Transition metal oxide (Ni, Co, Fe)-tin oxide nanocomposite sensing electrodes for a mixed-potential based NO₂ sensor

Bhardwaj, Aman,Kim, In-ho,Hong, Jae-woon,Kumar, Aniket,Song, Sun-Ju Elsevier Sequoia 2019 Sensors and actuators. B Chemical Vol.284 No.-

<P><B>Abstract</B></P> <P>A mixed-potential based sensor utilizing transition metal oxide (Ni, Co, Fe)-tin oxide nanocomposite sensing electrodes are fabricated for the first time and investigated for the gas sensing performance towards the highly toxic nitrogen dioxide. The nanocomposites are synthesized by solvo-combustion route and characterized for the physical, gas sensing and electrochemical properties in a temperature range of 600–700 ℃. The sensor equipped with Fe<SUB>2</SUB>O<SUB>3</SUB>-SnO<SUB>2</SUB> (Fe:Sn = 2:1) nanocomposite sensing electrodes sintered at 1000 ℃ shows the maximum response of 60 mV towards 100 ppm NO<SUB>2</SUB> with a relatively fast response and recovery dynamics at an operating temperature of 650 ℃. The sensor also shows a linear dependence of response over the logarithm of NO<SUB>2</SUB> concentration with a sensitivity of ∼44 mV/decade. Additionally, the oxygen concentration dependence, cyclability and cross-sensitivity towards interfering gases are also investigated. Finally, the sensing mechanism and electrochemical activity of the sensing electrodes are studied using polarization curve measurement and electrochemical impedance spectroscopy.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Mixed-potential based sensor utilizing transition metal oxide (Ni, Co, Fe)-tin oxide nanocomposite sensing electrodes. </LI> <LI> Fe<SUB>2</SUB>O<SUB>3</SUB>-SnO<SUB>2</SUB> nanocomposite sensing electrode responded 60mV towards 100ppm NO<SUB>2</SUB> at 650 ℃. </LI> <LI> The sensitivity of the sensor was found to be 44 mV/dec. in 10-100 ppm NO<SUB>2</SUB> concentration. </LI> <LI> The sensor displayed a low oxygen conc. dependence, high selectivity and high cyclability. </LI> <LI> Sensing mechanism and key parameters determining the sensing performance are discussed in details. </LI> </UL> </P>

Plasma-sprayed gadolinium-doped ceria (GDC) for intermediate temperature solid electrolyte

Chanjin Son,Aman Bhardwaj,Jaewoon Hong,Jin-Wook Kim,Heung-Soo Moon,Hyo-Seop Noh,Sun-Ju Song 한양대학교 세라믹연구소 2017 Journal of Ceramic Processing Research Vol.18 No.12

10 mol% gadolinium-doped cerium (IV) oxide was prepared by solid-state reaction route and deposited as a thick film usingthermal (plasma) spray technique. The phase development, microstructure and topography were characterized by X-raydiffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The mechanical strength of thedeposited film was determined by pull-off adhesion test. The plasma-sprayed GDC was characterized for its electricalproperties by dc four-probe conductivity experiments. The maximum conductivity for plasma-sprayed GDC was found to be3.60 × 10−2 Scm−1, which was lesser than 2.25 × 10−1 Scm−1for the CIP-sintered GDC at 1000 oC and pO2= 0.21 atm. Thedecrease in the conductivity is attributed to the larger intergranular spaces and uneven networking observed in themicrostructure resulted in higher activation energy and low conductivity.

Fast ionic conduction in tetravalent metal pyrophosphate-alkali carbonate composites: New potential electrolytes for intermediate-temperature fuel cells

Singh, Bhupendra,Bhardwaj, Aman,Gautam, Sandeep K.,Kumar, Devendra,Parkash, Om,Kim, In-Ho,Song, Sun-Ju Elsevier 2017 Journal of Power Sources Vol.345 No.-

<P><B>Abstract</B></P> <P>Here we present a report on synthesis and characterization of tetravalent metal pyrophosphate (TMP) and alkali carbonate (A<SUB>2</SUB>CO<SUB>3</SUB>; A = Li and/or Na) composites. The TMP-carbonate composites are prepared by mixing indium-doped tin pyrophosphate or yttrium-doped zirconium pyrophosphate with Li<SUB>2</SUB>CO<SUB>3</SUB> or an eutectic mixture of Li<SUB>2</SUB>CO<SUB>3</SUB>-Na<SUB>2</SUB>CO<SUB>3</SUB> in different wt.% ratios. The phase composition, microstructure and electrical conductivity of the sintered specimen are analyzed. In addition, the effect of different TMP and A<SUB>2</SUB>CO<SUB>3</SUB> phases is investigated. A maximum ionic conductivity of 5.5 × 10<SUP>−2</SUP> S cm<SUP>−1</SUP> at 630 °C is observed in this study with a Sn<SUB>0.9</SUB>In<SUB>0.1</SUB>P<SUB>2</SUB>O<SUB>7</SUB>-Li<SUB>2</SUB>CO<SUB>3</SUB> composite. Based on the literature data, TMP-carbonate composites can be considered to be primarily a proton and oxygen-ion co-ionic conductor and, therefore, have strong potential as electrolytes in fuel cells in 500–700 °C range.</P> <P><B>Highlights</B></P> <P> <UL> <LI> New tetravalent metal pyrophosphate (TMP)-alkali carbonate composites are reported. </LI> <LI> TMP-carbonate composites sintered at 750 °C are dense. </LI> <LI> SIP21-L10 composite showed max. conductivity of 5.5 × 10<SUP>−2</SUP> S cm<SUP>−1</SUP> at 630 °C. </LI> <LI> Conductivity of TMP-carbonate is comparable to ceria-carbonate composites. </LI> </UL> </P>

A Facile Combustion Synthesis Route for Performance Enhancement of La_0.6Sr_0.4Co_0.2Fe_0.8O_3-_δ (LSCF6428) as a Robust Cathode Material for IT-SOFC

Yoo, Young-Sung,Namgung, Yeon,Bhardwaj, Aman,Song, Sun-Ju The Korean Ceramic Society 2019 한국세라믹학회지 Vol.56 No.5

Lanthanum-based transition metal cations containing perovskites have emerged as potential catalysts for the intermediate-temperature (600-800℃) oxygen reduction reaction (ORR). Here, we report a facile acetylacetone-assisted combustion route for the synthesis of nanostructured La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF6428) cathodes for intermediate-temperature solid-oxide fuel cells (IT-SOFCs). The as-prepared powder was analyzed by thermogravimetry analysis-differential scanning calorimetry. The powder calcined at 800℃ was characterized by X-ray diffraction, scanning electrode microscopy, energy dispersive X-ray spectroscopy, and Brunauer-Emmett-Teller surface area measurements. It was found that the porosity of the air electrode significantly increased by utilizing the nanostructured LSCF6428 instead of commercial powder. The performance of a single cell fabricated with the nanostructured LSCF6428 cathode increased by 112%, from 0.4 to 0.85 W cm^-2, at 700℃. Electrochemical impedance spectroscopy showed a considerable reduction in the area-specific resistance and activation energy from 133.5 to 61.5 kJ/mol, resulting in enhanced electrocatalytic activity toward ORR and overall cell performance.

A Facile Combustion Synthesis Route for Performance Enhancement of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF6428) as a Robust Cathode Material for IT-SOFC

Young-Sung Yoo,Yeon Namgung,Aman Bhardwaj,송선주 한국세라믹학회 2019 한국세라믹학회지 Vol.56 No.5

Lanthanum-based transition metal cations containing perovskites have emerged as potential catalysts for the intermediatetemperature (600–800oC) oxygen reduction reaction (ORR). Here, we report a facile acetylacetone-assisted combustion route for the synthesis of nanostructured La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF6428) cathodes for intermediate-temperature solid-oxide fuel cells (ITSOFCs). The as-prepared powder was analyzed by thermogravimetry analysis–differential scanning calorimetry. The powder calcined at 800oC was characterized by X-ray diffraction, scanning electrode microscopy, energy dispersive X-ray spectroscopy, and Brunauer–Emmett–Teller surface area measurements. It was found that the porosity of the air electrode significantly increased by utilizing the nanostructured LSCF6428 instead of commercial powder. The performance of a single cell fabricated with the nanostructured LSCF6428 cathode increased by 112%, from 0.4 to 0.85 W cm2, at 700oC. Electrochemical impedance spectroscopy showed a considerable reduction in the area-specific resistance and activation energy from 133.5 to 61.5 kJ/mol, resulting in enhanced electrocatalytic activity toward ORR and overall cell performance.

Influence of different parameters on total fluoride concentration evaluation in ex-situ chemical degradation of nafion based membrane

애니켓 쿠마르,윤예진,홍재운,김인호,Aman Bhardwaj,송선주 한국화학공학회 2021 Korean Journal of Chemical Engineering Vol.38 No.10

The impact of different parameters on the chemical degradation of the Nafion polymer electrolyte membrane was investigated in detail under different concentrations of Fenton solution. As a consequence of chemical degradation, the performance and durability of the perfluorosulfonic acid-based electrolyte membrane in fuel cells was studied. Quantitative estimation of fluoride emitted after chemical degradation of the electrolyte membrane is done by an ex-situ fluoride emission rate-test using a potentiometric with an ion-selective electrode. The concentration of fluoride ions is easily affected by several external factors, such as total ionic strength, pH, temperature, and stirring speed, which causes many errors while reporting the fluoride concentration. Furthermore, the micromorphology of recast Nafion membranes before and after FER rest was thoroughly examined by scanning electron microscope (SEM) and X-ray photoelectric spectroscopy. Here, we report the influence of several external parameters over total fluoride concentration during the estimation of fluoride concentration for the proper correlation of the rate of chemical degradation in polymer electrolytes. This systematic study is beneficial for removing errors while measuring fluoride concentration and removing the discrepancy present in FER results reported in the literature.