Ternary Pt/Rh/SnO2 electrocatalysts for oxidizing ethanol to CO2

Surface-modification of SnO2 nanoparticles by incorporation of Al for the detection of combustible gases in a humid atmosphere

Aluminium-doped SnO₂ nanoparticles inhibited hydroxyl poisoning and enhanced the sensor response in a humid atmosphere.

Size-dependent electronic structure controls activity for ethanol electro-oxidation at Ptn/indium tin oxide (n = 1 to 14)

Activity of small Pt_n clusters on ITO is strongly dependent on cluster size, and anti-correlated with the Pt 4d core level binding energy, demonstrating that electron-rich Pt clusters are required for high activity.

New insights into electronic and geometric effects in the enhanced photoelectrooxidation of ethanol Using ZnO nanorod/ultrathin Au nanowire hybrids

Oxidation of small organic molecules in a fuel cell is a viable method for energy production. However, the key issue is the development of suitable catalysts that exhibit high efficiencies and remain stable during operation. Here, we demonstrate that amine-modified ZnO nanorods on which ultrathin Au nanowires are grown act as an excellent catalyst for the oxidation of ethanol. We show that the modification of the ZnO nanorods with oleylamine not only modifies the electronic structure favorably but also serves to anchor the Au nanowires on the nanorods. The adsorption of OH(-) species on the Au nanowires that is essential for ethanol oxidation is facilitated at much lower potentials as compared to bare Au nanowires leading to high activity. While ZnO shows negligible electrocatalytic activity under normal conditions, there is significant enhancement in the activity under light irradiation. We demonstrate a synergistic enhancement in the photoelectrocatalytic activity of the ZnO/Au nanowire hybrid and provide mechanistic explanation for this enhancement based on both electronic as well as geometric effects. The principles developed are applicable for tuning the properties of other metal/semiconductor hybrids with potentially interesting applications beyond the fuel cell application demonstrated here.

Stimulation of electro-oxidation catalysis by bulk-structural transformation in intermetallic ZrPt₃ nanoparticles

Although compositional tuning of metal nanoparticles (NPs) has been extensively investigated, possible control of the catalytic performance through bulk-structure tuning is surprisingly overlooked. Here we report that the bulk structure of intermetallic ZrPt3 NPs can be engineered by controlled annealing and their catalytic performance is significantly enhanced as the result of bulk-structural transformation. Chemical reduction of organometallic precursors yielded the desired ZrPt3 NPs with a cubic FCC-type structure (c-ZrPt3 NPs). The c-ZrPt3 NPs were then transformed to a different phase of ZrPt3 with a hexagonal structure (h-ZrPt3 NPs) by annealing at temperatures between 900 and 1000 °C. The h-ZrPt3 NPs exhibited higher catalytic activity and long-term stability than either the c-ZrPt3 NPs or commercial Pt/C NPs toward the electro-oxidation of ethanol. Theoretical calculations have elucidated that the enhanced activity of the h-ZrPt3 NPs is attributed to the increased surface energy, whereas the stability of the catalyst is retained by the lowered bulk-free-energy.

Density Functional Investigation of the Adsorption of Isooctane, Ethanol, and Acetic Acid on a Water-Covered Fe(100) Surface

The presence of water in biofuels poses the question of how it affects the frictional performance of additives in fuels containing organic substances. To investigate the effect of water on the adsorption of molecules present in fuel and its additives we simulated within the framework of density functional theory the adsorption of ethanol, isooctane (2,2,4-trimethylpentane), and acetic acid on a bare and a water-covered Fe(100) surface. Van der Waals interactions are taken into account in our computations. In those molecules, where dispersion forces contribute significantly to the binding mechanism, the water layer has a stronger screening effect. Additionally, this effect can be enhanced by the presence of polar functional groups in the molecule. Thus, with the introduction of a water layer, the adsorption energy of isooctane and ethanol is reduced but it is increased in the case of the acetic acid. The adsorption configuration of ethanol is changed, while the one of acetic acid is moderately, and for isooctane only very slightly altered. Therefore, the effect of a water layer in the adsorption of organic molecules on an Fe(100) surface strongly depends on the type of bond and consequently, so do the tribological properties.

Mechanistic insight into oxide-promoted palladium catalysts for the electro-oxidation of ethanol

Recent advancements in the development of alternatives to proton exchange membrane fuel cells utilizing less-expensive catalysts and renewable liquid fuels, such as alcohols, has been observed for alkaline fuel cell systems. Alcohol fuels present the advantage of not facing the challenge of storage and transportation encountered with hydrogen fuel. Oxidation of alcohols has been improved by the promotion of alloyed or secondary phases. Nevertheless, currently, there is no experimental understanding of the difference between an intrinsic and a synergistic promotion effect in high-pH environments. This report shows evidence of different types of promotion effects on palladium electrocatalysts obtained from the presence of an oxide phase for the oxidation of ethanol. The correlation of mechanistic in situ IR spectroscopic studies with electrochemical voltammetry studies on two similar electrocatalytic systems allow the role of either an alloyed or a secondary phase on the mechanism of oxidation of ethanol to be elucidated. Evidence is presented for the difference between an intrinsic effect obtained from an alloyed system and a synergistic effect produced by the presence of an oxide phase.

Rational construction of strongly coupled metal-metal oxide-graphene nanostructure with excellent electrocatalytic activity and durability

The interaction within heterogeneous nanostructures can provide a great opportunity to radically enhance their electrocatalytic properties and increase their activity and durability. Here a rational, simple, and integrated strategy is reported to construct uniform and strongly coupled metal-metal oxide-graphene nanostructure as an electrocatalyst with high performance. We first simply synthesized the interacted SnO2-prGO (protected and reduced graphene oxide) hybrid with SnO2 nanoparticles (∼4 nm) selectively anchored on the oxygenated defects of rGO using an in situ redox and hydrolysis reaction. After the deposition of Pt, uniform Pt NPs are found to contact intimately and exclusively with the SnO2 phase in the SnO2-prGO hybrid. This constructed nanostructure (Pt-SnO2-prGO) exhibits significantly improved electrocatalytic activity (2.19-fold) and durability (2.08-fold) toward methanol oxidation over that of the state-of-the-art Pt/C catalyst. The detailed explanation of the strong coupling between SnO2 and graphene as well as between Pt and SnO2 is discussed, revealing that such a process can be used to immobilize various metal catalysts on metal-oxide-decorated catalysts for realizing advanced catalytic systems with enhanced performance.

Palladium and gold nanotubes as oxygen reduction reaction and alcohol oxidation reaction catalysts in base

Palladium (PdNTs) and gold nanotubes (AuNTs) were synthesized by the galvanic displacement of silver nanowires. PdNTs and AuNTs have wall thicknesses of 6 nm, outer diameters of 60 nm, and lengths of 5-10 and 5-20 μm, respectively. Rotating disk electrode experiments showed that the PdNTs and AuNTs have higher area normalized activities for the oxygen reduction reaction (ORR) than conventional nanoparticle catalysts. The PdNTs produced an ORR area activity that was 3.4, 2.2, and 3.7 times greater than that on carbon-supported palladium nanoparticles (Pd/C), bulk polycrystalline palladium, and carbon-supported platinum nanoparticles (Pt/C), respectively. The AuNTs produced an ORR area activity that was 2.3, 9.0, and 2.0 times greater than that on carbon-supported gold nanoparticles (Au/C), bulk polycrystalline gold, and Pt/C, respectively. The PdNTs also had lower onset potentials than Pd/C and Pt/C for the oxidation of methanol (0.236 V), ethanol (0.215 V), and ethylene glycol (0.251 V). In comparison to Pt/C, the PdNTs and AuNTs further demonstrated improved alcohol tolerance during the ORR.

PtIr-WO3 nanostructured alloy for electrocatalytic oxidation of ethylene glycol and ethanol

In this article, we characterized tungsten oxide-decorated carbon-supported PtIr nanoparticles and tested it for the electrooxidation reactions of ethylene glycol and ethanol. Phase and morphological evaluation of the proposed electrocatalytic materials are investigated employing various characterization techniques including X-ray diffraction (XRD) and transmission electron microscopy (TEM). Electrochemical diagnostic measurements such as cyclic voltammetry, chronoamperometry, and linear sweep voltammetry revealed that the tungsten oxide-modified PtIr/Vulcan nanoparticles have higher catalytic activity for ethylene glycol and ethanol electrooxidation than that of PtIr/Vulcan. A significant enhancement for electrooxidation of CO-adsorbate monolayers occurred in the presence of a transition metal oxide relative to that of pure PtIr/Vulcan electrocatalyst. The likely reasons for this are modification on the Pt center electronic structure and/or increasing the population of reactive oxo groups at the PtIr/Vulcan electrocatalytic interface in different potential regions.

The origin of high activity but low CO2 selectivity on binary PtSn in the direct ethanol fuel cell

Combined electrochemical in situ FTIR and DFT study provides an insight into ethanol fuel cell catalysis on the most active binary catalyst, PtSn, at the atomic and molecular levels.

Electrochemical characteristics of nanostructured platinum electrodes – a cyclic voltammetry study

This article describes the electrochemical phenomena occurring at nanostructured platinum electrodes with high electrochemically active surface areas.

Galvanic displacement as a route to highly active and durable extended surface electrocatalysts

Spontaneous galvanic displacement has been utilized in the development of novel electrocatalysts.

Improved electrocatalytic activity for ethanol oxidation by Pd@N-doped carbon from biomass

The incorporation of nitrogen makes Pd@CN exhibit superior catalytic activity towards ethanol oxidation to Pd@AC and Pd@HC.

Electronic and structural study of Pt-modified Au vicinal surfaces: a model system for Pt–Au catalysts

Morphology and electronic properties of Pt nanostructures are influenced by the underlying Au surface orientation and surface alloy formation, respectively.

Improved electrocatalytic ethanol oxidation activity in acidic and alkaline electrolytes using size-controlled Pt-Sn nanoparticles

The promotion of the electrocatalytic ethanol oxidation reaction (EOR) on extended single-crystal Pt surfaces and dispersed Pt nanoparticles by Sn under acidic conditions is well known. However, the correlation of Sn coverage on Pt nanoparticle electrocatalysts to their size has proven difficult. The reason is that previous investigations have typically relied on commercially difficult to reproduce electrochemical treatments of prepared macroscopic electrodes to adsorb Sn onto exposed Pt surfaces. We demonstrate here how independent control over both Sn coverage and particle size can yield a significant enhancement in EOR activity in an acidic electrolyte relative to previously reported electrocatalysts. Our novel approach uses electroless nanoparticle synthesis where surface-adsorbed Sn is intrinsic to Pt particle formation. Sn serves as both a reducing agent and stabilizing ligand, producing particles with a narrow particle size distribution in a size range where the mass-specific electrocatalytic activity can be maximized (ca. 1-4 nm) as a result of the formation of a fully developed Sn shell. The extent of fractional Sn surface coverage on carbon-supported Pt nanoparticles can be systematically varied through wet-chemical treatment subsequent to nanoparticle formation but prior to incorporation into macroscopic electrodes. EOR activity for Pt nanoparticles is found to be optimum at a fractional Sn surface coverage of ca. 0.6. Furthermore, the EOR activity is shown to increase with Pt particle size and correlate with the active area of available Pt (110) surface sites for the corresponding Sn-free nanoparticles. The maximum area- and mass-specific EOR activities for the most active catalyst investigated were 17.9 μA/cm(2)Pt and 12.5 A/gPt, respectively, after 1 h of use at 0.42 V versus RHE in an acidic electrolyte. Such activity is a substantial improvement over that of commercially available Pt, Pt-Sn, and Pt-Ru alloy catalysts under either acidic or alkaline conditions.

Tuning the electronic structure of titanium oxide support to enhance the electrochemical activity of platinum nanoparticles

Two times higher activity and three times higher stability in methanol oxidation reaction, a 0.12 V negative shift of the CO oxidation peak potential, and a 0.07 V positive shift of the oxygen reaction potential compared to Pt nanoparticles on pristine TiO2 support were achieved by tuning the electronic structure of the titanium oxide support of Pt nanoparticle catalysts. This was accomplished by adding oxygen vacancies or doping with fluorine. Experimental trends are interpreted in the context of an electronic structure model, showing an improvement in electrochemical activity when the Fermi level of the support material in Pt/TiOx systems is close to the Pt Fermi level and the redox potential of the reaction. The present approach provides guidance for the selection of the support material of Pt/TiOx systems and may be applied to other metal-oxide support materials, thus having direct implications in the design and optimization of fuel cell catalyst supports.

Synergistic effect of tungsten carbide and palladium on graphene for promoted ethanol electrooxidation

The synergistic effect of WC and Pd has large benefit for ethanol electrooxidation. The small-sized Pd nanoparticles (NPs) decorated tungsten carbide on graphene (Pd-WC/GN) will be a promising anode catalyst for the direct ethanol fuel cells. The density functional theory (DFT) calculations reveal that the strong interaction exists at the interface between Pd and WC, which induces the electron transfer from WC to Pd. Fortunately, the nanoscale architecture of Pd-WC/GN has been successfully fabricated in our experiments. X-ray photoelectron spectrum further confirms the existence of electron transfer from WC to Pd in a Pd-WC/GN nanohybrid. Notably, electrochemical tests show that the Pd-WC/GN catalyst exhibits low onset potential, a large electrochemical surface area, high activity, and stability for ethanol electrooxidation in alkaline solution compared with Pd/graphene and Pd/commercial Vulcan 72R carbon catalysts. The enhancement can be attributed to the synergistic effect of Pd and WC on graphene. At the interface between Pd and WC, the electron transfer from WC to Pd leads to the increased electron densities of surface Pd, which is available for weakening adsorption of intermediate oxygen-containing species such as CO and activating catalyst. Meanwhile, the increased tungsten oxide induced by electron transfer can facilitate the effective removal of intermediate species adsorbed on the Pd surface through a bifunctional mechanism or hydrogen spillover effect.

Catalytic and electrocatalytic oxidation of ethanol over palladium-based nanoalloy catalysts

The control of the nanoscale composition and structure of alloy catalysts plays an important role in heterogeneous catalysis. This paper describes novel findings of an investigation for Pd-based nanoalloy catalysts (PdCo and PdCu) for ethanol oxidation reaction (EOR) in gas phase and alkaline electrolyte. Although the PdCo catalyst exhibits a mass activity similar to Pd, the PdCu catalyst is shown to display a much higher mass activity than Pd for the electrocatalytic EOR in alkaline electrolyte. This finding is consistent with the finding on the surface enrichment of Pd on the alloyed PdCu surface, in contrast to the surface enrichment of Co in the alloyed PdCo surface. The viability of C-C bond cleavage was also probed for the PdCu catalysts in both gas-phase and electrolyte-phase EOR. In the gas-phase reaction, although the catalytic conversion rate for CO2 product is higher over Pd than PdCu, the nanoalloy PdCu catalyst appears to suppress the formation of acetic acid, which is a significant portion of the product in the case of pure Pd catalyst. In the alkaline electrolyte, CO2 was detected from the gas phase above the electrolyte upon acid treatment following the electrolysis, along with traces of aldehyde and acetic acid. An analysis of the electrochemical properties indicates that the oxophilicity of the base metal alloyed with Pd, in addition to the surface enrichment of metals, may have played an important role in the observed difference of the catalytic and electrocatalytic activities. In comparison with Pd alloyed with Co, the results for Pd alloyed with Cu showed a more significant positive shift of the reduction potential of the oxygenated Pd species on the surface. These findings have important implications for further fine-tuning of the Pd nanoalloys in terms of base metal composition toward highly active and selective catalysts for EOR.