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Park, Joohyuk,Risch, Marcel,Nam, Gyutae,Park, Minjoon,Shin, Tae Joo,Park, Suhyeon,Kim, Min Gyu,Shao-Horn, Yang,Cho, Jaephil Royal Society of Chemistry 2017 ENERGY AND ENVIRONMENTAL SCIENCE Vol.10 No.1
<P>Oxygen reduction reaction (ORR) or oxygen evolution reaction (OER) electrocatalysts including carbon-, non-precious metal-, metal alloy-, metal oxide-, and carbide/nitride-based materials are of great importance for energy conversion and storage technologies. Among them, metal oxides (<I>e.g.</I>, perovskite and pyrochlore) are known to be promising candidates as electrocatalysts. Nevertheless, the intrinsic catalytic activities of pyrochlore oxides are still poorly understood because of the formation of undesirable phases derived from the synthesis processes. Herein, we present highly pure single crystalline pyrochlore nanoparticles with metallic conduction (Pb2Ru2O6.5) as an efficient bi-functional oxygen electrocatalyst. Notably, it has been experimentally shown that the covalency of Ru-O bonds affects the ORR and OER activities by comparing the X-ray absorption near edge structure (XANES) spectra of the metallic Pb2Ru2O6.5and insulating Sm2Ru2O7for the first time. Moreover, we followed the interatomic distance changes of Ru-O bonds using<I>in situ</I>X-ray absorption spectroscopy (XAS) to investigate the structural stabilities of the pyrochlore catalysts during electrocatalysis. The highly efficient metallic Pb2Ru2O6.5exhibited outstanding bi-functional catalytic activities and stabilities for both ORR and OER in aqueous Zn-air batteries.</P>
Optimizing nanoparticle perovskite for bifunctional oxygen electrocatalysis
Jung, Jae-Il,Risch, Marcel,Park, Seungkyu,Kim, Min Gyu,Nam, Gyutae,Jeong, Hu-Young,Shao-Horn, Yang,Cho, Jaephil The Royal Society of Chemistry 2016 ENERGY AND ENVIRONMENTAL SCIENCE Vol.9 No.1
<P>Highly efficient bifunctional oxygen electrocatalysts are indispensable for the development of highly efficient regenerative fuel cells and rechargeable metal-air batteries, which could power future electric vehicles. Although perovskite oxides are known to have high intrinsic activity, large particle sizes rendered from traditional synthesis routes limit their practical use due to low mass activity. We report the synthesis of nano-sized perovskite particles with a nominal composition of La-x(Ba0.5Sr0.5)(1-x)Co0.8Fe0.2O3-delta (BSCF), where lanthanum concentration and calcination temperature were controlled to influence oxide defect chemistry and particle growth. This approach produced bifunctional perovskite electrocatalysts similar to 50 nm in size with supreme activity and stability for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The electrocatalysts preferentially reduced oxygen to water (o5% peroxide yield), exhibited more than 20 times higher gravimetric activity (A g(-1)) than IrO2 in OER half-cell tests (0.1 M KOH), and surpassed the charge/discharge performance of Pt/C (20 wt%) in zinc-air full cell tests (6 M KOH). Our work provides a general strategy for designing perovskite oxides as inexpensive, stable and highly active bifunctional electrocatalysts for future electrochemical energy storage and conversion devices.</P>
Quan, Li Na,Jang, Yoon Hee,Stoerzinger, Kelsey A.,May, Kevin J.,Jang, Yu Jin,Kochuveedu, Saji Thomas,Shao-Horn, Yang,Kim, Dong Ha The Royal Society of Chemistry 2014 Physical chemistry chemical physics Vol.16 No.19
<P>Hierarchically organized mesoporous carbon–TiO<SUB>2</SUB> inverse opal nanostructures were synthesized by complementary colloid and block copolymer (BCP) self-assembly, where the triblock copolymer P123 acts simultaneously as the template and the carbon source. Highly ordered mesoporous inverse opal nanostructures with a nano-textured surface morphology and multiple-length scale nanopores provide increased light-activated surface area and scattering effects, leading to enhanced photoabsorption efficiency and the transport of matter. UV-vis absorption, X-ray photoelectron spectroscopy and Mott–Schottky measurement studies show that incorporation of carbon moieties into TiO<SUB>2</SUB><I>via</I> direct conversion of BCPs creates a new energy level above the valence band of TiO<SUB>2</SUB>, resulting in an effective decrease in the band gap. A significantly enhanced visible light photocatalytic activity was demonstrated for the mesoporous carbon–TiO<SUB>2</SUB> inverse opals in terms of the degradation of <I>p</I>-nitrophenol (∼79%) and photoelectrochemical water splitting (∼0.087%).</P> <P>Graphic Abstract</P><P>A significantly enhanced visible light photocatalytic activity was demonstrated for highly ordered mesoporous carbon–TiO<SUB>2</SUB> inverse opal nanostructures. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4cp00803k'> </P>
Roles of Surface Steps on Pt Nanoparticles in Electro-oxidation of Carbon Monoxide and Methanol
Lee, Seung Woo,Chen, Shuo,Sheng, Wenchao,Yabuuchi, Naoaki,Kim, Yong-Tae,Mitani, Tadaoki,Vescovo, Elio,Shao-Horn, Yang American Chemical Society 2009 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.131 No.43
<P>Design of highly active nanoscale catalysts for electro-oxidation of small organic molecules is of great importance to the development of efficient fuel cells. Increasing steps on single-crystal Pt surfaces is shown to enhance the activity of CO and methanol electro-oxidation up to several orders of magnitude. However, little is known about the surface atomic structure of nanoparticles with sizes of practical relevance, which limits the application of fundamental understanding in the reaction mechanisms established on single-crystal surfaces to the development of active, nanoscale catalysts. In this study, we reveal the surface atomic structure of Pt nanoparticles supported on multiwall carbon nanotubes, from which the amount of high-index surface facets on Pt nanoparticles is quantified. Correlating the surface steps on Pt nanoparticles with the electrochemical activity and stability clearly shows the significant role of surface steps in enhancing intrinsic activity for CO and methanol electro-oxidation. Here, we show that increasing surface steps on Pt nanoparticles of approximately 2 nm can lead to enhanced intrinsic activity up to approximately 200% (current normalized to Pt surface area) for electro-oxidation of methanol.</P>