Browsing by Author "Zhu, ZH"

Now showing 1 - 3 of 3
  • No Thumbnail Available
    Item
    A comparative study of SrCo0.8Nb0.2O3−δ and SrCo0.8Ta0.2O3−δ as low-temperature solid oxide fuel cell cathodes: effect of non-geometry factors on the oxygen reduction reaction
    (Royal Society of Chemistry, 2015-11-11) Li, MR; Zhou, W; Peterson, VK; Zhao, MW; Zhu, ZH
    The oxygen reduction reaction (ORR) activity of cathodes has to be improved to realize the low-temperature operation of solid-oxide fuel cells (SOFCs). Whilst geometric factors are conventionally accepted to influence the ORR activity of perovskite cathodes, other factors may also contribute and therefore need to be explored. Here, we substituted 20% niobium and tantalum which have similar ionic radii into strontium cobaltites to obtain the two perovskite oxides SrCo0.8Nb0.2O3−δ (SCN20) and SrCo0.8Ta0.2O3−δ (SCT20), respectively. Our study of the isostructural SCN20 and SCT20 allows geometric effects to be separated from other factors, and we observe better cathode performance of SCT20 cathode, which may be related to the lower electronegativity of Ta5+, thus resulting in higher oxygen surface exchange kinetics and diffusivity as compared with Nb5+. © Royal Society of Chemistry 2015
  • No Thumbnail Available
    Item
    Enhancing oxygen reduction reaction activity and CO2 tolerance of cathode for low-temperature solid oxide fuel cells by in situ formation of carbonates
    (American Chemical Society, 2019-07-31) Rehman, AU; Li, MR; Knibbe, R; Khan, MS; Peterson, VK; Brand, HEA; Li, ZH; Zhou, W; Zhu, ZH
    Development of low-cost and cobalt-free efficient cathode materials for oxygen reduction reaction (ORR) remains one of the paramount motivations for material researchers at a low temperature (<650 °C). In particular, iron-based perovskite oxides show promise as electrocatalysts for ORR because Fe metal is cheaper and naturally abundant, exhibit matched thermal expansion with contacting components such as electrolytes, and show high tolerance in a CO2-containing atmosphere. Herein, we demonstrated a new mechanism, the in situ formation of alkali metal carbonates at the cathode surface. This new mechanism leads to an efficient and robust cobalt-free electrocatalyst (Sr0.95A0.05Fe0.8Nb0.1Ta0.1O3−δ, SAFNT5, A = Li, Na, and K) for the application of low-temperature solid oxide fuel cells (LT-SOFCs). Our results revealed that the formation of Li\K carbonates boosts the ORR activity with an area-specific resistance as low as 0.12 and 0.18 Ω cm2 at 600 °C, which show the highest performance of the cobalt-free single-phase cathode that has been ever reported so far. We also find that the chemical stability and tolerance of tested cathodes toward CO2 poisoning significantly improved with alkali carbonates, as compared to the pristine SrFe0.8Nb0.1Ta0.1O3−δ (SFNT) at 600 °C. This work demonstrates the conclusive role of alkali carbonates in developing highly efficient and stable cobalt-free cathodes for LT-SOFCs and CO2 neutralization. © 2019 American Chemical Society
  • Thumbnail Image
    Item
    A niobium and tantalum co-doped perovskite cathode for solid oxide fuel cells operating below 500 °C
    (Springer Nature, 2017-01-03) Li, MR; Zhao, MW; Li, F; Zhou, W; Peterson, VK; Xu, XY; Shao, ZP; Gentle, IR; Zhu, ZH
    The slow activity of cathode materials is one of the most significant barriers to realizing the operation of solid oxide fuel cells below 500 °C. Here we report a niobium and tantalum co-substituted perovskite SrCo0.8Nb0.1Ta0.1O3−δ as a cathode, which exhibits high electroactivity. This cathode has an area-specific polarization resistance as low as ∼0.16 and ∼0.68 Ω cm2 in a symmetrical cell and peak power densities of 1.2 and 0.7 W cm−2 in a Gd0.1Ce0.9O1.95-based anode-supported fuel cell at 500 and 450 °C, respectively. The high performance is attributed to an optimal balance of oxygen vacancies, ionic mobility and surface electron transfer as promoted by the synergistic effects of the niobium and tantalum. This work also points to an effective strategy in the design of cathodes for low-temperature solid oxide fuel cells. © 2017 Springer Nature Limited. Open Access. This work is licensed under a Creative Commons Attribution 4.0 International License.