In this paper, we present a study of a series of carbon-supported Pd−Sn binary alloyed catalysts prepared through a modified Polyol method as anode electrocatalysts for direct ethanol fuel cell reactions in an alkaline medium. Transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and aberration-corrected scanning transmission electron microscopy equipped with electron energy loss spectroscopy were used to characterize the Pd−Sn/C catalysts, where homogeneous Pd−Sn alloys were determined to be present with the surface Sn being partially oxidized. Among various Pd−Sn catalysts, Pd 86 Sn 14 /C catalysts showed much enhanced current densities in cyclic voltammetric and chronoamperometric measurements, compared to commercial Pd/C (Johnson Matthey). The overall rate law of ethanol oxidation reaction for both Pd 86 Sn 14 /C and commercial Pd/C were also determined, which clearly showed that Pd 86 Sn 14 /C was more favorable in high ethanol concentration and/or high pH environment. Density functional theory calculations also confirmed Pd−Sn alloy structures would result in lower reaction energies for the dehydrogenation of ethanol, compared to the pure Pd crystal.

Platinum-tin (Pt/Sn) binary nanoparticles are active electrocatalysts for the ethanol oxidation reaction (EOR), but inactive for splitting the C-C bond of ethanol to CO2. Here we studied detailed structure properties of Pt/Sn catalysts for the EOR, especially CO2 generation in situ using a CO2 microelectrode. We found that composition and crystalline structure of the tin element played important roles in the CO2 generation: non-alloyed Pt46-(SnO2)54 core-shell particles demonstrated a strong capability for C-C bond breaking of ethanol than pure Pt and intermetallic Pt/Sn, showing 4.1 times higher CO2 peak partial pressure generated from EOR than commercial Pt/C.

Ethanol is a promising fuel for low-temperature direct fuel cell reactions due to its low toxicity, ease of storage and transportation, high-energy density, and availability from biomass. However, the implementation of ethanol fuel cell technology has been hindered by the lack of low-cost, highly active anode catalysts. In this paper, we have studied Iridium (Ir)-based binary catalysts as low-cost alternative electrocatalysts replacing platinum (Pt)-based catalysts for the direct ethanol fuel cell (DEFC) reaction. We report the synthesis of carbon supported Ir(71)Sn(29) catalysts with an average diameter of 2.7 ± 0.6 nm through a "surfactant-free" wet chemistry approach. The complementary characterization techniques, including aberration-corrected scanning transmission electron microscopy equipped with electron energy loss spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy, are used to identify the "real" heterogeneous structure of Ir(71)Sn(29)/C particles as Ir/Ir-Sn/SnO(2), which consists of an Ir-rich core and an Ir-Sn alloy shell with SnO(2) present on the surface. The Ir(71)Sn(29)/C heterogeneous catalyst exhibited high electrochemical activity toward the ethanol oxidation reaction compared to the commercial Pt/C (ETEK), PtRu/C (Johnson Matthey) as well as PtSn/C catalysts. Electrochemical measurements and density functional theory calculations demonstrate that the superior electro-activity is directly related to the high degree of Ir-Sn alloy formation as well as the existence of nonalloyed SnO(2) on surface. Our cross-disciplinary work, from novel "surfactant-free" synthesis of Ir-Sn catalysts, theoretical simulations, and catalytic measurements to the characterizations of "real" heterogeneous nanostructures, will not only highlight the intriguing structure-property correlations in nanosized catalysts but also have a transformative impact on the commercialization of DEFC technology by replacing Pt with low-cost, highly active Ir-based catalysts.

In this paper, we reported a facile synthesis of Birnessite K 0.15 MnO 2 •0.43H 2 O nanosheets in a solution phase. The structural and electrochemical properties of the K 0.15 MnO 2 nanosheets for supercapacitor (SC) reactions were studied, and a gravimetric capacitance of 303 F/g was obtained at a charge/discharge current of 0.2 A/g. Electrochemical kinetics showed that a non-Faradaic (electrical double layer) current existed throughout the charging potential range, while a dominant Faradaic (pseudocapacitive) current was observed at high and low potentials during anodic and cathodic scans, respectively. Asymmetric pseudocapacitive full-cells were constructed with both anodic and cathodic K 0.15 MnO 2 composite materials and subjected to long-term galvanostatic charge/discharge analyses. A specific capacitance of 67.8 F/g was obtained for the cathodic K 0.15 MnO 2 full-cells after 1000 cycles, with a capacitive retention of 87.8% and Coulombic and energy efficiencies of ∼100 and ∼90%, respectively. In situ X-ray absorption near edge spectroscopy further corroborated the potential-dependent Faradaic reactions, suggesting a predominant change in valence state of K 0.15 MnO 2 to occur between 0.3 and 0.6 V (vs Ag/AgCl). The present study not only underscores the structure−function relationship of MnO 2 -based electrode materials for SC reactions but also provides a new approach in fabricating advanced pseudocapacitors by utilizing cost-effective transition metal oxide materials.

We have reported the synthesis of Au(25)Pt(75) and Au(48)Pt(52) alloyed ultrathin nanowires with average widths of less than 3 nm via a wet chemistry approach at room temperature. Using a combination of techniques, including scanning transmission electron microscopy equipped with X-ray energy dispersive spectroscopy, ultraviolet-visible spectroscopy, and X-ray absorption near-edge structure and extended X-ray absorption fine structure spectroscopies, we identified the stoichiometry-dependent heterogeneous crystalline structures, as well as electronic structures with respect to the charge transfer between Pt and Au within both nanowires. In particular, we observed d-charge depletion at the Au site and the d-charge gain at the Pt site in Au(48)Pt(52) nanowires, which accounted for its ferromagnetic magnetic behavior, in contrast to the paramagnetism and diamagnetism appearing respectively in bulk Pt and Au.