Facile Fabrication of Platinum-Cobalt Alloy Nanoparticles with Enhanced Electrocatalytic Activity for a Methanol Oxidation Reaction

Decreasing the cost associated with platinum-based catalysts along with improving their catalytic properties is a major challenge for commercial direct methanol fuel cells. In this work, a simple and facile strategy was developed for the more efficient preparation of multi-walled carbon nanotube (MWCNT) -supported Pt/CoPt composite nanoparticles (NPs) via solution plasma sputtering with subsequent thermal annealing. Quite different from general wet synthesis methods, Pt/CoPt composite NPs were directly derived from metal wire electrodes without any additions. The obtained Pt/CoPt/MWCNTs composite catalysts exhibited tremendous improvement in the electro-oxidation of methanol in acidic media with mass activities of 1719 mA mg⁻¹_Pt. This value is much higher than that of previous reports of Pt-Co alloy and commercial Pt/C (3.16 times) because of the many active sites and clean surface of the catalysts. The catalysts showed good stability due to the special synergistic effects of the CoPt alloy. Pt/CoPt/MWCNTs can be used as a promising catalyst for direct methanol fuel cells. In addition, this solution plasma sputtering-assisted synthesis method introduces a general and feasible route for the synthesis of binary alloys.

Ultra-small Tetrametallic Pt-Pd-Rh-Ag Nanoframes with Tunable Behavior for Direct Formic Acid/Methanol Oxidation

Reversible tuning of ultra-small multimetallic Pt-Pd-Rh-Ag nanoframes is achieved. These nanoframes showed tunable and reversible modes for the oxidation of small organic molecules by simply inducing segregation with adsorbates, such as SO₄^2- and OH^- . This is the first example of reversible segregation under electrocatalytic conditions in atomic-sized electrocatalysts. These nanoframes also showed a controllable activity and good stability for the oxidation of small organic molecules.

Fabrication of electrodes with ultralow platinum loading by RF plasma processing of self-assembled arrays of Au@Pt nanoparticles

Conductive, carbon-free, electrocatalytically active, nanostructured electrodes with ultra-low platinum loading were fabricated using self-assembly of octadecanethiol-coated Au@Pt nanoparticles followed by RF plasma treatment. Bilayer arrays of Au@Pt nanoparticles with platinum loadings of 0.50, 1.04, 1.44, and 1.75 μg cm(-2) (corresponding to 0.5, 1, 1.5 and 2 atomic layer coverage of platinum on nominally 5 nm gold core) were subjected to RF argon plasma treatment for various durations and their electrical conductivity, morphological evolution, and electrocatalytic activity characterized. Samples with monolayer and above platinum coverages exhibit maximum electrochemically active surface areas values of ∼100 m(2)/gpt and specific activities that are ∼4× to 6× of a reference platinum nanoparticle bilayer array. The underlying gold core influences the structural evolution of the samples upon RF plasma treatment and leads to the formation of highly active Pt(110) facets on the surface at an optimal plasma treatment duration, which also corresponds to the onset of a sharp decline in lateral sheet resistance. The sample having a two atom thick platinum coating has the highest total mass activity of 48 ± 3 m(2)/g(pt+au), corresponding to 44% Pt atom utilization, while also exhibiting enhanced CO tolerance as well as high methanol oxidation reaction and oxygen reduction reaction activity.

A General Method for Constructing Two-Dimensional Layered Mesoporous Mono- and Binary-Transition-Metal Nitride/Graphene as an Ultra-Efficient Support to Enhance Its Catalytic Activity and Durability for Electrocatalytic Application

We constructed a series of two-dimensional (2D) layered mesoporous mono- and binary-transition-metal nitride/graphene nanocomposites (TMN/G, TM = Ti, Cr, W, Mo, TiCr, TiW, and TiMo) via an efficient and versatile nanocasting strategy for the first time. The 2D layered mesoporous TMN/G is constituted of small TMN nanoparticles composited with graphene nanosheets and has a large surface area with high porosity. Through decoration with well-dispersed Pt nanoparticles, 2D layered mesoporous Pt/TMN/G catalysts can be obtained that display excellent catalytic activity and stability for methanol electro-oxidation reactions (MOR) and oxygen reduction reactions (ORR) in both acidic and alkaline media. The 2D layered mesoporous binary-Pt/TMN/G catalysts possess catalytic activity superior to that of mono-Pt/TMN/G, graphene free Pt/TMN, Pt/G, and Pt/C catalysts. Encouragingly, the 2D layered mesoporous Pt/Ti0.5Cr0.5N/G catalyst exhibits the best electrocatalytic performance for both MOR and ORR. The outstanding electrocatalytic performance of the Pt/Ti0.5Cr0.5N/G catalyst is rooted in its large surface area, high porosity, strong interaction among Pt, Ti0.5Cr0.5N, and graphene, an excellent electron transfer property facilitated by N-doped graphene, and the small size of Pt and Ti0.5Cr0.5N nanocrystals. The outstanding catalytic performance provides the 2D layered mesoporous Pt/Ti0.5Cr0.5N/G catalyst with a wide range of application prospects in direct methanol fuel cells in both acidic and alkaline media. The synthetic method may be available for constructing other 2D layered mesoporous metal nitrides, carbides, and phosphides.

High Efficiency Photoelectrocatalytic Methanol Oxidation on CdS Quantum Dots Sensitized Pt Electrode

A cadmium sulfide quantum dots sensitized Pt (Pt-CdS) composite was synthesized using a solvothermal method and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflectance spectroscopy. The catalytic properties of the as-prepared electrode for methanol oxidation were evaluated by cyclic voltammetry (CV), chronoamperometry, electrochemical impedance spectrum (EIS) and photocurrent responses. The as-prepared Pt-CdS electrode displayed a significant enhancement in the electrocatalytic activity and stability for methanol oxidation in the presence of visible light irradiation. The synergistic effect of both the electro- and photocatalytic reaction contributes to this enhanced catalytic performance. Our result suggests a new paradigm to construct photoelectrocatalysts with high performance and good stability for direct methanol fuel cells with the assistance of visible-light illumination.

Three-Dimensionally Costabilized Metal Catalysts toward an Oxygen Reduction Reaction

Improving the long-term stability of metal catalysts is crucial to developing polymer electrolyte fuel cells (PEFCs). In this work, we first report an inorganic (TiO2)-organic (perfluorosulfonic acid, PFSA) costabilized Pt catalyst supported on graphene nanosheets (GNS) (Pt-PFSA-TiO2/GNS). Herein, TiO2, as a robust wall, impedes the collision between the metal nanoparticles (NPs) in plane along the horizontal x and y axes, while PFSA mainly anchors the metal NPs to constrain detachment along the vertical z axis. The resulting catalyst displays higher oxygen reduction reaction (ORR) activity in comparison to that of commercial Pt/C. Significantly, the stability is particularly better than that of only PFSA- or TiO2-decorated catalysts (Pt-PFSA/GNS or Pt-TiO2/GNS) and far better than that of Pt/C. After 6000 potential cycles, the half-wave potential (E1/2) of Pt-PFSA-TiO2/GNS decreases by only 16 mV, far less than that of Pt/C (56 mV). The excellent electrochemical property of Pt-PFSA-TiO2/GNS is predominantly attributed to the synergistic effect of PFSA and TiO2 in costabilizing the Pt NP by anchoring and blocking Pt NPs in all three spatial directions. The structural dynamics and mechanism of enhanced properties are also discussed.

Alkaline Ammonia Electrolysis on Electrodeposited Platinum for Controllable Hydrogen Production

Ammonia is beginning to attract a great deal of attention as an alternative energy source carrier, because clean hydrogen can be produced through electrolytic processes without the emission of COx . In this study, we deposited various shapes of Pt catalysts under potentiostatic mode; the electrocatalytic oxidation behavior of ammonia using these catalysts was studied in alkaline media. The electrodeposited Pt was characterized by both qualitative and quantitative analysis. To discover the optimal structure and the effect of ammonia concentration, the bulk pH value, reaction temperature, and applied current of ammonia oxidation were investigated using potential sweep and galvanostatic methods. Finally, ammonia electrolysis was conducted using a zero-gap cell, producing highly pure hydrogen with an energy efficiency over 80 %.

Polyaniline-Reduced Graphene Oxide Hybrid Nanosheets with Nearly Vertical Orientation Anchoring Palladium Nanoparticles for Highly Active and Stable Electrocatalysis

We report a nearly vertical reduced graphene oxide (VrGO) nanosheet coupled with polyaniline (PANI) for supporting palladium (Pd) nanoparticles. The PANI-coupled VrGO (PANI@VrGO) nanosheet is prepared by a simple one-step electrodeposition technique ,and Pd nanoparticles are anchored on the support of PANI@VrGO through the spontaneous redox reaction of PANI with a palladium salt. The designed PANI@VrGO nanosheet efficiently exposes the surface of rGO sheets and stabilizes metal nanoparticles. Consequently, the Pd/PANI@VrGO electrocatalyst exhibits high catalytic activity and excellent durability for alcohol oxidation reaction. The proposed nanoarchitecture offers a new pathway to greatly promote the performances of rGO in various applications; moreover, this work provides a powerful and universal synthetic strategy for such an architecture.

Boron, nitrogen, and phosphorous ternary doped graphene aerogel with hierarchically porous structures as highly efficient electrocatalysts for oxygen reduction reaction

Highly efficient catalysts (mainly 4e⁻ mechanism, J_k: −4.6 mA cm⁻²) for ORR based on B/N/P ternary-doped graphene aerogels were developed.

Ultralong PtNi alloy nanowires enabled by the coordination effect with superior ORR durability

Ultralong PtNi nanowires were prepared by taking advantage of the coordination effect to delicately control the reduction and alloying kinetics.

Uniformly deposited Pt nanoparticles onto crosslinked ionic liquids wrapped carbon nanotubes for methanol electrooxidation

A type of skin-core structured hybrid with a multi-walled carbon nanotube (MWCNT) center was synthesized by in situ free-radical polymerization of vinyl-benzyl ionic liquid and divinylbenzene on the outer surface of MWCNTs.

One-pot synthesis of single-crystalline PtPb nanodendrites with enhanced activity for electrooxidation of formic acid

Bimetallic PtPb nanodendrites with a single-crystalline structure were obtained by a facile one-pot strategy.

Surface Segregation of Fe in Pt-Fe Alloy Nanoparticles: Its Precedence and Effect on the Ordered-Phase Evolution during Thermal Annealing

Coupling electron microscopy techniques with in situ heating ability allows us to study phase transformations on the single-nanoparticle level. We exploit this setup to study disorder-to-order transformation of Pt-Fe alloy nanoparticles, a material that is of great interest to fuel-cell electrocatalysis and ultrahigh density information storage. In contrast to earlier reports, we show that Fe (instead of Pt) segregates towards the particle surface during annealing and forms a Fe-rich FeO x outer shell over the alloy core. By combining both ex situ and in situ approaches to probe the interplay between ordering and surface-segregation phenomena, we illustrate that the surface segregation of Fe precedes the ordering process and affects the ordered phase evolution dramatically. We show that the ordering initiates preferably at the pre-existent Fe-rich shell than the particle core. While the material-specific findings from this study open interesting perspectives towards a controlled phase evolution of Pt-Fe nanoalloys, the characterization methodologies described are general and should prove useful to probing a wide-range of nanomaterials.

Direct alcohol fuel cells: toward the power densities of hydrogen-fed proton exchange membrane fuel cells

A 2 μm thick layer of TiO2 nanotube arrays was prepared on the surface of the Ti fibers of a nonwoven web electrode. After it was doped with Pd nanoparticles (1.5 mgPd  cm(-2) ), this anode was employed in a direct alcohol fuel cell. Peak power densities of 210, 170, and 160 mW cm(-2) at 80 °C were produced if the cell was fed with 10 wt % aqueous solutions of ethanol, ethylene glycol, and glycerol, respectively, in 2 M aqueous KOH. The Pd loading of the anode was increased to 6 mg cm(-2) by combining four single electrodes to produce a maximum peak power density with ethanol at 80 °C of 335 mW cm(-2) . Such high power densities result from a combination of the open 3 D structure of the anode electrode and the high electrochemically active surface area of the Pd catalyst, which promote very fast kinetics for alcohol electro-oxidation. The peak power and current densities obtained with ethanol at 80 °C approach the output of H2 -fed proton exchange membrane fuel cells.

One-pot synthesis of a three-dimensional graphene aerogel supported Pt catalyst for methanol electrooxidation

A Pt/graphene aerogel hybrid catalyst synthesized via a facile one-pot solvothermal method exhibits 2.86 times higher activity for methanol electrooxidation than that of Pt/graphene and the stability is improved by 10% as compared with Pt/graphene.

Attachment-based growth: building architecturally defined metal nanocolloids particle by particle

This review highlights the principles and recent mechanistic insight into the synthesis of metal nanostructures using nanoparticles as primary building blocks.

Influence of electrode assembly on catalytic activation and deactivation of a Pt film immobilized H+ conducting solid electrolyte in electrocatalytic reduction reactions

Symmetric assembly deactivated the electrocatalytic nitrate reduction process due to oxidation of copper atoms on the anode surface. In case of assymetric assembly, H₂ evolution eroded copper oxides causing catalytic activation.

Facile large-scale synthesis of Au–Pt alloyed nanowire networks as efficient electrocatalysts for methanol oxidation and oxygen reduction reactions

A rapid one-pot wet-chemical method was developed for large-scale preparation of surface-clean AuPt alloyed nanowire networks with the assistance of N-methylimidazole as a structure-directing agent and a weak stabilizing agent.

Ordered intermetallic PtFe@Pt core–shell nanoparticles supported on carbon nanotubes with superior activity and durability as oxygen reduction reaction electrocatalysts

PtFe@Pt nanoparticles with ordered intermetallic cores and Pt shells were supported on CNTs and developed as an ORR electrocatalyst.

Dispersing Pt and Pd atoms on Au nanoparticles deposited on n-GaN substrates for formic acid oxidation

Au nanoparticles, with dispersed Pt and Pd atoms on them, supported on n-GaN substrates were prepared. The catalysts showed an enhanced performance for formic acid oxidation, and the mass activity reached 3.5 mA μg_PtPd⁻¹.

Enhancement of the catalytic performance of a CNT supported Pt nanorod cluster catalyst by controlling their microstructure

Novel catalysts with Pt nanorod clusters distributed in both interior and exterior of CNTs were prepared and confirmed by TEM tomography. This structure benefits higher performance due to the CNTs' confinement effect.

Visible-light-assisted electrocatalytic oxidation of methanol using reduced graphene oxide modified Pt nanoflowers-TiO2 nanotube arrays

In this work, Pt nanoflowers deposited on highly ordered TiO2 nanotube arrays (TNTs) by modification of reduced graphene oxide (RGO) nanostructures have been synthesized. The ternary complex (Pt-TNTs/RGO) displays efficient electrocatalytic performance toward methanol oxidation in alkaline medium. The electrochemical impedance spectroscopy (EIS) and responsive photocurrent results indicate that the presence of graphene could effectively promote charge separation during electrocatalytic process. Interestingly, with assistance of visible light illumination, the electrocatalytic activity and stability of the ternary complex electrode toward methanol oxidation are distinctly improved. Both electro- and photo-catalytic processes for methanol oxidation contribute to the enhanced catalytic performance and stability. Moreover, the ternary electrode also displays efficient photoelectrocatalytic degradation of methylene blue (MB) under visible light illumination. The present work sheds light on developing highly efficient and long-term stability catalysts for methanol oxidation with assistance of visible-light illumination.

Synthesis of ultrafine Pt nanoparticles stabilized by pristine graphene nanosheets for electro-oxidation of methanol

In this study, the pristine graphene nanosheets (GNS) derived from chemical vapor deposition process were employed as catalyst support. In spite of the extremely hydrophobic GNS surface, ultrafine Pt nanoparticles (NPs) were successfully assembled on the GNS through a surfactant-free solution process. The evolution of Pt NPs in the GNS support was studied using transmission electron microscopy. It was found that the high-energy surface sites in the GNS, such as edges and defects, played a critical role on anchoring and stabilizing Pt nuclei, leading to the formation of Pt NPs on the GNS support. The concentration of the Pt precursor, i.e., H2PtCl6 solution had significant effects on the morphology of Pt/GNS hybrids. The resulting Pt/GNS hybrids were examined as catalysts for methanol electro-oxidation. It was indicated that the electrochemical active surface area and catalytic activity of the Pt/GNS hybrids were highly dependent on Pt loadings. The superior activity of the catalysts with low Pt loadings was attributed to the presence of Pt subnanoclusters as well as the strong chemical interaction of Pt NPs with the GNS support.

Facile synthesis of PVP-assisted PtRu/RGO nanocomposites with high electrocatalytic performance for methanol oxidation

With the assistance of PVP surfactant, well-dispersed PtRu nanoclusters supported on a graphene surface exhibited efficient electrocatalytic activity and stability in methanol oxidation.

Pt-based nanoparticles on non-covalent functionalized carbon nanotubes as effective electrocatalysts for proton exchange membrane fuel cells

This review presents the latest progress in the development of non-covalent functionalized CNT supported Pt-based electrocatalysts for fuel cells.