Porous Ni@Pt Core‐Shell Nanotube Array Electrocatalyst with High Activity and Stability for Methanol Oxidation

Surfactant-Free Monodispersed Pd Nanoparticles Template for Core-Shell Pd@PdPt Nanoparticles as Electrocatalyst towards Methanol Oxidation Reaction (MOR)

An eco-friendly two-step synthetic method for synthesizing Pd@PdPt/CNTs nanoparticles was introduced and studied for the methanol oxidation reaction. The Pd@PdPt alloy core-shell structure was synthesized by preparing a surfactant-free monodispersed Pd/CNTs precursor through the hydrolysis of tetrachloropalladate (II) ion ([PdCl₄]²⁻) in the presence of carbon nanotubes (CNTs) and the subsequent hydrogen reduction and followed by a galvanic replacement reaction. This method opens up an eco-friendly, practical, and straightforward route for synthesizing monometallic or bimetallic nanoparticles with a clean surfactant-free electrocatalytic surface. It is quite promising for large-scale preparation. The Pd@PdPt/CNTs electrocatalyst demonstrated a high specific mass activity for methanol oxidation (400.2 mAmg_Pt⁻¹) and excellent stability towards direct methanol oxidation compared to its monometallic counterparts.

PtSn Nanoalloy Thin Films as Anode Catalysts in Methanol Fuel Cells

Reactions of SnX₂ (X = Cl, Br) with [PtMe₂(bipy)], 1, (bipy = 2,2'-bipyridine), followed by NaBH₄ reduction at the toluene/water interface in the presence or absence of graphene oxide support rendered PtSn nanoalloy thin films. They were characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. The electrocatalytical activity of the PtSn thin films was investigated in the methanol oxidation reaction. Our studies showed that the PtSn/reduced-graphene oxide (RGO) thin film gave better catalytic results for MOR in comparison to bare PtSn or Pt thin films. A maximum j_f/j_b ratio (j_f and j_b are the maximum current densities in the forward and backward scans, respectively) of 6.77 was obtained for the PtSn/RGO thin film deriving from the 1 + SnBr₂ + NaBH₄ sequence.

Synthesis of octahedral Pt-Ni-Ir yolk-shell nanoparticles and their catalysis in oxygen reduction and methanol oxidization under both acidic and alkaline conditions

Fuel cells are expected to be one of the most promising alternatives to the increasingly scarce fossil fuels, and Pt is the most commonly used catalyst for anodic and cathodic electrochemical reactions. To realize large-scale commercialization, it is most urgent to improve the efficiency of Pt and reduce the cost. Here, we synthesized an octahedral Pt-Ni-Ir yolk-shell catalyst through stepwise co-deposition (SCD), surface-limited Pt deposition (SLPD) and Ni-coordinating etching (NCE) processes. Experimental studies showed that the catalytic activities of the as-prepared trimetal yolk-shell catalyst were several times higher than that of the commercial Pt/C towards oxygen reduction and methanol oxidization under both acidic and alkaline conditions. This work may be extended to designing other multimetallic functional materials with complex hierarchical nanostructures, which is conducive to greatly enhancing the performance.

Recent Advances on Controlled Synthesis and Engineering of Hollow Alloyed Nanotubes for Electrocatalysis

The past decade has witnessed great progress in the synthesis and electrocatalytic applications of 1D hollow alloy nanotubes with controllable compositions and fine structures. Hollow nanotubes have been explored as promising electrocatalysts in the fuel cell reactions due to their well-controlled surface structure, size, porosity, and compositions. In addition, owing to the self-supporting ability of 1D structure, hollow nanotubes are capable of avoiding catalyst aggregation and carbon corrosion during the catalytic process, which are two other issues for the widely investigated carbon-supported nanoparticle catalysts. It is currently a great challenge to achieve high activity and stability at a relatively low cost to realize commercialization of these catalysts. An overview of the structural and compositional properties of 1D hollow alloy nanotubes, which provide a large number of accessible active sites, void spaces for electrolytes/reactants impregnation, and structural stability for suppressing aggregation, is presented. The latest advances on several strategies such as hard template and self-templating methods for controllable synthesis of hollow alloyed nanotubes with controllable structures and compositions are then summarized. Benefiting from the advantages of the unique properties and facile synthesis approaches, the capability of 1D hollow nanotubes is then highlighted by discussing examples of their applications in fuel-cell-related electrocatalysis. Finally, the remaining challenges and potential solutions in the field are summarized to provide some useful clues for the future development of 1D hollow alloy nanotube materials.

Co-Sn Nanocrystalline Solid Solutions as Anode Materials in Lithium-Ion Batteries with High Pseudocapacitive Contribution

Co-Sn solid-solution nanoparticles with Sn crystal structure and tuned metal ratios were synthesized by a facile one pot solution-based procedure involving the initial reduction of a Sn precursor followed by incorporation of Co within the Sn lattice. These nanoparticles were used as anode materials for Li-ion batteries. Among the different compositions tested, Co_0.7 Sn and Co_0.9 Sn electrodes provided the highest capacities with values above 1500 mAh g^-1 at a current density of 0.2 A g^-1 after 220 cycles, and up to 800 mAh g^-1 at 1.0 A g^-1 after 400 cycles. Up to 81 % pseudocapacitance contribution was measured for these electrodes at a sweep rate of 1.0 mV s^-1 , thereby indicating fast kinetics and long durability. The excellent performance of Co-Sn nanoparticle alloy-based electrodes was attributed to both the small size of the crystal domains and their suitable composition, which buffered volume changes of Sn and contributed to a suitable electrode restructuration.

The Modification of Pt/Graphene Composites with Oxophilic Metal Bi (Bi2O3) and Its Dual-Functional Electro-Photo Catalytic Performance

The Pt-Bi (Bi2O3)/GNs (PVP) composite was synthesized using aqueous solution synthesis and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and Raman spectroscopy. It was found that the water-soluble polyvinyl pyrrolidone (PVP) helped to tune the particles’ morphology, resulting in a uniform distribution of Pt-Bi nanoclusters on the surface of graphene. Cyclic voltammetry, chronoamperometry and linear scanning voltammetry (LSV) were used to study the electrocatalytic properties towards a methanol oxidation reaction (MOR) and an oxygen reduction reaction (ORR). The results show that Pt-Bi (Bi2O3)/GNs (PVP) exhibits superior bifunctional electrocatalytic properties for both MOR and ORR, mainly due to the introduction of oxophilic Bi species and the better dispersion of the Pt-Bi nanoclusters. In particular, the electro-photo catalysis for both MOR and ORR occurred under simulated sunlight irradiation due to the existence of photo-responsive Bi species, which is helpful for converting solar energy into electric energy during a traditional electrocatalytic process.

1D Nanomaterials: Design, Synthesis, and Applications in Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have received extensive attention as ideal candidates for large-scale energy storage systems (ESSs) owing to the rich resources and low cost of sodium (Na). However, the larger size of Na⁺ and the less negative redox potential of Na⁺ /Na result in low energy densities, short cycling life, and the sluggish kinetics of SIBs. Therefore, it is necessary to develop appropriate Na storage electrode materials with the capability to host larger Na⁺ and fast ion diffusion kinetics. 1D materials such as nanofibers, nanotubes, nanorods, and nanowires, are generally considered to be high-capacity and stable electrode materials, due to their uniform structure, orientated electronic and ionic transport, and strong tolerance to stress change. Here, the synthesis of 1D nanomaterials and their applications in SIBs are reviewed. In addition, the prospects of 1D nanomaterials on energy conversion and storage as well as the development and application orientation of SIBs are presented.

Porous One-Dimensional Nanomaterials: Design, Fabrication and Applications in Electrochemical Energy Storage

Electrochemical energy storage technology is of critical importance for portable electronics, transportation and large-scale energy storage systems. There is a growing demand for energy storage devices with high energy and high power densities, long-term stability, safety and low cost. To achieve these requirements, novel design structures and high performance electrode materials are needed. Porous 1D nanomaterials which combine the advantages of 1D nanoarchitectures and porous structures have had a significant impact in the field of electrochemical energy storage. This review presents an overview of porous 1D nanostructure research, from the synthesis by bottom-up and top-down approaches with rational and controllable structures, to several important electrochemical energy storage applications including lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, lithium-oxygen batteries and supercapacitors. Highlights of porous 1D nanostructures are described throughout the review and directions for future research in the field are discussed at the end.

Facile synthesis of hollow dendritic Ag/Pt alloy nanoparticles for enhanced methanol oxidation efficiency

Hollow dendritic Ag/Pt alloy nanoparticles were synthesized by a double template method.

Efficient Dual-Site Carbon Monoxide Electro-Catalysts via Interfacial Nano-Engineering

Durable, highly efficient, and economic sound electrocatalysts for CO electrooxidation (COE) are the emerging key for wide variety of energy solutions, especially fuel cells and rechargeable metal-air batteries. Herein, we report the novel system of nickel-aluminum double layered hydroxide (NiAl-LDH) nanoplates on carbon nanotubes (CNTs) network. The formulation of such complexes system was to be induced through the assistance of gold nanoparticles in order to form dual-metal active sites so as to create a extended Au/NiO two phase zone. Bis (trifluoromethylsulfonyl)imide (NTf2) anion of ionic liquid electrolyte was selected to enhance the CO/O2 adsorption and to facilitate electro-catalyzed oxidation of Ni (OH)2 to NiOOH by increasing the electrophilicity of catalytic interface. The resulting neutral catalytic system exhibited ultra-high electrocatalytic activity and stability for CO electrooxidation than commercial and other reported precious metal catalysts. The turnover frequency (TOF) of the LDH-Au/CNTs COE catalyst was much higher than the previous reported other similar electrocatalysts, even close to the activity of solid-gas chemical catalysts at high temperature. Moreover, in the long-term durability testing, the negligible variation of current density remains exsisting after 1000 electrochemistry cycles.

Metal-Free and Noble Metal-Free Heteroatom-Doped Nanostructured Carbons as Prospective Sustainable Electrocatalysts

The large-scale deployment of many types of fuel cells and electrolyzers is currently constrained by the lack of sustainable and efficient catalysts that can replace the less earth-abundant, noble metal-based catalysts, which are commonly used in these renewable energy systems. This burgeoning issue has led to explosive research efforts worldwide to find alternative, metal-free and noble metal-free catalysts that are composed of inexpensive and earth-abundant elements. Hence, the recent discoveries that doping carbon nanomaterials with heteroatoms (such as N, S, B, etc.) can give sustainable materials with good electrocatalytic activity for reactions carried out in fuel cells and electrolyzers have been not only quite exciting but also very promising to address these challenging issues. Interestingly, even though they contain no metals or involve only the inexpensive, more earth-abundant ones, the catalytic activity of some of these materials fares well with those of the commercially used noble metal-based electrocatalysts, such as Pt/C. However, research efforts to improve the catalytic activity, selectivity, and stability of some of these materials for various reactions are still necessary and thus continuing. While some of these efforts have focused on finding synthetic methods that can tune the structures and compositions of already known materials and thereby improve their catalytic properties (activity, selectivity, stability, etc.), others have focused on developing entirely new materials that can exhibit better or superior catalytic properties. In these efforts, additional considerations are also being paid to find facile synthetic routes or renewable and inexpensive precursors that can lead to such types of catalysts in order to make the entire process highly sustainable and widely applicable. In this Account, notable heteroatom-doped carbon catalysts that have been developed for reactions in fuel cells and water electrolyzers, the various synthetic procedures employed to make them, and the challenges involved in their synthesis as well as their characterizations are discussed. The methods used to systematically vary the structures and compositions of the precursors of these materials, as well as the materials themselves, and the different experimental, imaging, and spectroscopic methods used to investigate the properties and structure-property relationships of the materials for various energy related reactions are also included. The discussions focus mainly around the recent notable results reported on these materials by the author's and other research groups worldwide, albeit not exhaustively. Finally, the author's perspective about the challenges remaining in the field that need to be addressed, the many existing unanswered questions that beg for more research, and the future prospects for research related to the above topics are also mentioned.

Template-based syntheses for shape controlled nanostructures

A variety of nanostructured materials are produced through template-based synthesis methods, including zero-dimensional, one-dimensional, and two-dimensional structures. These span different forms such as nanoparticles, nanowires, nanotubes, nanoflakes, and nanosheets. Many physical characteristics of these materials such as the shape and size can be finely controlled through template selection and as a result, their properties as well. Reviewed here are several examples of these nanomaterials, with emphasis specifically on the templates and synthesis routes used to produce the final nanostructures. In the first section, the templates have been discussed while in the second section, their corresponding synthesis methods have been briefly reviewed, and lastly in the third section, applications of the materials themselves are highlighted. Some examples of the templates frequently encountered are organic structure directing agents, surfactants, polymers, carbon frameworks, colloidal sol-gels, inorganic frameworks, and nanoporous membranes. Synthesis methods that adopt these templates include emulsion-based routes and template-filling approaches, such as self-assembly, electrodeposition, electroless deposition, vapor deposition, and other methods including layer-by-layer and lithography. Template-based synthesized nanomaterials are frequently encountered in select fields such as solar energy, thermoelectric materials, catalysis, biomedical applications, and magnetowetting of surfaces.

A PtPdCu thin-film catalyst based on titanium nitride nanorod arrays with high catalytic performance for methanol electro-oxidation

Here, we present a novel MOR anode catalyst based on TiN nanorod arrays with high performance towards MOR.

Pt/Ni(OH)2-NiOOH/Pd multi-walled hollow nanorod arrays as superior electrocatalysts for formic acid electrooxidation

The catalytic activity and durability are crucial for the development of high-performance electrocatalysts. To design electrocatalysts with excellent electroactivity and durability, the structure and composition are two important guiding principles. In this work, novel Pt/Ni(OH)2-NiOOH/Pd multi-walled hollow nanorod arrays (MHNRAs) are successfully synthesized. The unique MHNRAs provide fast transport and short diffusion paths for electroactive species and high utilization rate of catalysts. Because of the special surface and synergistic effects, the Pt/Ni(OH)2-NiOOH/Pd MHNRA electrocatalysts exhibit high catalytic activity, high durability and superior CO poisoning tolerance for the electrooxidation of formic acid in comparison with Pt@Pd MHNRAs, commercial Pt/C, Pd/C and PtRu/C catalysts.

A strategy for fabricating porous PdNi@Pt core-shell nanostructures and their enhanced activity and durability for the methanol electrooxidation

Three-dimensionally (3D) porous morphology of nanostructures can effectively improve their electrocatalytic activity and durability for various electrochemical reactions owing to big surface area and interconnected structure. Cyanogel, a jelly-like inorganic polymer, can be used to synthesize various three-dimensionally (3D) porous alloy nanomaterials owing to its double-metal property and particular 3D backbone. Here, 3D porous PdNi@Pt core-shell nanostructures (CSNSs) are facilely synthesized by first preparing the Pd-Ni alloy networks (Pd-Ni ANWs) core via cyanogel-reduction method followed by a galvanic displacement reaction to generate the Pt-rich shell. The as-synthesized PdNi@Pt CSNSs exhibit a much improved catalytic activity and durability for the methanol oxidation reaction (MOR) in the acidic media compared to the commercial used Pt black because of their specific structural characteristics. The facile and mild method described herein is highly attractive for the synthisis of 3D porous core-shell nanostructures.

Autocatalysis and selective oxidative etching induced synthesis of platinum-copper bimetallic alloy nanodendrites electrocatalysts

The controllable synthesis of noble metal alloy nanostructures with highly branched morphology has attracted much attention because of their specific physical and chemical properties. This article reports the synthesis of platinum-copper bimetallic alloy nanodendrites (Pt-Cu BANDs) by a facile, one-pot, templateless, and seedless hydrothermal method in the presence of poly(allylamine hydrochloride) (PAH) and formaldehyde (HCHO). The morphology, composition, and structure of Pt-Cu BANDs are fully characterized by various physical techniques, demonstrating Pt-Cu BANDs are highly alloying, porous, and self-supported nanostructures. The formation/growth mechanism of Pt-Cu BANDs is explored and discussed based on the experimental observations. The autocatalytic growth and interdiffusion are responsible for the formation of Pt-Cu alloy whereas selective oxidative etching results in dendritic morphology of Pt-Cu alloy nanostructures. In addition, the electrocatalytic activity and stability of Pt-Cu BANDs for the methanol oxidation reaction (MOR) are investigated by various electrochemical techniques. The synthesized Pt-Cu BANDs show higher electrocatalytic activity and stability than commercially available Pt black.

Effective electrocatalysis based on Ag2O nanowire arrays supported on a copper substrate

Silver oxide nanowire arrays (Ag2O NWAs) were first synthesized on a copper (Cu) rod by a simple and facile wet-chemistry approach without using any surfactants. The as-synthesized Ag2O NWA/Cu rod not only can be used as an integrated electrode (called a Ag2O NWA/CRIE) to detect hydrazine (HZ) but also can serve as the catalyst layer for a direct HZ fuel cell. The current density of HZ oxidation on Ag2O NWA (94.4 mA cm(-2)) is much bigger than that on a bare Cu rod (3.9 mA cm(-2)) at -0.6 V, and other Ag2O NWAs have the lowest onset potential (-0.85 V). This suggests that a Ag2O NWA integrated electrode has potential application in catalytic fields that contain the HZ fuel cell.

Controllable growth of conducting polymers shell for constructing high-quality organic/inorganic core/shell nanostructures and their optical-electrochemical properties

High-quality metal oxide/conducting polymer (CP) heterostructured nanoarrays are fabricated by controllable electrochemical polymerization of CP shells on preformed metal oxides nanostructures for both electrochromic and electrochemical energy storage applications. Coaxial and branched CP shells can be obtained on different backbones (nanowire, nanorod, and nanoflake) simply by controlling the electrodeposition time. "Solvophobic" and "electrostatic" interactions are proposed to account for the preferential growth of CP along metal oxides to form core/shell heterostructures. The coaxial TiO2/polyaniline core/shell nanorod arrays exhibit remarkable electrochromic performance with rich color changes, fast optical modulation, and superior cycling stability. In addition, the Co3O4/polyaniline core/shell nanowire arrays are evaluated as an anode material of Li ion battery and exhibit enhanced electrochemical property with higher and more stable capacity than the bare Co3O4 nanowires electrode. These unique organic-inorganic heterostructures with synergy pave the way for developing new functional materials with enhanced properties or new applications.

Direct growth of NiCo2O4 nanostructures on conductive substrates with enhanced electrocatalytic activity and stability for methanol oxidation

In this report, NiCo2O4 nanostructures with different morphologies were directly grown on conductive substrates (stainless steel and ITO) by a facile electrodeposition method in addition to a post-annealing process. The morphology changes on different conductive substrates are discussed in detail. The NiCo2O4 on stainless steel (SS) had a high surface area (119 m(2) g(-1)) and was successfully used in the electrocatalytic oxidation of methanol. The electrocatalytic performance was investigated by cyclic voltammetry (CV), chronoamperometry and electrochemical impedance spectroscopy (EIS) measurements. Impressively, the NiCo2O4 showed much higher electrocatalytic activity, lower overpotential and greater stability compared to that of only NiO or Co3O4 synthesized by the same method. The higher electrocatalytic activity is due to the high electron conductivity, large surface area of NiCo2O4 and the fast ion/electron transport in the electrode and at the electrolyte-electrode interface. This is important for further development of high performance non-platinum electrocatalysts for application in direct methanol fuel cells.

Effect of Ni Core Structure on the Electrocatalytic Activity of Pt-Ni/C in Methanol Oxidation

Methanol oxidation catalysts comprising an outer Pt-shell with an inner Ni-core supported on carbon, (Pt-Ni/C), were prepared with either crystalline or amorphous Ni core structures. Structural comparisons of the two forms of catalyst were made using transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), and methanol oxidation activity compared using CV and chronoamperometry (CA). While both the amorphous Ni core and crystalline Ni core structures were covered by similar Pt shell thickness and structure, the Pt-Ni(amorphous)/C catalyst had higher methanol oxidation activity. The amorphous Ni core thus offers improved Pt usage efficiency in direct methanol fuel cells.

Fabrication of metal oxide nanobranches on atomic-layer-deposited TiO2 nanotube arrays and their application in energy storage

Due to the chemical stability and easy fabrication by atomic layer deposition (ALD), TiO2 nanotubes are regarded highly useful in constructing branched nanostructured electrodes for solar conversion and electrochemical energy storage devices. Here we present a facile and scalable fabrication of metal oxide nanobranches on ALD pre-formed TiO2 nanotubes. The metal oxide branches can be a wide range (nearly any) of desirable materials, including NiO and Co3O4 demonstrated herein. As an example, the TiO2/NiO nanoarray battery cathode exhibits a relatively high gravimetric capacity value of ~153 mA h g(-1) and a fairly good stability up to 12,000 cycles with a capacitance of 132 mA h g(-1) at 2 A g(-1).

Electrochemical synthesis of nanostructured materials for electrochemical energy conversion and storage

Electrochemical synthesis represents a highly efficient method for the fabrication of nanostructured energy materials, and various nanostructures, such as nanorods, nanowires, nanotubes, nanosheets, dendritic nanostructures, and composite nanostructures, can be easily fabricated with advantages of low cost, low synthetic temperature, high purity, simplicity, and environmental friendliness. The electrochemical synthesis, characterization, and application of electrochemical energy nanomaterials have advanced greatly in the past few decades, allowing an increasing understanding of nanostructure-property-performance relationships. Herein, we highlight some recent progress in the electrochemical synthesis of electrochemical energy materials with the assistance of additives and templates in solution or grafted onto metal or conductive polymer supports, with special attention to the effects on surface morphologies, structures and, more importantly, electrochemical performance. The methodology for preparing novel electrochemical energy nanomaterials and their potential applications has been summarized. Finally, we outline our personal perspectives on the electrochemical synthesis and applications of electrochemical energy nanomaterials.

Facile solution synthesis of Ag@Pt core-shell nanoparticles with dendritic Pt shells

Ag@Pt nanoparticles with various dendritic Pt shells were successfully synthesized by using nonionic surfactants at room temperature. Our recent study demonstrated that the addition of nonionic surfactant plays an important key role in the synthesis of dendritic Pt nanostructures (J. Am. Chem. Soc., 2010, 132, 13636). Here we extend this synthetic concept to prepare various Ag@Pt nanoarchitectures. The different nanostructured Pt shells on the Ag core were confirmed by ultraviolet-visible absorption spectroscopy and transmission electron microscopy. As a preliminary electrochemical application, the obtained Ag@Pt nanostructures were applied in the methanol oxidation reaction (MOR) in 0.5 M H(2)SO(4) solution containing 0.5 M methanol. The Ag@Pt nanoparticles with thin dendritic Pt shells show superior CO-tolerance performance with a I(f)/I(b) value reaching 3.71. Our Ag@Pt nanostructures with good CO tolerant activity will be prominent catalysts for MOR.