Oxygen reduction at Pt and Pt70Ni30 in H2SO4/CH3OH solution

The electrochemical oxygen reduction reaction (ORR) was studied at Pt and Pt alloyed with 30 atom% Ni in 1 M H₂SO₄ and in 1 M H₂SO₄/0.5 M CH₃OH by means of rotating disc electrode. In pure sulphuric acid, the overpotential of ORR at 1 mA cm⁻² is about 80 mV lower at Pt₇₀Ni₃₀ than at pure Pt. It was found that in methanol containing electrolyte solution the onset potential for oxygen reduction at PtNi is shifted to more positive potentials and the alloy catalyst has an 11 times higher limiting current density for oxygen reduction than Pt. Thus, PtNi as cathode catalyst should have a higher methanol tolerance for fuel cell applications. On the other hand, no significant differences in the methanol oxidation on both electrodes was found using cycling voltammetry, especially regarding the onset potential for methanol oxidation. During all the measurements no significant electrochemical activity loss was observed at Pt_0.7Ni_0.3. Ex-situ XPS investigations before and after the electrochemical experiments have revealed Pt enrichment in the first surface layers of the PtNi.     

Selective Hydrogenation of Cinnamaldehyde over Pt/ZrO2 Catalyst Modified by Cr, Mn, Fe, Co and Ni

Hydrogenation properties of cinnamaldehyde (CMA) have been studied over Pt/ZrO₂ and PtM/ZrO₂ catalysts (M = Cr, Mn, Fe, Co and Ni) in ethanol at 343 K and 2.0 MPa. The effect of different content of Ni and base has also been investigated over PtNi/ZrO₂ catalyst. With introduction of transition metals to Pt/ZrO₂ catalyst shows a significant influence on the catalytic properties. PtCo/ZrO₂ catalysts show the best yield of cinnamyl alcohol (CMO), and PtNi/ZrO₂ catalyst shows good yield of hydrocinnamaldehyde (HCMA). In the presence of base solution, rate of the hydrogenation of CMA over PtNi/ZrO₂(0.4 wt%) catalyst increases significantly and side reaction is remarkably inhibited. More bare metal atoms situated remote from the interface region on PtNi/ZrO₂ catalyst surface are the reason of good selectivity of HCMA for PtNi/ZrO₂ catalyst.     

Influence of chloride ions on the stability of PtNi alloys for PEMFC cathode

The dependence of the rate of Ni dissolution from PtNi alloys on the chloride concentration was studied electrochemically in 0.5 M HClO₄ at room temperature. Electrodeposited PtNi catalysts were subjected to extensive potential cycling between 20 mV and 1.3 V at various Cl⁻ concentrations and the cyclic voltammograms (CV) response and the oxygen reduction reaction (ORR) activity of the catalysts were determined at different intervals. Energy dispersive X-ray spectroscopy (EDS) and inductively coupled plasma spectroscopy (ICP) analyses were carried out to determine the elemental composition of the alloys and the amount of dissolved Ni at different stages of the potential cycling. It was found that the presence of Cl⁻ increases the rate of Ni dissolution and by this accelerates the dealloying process relative to potential cycling in chlorine-free solutions. Dealloying is most pronounced during the initial stages of potential cycling. Already a small amount of Cl⁻ is sufficient to dissolve the majority of the non-noble metal from the alloys. Even then, under oxygen reduction conditions, the blockage of Pt surface by Cl⁻ is less pronounced for the alloys than for pure Pt catalysts, leading to marginally improved ORR activity for the PtNi alloys at low Cl⁻ concentrations. From a practical point of view, the effect of chloride ion leakage from a commercially available saturated KCl reference electrode on the electrocatalytic activity was also investigated.     

Activity and selectivity of PtNi/TiO2 catalysts for hydrogenation of crotonaldehyde

The hydrogenation of crotonaldehyde over a series of titania supported PtNi catalysts was investigated. Pt/TiO₂ had the highest activity to hydrogenate the bond of crotonaldehyde. With the addition of Ni to Pt the activity for carbonyl group hydrogenation decreased, while that for the bond hydrogenation increased. Two different types of sites were established to be active for bond hydrogenation, located at (i) the Pt-TiO₂ interface and (ii) the PtNi bimetallic phase. For the Pt-TiO₂ interface the presence of accessible Ti ^x+ cations in close distance to Pt and for the PtNi phase a slightly positively charged Ni on the surface of these alloy particles were concluded to be responsible for the enhanced selectivity to crotylalcohol. The hydrogenation of the bond occurs mainly on the clean metal surfaces of Ni and Pt.     

Multi-walled carbon nanotubes modified by sulfated TiO2 - A promising support for Pt catalyst in a direct ethanol fuel cell

We report the synthesis of multi-walled carbon nanotubes coated with sulfated TiO₂ (S-TiO₂/MWCNTs) as a promising support for Pt catalyst in a direct ethanol fuel cell. Highly dispersed Pt nanoparticles were supported on the S-TiO₂/MWCNT composites by NaBH₄ reduction procedure (Pt-S-TiO₂/MWCNTs). The presence and nature of the catalyst were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, high-resolution transmission electron microscopy. The size of the sulfated TiO₂ product was about 8 nm, and that of the Pt nanoparticle on the S-TiO₂/MWCNT composites was about 5 nm. The Pt-S-TiO₂/MWCNTs were used to study the electrochemical ethanol oxidation reaction using cyclic voltammetry, chronoamperometry and impedance spectroscopy. The results show that Pt-S-TiO₂/MWCNT catalysts show higher catalytic activity for ethanol oxidation compared with Pt supported on non-sulfated TiO₂/MWCNT composites and commercial Pt/C catalysts.     

Role of Pt in the Activity and Stability of PtNi/CeO2–Al2O3 Catalysts in Ethanol Steam Reforming for H2 Production

Hydrogen production from ethanol reforming was investigated on bimetallic PtNi catalysts supported on CeO₂/Al₂O₃. Pt content was varied from 0.5 to 2.5 %. Physico-chemical characterization of the as-prepared and H₂-reduced catalysts by TPR, XRD and XPS showed that Pt phase interacted with the Ni and Ce species present at the surface of the catalysts. This interaction leads to an enhancement of the reducibility of both Ni and Ce species. Loadings of Pt higher than 1.0 wt% improved the activity and stability of the Ni/CeO₂–Al₂O₃ catalyst in ethanol steam reforming, in terms of lower formation of coke, C₂ secondary products and a constant production of CO₂ and H₂. The amount and type of carbon deposited on the catalyst was analyzed by TG–TPO while the changes in crystalline phases after reaction were studied by XRD. It was found that for Pt contents higher than 1 wt% in the catalysts, a better contact between Pt and Ce species is achieved. This Pt–Ce interaction facilitates the dispersion of small particles of Pt and thereby improves the reducibility of both Ce and Ni components at low temperatures. In this type of catalysts, the cooperative effect between Pt⁰, Ni⁰ and reduced Ce phases leads to an improvement in the stability of the catalysts: Ni provides activity in C–C bond breakage, Pt particles enhance the hydrogenation of coke precursors (C_xH_y) formed in the reaction, and Ce increases the availability of oxygen at the surface and thereby further enhances the gasification of carbon precursors.     

Constructing synergy of sufficient hydroxyl and oxygen in PtNi/Al2O3 enables room-temperature catalytic HCHO oxidation

Rational engineering of noble metal/transition metal bimetallic catalysts is considered as an effective way to constructing synergistic effect between adsorbed oxygen and hydroxyl for enhanced catalytic formaldehyde oxidation. Herein, we developed a Pt–Ni bimetallic catalysts loading on γ-Al₂O₃ support for room-temperature formaldehyde oxidation. Catalytic experiment results showed that the conversion rate was >97% with a >100 h stability. Several noble metals (Pd, Au, and Ag) were compared to identify the activity effect in formaldehyde oxidation. The activity and stability test in different atmospheres and in situ infrared test suggested that the PtNi/γ-Al₂O₃ has the best activity and stability. At a meantime, the results also demonstrated that Pt sites motivate more surface adsorbed oxygen through activating ambient oxygen molecules, while the neighboring Ni atoms contribute to adsorbed hydroxyl, thereby offering sustainable activity. The high efficiency and stability of PtNi/γ-Al₂O₃ catalysts for formaldehyde oxidation could be a promising candidate for air purification.     

Ultrasonic synthesis of highly dispersed Pt nanoparticles supported on MWCNTs and their electrocatalytic activity towards methanol oxidation

A new method of synthesis of highly dispersed Pt nanoparticles with large catalytic surface area on multi-walled carbon nanotubes (MWCNTs) under high-intensity ultrasonic field was developed. The method, with low processing temperature at 25 °C, took only about 5 min. The surface characterization of MWCNTs was carried out by fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy methods. The electrochemical surface area and pore volume of MWCNTs were also examined. The result showed that functional groups of the MWCNTs which favored the high loading and high dispersion of particles and electrochemical surface area of MWCNTs were reinforced in the case of high-intensity ultrasonic field. The Pt/MWCNT catalysts were characterized by energy dispersion X-ray spectra analysis (EDX), transmission electron microscopy (TEM) and X-ray diffraction (XRD) measurements. The prepared Pt nanoparticles were uniformly dispersed on the MWCNT surface. The mean size of Pt particles was 3.4 ± 0.2 nm. The electrocatalytic properties of Pt/MWCNT composites and kinetic characterization for methanol electro-oxidation were investigated by cyclic voltammetry. The Pt/MWCNT catalysts prepared for 5 min in ultrasonic field present excellent electrochemical activities. The schematic of the reaction was also introduced.     

Synthesis of sulfated ZrO2/MWCNT composites as new supports of Pt catalysts for direct methanol fuel cell application

Sulfated zirconia supported on multi-walled carbon nanotubes as new supports of Pt catalyst (Pt–S-ZrO₂/MWCNT) was synthesized with aims to enhance electron and proton conductivity and also catalytic activity of Pt electrocatalyst in terms of larger concentrations of ionizable OH groups on surfaces. Fourier transform infrared spectroscopy analysis shows that the sample surfaces were modified with sulfate. Transmission electron microscopy results show that the Pt and sulfated ZrO₂ particles dispersed relatively uniformly on the surface of the multi-walled carbon nanotube. X-ray diffraction shows that S-ZrO₂ and Pt coexist in the Pt–S-ZrO₂/MWCNT composites and S-ZrO₂ has no effect on the crystalline lattice of Pt. Pt–S-ZrO₂/MWCNT catalyst was evaluated in terms of the electrochemical activity for methanol electro-oxidation using cyclic voltammetry, steady-state polarization experiments and electrochemical impedance spectroscopy technique at room temperature. Pt–S-ZrO₂/MWCNT catalyst show higher catalytic activity for methanol electro-oxidation compared with Pt catalyst on non-sulfated ZrO₂/MWCNT support and commercial Pt/C (E-TEK).     

A high-throughput study of PtNiZr catalysts for application in PEM fuel cells

The effects of adding Zr to PtNi oxygen reduction reaction (ORR) electrocatalyst alloys were examined in a study aimed at probing the possibility of creating catalysts with enhanced resistance to corrosion in a PEM fuel cell environment. Samples consisting of pure Pt or PtNiZr alloys with a range of compositions (not exceeding 11 at.% Zr) were fabricated using co-sputter deposition. A high-throughput fabrication approach was used wherein 18 distinct thin film catalyst alloy samples with varying compositions were deposited onto a large-area substrate with individual Au current collector structures. A multi-channel pseudo-potentiostat allowed for the simultaneous quantitative study of catalytic activity for all 18 electrodes in a single test bath, a first for the study of ORR electrocatalysts. A properly stirred oxygenated 1 M H₂SO₄ electrolyte solution was used to provide each electrode with a steady-state flow of reactants during electrochemical evaluation. The onset potentials, absolute current density values, and Tafel analysis data obtained using this technique were compared with literature reports. The analyses showed that most PtNiZr alloys tested offered improvements over pure Pt, however those surfaces with a high mole fraction (>4 at.%) of Zr exhibited reduced activity that was roughly inversely correlated to the amount of Zr present. Film composition, morphology, and crystallographic properties were examined using X-ray energy dispersive spectroscopy (XEDS), X-ray photoelectron spectroscopy (XPS), SEM, and synchrotron X-ray diffraction. These data were then correlated with electrochemical data to elucidate the relationships between composition, structure, and relative performance for this ternary system.     

Stabilization and dispersion of PtRu and Pt nanoparticles on multiwalled carbon nanotubes using phosphomolybdic acid,and the use of the resulting materials in a direct methanol fuel cell

PtRu and Pt nanoparticles were deposited on the surface of multiwalled carbon nanotubes (MWCNTs) with the assistance of phosphomolybdic acid (PMo) by a one-pot hydrothermal reduction strategy. Transmission electron microscopy shows a high-density PtRu (or Pt) nanoparticles uniformly dispersed on the surface of the MWCNTs with an average diameter of 1.8 nm for PtRu nanoparticles and 2.4 nm for Pt nanoparticles. Moreover, the as-prepared PMo/PtRu/MWCNT and PMo/Pt/MWCNT electrocatalysts are highly electroactive for the electrochemical oxidation of methanol. Cyclic voltammograms show a high electrochemical surface area (ESA) and a large current density for methanol oxidation at the modified electrode by PMo/PtRu/MWCNT and PMo/Pt/MWCNT electrocatalysts. Electrochemical impedance spectroscopy reveals a high CO tolerance for PMo/PtRu/MWCNT and PMo/Pt/MWCNT electrocatalysts in the electrochemical catalysis of methanol oxidation. For comparison, PtRu/MWCNT and Pt/MWCNT electrocatalysts were prepared in control experiments without PMo. The results demonstrate that PtRu and Pt nanoparticles deposited on MWCNTs in the presence of PMo were superior to those on MWCNTs without PMo in several respects including: (1) a smaller size and a higher dispersion; (2) a higher ESA; (3) a larger current density for methanol oxidation; (4) a higher tolerance for CO poisoning.     

Electroreduction of oxygen on Pt nanoparticle/carbon nanotube nanocomposites in acid and alkaline solutions

The kinetics of O₂ reduction on novel electrocatalyst materials deposited on carbon substrates were studied in 0.5 M H₂SO₄ and in 0.1 M NaOH solutions using the rotating disk electrode (RDE) technique. Pt nanoparticles (PtNP) supported on single-walled (PtNP/SWCNT) and multi-walled carbon nanotubes (PtNP/MWCNT) were prepared using two different synthetic routes. Before use, the CNTs were cleaned to minimize the presence of metal impurities coming from the catalyst used in the synthesis of this material, which can interfere in the electrochemical response of the supported Pt nanoparticles. The composite catalyst samples were characterised by transmission electron microscopy (TEM) showing a good dispersion of the particles at the surface of the carbon support and an average Pt particle size of 2.4 ± 0.7 nm in the case of Pt/CNTs prepared in the presence of citrate and of 3.8 ± 1.1 nm for Pt/CNTs prepared in microemulsion. The values of specific activity (SA) and other kinetic parameters were determined from the Tafel plots taking into account the real electroactive area of each electrode. The electrodes exhibited a relatively high electrocatalytic activity for the four-electron oxygen reduction reaction to water.     

Direct electrochemical regeneration of enzymatic cofactor 1,4‐NADH on a cathode composed of multi‐walled carbon nanotubes decorated with nickel nanoparticles

Multi‐walled carbon nanotubes (MWCNTs) were grown on a stainless steel mesh and decorated with nickel nanoparticles (Ni NPs). The developed Ni NP‐MWCNT material was then used as a cathode in an electrochemical batch reactor to electrocatalytically convert NAD⁺ to enzymatically‐active 1,4‐NADH. The regeneration of 1,4‐NADH was studied at various electrode potentials. At electrode potential of ?1.6 V, a very high recovery (relative amount of 1,4‐NADH in the product mixture) was obtained, 98 ± 1 %. In comparison, to achieve the same recovery on a non‐decorated MWCNT cathode, a much higher cathodic potential was needed (?2.3 V), establishing the importance of Ni NPs on the electrocatalytic activity in reducing NAD⁺ to 1,4‐NADH. It was postulated that hydrogen adsorbs on Ni NPs immobilized on MWCNTs to form Ni‐H_ads, and this activated hydrogen rapidly reacts with neighbouring NAD‐radicals, preventing the dimerization of the latter species, ultimately yielding 1,4‐NADH.     

Characterization and photodegradation characteristics of organic dye for Pt–titania combined multi-walled carbon nanotube composite catalysts

Multi-walled carbon nanotubes (MWCNTs), titanium(IV) isopropoxide (TIP) and potassium hexachloroplatinate(IV) (K₂PtCl₆) were used for the preparation of Pt/MWCNT/TiO₂ composites. The composites were comprehensively characterized by Brauer–Emett–Teller surface area, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy dispersive X-ray and UV–vis absorption spectroscopy. The photoactivity of the prepared materials under UV irradiation was tested using the conversion of methylene blue (MB) in aqueous solution. According to the results of MB removal experiment, it can be considered that the MB removal effect of the Pt/MWCNT/TiO₂ composites is affected by two kinds of effects: adsorption effect by MWCNTs and photocatalytic effect by TiO₂. Finally, the photocatalytic effect increases due to photo-induced-electron absorption effect by MWCNTs and electron trap effect by Pt metal.     

A different method for producing a flexible LiMn2O4/MWCNT composite electrode for lithium ion batteries

A flexible lithium manganese oxide (LiMn₂O₄)/multi-wall carbon nanotube (MWCNT) composite electrode was produced by casting a slurry-containing powdered LiMn₂O₄ on a previously prepared MWCNT paper. The structure of this new LiMn₂O₄/MWCNT composite electrode was characterized using scanning electron microscopy and X-ray diffraction patterns. Furthermore, the surfaces of these electrodes were coated with gold–palladium alloy using an RF magnetron sputtering technique to prevent Mn dissolution. To investigate the electrochemical performance of this flexible LiMn₂O₄/MWCNT composite electrode, a bare-LiMn₂O₄ electrode was prepared. The discharge capacity of the produced LiMn₂O₄/MWCNT nanocomposite electrode was cyclically tested, and the charge transfer resistance of the electrodes was studied using electrochemical impedance spectroscopy. Consequently, the Au–Pd-coated LiMn₂O₄/MWCNT had a 120 mAh g^?1 discharge capacity and 90 % capacity retention after 100 cycles.     

Evaluation of the Performance of Carbon Supported Pt–Ru–Ni–P as Anode Catalyst for Methanol Electrooxidation

This research is aimed to improve the activity and stability of ternary alloy Pt–Ru–Ni/C catalyst. A novel anodic catalyst for direct methanol fuel cell (DMFC), carbon supported Pt–Ru–Ni–P nanoparticles, has been prepared by chemical reduction method by using NaH₂PO₂ as a reducing agent. One glassy carbon disc working electrode is used to test the catalytic performances of the homemade catalysts by cyclic voltammetric (CV), chronoamperometric (CA) and amperometric i–t measurements in a solution of 0.5 mol L^–1 H₂SO₄ and 0.5 mol L^–1 CH₃OH. The compositions, particle sizes and morphology of home‐made catalysts are evaluated by means of energy dispersive analysis of X‐ray (EDAX), X‐ray diffraction (XRD) and transmission electron micrographs (TEM), respectively. TEM images show that Pt–Ru–Ni–P nanoparticles have an even size distribution with an average diameter of less than 2 nm. The results of CV, CA and i–t curves indicate that the Pt–Ru–Ni–P/C catalyst shows significantly higher activity and stability for methanol electrooxidation due to the presence of non‐metal phosphorus in comparison to Pt–Ru–Ni/C one. All experimental results indicate that the addition of non‐metallic phosphorus into the Pt–Ru–Ni/C catalyst has definite value of research and practical application for enhancing the performance of DMFC.     

SnO2-coated multiwall carbon nanotube composite anode materials for rechargeable lithium-ion batteries

SnO₂-coated multiwall carbon nanotube (MWCNT) nanocomposites were synthesized by a facile hydrothermal method. The as-prepared nanocomposites were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The SnO₂/MWCNT composites, when combined with carboxymethyl cellulose (CMC) as a binder, show excellent cyclic retention, with the high specific capacity of 473 mAh g⁻¹ beyond 100 cycles, much greater than that of the bare SnO₂ which was also prepared by the hydrothermal method in the absence of MWCNTs. The enhanced capacity retention could be mainly attributed to good dispersion of the tin dioxide particles in the matrix of MWCNTs, which protected the particles from agglomeration during the cycling process. Furthermore, the usage of CMC as a binder is responsible for the low cost and environmental friendliness of the whole electrode fabrication process.     

Electrochemical behavior of glassy carbon electrodes modified by multi-walled carbon nanotube/surfactant films in a buffer solution and an ionic liquid

The electrochemical behavior of glassy carbon (GC) electrodes coated with multi-walled carbon nanotube (MWCNT)/surfactant films was studied in an ionic liquid and a phosphate buffer solution (pH = 6.86), using cyclic voltammetry. The dispersion of MWCNTs in different media was investigated by scanning and transmission electron microscopy. Cast films of MWCNT/zwitterionic dodecyldimethylamine oxide on a GC electrode show a typical redox couple in phosphate buffer solution, which is better than that of MWCNT/anionic sodium dodecyl sulfate and cationic alkyltrimethylammonium bromide. However in the ionic liquid, 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]), the GC electrode modified by MWCNT/cationic surfactant films shows a well-defined irreversible reduction of MWCNTs. The cyclic voltammograms clearly show that the surfactant hydrophilic group plays an important role in the electrochemical behavior of the MWCNTs. The electrolytes also have an important effect. In an ionic liquid, the strong binding of the ionic liquid cations with the MWCNTs may change the structure of the modified films and lead to changes of electrochemical behavior.     

Stability characteristics of Pt1Ni1/C as cathode catalysts in membrane electrode assembly of polymer electrolyte membrane fuel cell

To understand the difference in degradation characteristics between carbon-supported platinum (Pt/C) and platinum–nickel alloy (Pt₁Ni₁/C) cathode catalysts in membrane electrode assemblies (MEAs) of a polymer electrolyte membrane fuel cell (PEMFC), constant current operation of MEA in a single cell was conducted for 1100 h. A significant change in cell potential for the Pt₁Ni₁/C MEA was observed throughout the test. High-resolution transmission electron microscopy showed that sintering and detachment of metal particles in the Pt₁Ni₁/C catalyst occurred more sparingly than in the Pt/C catalyst. Instead, X-ray photoelectron spectroscopy element mapping revealed dissolution of Ni atoms in the Pt₁Ni₁ catalysts even when the Pt₁Ni₁/C catalyst used in the MEA was well synthesized.     

Catalytic performance of Pt nanoparticles on reduced graphene oxide for methanol electro-oxidation

We have investigated a simple approach for the deposition of platinum (Pt) nanoparticles onto surfaces of graphite oxide (GO) nanosheets with particle size in the range of 1-5 nm by ethylene glycol reduction. During Pt deposition, a majority of oxygenated functional groups on GO was removed, which resulted in a Pt/chemically converted graphene (Pt/CCG) hybrid. The electrochemically active surface areas of Pt/CCG and a comparative sample of Pt/multi-walled carbon nanotubes (Pt/MWCNT) are 36.27 and 33.43 m²/g, respectively. The Pt/CCG hybrid shows better tolerance to CO for electro-oxidation of methanol compared to the Pt/MWCNT catalyst. Our study demonstrates that CCG can be an alternative two-dimensional support for Pt in direct methanol fuel cells.