Ir-Doped CuPd Single-Crystalline Mesoporous Nanotetrahedrons for Ethylene Glycol Oxidation Electrocatalysis: Enhanced Selective Cleavage of C-C Bond.

The development of highly efficient electrocatalysts for complete oxidation of ethylene glycol (EG) in direct EG fuel cells is of decisive importance to hold higher energy efficiency. Despite some achievements, their progress, especially electrocatalytic selectivity to complete oxidated C1 products, is remarkably slower than expected. In this work, we developed a facile aqueous synthesis of Ir-doped CuPd single-crystalline mesoporous nanotetrahedrons (Ir-CuPd SMTs) as high-performance electrocatalyst for promoting oxidation cleavage of C-C bond in alkaline EG oxidation reaction (EGOR) electrocatalysis. The synthesis relied on precise reduction/co-nucleation and epitaxial growth of Ir, Cu and Pd precursors with cetyltrimethylammonium chloride as the mesopore-forming surfactant and extra Br- as the facet-selective agent under ambient conditions. The products featured concave nanotetrahedron morphology enclosed by well-defined (111) facets, single-crystalline and mesoporous structure radiated from the center, and uniform elemental composition without any phase separation. Ir-CuPd SMTs disclosed remarkably enhanced electrocatalytic activity and excellent stability as well as superior selectivity of C1 products for alkaline EGOR electrocatalysis. Detailed mechanism studies demonstrated that performance improvement came from structural and compositional synergies, which kinetically accelerated transports of electrons/reactants within active sites of penetrated mesopores and facilitated oxidation cleavage of high-energy-barrier C-C bond of EG for desired C1 products. More interestingly, Ir-CuPd SMTs performed well in coupled electrocatalysis of anode EGOR and cathode nitrate reduction, highlighting its high potential as bifunctional electrocatalyst in various applications.

Pd/Co Catalyst with High Pd Atom Utilization Efficiency for Nitrobenzene Hydrogenation at Room Temperature: Experimental and DFT Studies.

Enhancing catalytic performance as well as reducing catalyst cost are the eternal pursuit for the catalysis community. Herein, a simple and effective palladium-doped cobalt (Pd/Co) catalyst with high Pd atom utilization efficiency was synthesized via galvanic replacement reaction for the selective hydrogenation of nitrobenzene with H2 at room temperature, delivering >99 % yield of aniline with up to 158 times higher catalytic activity than commercial palladium powder. Detailed characterizations and DFT calculations revealed that Co-Pd interaction leads to a decrease in electron density of Pd and the distance between Pd atoms that results in the enhanced catalytic performance. Further experiments indicated that the Pd/Co catalyst serves as a highly efficient, selective, and recyclable catalyst for a range of nitroarene substrates. This work might provide a green and sustainable methodology to design and synthesize highly active catalysts with high utilization efficiency of the noble metals in fundamental and applied research.

CO2 and Formate Pathway of Methanol Electrooxidation at Rhodium Electrodes in Alkaline Media: An In Situ Electrochemical Attenuated Total Refection Surface-Enhanced Infrared Absorption Spectroscopy and Infrared Reflection Absorption Spectroscopy Investigation.

Rh catalysts exhibit unexpected high activity for the methanol oxidation reaction (MOR) in alkaline conditions, making them potential anodic catalysts for direct methanol fuel cells (DMFCs). Nevertheless, the MOR mechanism on Rh electrodes has not been clarified thus far, which impedes the development of high-efficiency Rh-based MOR catalysts. To investigate it, a combination of in situ electrochemical techniques called attenuated total refection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and infrared reflection absorption spectroscopy (IRAS) is used. Cyclic voltammograms of MOR at Rh electrodes show considerable activity in alkaline media rather than acidic media, although the real-time ATR-SEIRA spectral results demonstrate that methanol can rarely self-decompose on Rh at open-circuit conditions. Meanwhile, in combination of ATR-SEIRAS and IRAS results, CO2 and formate are thought to be MOR products, suggesting a dual-pathway mechanism ("CO2 pathway" and "formate pathway"). Specifically, COad species, which are the major intermediates in the CO2 pathway, can produce at lower potentials and be oxidized into CO2 at a potential of 0.5-0.75 V. Concurrently, the formate can be produced from 0.5 V and diffuse into the bulk electrolyte to become one of the MOR products, while the further electrochemical conversion of formate to CO2 is essentially negligible. More directly, the apparent selectivity (r) of the CO2 pathway is estimated to reach ca. 0.63 at 0.9 V, confirming the potential-dependent selectivity of MOR at Rh surfaces. This study might provide fresh insights into the design and fabrication of effective Rh-based catalysts for MOR.

Ethanol Electrooxidation on Rhodium-Lead Catalysts in Alkaline Media: High Mass Activity, Long-Term Durability, and Considerable CO2 Selectivity.

Rhodium (Rh)-based catalysts may solve the long-standing inefficient oxidation of ethanol for direct ethanol fuel cells (DEFCs); however, the performance of ethanol oxidation reaction (EOR) on existing Rh-based catalysts are far limited. Herein, the Rh-Pb catalysts are synthesized by building Pb and Pb oxide around Rh nanodomain, which shows highly efficient splitting CC bond and facile further oxidation of as-generated C1 intermediates (COad and CHx fragments). It exhibits an ever-highest EOR peak mass activity of ≈2636 mA mg-1 Rh among Rh-based catalysts in alkaline media. Meanwhile, its anodic current remains ≈50% even after a 4 h durability test at 0.53 V versus RHE. As for the C1-pathway selectivity, in situ infrared adsorption spectral (IRAS) results demonstrate that it could significantly improve the production of CO2 . More directly, the apparent faraday efficiency of EOR C1 pathway is estimated to be as high as 20% (at 0.53 V versus RHE). This Rh-Pb catalyst could hold great promise for developing the commercial DEFCs.

Superior activity of Pd nanoparticles confined in carbon nanotubes for hydrogen production from formic acid decomposition at ambient temperature.

Designing highly efficient and low-cost catalysts is essential toward realizing the practical application of hydrogen generation by formic acid decomposition (FAD) under ambient conditions. Herein, we report the synthesis of a hybrid material of Pd nanoparticles encapsulated within carbon nanotubes (CNTs) (Pd-CNTs-in). Transmission electron microscopy images show that most Pd nanoparticles (mean diameter 4.2 ±â€¯0.8 nm) are located inside the nanotubes. Temperature-programmed reduction studies of H2 reveal that the average reduction temperature of the Pd(II) species adsorbed on the interior wall of the CNTs is 12 °C lower than those adsorbed on the outer walls of the CNT. Moreover, the as-prepared Pd-CNTs-in catalysts show extremely high FAD activity and durability at ambient temperature. The turn over frequency (TOF) value is as high as 1135 h-1 for the initial 10 min and does not decay significantly during the consecutive 3-time recycling studies. X-Ray photoelectron spectroscopy (XPS), surface-enhanced infrared spectroscopy (SEIRAS), and gas chromatography (GC) studies indicate that CNT confinement induced electronic structure modulation of Pd could be the major reason for the enhancement of FAD catalysis on the Pd-CNTs-in surface. This work could provide promising strategies for the fabrication of cost-effective and high-active Pd-based catalysts for formic acid dehydrogenation.

Infrared spectroelectrochemical study of dissociation and oxidation of methanol at a palladium electrode in alkaline solution.

The dissociative adsorption and electrooxidation of CH(3)OH at a Pd electrode in alkaline solution are investigated by using in situ infrared spectroscopy with both internal and external reflection modes. The former (ATR-SEIRAS) has a higher sensitivity of detecting surface species, and the latter (IRAS) can easily detect dissolved species trapped in a thin-layer-structured electrolyte. Real-time ATR-SEIRAS measurement indicates that CH(3)OH dissociates to CO(ad) species at a Pd electrode accompanied by a "dip" at open circuit potential, whereas deuterium-replaced CH(3)OH doesn't, suggesting that the breaking of the C-H bond is the rate-limiting step for the dissociative adsorption of CH(3)OH. Potential-dependent ATR-SEIRAS and IRAS measurements indicate that CH(3)OH is electrooxidized to formate and/or (bi)carbonate, the relative concentrations of which depend on the potential applied. Specifically, at potentials negative of ca. -0.15 V (vs Ag/AgCl), formate is the predominant product and (bi)carbonate (or CO(2) in the thin-layer structure of IRAS) is more favorable at potentials from -0.15 to 0.10 V. Further oxidation of the CO(ad) intermediate species arising from CH(3)OH dissociation is involved in forming (bi)carbonate at potentials above -0.15 V. Although the partial transformation from interfacial formate to (bi)carbonate may be justified, no bridge-bonded formate species can be detected over the potential range under investigation.

Surface-Enhanced Infrared Spectroscopic Study of a CO-Covered Pt Electrode in Room-Temperature Ionic Liquid.

ATR-SEIRAS is extended for the first time to study potential-induced surface and interface structure variation of a CO-covered Pt electrode in a room-temperature ionic liquid of N-butyl-N-methyl-piperidinium bis((trifluoromethyl)sulfonyl)imide (or [Pip14][TNf2]). Owing to a wide effective potential window of [Pip14][TNf2], a gradual conversion from bridged COad (COB) to terminal COad (COL) is observed in response to positively going potentials, suggesting that [Pip14](+) may be involved in a strong electrostatic interaction with the COad. This site conversion enables the ratio of the apparent absorption coefficient of COL to that of COB to be determined. Also, the spectral results reveal the potential-dependent COad frequency variations as well as the potential-induced interfacial ionic reorientation and movement at the Pt/CO/[Pip14][TNf2] interface.

Facile synthesis of Ag@Pd satellites-Fe3O4 core nanocomposites as efficient and reusable hydrogenation catalysts.

Well-dispersed Ag@Pd supported on magnetite nanoparticles have been obtained through a simple colloidal impregnation method. The as-synthesised nanocomposite exhibits greatly enhanced catalytic reactivity and reusability towards 4-nitrophenol hydrogenation.