaffold materials would have sufficient electronic and ionic conductivity. Laminated tapes were cofired to produce 50 μm YSZ electrolytes and 50 μm scaffolds, supported on LSF-YSZ cathodes. The electronic conductivities of LST-YSZ composites were a function of the porosity and the weight fraction of LST but could be sufficient for use in thin functional layers. However, anodes made with LST-YSZ composites had higher nonohmic losses than cells made with YSZ scaffolds. With CZY scaffolds, some migration of Ce into the YSZ electrolyte was observed after cofiring. While CZY exhibited electronic conductivity, the loss in ionic conductivity compared to YSZ again resulted in higher nonohmic losses. The implications of these results for producing better ceramic anodes are discussed.

To what extent can instructors influence student motivation in the classroom

Understanding student motivation is an essential aspect of effective course design. Since motivations are related to learning outcomes ranging from critical thinking to creativity to lifelong learning, helping students develop positive motivations toward learning is critical for the engagement and success of tomorrows STEM graduates. In this workshop, we explore the specific roles that instructors may play in influencing students activity-level, or situational, motivation. The workshop offers an opportunity for instructors to directly apply motivation theory and empirical research findings to practical course design, and to identify specific ways in which they may positively influence their students motivational responses in the classroom.