Browsing by Author "Zhao, MW"

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    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
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    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.
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    Novel CaO-SiO2 sorbent and bifunctional Ni/Co-CaO/SiO2 complex for selective H-2 synthesis from cellulose
    (American Chemical Society, 2012-01-17) Zhao, MW; Yang, XS; Church, TL; Harris, AT
    Catalysis- and sorption-enhanced biomass gasification is a promising route to high-purity hydrogen (H-2); however, most CaO-based sorbents for CO2 capture have poor surface area and mechanical properties, lose carrying capacity over multiple uses, and have insufficient porosity to accommodate extra catalyst sites. We aimed to develop a high-surface-area CaO-SiO2 framework onto which catalysts could be grafted. The best CaO-SiO2 sorbent (n(Ca)/n(Si) = 2:1) maintained a Cao conversion of 65% even after 50 carbonation-decarbonation cycles, better than commercial micrometer-sized CaO or tailored CaO, because of stabilization via Ca-O-Si interactions and an ordered porous structure. Bimetallic catalyst grains (Ni/Co alloy, <20 nm) could be evenly loaded onto this structure by impregnation. The resulting bifunctional complex produced H-2 at nearly the same rate as a mixture of catalyst and commercial CaO while using less total sorbent/catalyst. Furthermore, this complex was much more durable due to its higher coking resistance and stable structure. After 25 carbonation decarbonation cycles, the new catalyst sorbent complex enhanced the H-2 yield from cellulose far more than a mixture of catalyst and commercial CaO did following the same treatment. © 2012, American Chemical Society.
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    Pretreatment control of carbon nanotube array growth for gas separation: alignment and growth studied using microscopy and small-angle x-ray scattering
    (Americal Chemical Society, 2013-04-24) Yang, XS; Yuan, LX; Peterson, VK; Minett, AI; Zhao, MW; Kirby, N; Mudie, ST; Harris, AT
    Aligned multiwalled carbon nanotube (CNT) arrays were prepared using chemical vapor deposition of C2H4 on Fe catalyst at 750 degrees C. CNT array height and alignment depends strongly on the duration of H-2 pretreatment, with optimal height and alignment achieved using 10-15 min pretreatment. Small-angle X-ray scattering (SAXS) was used to quantify the alignment, distribution, and size of the CNTs in arrays produced from varying pretreatment times and the results correlated with microscopy measurements. SAXS analysis revealed that the higher section of the CNT arrays exhibited better alignment than the lower section. Combining these insights with transmission electron microscopy measurements of the CNT defects within each array enable a mechanism for the CNT growth to be proposed, where the loss of alignment arises from deformation of the CNTs during their growth. Gas permeation test across densified CNT arrays indicated that the alignment of the CNT array plays an important role in the gas transport, and that the gas diffusion across the well-aligned CNT arrays was enhanced by a factor of 45, which is much more than that across the poorly aligned CNT arrays, with an enhancement factor of similar to 8. © 2013, American Chemical Society.