Electrocatalytic Oxidation Properties Research Articles

Formation of Bi-Containing sea urchin-like Pt nanoparticles induced by the addition of bismuth element and their enhanced electrocatalytic properties for methanol oxidation

A facile method to synthesize Bi-containing sea urchin-like Pt nanoparticles is demonstrated. The morphology and chemical composition of the prepared Bi-containing sea urchin-like Pt nanoparticles were characterized using scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. Electrochemical studies of the oxidation of methanol in an acidic medium using the Bi-containing sea urchin-like Pt nanoparticles were performed. The prepared nanoparticles exhibited enhanced electrocatalytic activity for methanol oxidation with a seven-fold higher oxidation current density and a more negative onset potential than commercial Pt/C (Pt 20%). Moreover, the current density of the Bi-containing sea urchin-like Pt nanoparticle/C catalysts was high even after 900 s of continuous electrocatalysis at 0.56 V. The synthesized Bi-containing sea urchin-like Pt nanoparticles should find attractive applications in various fields, such as fuel cells, sensors, and eletro- or organic catalysis.

Synthesis and Activation of Pt–Cu Alloy Nanocrystals with Controlled Structure and Exposed Facets for Ethylene Glycol Oxidation

The ability to control the shape, structure and faceting characteristics of bimetallic alloy nanocrystals (NCs) has been vital for designing a catalyst with excellent activity and durability in fuel cells. However, it has remained a significant challenge to synthesize platinum–copper (Pt–Cu) alloy NCs with controlled structure and exposed facets. Herein, Pt–Cu alloy NCs with different shapes, structures and facets were synthesized via a one-step direct chemical co-reduction method employing various glucose concentrations. The results showed that the prepared Pt–Cu alloy NCs exhibited very interesting facet-dependent electrocatalytic properties for ethylene glycol oxidation. In comparison with other prepared Pt–Cu alloy NCs and commercial Pt/C, Pt–Cu alloy NPs with (111)-dominant facets showed higher electrocatalytic activity and durability for ethylene glycol oxidation. Alloy NPs showing prominent electrocatalytic performance were attributed to the predominant (111) facets on NP surfaces serving as catalytic active sites, in addition to added Cu providing unique electronic and synergistic effects. The present work highlighted that these NPs with (111)-dominant facets were indeed promising candidates as electrocatalysts with excellent activity and superior durability.

Enhanced electrocatalytic methanol oxidation properties by photo-assisted Fe2O3 nanoplates

Abstract In this paper, visible-light-driven two-dimensional (2D) Fe2O3 nanoplates with exposed (001) facets were first adopted to act as Pt support for photo-assisted electrocatalytic methanol oxidation. Under simulated solar light and visible light illumination Pt-2D Fe2O3 nanoplates displayed 2.32 and 1.30 times higher electrocatalytic activities for methanol oxidation than in dark condition, respectively. Besides, 2D Fe2O3 nanoplates owns much better electrocatalytic activities for methanol oxidation than Fe2O3 particles whether in dark, visible light or simulated solar light illumination. The nice photo-assisted electrocatalytic methanol oxidation activities of Pt-2D Fe2O3 nanoplates can be attributed to 2D structure enhanced the oxidation activities of photogenerated holes to oxidize OH− to hydroxyl radical (·OH) as well as its large specific surface area. Our experimental results suggest that photo-assisted and two-dimensional strategy of semiconductors are promising ways to further improve the electrocatalytic activities for methanol oxidation in DMFCs.

Concave cubic PtLa alloy nanocrystals with high-index facets: Controllable synthesis in deep eutectic solvents and their superior electrocatalytic properties for ethanol oxidation

Due to their strong electronic interactions and excellent electrochemical properties, noble metal-based rare earth nanoalloys are considered to be promising electrocatalytic materials for fuel cell applications. However, due to the limitation of the very negative reduction potential for rare earth metals, the wet chemical or electrochemical preparation of noble metal/rare earth nanoalloys is still challenging. Herein, we report a novel and effective strategy for the electrochemical synthesis in deep eutectic solvents of concave cubic PtLa alloy nanocrystals with high-index facets and superior electrocatalytic properties for the ethanol oxidation reaction. Scanning electron microscopy and transmission electron microscopy characterizations confirm that the concave cubic PtLa alloy nanocrystals of approximately 47.5 nm in size are uniformly electro-deposited on the glassy carbon substrate in deep eutectic solvents and are bounded with the {410} and adjacent high-index facets. X-ray photoelectron spectroscopy analysis indicates the presence of strong charge transfer interactions from La to Pt atoms in the concave cubic PtLa alloy nanocrystals. Due to the synergetic effect of the high-index facets and the charge transfer interactions between Pt and La, the synthesized concave cubic PtLa alloy nanocrystals exhibit enhanced specific current activity and long-term durability for the ethanol oxidation reaction.

Synthesis of Nanostructured Bimetallic Catalysts for Electrochemical Applications

Bimetallic nanostructures of specific compositions and enclosed by certain facets can significantly alter their physical and chemical properties and thus provide the opportunities to tailor them for particular electrochemical applications. Despite significant progress in recent years, it is still a grand challenge to control the spatial distribution of elements and surface structure of bimetallic nanoparticles. Thus, it remains very difficult to understand the properties of bimetallic nanoparticles, and even more challenging to overcome the formidable barriers to the rational design of bimetallic nanoparticles with the desired performance. This research focuses on the development of seed-mediated synthesis in solution aiming to precisely control the atomic arrangement in the bimetallic catalysts to establish the structure-composition-property relationship for electrocatalytic applications. In seed-mediated synthesis, the seeds can be preformed or in situ formed as a primary nanoscale substrate, followed by reducing secondary precursors to form bimetallic or multimetallic nanocatalysts. By controlling the shape of the seeds and reduction kinetics, well-defined bimetallic and multimetallic nanostructures can be obtained. In this work, CuPt and CuPtRu nanomaterials will be used as an example to demonstrate how changes of spatial atomic arrangement in the nanostructures influence their electrocatalytic properties for methanol oxidation. Fine tuning and mechanistic study of these synthetic strategies provide us fundamental understanding for precise control of bimetallic nanostructures to tackle problems in materials chemistry and open up the possibility for rational design and synthesis of future complex nanoarchitectures towards electrochemical applications.

Size-controllable synthesis of dendritic Pd nanocrystals as improved electrocatalysts for formic acid fuel cells’ application

Control over size and shape of Pd nanocrystals is critical for highly active and stable catalysts in direct formic acid fuel cells’ application. In this work, dendritic Pd nanocrystals have been successfully synthesized using a facile, environmentally friendly approach in an aqueous solution below 100 °C. The size of as-synthesized dendritic Pd nanocrystals has a narrow distribution, about 57.5 ± 7.5 nm. The dendritic Pd nanocrystals exhibit much superior electrocatalytic properties for formic acid oxidation compared with commercial Pd black in acidic medium. The specific activity and mass activity toward formic acid oxidation on dendritic Pd nanocrystals are 5.14 mA/cm2 and 3.3 A/mg in perchloric acid solution, 2.0 mA/cm2 and 1.08 A/mg in sulfuric acid solution, respectively. And for commercial Pd black, the specific activity and mass activity are 2.08 mA/cm2 and 0.36 A/mg in perchloric acid solution, 0.68 mA/cm2 and 0.12 A/mg in sulfuric acid solution. Furthermore, chronoamperometric measurements show that the dendritic Pd nanocrystals have excellent stability over commercial Pd black.

Quasi-single-crystalline CoO hexagrams with abundant defects for highly efficient electrocatalytic water oxidation.

Defects and structural long-range ordering have been recognized as two crucial characters for advanced electrocatalysts. However, these two features have rarely been achieved together. Herein, we report the preparation of single-crystalline CoO hexagrams and demonstrate their exceptional electrocatalytic properties for water oxidation. The quasi-single-crystalline CoO hexagrams, prepared at the critical phase transition point of β-Co(OH)2/Co(OH)F hexagrams, possess both abundant oxygen vacancies as defects and structural long-range ordering. The matching between the b-axis of Co(OH)F crystals and the a-axis of β-Co(OH)2 crystals is critical for the formation of the CoO hexagram single crystals. The quasi-single-crystalline CoO hexagrams with abundant defects are highly efficient for water oxidation by delivering a 10 mA cm-2 current density at a low overpotential of 269 mV in a 1 M KOH aqueous solution.

Flower-like PdCu catalyst with high electrocatalytic properties for ethylene glycol oxidation

A highly efficient PdCu alloy nanocatalyst has been designed and synthesized, which exhibited excellent selectivity and activity toward ethylene glycol (EG) oxidation reaction with a low loading of electrocatalyst. The results of characterization show that the atom ratio of 1:1 (Pd:Cu) as well as the addition of polyvinyl pyrrolidone (PVP) and potassium bromide (KBr) contributed to the unique morphology of the as-prepared PdCu catalyst. Owing to the flower-like nanostructure and the synergistic effect between Pd and Cu, PdCu electrocatalyst has distinct enhancement in electrocatalytic performance whose forward peak current density is almost 3.2 and 4.3 times higher than that of pure Pd and commercial Pd/C electrocatalysts. We put forward that the prepared PdCu catalyst may have promising and alternative applications in direct EG alkaline fuel cells.

Carbon-supported Pt nanoparticles with (100) preferential orientation with enhanced electrocatalytic properties for carbon monoxide, methanol and ethanol oxidation in acidic medium

The relationship between atomic arrangement (morphology) and catalytic activity/selectivity in heterogeneous catalysis is an actual hot research topic concerning a range of reactions. This article evaluates one-pot synthesized carbon-supported Pt nanoparticles with preferential Pt(100) orientation prepared with an environmentally friendly shape-directing agent and compares this with Pt/C polycrystalline towards CO, methanol and ethanol electrooxidation reactions. The preferentially cubic nanomaterial (Pt-(100)) interacts differently with CO molecule and presents distinct hydrogen adsorption/desorption characteristics. Pt/C polycrystalline exhibits a CO-stripping profile with one peak at 0.86 V in contrast to three peaks between 0.75 and 0.86 V and a pre-peak at about 0.4–0.6 V for the Pt/C-(100), which may be associated to the unique surface characteristics of the cubic material. The onset potentials towards carbon monoxide, methanol and ethanol electro-oxidation reactions on Pt/C-(100) are 22%, 21% and 54% lower than on Pt/C polycrystalline. The ratio between the forward per backward peak current densities for the electrooxidation of ethanol and methanol are higher on Pt/C-(100), which suggests that Pt(100) domains are more tolerant to undergo poisoning by the intermediates/by-products formed in these reactions. Proton exchange membrane fuel cells fed with pure hydrogen and with a H2/CO mixture show superior performance using Pt/C-(100) as anode in comparison to Pt/C polycrystalline catalyst. These results evidence that controlling the morphology of Pt nanoparticles is a key factor to improve the catalytic activity of the polymer electrolyte fuel cell fueled with fuels that involve the electro-oxidation of CO.

Fabrication of a composite of platinum, N-g-C3N4 and Ketjen Black for photo-electrochemical methanol oxidation

Recently N-doped graphitic carbon-incorporated g-C3N4 (denoted as N-g-C3N4) exhibits better electroconductivity and photo-catalytic property compared with pure g-C3N4 as a support material for Pt nanoparticles (NPs). A composite catalyst consisting of Pt nanoparticles and N-g-C3N4-modified KB was designed and fabricated. Pt nanoparticles were prepared through a solution plasma process; N-g-C3N4 was prepared by direct heating the mixture of urea and citric acid monohydrate and subsequently treated by hydrothermal method. Their chemical composition, particle size and microstructure were investigated by X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy. Compared with the Pt/KB catalyst, ternary Pt/N-g-C3N4/KB nanocomposites exhibit excellent electrocatalytic properties for methanol oxidation owning to the significant synergistic effects of individual components. Once light irradiation was supplied, Pt/N-g-C3N4/KB catalyst exhibits exceptional forward peak current densities as high as 2800 mA mg Pt −1 . And Pt/N-g-C3N4/KB catalyst also shows better CO tolerance than Pt/KB. Such a Pt/N-g-C3N4/KB composite catalyst may bring new design ideas for photo-assisted direct methanol fuel cell in the future.

Heterostructures in carbon-doped tungsten nitride and its effect on electrocatalytic properties for methanol oxidation

The hexagonal carbon-doped tungsten nitride nanoparticles (WC|N) have been derived from the cubic WN by inducing carbon atoms to WN lattices via a controlled carbonization method. The heterostructures discrepancy in WC|N catalysts involving constitutions of crystal phases and concentration of carbon and nitrogen could be effectively adjusted by simply changing carbonization time, and then had a great impact on the electrocatalytic behaviors of WC|N. Porous morphology of WC|N catalysts was also inherited from tungsten nitrides to provide the large surface area. The ternary Pt/WC|N catalysts were fabricated by an ethylene glycol reduction method with microwave-assisted heating. The intimate contact and intensive interaction between Pt and WC|N catalyst were verified. Impressively, the Pt/WC|N hybrid exhibited superior electrocatalytic activity for methanol oxidation and improved CO anti-poisoning capacity which higher than that of commercial Pt/C catalyst. The catalytic activity was enhanced due to the large amount of distortion which was induced during the diffusion of C into WN lattice and resultant phase transformation. Samples which were carbonized for 120min displayed the outstanding catalytic activity among all the materials even from the different tungsten sources suggest that the extent of distortion in catalyst is the crucial factor for the catalyst activity in electrochemistry reaction.

Poly(ionic liquid) assisted synthesis of hierarchical gold-platinum alloy nanodendrites with high electrocatalytic properties for ethylene glycol oxidation and oxygen reduction reactions

Herein, a facile one-pot method is developed to prepare three-dimensional (3D) hierarchical AuPt alloy nanodendrites (AuPt NDs) with the assistance of poly(ionic liquid) as the green shape-regulator and stabilizer. The as-synthesized architectures show enlarged electrochemically active surface area, and enhanced maximum mass activity (3616 mA mg−1) for ethylene glycol oxidation reaction (EGOR) in alkaline media. Furthermore, the as-synthesized AuPt NDs exhibit superior catalytic activity and more positive onset potential (0.89 V vs. RHE) toward oxygen reduction reaction (ORR) in 0.1 M HClO4 via the four-electron pathway, owing to the unique nanostructures as well as the synergistic effects between Au and Pt.

Fabrication of mesoporous NiFe2O4 nanorods as efficient oxygen evolution catalyst for water splitting

Designing and fabricating inexpensive, active oxygen evolving catalysts are significant for promoting the performances of water splitting. Here we report the synthesis of mesoporous, one-dimensional NiFe2O4 spinel by thermal decomposing of NiFe-based coordination polymer precursor. The annealed temperature and structural/compositional of these as-prepared electrocatalysts were found to have a striking correlation with their electrocatalytic water oxidation properties. The NiFe2O4 nanorods with a surface area of 165.9m2/g obtained at 350°C was found to be the most active oxygen evolving catalyst in alkaline solution, an overpotential of 342mV at 10mA/cm2 with a Tafel slope of 44mV/dec was detected, comparing with those of electrocatalysts obtained under other decomposed temperature. The OER mechanism in alkaline electrolytes on NiFe2O4 was also proposed. The high oxygen evolving activity can be attributed to the mesoporous one-dimensional nanostructure with abundant surface electrochemically active sites and improved electric conductivity, thus facilitating the charge/electron transfer and further improving the efficiency of water electrolysis. The efficient water oxidation activity and scalable, low-cost synthesis make the NiFe2O4 nanorods a very attractive oxygen evolving catalyst using for water splitting.

PdPt@Au core@shell nanoparticles: Alloyed-core manipulation of CO electrocatalytic oxidation properties

A series of PdPt@Au core@shell nanopaticles (NPs) of similar size are synthesized with composition controlled cores and thickness controlled shells. Their CO electrocatalytic oxidation properties change with the composition of the cores, showing a volcano curve. A correlation between the properties of CO electrocatalytic oxidation and the location of adsorbed CO ATR-IR peak is discovered. Attenuated Total Reflection-Infrared Spectroscopy (ATR-IR) shows that samples which have the strongest monodentate CO are most active in CO electrocatalytic oxidation.

Electrocatalytic performance of Ni-Ti-O nanotube arrays/NiTi alloy electrode annealed under H2 atmosphere for electro-oxidation of methanol

In the present study, Ni-Ti-O nanotube arrays (Ni-Ti-O NTs) were fabricated by anodizing NiTi alloy in a mixed solution consisted of ethylene glycol and glycerol. Then the Ni-Ti-O NTs were suffered annealing treatment under hydrogen atmosphere, leading to the significant improved electrocatalytic performance. The morphologies, the phases and the surface electronic states of Ni-Ti-O NTs samples before and after annealing were characterized by SEM, XRD and XPS, respectively. And their electrocatalytic properties for methanol oxidation were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in the alkaline media. Results show that electrocatalytic activity of the Ni-Ti-O NTs samples annealed under H2 exhibits a significant improvement because of the increases of the conductivity and the active sites provided by reduction of Ni3+. The Ni-Ti-O NTs samples with lower crystallinity annealed at 500 °C for 2 h have better electrocatalytic performance for methanol electro-oxidation in alkaline medium. The peak current density increases after a consecutive sweep for 1000 times and varies indistinctively after placing in the air for 30 days, indicating the excellent long-term electrocatalytic stability. The in situ formation of Ni-base material catalyst in Ni-Ti-O nanotube benefits improvement of the catalytic properties during long-term operation. The Ni-Ti-O NTs/Ni-Ti alloy is a desirable substitute of catalysts support material or it is also a promising electrocatalytic electrode for direct methanol fuel cells.

Effect of nitrogen-doped PtRu/graphene catalyst on its activity and durability for methanol oxidation

Pt–Ru catalysts are highly regarded and investigated by many investigators. However, how to reduce Ru dissolution remains a major concern for their applications under realistic operating conditions. In this study, nitrogen-doped graphene supporting PtRu catalyst was synthesized by a mild microwave-assisted ethanol reduction process, which exhibited superior electrocatalytic properties for methanol oxidation. The morphologies and microstructures of the as-prepared catalysts were characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. Long-term catalytic stability was evaluated by the accelerated aging cyclic voltammetry test. The results reveal that N-doping is beneficial for the minimization of metal migration and coalescence, and meanwhile it slows Ru dissolution.

Preparation of platinum catalysts supported on functionalized graphene and the electrocatalytic properties for ethanol oxidation in direct ethanol fuel cell

In this work, we develop a facile method under mild conditions to synthesize 2-aminoethanesulfonic acid (taurine)-functionalized-graphene (T-fGN) and to prepare Pt catalysts supported on T-fGN through a self-assembly route. The structure, morphologies and electrochemical properties of T-fGN and Pt/T-fGN were examined by atomic force microscope, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and different electrochemical techniques. The electrocatalytic properties of Pt/T-fGN were investigated for ethanol oxidation reaction (EOR) in comparison to Pt supported on Vulcan XC-72 (Pt/VC). The results indicate that the as-prepared Pt/T-fGN catalyst possesses a much higher electrocatalytic activity, faster reaction kinetics and a better stability for EOR than Pt/VC.

Facile synthesis of graphene nanoplate-supported porous Pt–Cu alloys with high electrocatalytic properties for methanol oxidation

A porous Pt1Cu1 alloy nanocrystal catalyst supported on 1-aminopyrene functionalized graphene nanoplates, which is a highly active catalyst for methanol oxidation in alkaline medium, is synthesized by a one-step method without any high boiling point organic solvents, surfactants, stabilizers and templates.

Concave and duck web-like platinum nanopentagons with enhanced electrocatalytic properties for formic acid oxidation

Pt-branched structures featuring concave and duck web-like nanopentagons with high-energy {110} and {554} facets, multiple twin boundaries, duck web-like edges and inherent anisotropic branches are prepared.

Metformin mediated facile synthesis of AuPt alloyed nanochains with enhanced electrocatalytic properties for alcohol oxidation

In this work, a simple and rapid one-pot wet-chemical approach was developed for large-scale synthesis of bimetallic AuPt alloyed nanochains with hierarchical structures. Metformin was employed as a structure-director in the synthetic process. There was no any premade seed, organic solvent, polymer or special apparatus involved. The characterization techniques included X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), and transmission electron microscopy (TEM). The as-fabricated nanocrystals had enlarged electrochemical active surface area (ECSA, 43.87m2gPt−1), and exhibited improved electrocatalytic activity and durability for ethanol oxidation reaction (EOR) and methanol oxidation reaction (MOR) using Pt nanochains and commercial Pt black as contrasts.