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High-performance direct ethanol fuel cell using nitrate reduction reaction
Ma, Kyeng-Bae,Han, Sang-Beom,Kwon, Suk-Hui,Kwak, Da-Hee,Park, Kyung-Won Elsevier 2018 International journal of hydrogen energy Vol.43 No.36
<P><B>Abstract</B></P> <P>In this study, we propose a high-performance direct ethanol fuel cell (DEFC) using nitrate reduction reaction with a carbon felt electrode (DEFC-HNO<SUB>3</SUB>) instead of oxygen reduction reaction (ORR) on a Pt catalyst (DEFC-O<SUB>2</SUB>). The activation energy for the nitrate reduction reaction on the carbon electrode is found to be relatively low at ∼14.2 kJ mol<SUP>−1</SUP>, compared to the ORR. By using the nitrate reduction reaction at the cathode and oxidation of ethanol as a fuel at the anode, the DEFC shows a significantly high open circuit voltage of 0.85 V and two-fold maximal power density of 68 mW cm<SUP>−2</SUP> at 80 °C, compared to the DEFC-O<SUB>2</SUB>, due to the significantly fast reaction rate of the nitrate reduction reaction.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We proposed a direct ethanol fuel cell using nitrate reduction reaction (DEFC-HNO<SUB>3</SUB>). </LI> <LI> The activation energy for the nitrate reduction reaction was lower than ORR. </LI> <LI> DEFC-HNO<SUB>3</SUB> showed significantly improved performance compared to DEFC-O<SUB>2</SUB>. </LI> <LI> The fast nitrate reduction reaction could result in the enhanced performance of DEFC. </LI> </UL> </P>
Han, Sang-Beom,Kwak, Da-Hee,Park, Hyun Suk,Park, Jin-Young,Ma, Kyeng-Bae,Won, Ji-Eun,Kim, Do-Hyoung,Kim, Min-Cheol,Park, Kyung-Won Elsevier 2018 Journal of Power Sources Vol.393 No.-
<P><B>Abstract</B></P> <P>(2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) with no free radical and non-volatile characteristic can be utilized as a liquid catalyst instead of O<SUB>2</SUB> at the cathode in a chemical regenerative redox fuel cell with H<SUB>2</SUB> as a fuel at the anode. In this study, the electrochemical properties and performance of TEMPO dissolved in sulfuric acid solution are investigated using half and unit cells. In the half-cell, TEMPO shows an activation energy of 1.27 kcal mol<SUP>−1</SUP> K<SUP>−1</SUP> for the reduction. A chemical regenerative redox fuel cell (CRRFC) using TEMPO as the liquid catalyst exhibits an open circuit voltage of 0.7 V and a maximum power density of 90 mW cm<SUP>−2</SUP> at 30 °C with a low activation loss. The regeneration cycling test of the CRRFC is performed at a constant voltage of 0.4 V under a flow rate of the oxygen-bubbled TEMPO solution. The performance of the CRRFC deteriorates, i.e., a power density of zero measured at >200 min. Thus, a highly efficient regeneration system needs to be developed for a high-performance CRRFC using TEMPO used as a liquid-type oxidant. Furthermore, stable liquid oxidants with relatively high standard reduction potentials can be proposed through various organic compounds.</P> <P><B>Highlights</B></P> <P> <UL> <LI> CRRFC was proposed using TEMPO instead of O<SUB>2</SUB> at the cathode. </LI> <LI> TEMPO showed fairly fast transport and low activation energy for the reduction. </LI> <LI> CRRFC exhibited an open circuit voltage of ∼0.7 V at 30 °C. </LI> <LI> CRRFC exhibited a maximum power density of ∼90 mW cm<SUP>−2</SUP> at 30 °C. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Park, Hyun-Suk,Han, Sang-Beom,Kwak, Da-Hee,Lee, Gyu-Ho,Choi, In-Ae,Kim, Do-Hyoung,Ma, Kyeng-Bae,Kim, Min-Cheol,Kwon, Hye-Jin,Park, Kyung-Won WILEY-VCH 2017 CHEM SUS CHEM Vol.10 No.10
<P>To develop doped carbon nanostructures as non-precious metal cathode catalysts, nanocomposites were synthesized by using SBA-15 and 5,10,15,20-tetrakis(4-methoxyphenyl)-porphyrin-iron(III) chloride with different ratios of amorphous MoS2 precursor. From various analyses, it was found that, during pyrolysis at 900 degrees C under an N-2 atmosphere, the amorphous MoS2 precursor decomposed into Mo and S, facilitating the formation of graphene sheet-like carbon with MoC and doping of sulfur in the carbon. In the nanocomposite formed from 10 wt% MoS2 precursor (denoted as Mo/S/PC-10), most of the MoS2 was decomposed, thus forming S-doped carbon, which was grown on the MoC phase without crystalline MoS2. Furthermore, Mo/S/PC-10 exhibited better performance in the oxygen reduction reaction (specific activity of 1.23 mA cm(-2) at 0.9 V and half-wave potential of 0.864 V) than a commercial Pt catalyst, owing to a heteroatom-doped carbon nanostructure with a fairly high specific surface area. In the polarization curve of the unit-cell performance measured at 80 degrees C under ambient pressure, Mo/S/PC-10 as a cathode catalyst exhibited an optimal power density of 314 mW cm(-2) and a current density of 280 mA cm(-2) at 0.6 V.</P>
Kwak, Da-Hee,Han, Sang-Beom,Lee, Young-Woo,Park, Hyun-Suk,Choi, In-Ae,Ma, Kyeng-Bae,Kim, Min-Cheol,Kim, Si-Jin,Kim, Do-Hyoung,Sohn, Jung-Inn,Park, Kyung-Won Elsevier 2017 Applied Catalysis B Vol.203 No.-
<P><B>Abstract</B></P> <P>Many alternatives to typical Pt-based catalysts have been developed to enhance oxygen reduction reaction (ORR) performance in acid medium due to their scarcity and high activation loss during the ORR. We synthesized mesoporous carbon nanostructures with multi-dopants such as iron, nitrogen, and sulfur as a cathode catalyst using the ordered silica templates and porphyrinic iron. The co-doped mesoporous carbon cathode catalysts exhibited a high ORR performance in an acid medium, <I>i.e.</I> complete ORR process and improved durability. The enhanced ORR properties of the catalysts might be ascribed to iron-containing catalytic active sites surrounded by nitrogen/sulfur species and a well-defined mesoporous carbon nanostructure.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Doped mesoporous carbon nanostructures were synthesized using a template method. </LI> <LI> The as-prepared samples exhibited a well-ordered mesoporous structure. </LI> <LI> The mesoporous carbon nanostructures contained multi-dopants such as Fe, N, and S. </LI> <LI> The doped carbon nanostructures showed highly improved ORR activity and stability. </LI> <LI> The improved properties were due to a well-doped mesoporous carbon nanostructure. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>