Morphology-dependent activity of Pt nanocatalysts for ethanol oxidation in acidic media: Nanowires versus nanoparticles

The Ethanol Oxidation Reaction Performance of Carbon-Supported PtRuRh Nanorods

In this study, carbon-supported Pt-based catalysts, including PtRu, PtRh, and PtRuRh nanorods (NRs), were prepared by the formic acid reduction method for ethanol oxidation reaction (EOR) application. The aspect ratio of all experimental NRs is 4.6. The X-ray photoelectron spectroscopy and H2-temperature-programmed reduction results confirm that the ternary PtRuRh has oxygen-containing species (OCS), including PtOx, RuOx and RhOx, on its surface and shows high EOR current density at 0.6 V. The corresponding physical structure results indicate that the surface OCS can enhance the adsorption of ethanol through bi-functional mechanism and thereby promote the EOR activity. On the other hand, the chronoamperometry (CA) results imply that the ternary PtRuRh has the highest mass activity, specific activity, and stability among all catalysts. The aforementioned pieces of evidence reveal that the presence of OCS facilitates the oxidation of adsorbed intermediates, such as CO or CHx, which prevents the Pt active sites from poisoning and thus simultaneously improves the current density and durability of PtRuRh NRs in EOR.

Wire-like Pt on mesoporous Ti0.7W0.3O2 Nanomaterial with Compelling Electro-Activity for Effective Alcohol Electro-Oxidation

Finding out robust active and sustainable catalyst towards alcohol electro-oxidation reaction is major challenges for large-scale commercialization of direct alcohol fuel cells. Herein, a robust Pt nanowires (NWs)/Ti_0.7W_0.3O₂ electrocatalyst, as the coherency of using non-carbon catalyst support and controlling the morphology and structure of the Pt nanocatalyst, was fabricated via an effortless chemical reduction reaction approach at room temperature without using surfactant/stabilizers or template to assemble an anodic electrocatalyst towards methanol electro-oxidation reaction (MOR) and ethanol electro-oxidation reaction (EOR). These observational results demonstrated that the Pt NWs/Ti_0.7W_0.3O₂ electrocatalyst is an intriguing anodic electrocatalyst, which can alter the state-of-the-art Pt NPs/C catalyst. Compared with the conventional Pt NPs/C electrocatalyst, the Pt NWs/Ti_0.7W_0.3O₂ electrocatalyst exhibited the lower onset potential (~0.1 V for MOR and ~0.2 for EOR), higher mass activity (~355.29 mA/mg_Pt for MOR and ~325.01 mA/mg_Pt for EOR) and much greater durability. The outperformance of the Pt NWs/Ti_0.7W_0.3O₂ electrocatalyst is ascribable to the merits of the anisotropic one-dimensional Pt nanostructure and the mesoporous Ti_0.7W_0.3O₂ support along with the synergistic effects between the Ti_0.7W_0.3O₂ support and the Pt nanocatalyst. Furthermore, this approach may provide a promising catalytic platform for fuel cell technology and a variety of applications.

Ultrathin Metallic Nanowire-Based Architectures as High-Performing Electrocatalysts

Fuel cells (FCs) convert chemical energy into electricity through electrochemical reactions. They maintain desirable functional advantages that render them as attractive candidates for renewable energy alternatives. However, the high cost and general scarcity of conventional FC catalysts largely limit the ubiquitous application of this device configuration. For example, under current consumption requirements, there is an insufficient global reserve of Pt to provide for the needs of an effective FC for every car produced. Therefore, it is absolutely necessary in the future to replace Pt either completely or in part with far more plentiful, abundant, cheaper, and potentially less toxic first row transition metals, because the high cost-to-benefit ratio of conventional catalysts is and will continue to be a major limiting factor preventing mass commercialization. We and other groups have explored a number of nanowire-based catalytic architectures, which are either Pt-free or with reduced Pt content, as an energy efficient solution with improved performance metrics versus conventional, currently commercially available Pt nanoparticles that are already well established in the community. Specifically, in this Perspective, we highlight strategies aimed at the rational modification of not only the physical structure but also the chemical composition as a means of developing superior electrocatalysts for a number of small-molecule-based anodic oxidation and cathodic reduction reactions, which underlie the overall FC behavior. In particular, we focus on efforts to precisely, synergistically, and simultaneously tune not only the size, morphology, architectural motif, surface chemistry, and chemical composition of the as-generated catalysts but also the nature of the underlying support so as to controllably improve performance metrics of the hydrogen oxidation reaction, the methanol oxidation reaction, the ethanol oxidation reaction, and the formic acid oxidation reaction, in addition to the oxygen reduction reaction.

The reactivity of platinum microelectrodes

Platinum ultramicroelectrodes exhibit lower reactivity towards surface sensitive reactions than macroelectrodes, typically due to (trace) contamination, making electrochemical characterization very important for a proper comparison.

Ambient synthesis of high-quality ruthenium nanowires and the morphology-dependent electrocatalytic performance of platinum-decorated ruthenium nanowires and nanoparticles in the methanol oxidation reaction

We report for the first time (a) the synthesis of elemental ruthenium nanowires (Ru NWs), (b) a method for modifying their surfaces with platinum (Pt), and (c) the morphology-dependent methanol oxidation reaction (MOR) performance of high-quality Pt-modified Ru NW electrocatalysts. The synthesis of our elemental Ru NWs has been accomplished utilizing a template-based method under ambient conditions. As-prepared Ru NWs are crystalline and elementally pure, maintain electrochemical properties analogous to elemental Ru, and can be generated with average diameters ranging from 44 to 280 nm. We rationally examine the morphology-dependent performance of the Ru NWs by comparison with commercial Ru nanoparticle (NP)/carbon (C) systems after decorating the surfaces of these structures with Pt. We have demonstrated that the deposition of Pt onto the Ru NWs (Pt~Ru NWs) results in a unique hierarchical structure, wherein the deposited Pt exists as discrete clusters on the surface. By contrast, we find that the Pt-decorated commercial Ru NP/C (Pt~Ru NP/C) results in the formation of an alloy-type NP. The Pt~Ru NPs (0.61 A/mg of Pt) possess nearly 2-fold higher Pt mass activity than analogous Pt~Ru NW electrocatalysts (0.36 A/mg of Pt). On the basis of a long-term durability test, it is apparent that both catalysts undergo significant declines in performance, potentially resulting from aggregation and ripening in the case of Pt~Ru NP/C and the effects of catalyst poisoning in the Pt~Ru NWs. At the conclusion of the test, both catalysts maintain comparable performance, despite a slightly enhanced performance in Pt~Ru NP/C. In addition, the measured mass-normalized MOR activity of the Pt~Ru NWs (0.36 A/mg of Pt) was significantly enhanced as compared with supported elemental Pt (Pt NP/C, 0.09 A/mg of Pt) and alloy-type PtRu (PtRu NP/C, 0.24 A/mg of Pt) NPs, both serving as commercial standards.

Ternary electrocatalysts for oxidizing ethanol to carbon dioxide: making ir capable of splitting C-C bond

Splitting the C-C bond is the main obstacle to electrooxidation of ethanol (EOR) to CO(2). We recently demonstrated that the ternary PtRhSnO(2) electrocatalyst can accomplish that reaction at room temperature with Rh having a unique capability to split the C-C bond. In this article, we report the finding that Ir can be induced to split the C-C bond as a component of the ternary catalyst. We characterized and compared the properties of several carbon-supported nanoparticle (NP) electrocatalysts comprising a SnO(2) NP core decorated with multimetallic nanoislands (MM' = PtIr, PtRh, IrRh, PtIrRh) prepared using a seeded growth approach. An array of characterization techniques were employed to establish the composition and architecture of the synthesized MM'/SnO(2) NPs, while electrochemical and in situ infrared reflection absorption spectroscopy studies elucidated trends in activity and the nature of the reaction intermediates and products. Both EOR reactivity and selectivity toward CO(2) formation of several of these MM'/SnO(2)/C electrocatalysts are significantly higher compared to conventional Pt/C and Pt/SnO(2)/C catalysts. We demonstrate that the PtIr/SnO(2)/C catalyst with high Ir content shows outstanding catalytic properties with the most negative EOR onset potential and reasonably good selectivity toward ethanol complete oxidation to CO(2).

Tailored design of architecturally controlled Pt nanoparticles with huge surface areas toward superior unsupported Pt electrocatalysts

Herein, we report a very simple and rapid method to synthesize two types of Pt nanoparticles with open porous structures (i.e., Pt nanodendrites and multiarmed Pt nanostars) in high yield. The present synthesis is performed by a simple sonication treatment of an aqueous solution containing K2PtCl4 and a nonionic block copolymer with branched alkyl chains in the presence of ascorbic acid (AA) at room temperature. Nanodendrites and multiarmed nanostars with different Pt nanostructures are selectively synthesized by simply controlling the dissolved block copolymer amounts in the reactive system. As-prepared 3D Pt nanodendrites and multiarmed Pt nanostars with well-defined morphologies are highly porous and self-supported structures assembled by staggered nanoarms as building blocks, thereby realizing extremely high surface areas (around 80 m(2) g(-1)). The present synthesis has a remarkable advantage in its simplicity for the synthesis of Pt nanocatalysts, in comparison with other previous approaches. Our Pt nanodendrites and Pt nanostars not only improve the active Pt surface area but also show superior electrochemical performance, which make them promising electrocatalysts for future.

Highly enhanced electrocatalytic oxygen reduction performance observed in bimetallic palladium-based nanowires prepared under ambient, surfactantless conditions

We have employed an ambient, template-based technique that is simple, efficient, and surfactantless to generate a series of bimetallic Pd(1-x)Au(x) and Pd(1-x)Pt(x) nanowires with control over composition and size. Our as-prepared nanowires maintain significantly enhanced activity toward oxygen reduction as compared with commercial Pt nanoparticles and other 1D nanostructures, as a result of their homogeneous alloyed structure. Specifically, Pd(9)Au and Pd(4)Pt nanowires possess oxygen reduction reaction (ORR) activities of 0.49 and 0.79 mA/cm(2), respectively, which are larger than the analogous value for commercial Pt nanoparticles (0.21 mA/cm(2)). In addition, core-shell Pt~Pd(9)Au nanowires have been prepared by electrodepositing a Pt monolayer shell and the corresponding specific, platinum mass, and platinum group metal mass activities were found to be 0.95 mA/cm(2), 2.08 A/mg(Pt), and 0.16 A/mg(PGM), respectively. The increased activity and catalytic performance is accompanied by improved durability toward ORR.

Nanoporous PtCo surface alloy architecture with enhanced properties for methanol electrooxidation

By selectively dealloying a PtCoAl ternary alloy, a novel nanoporous PtCo (np-PtCo) alloy with a three-dimensional bicontinuous pore-ligament structure is successfully fabricated. X-ray diffraction and electron microscopic characterizations demonstrate the single-crystal nature of the alloy ligament with a ligament size down to ~3 nm. After a mild electrochemical dealloying process, a nanoporous near-surface alloy structure with a Pt-rich surface and a PtCo alloy core is obtained. Electrochemical measurements show that the np-PtCo surface alloy has greatly enhanced catalytic activity and durability toward methanol electrooxidation compared with a state-of-the-art Pt/C catalyst. The peak current density of methanol electrooxidation on a np-PtCo surface alloy is more than 5 times of that on Pt/C. More importantly, continuous potential cycling from 0.6 to 0.9 V (vs RHE) in a 0.5 M H(2)SO(4) aqueous solution demonstrates that a np-PtCo surface alloy has excellent structure stability, with more than 90% of the initial electrochemical active surface area (EASA) retained after 5000 potential cycles. Under the same conditions, the EASA of Pt/C drops to ~70%. With evident advantages of facile preparation as well as enhanced electrocatalytic activity and durability, a np-PtCo surface alloy nanomaterial holds great potential as an anode catalyst in direct methanol fuel cells.