Electrospun bimetallic nanowires of PtRh and PtRu with compositional variation for methanol electrooxidation

Synergetic Structural Transformation of Pt Electrocatalyst into Advanced 3D Architectures for Hydrogen Fuel Cells

A new direction for developing electrocatalysts for hydrogen fuel cell systems has emerged, based on the fabrication of 3D architectures. These new architectures include extended Pt surface building blocks, the strategic use of void spaces, and deliberate network connectivity along with tortuosity, as design components. Various strategies for synthesis now enable the functional and structural engineering of these electrocatalysts with appropriate electronic, ionic, and electrochemical features. The new architectures provide efficient mass transport and large electrochemically active areas. To date, although there are few examples of fully functioning hydrogen fuel cell devices, these 3D electrocatalysts have the potential to achieve optimal cell performance and durability, exceeding conventional Pt powder (i.e., Pt/C) electrocatalysts. This progress report highlights the various 3D architectures proposed for Pt electrocatalysts, advances made in the fabrication of these structures, and the remaining technical challenges. Attempts to develop design rules for 3D architectures and modeling, provide insights into their achievable and potential performance. Perspectives on future developments of new multiscale designs are also discussed along with future study directions.

Optimizing the structural design of a nanocomposite catalyst layer for PEM fuel cells for improving mass-specific power density

For the purpose of redesigning a PEM fuel cell with ultralow Pt loading, this review comprehensively summarizes and comments on recent important findings on ultrathin catalyst layer structures. We introduce recent advances in electrocatalyst research and development (R&D), highlighting the urgency of ultralow Pt loading in the total design of PEM fuel cells. Following that, the reason for a thinner and more ordered electrode structure is presented for the next generation of PEM fuel cells. We then review recent progress in methods for preparing Pt nanoparticles on high-aspect-ratio supports, extended surface area of nanowires (confined agglomerates and nanowires) and ordered arrays. Regarding the ordered arrays, we expatiate on proton conductor arrays and electron conductor arrays, including carbon nanotube-assisted arrays, TiO₂ nanotube-assisted arrays, Co-OH-CO₃ nanowire-assisted arrays, and pigment red 149-assisted arrays. Challenges related to proton transport and transfer, electron conduction and mass transport are then discussed to supply further research direction.

Tunable Hollow Pt@Ru Dodecahedra via Galvanic Replacement for Efficient Methanol Oxidation

Pt-Ru nanocrystals are promising electrocatalysts for methanol oxidation in fuel cells. However, owing to the lattice mismatch and high reduction potential of Ru, the shape-controlled synthesis of Pt-Ru nanocrystals faces great challenges. Herein, we employ a galvanic replacement method to synthesize tunable hollow Pt@Ru dodecahedra via controlling the precursor concentration. Two typical structures, hollow Pt@Ru dodecahedra (h-Pt@Ru) and deformed hollow Pt@Ru dodecahedra (d-Pt@Ru), are obtained to exhibit superior electrocatalytic activities for methanol oxidation. The optimal d-Pt@Ru dodecahedra present a mass activity of 0.80 A mg_Pt^-1 and a specific activity of 1.61 mA cm_Pt^-2, which are 5.25 and 7.78 times higher than those of the commercial Pt/C, respectively. Remarkably, both h-Pt@Ru and d-Pt@Ru show lower oxidation potentials and higher CO-poisoning resistance for methanol oxidation than PtRu nanoparticles (NPs) and commercial Pt/C. This is attributed to the hollow dodecahedron structures with optimal spatial elemental distributions, leading to high utilization of Pt at edges and corners and the exposure of abundant Pt-Ru interfaces. Our strategy offers a facile method to engineer bimetallic metal catalysts regardless of lattice mismatch.

Advanced electrospun nanomaterials for highly efficient electrocatalysis

We highlight the recent developments of electrospun nanomaterials with controlled morphology, composition and architecture for highly efficient electrocatalysis.

Synthesis and catalytic activity of electrospun NiO/NiCo2O4 nanotubes for CO and acetaldehyde oxidation

NiO/NiCo₂O₄ nanotubes with a diameter of approximately 100 nm are synthesized using Ni and Co precursors via electro-spinning and subsequent calcination processes. The tubular structure is confirmed via transmission electron microscopy imaging, whereas the structures and elemental compositions of the nanotubes are determined using x-ray diffraction, energy dispersive x-ray spectroscopy, and x-ray photoelectron spectroscopy. N₂ adsorption isotherm data reveal that the surface of the nanotubes consists of micropores, thereby resulting in a significantly higher surface area (∼20 m² g^-1) than expected for a flat-surface structure (<15 m² g^-1). Herein, we present a study of the catalytic activity of our novel NiO/NiCo₂O₄ nanotubes for CO and acetaldehyde oxidation. The catalytic activity of NiO/NiCo₂O₄ is superior to Pt below 100 °C for CO oxidation. For acetaldehyde oxidation, the total oxidation activity of NiO/NiCo₂O₄ for acetaldehyde is comparable with that of Pt. Coexistence of many under-coordinated Co and Ni active sites in our structure is suggested be related to the high catalytic activity. It is suggested that our novel NiO/NiCo₂O₄ tubular structures with surface microporosity can be of interest for a variety of applications, including the catalytic oxidation of harmful gases.

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.

Ternary Pt9RhFex Nanoscale Alloys as Highly Efficient Catalysts with Enhanced Activity and Excellent CO-Poisoning Tolerance for Ethanol Oxidation

To address the problems of high cost and poor stability of anode catalysts in direct ethanol fuel cells (DEFCs), ternary nanoparticles Pt₉RhFe_x (x = 1, 3, 5, 7, and 9) supported on carbon powders (XC-72R) have been synthesized via a facile method involving reduction by sodium borohydride followed by thermal annealing in N₂ at ambient pressure. The catalysts are physically characterized by X-ray diffraction, scanning transmission electron microscopy, and X-ray photoelectron spectroscopy, and their catalytic performance for the ethanol oxidation reaction (EOR) is evaluated by cyclic and linear scan voltammetry, CO-stripping voltammograms, and chronopotentiometry. All the Pt₉RhFe_x/C catalysts of different atomic ratios produce high EOR catalytic activity. The catalyst of atomic ratio composition 9:1:3 (Pt/Rh/Fe) has the highest activity and excellent CO-poisoning tolerance. Moreover, the enhanced EOR catalytic activity on Pt₉RhFe₃/C when compared to Pt₉Rh/C, Pt₃Fe/C, and Pt/C clearly demonstrates the presence of Fe improves catalytic performance. Notably, the onset potential for CO oxidation on Pt₉RhFe₃/C (0.271 V) is ∼55, 75, and 191 mV more negative than on Pt₉Rh/C (0.326 V), Pt₃Fe/C (0.346 V), and Pt/C (0.462 V), respectively, which implies the presence of Fe atoms dramatically improves CO-poisoning tolerance. Meanwhile, compared to the commercial PtRu/C catalyst, the peak potential on Pt₉RhFe₃/C for CO oxidation was just slightly changed after several thousand cycles, which shows high stability against the potential cycling. The possible mechanism by which Fe and Rh atoms facilitate the observed enhanced performance is also considered herein, and we conclude Pt₉RhFe₃/C offers a promising anode catalyst for direct ethanol fuel cells.

Electrospinning of Nanofibers for Energy Applications

With global concerns about the shortage of fossil fuels and environmental issues, the development of efficient and clean energy storage devices has been drastically accelerated. Nanofibers are used widely for energy storage devices due to their high surface areas and porosities. Electrospinning is a versatile and efficient fabrication method for nanofibers. In this review, we mainly focus on the application of electrospun nanofibers on energy storage, such as lithium batteries, fuel cells, dye-sensitized solar cells and supercapacitors. The structure and properties of nanofibers are also summarized systematically. The special morphology of nanofibers prepared by electrospinning is significant to the functional materials for energy storage.

Rapid synthesis of a PtRu nano-sponge with different surface compositions and performance evaluation for methanol electrooxidation

A rapid strategy to synthesize a highly active PtRu alloy nano-sponge catalyst system for methanol electro-oxidation is presented. The greatly increased Pt utilization, anti-CO poisoning ability and electronic effect resulting from the porous nano-sponge structure could account for the performance improvement.

Preparation of continuous gold nanowires by electrospinning of high-concentration aqueous dispersions of gold nanoparticles

Gold nanowires are prepared by the electrospinning of highly concentrated aqueous dispersions of gold nanoparticles (AuNPs) in the presence of poly(vinyl alcohol) and subsequent annealing at higher temperatures. Continuous wires of sintered AuNPs are obtained as a result of this process. The Au wires are characterized by transmission electron microscopy, helium ion microscopy, optical microscopy, and X-ray diffractometry.

Nanoporous PtRu alloys for electrocatalysis

We describe a facile route to the straightforward fabrication of nanoporous (NP) PtRu alloys with predetermined bimetallic compositions. Electron microscopy and X-ray diffraction characterizations demonstrate that selective etching of Al from ternary PtRuAl source alloys generates three-dimensional bicontinuous NP-PtRu alloy nanostructures with a single-phase face-centered-cubic crystalline structure. X-ray photoelectron spectroscopy shows a slight electronic structure modification of Pt by alloying with Ru as well as uniform surface and bulk bimetallic ratio. With characteristic structural dimensions less than 5 nm, these high surface area bimetallic nanostructures show distinct electrocatalytic performance as the Ru content varies within the structure. Among all samples, NP-Pt(70)Ru(30) shows the highest specific activity as well as the most negative onset potential toward methanol oxidation reaction. NP-Pt(50)Ru(50) was found to possess a similar specific activity to the commercial E-TEK Pt(50)Ru(50)/C catalyst, but its onset and peak potentials are about 70 mV more negative. CO stripping experiments demonstrate that the adsorption of CO is the weakest on NP-Pt(70)Ru(30), and further increasing the Ru content actually shifts the CO stripping peak to a more positive potential. Thus, the overall sequence for CO-tolerance is NP-Pt(70)Ru(30) > NP-Pt(50)Ru(50) approximately = Pt(50)Ru(50)/C > NP-Pt(30)Ru(70) > Pt/C.