Pt nanoparticles modified Au dendritic nanostructures: Facile synthesis and enhanced electrocatalytic performance for methanol oxidation

A facile and simple method is presented for the synthesis of bimetallic composites, Pt nanoparticles modified dendritic Au nanostructures (PtNPs/DGNs), in which dendritic Au was deposited on a glassy carbon electrode via a potentiostatic method and sphere-like Pt nanoparticles were decorated on Au substrates through a chemical reduction reaction. The compositions, morphologies, and structures of the PtNPs/DGNs were characterized by X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and energy dispersive X-ray spectroscopy. Results indicated that bimetallic composites were successfully synthesized and spherical Pt nanoparticles were dispersed evenly on dendritic Au substrates. The number of Pt nanoparticles on Au surface was regulated by controlling the chemical reduction deposition time, allowing the electrocatalytic properties of the composite towards methanol oxidation to be tuned. Electrochemical measurements, including cyclic voltammetry and chronoamperometry, were performed to investigate the electrochemical properties and electrocatalytic behaviors of the PtNPs/DGNs towards methanol oxidation. Pt nanoparticles partially covered dendritic Au exhibited dramatically enhanced electrocatalytic activity (3.947 mA cm^?2), which was 2.65 times that of commercial carbon-supported Pt nanoparticles (1.487 mA cm^?2), along with much improved poisoning tolerance (current decline: 70.85% vs 99.36%). These enhanced performances were likely caused by the large active electrochemical area of the bimetallic nanocomposites and the change in the electronic structure of Pt when the Au surface was modified with fewer Pt nanoparticles.     

Facile synthesis of porous dendritic Pt68Ag32 nanodandelions for greatly boosting electrocatalytic activity towards oxygen reduction and hydrogen evolution

Contrary to single counterparts, Pt-based bimetallic nanocrystals are attractive and feasible to decrease the cost, improve the catalytic activity and enhance the stability via morphology-, structure- and composition-engineering. Herein, porous dendritic alloyed Pt₆₈Ag₃₂ nanodandelions (NDs) were synthesized by a one-pot successive co-reduction method, using amrinone as the new stabilizer and structure director, without any template, seed or complicated instrument. The correlative shapes, composition, and crystalline structure were examined by a range of characterization techniques. It is found that the molar ratio of the precursors (AgNO₃ and H₂PtCl₆), the dosage of amrinone, and different reductants play the essential roles during the synthesis process. The Pt₆₈Ag₃₂ NDs exhibited dramatically enlarged electrochemically active surface area, enhanced catalytic activity and stability for hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) as compared to commercial Pt/C, Pt black, home-made Pt₇₅Ag₂₅ nanocrystals (NCs) and Pt₅₆Ag₄₄ NCs catalysts.     

Pt nanoparticles supported on WO3/C hybrid materials and their electrocatalytic activity for methanol electro-oxidation

A simple and novel method for the preparation of WO₃/C is presented. This method includes the adsorption and decomposition of phosphotungstic acid (PWA) on carbon. For the purpose of comparison, WO₃/C is also prepared by a conventional method using sodium tungstate as the precursor. These two WO₃/C species are denoted as WO₃/C-1 and WO₃/C-2, respectively. It is shown from transmission electron microscopy (TEM) that the WO₃ particles in WO₃/C-1 present a more even distribution and smaller particle size than those in WO₃/C-2. Pt particles dispersed on WO₃/C-1 display the characteristic diffraction peaks of Pt in the face-centered cubic phase. Cyclic voltammetry and chronoamperometry show that the Pt-WO₃/C-1 catalyst exhibits much better methanol oxidation activity than the Pt-WO₃/C-2 and Pt/C catalysts. This significant improvement in catalytic performance may be attributed to the hydrogen spillover effect and the uniform distribution of Pt and WO₃ particles.     

Investigation of Pt/WC/C catalyst for methanol electro-oxidation and oxygen electro-reduction

A Pt/WC/C catalyst is developed to increase the methanol electro-oxidation (MOR) and oxygen electro-reduction (ORR) activities of the Pt/C catalyst. Cyclic voltammetry and CO stripping results show that spill-over of H⁺ occurs in Pt/WC/C, and this is confirmed by comparing the desorption area values for H⁺ and CO. A significant reduction in the potential of the CO electro-oxidation peak from 0.81 V for Pt/C to 0.68 V for Pt/WC/C is observed in CO stripping test results. This indicates that an increase in the activity for CO electro-oxidation is achieved by replacing the carbon support with WC. Preferential deposition of Pt on WC rather than on the carbon support is investigated by complementary analysis of CO stripping, transmission electron microscopy and concentration mapping by energy dispersive spectroscopy. The Pt/WC/C catalyst exhibits a specific activity of 170 mA m⁻² for MOR. This is 42% higher than that for the Pt/C catalyst, viz., 120 mA m⁻². The Pt/WC/C catalyst also exhibits a much higher current density for ORR, i.e., 0.87 mA cm⁻² compared with 0.36 mA cm⁻² for Pt/C at 0.7 V. In the presence of methanol, the Pt/WC/C catalyst still maintains a higher current density than the Pt/C catalyst.     

ZnO/Polytyramine nanocomposite film: Facile electrosynthesis and high performance electrocatalytic activity toward methanol oxidation

In the present study, the methanol oxidation reaction was investigated on a nickel ion incorporated to the zinc oxide-sodium dodecyl sulfate-polytyramine (ZnO-SDS-Pty) nanocomposite film by cyclic voltammetry and chronoamperometry. ZnO-SDS-Pty nanocomposite was prepared by using the repeated potential cyclic voltammetry in a solution containing ZnO nanoparticles and tyramine in an acidic solution of SDS by cycling the potential. The electrochemical oxidation of methanol was investigated by a stable redox behavior of the Ni(III)/Ni(II) couple at the potential of 0.4 V, after the immersion of the modified electrode (ZnO-SDS-Pty/G) in an alkaline media (i.e. NaOH 0.1 molL^?1) of nickel chloride solution. The electrochemical characterization of the modified electrode exhibited that the ZnO-SDS-Pty nanocomposite, electrodeposited on the electrode surface, improved the catalytic efficiency of the dispersed nickel ions toward methanol oxidation. The catalytic rate constant and diffusion coefficient of the methanol oxidation reaction were calculated by chronoamperometry. The Ni-ZnO-SDS-Pty nanocomposite displayed a highly stable response during the oxidation of methanol, proving to be a suitable electrode material in methanol fuel cells.     

Effect of Ti addition to Pt/C catalyst on methanol electro-oxidation and oxygen electro-reduction reactions

Carbon supported binary Pt-Ti alloys were investigated for application in methanol electro-oxidation (MOR) and oxygen electro-reduction reactions (ORR). Various compositions of Pt_100−xTi_x/C (x = 0, 25, 50, and 75) catalysts were synthesized by sequential impregnation of Pt and Ti followed by annealing at 900 °C for 30 min under H₂/Ar flow. X-ray diffraction results showed formation of the Pt₃Ti intermetallic phase in Pt₅₀Ti₅₀ and Pt₂₅Ti₇₅ catalysts after annealing at 900 °C. The Pt₅₀Ti₅₀/C-900 and Pt₂₅Ti₇₅/C-900 catalysts (the ‘-900’ designation indicates the catalyst was annealed at 900 °C) exhibited 103% () and 198% () higher MOR activity, respectively, than in the Pt/C-900 catalyst () at 0.7 V (vs. reversible hydrogen electrode (RHE)). These two catalysts also showed high ORR activity. From a specific activity basis, the Pt₅₀Ti₅₀/C-900 and Pt₂₅Ti₇₅/C-900 catalysts exhibited , respectively, which were 171 and 154% higher than the value of the Pt/C catalyst at 0.8 V (vs. RHE). Methanol-tolerant ORR activity was also investigated, but in the presence of methanol, the Pt₅₀Ti₅₀/C-900 and Pt₂₅Ti₇₅/C-900 catalysts both exhibited poor ORR activity.     

Pt modified TiO2 nanotubes electrode: Preparation and electrocatalytic application for methanol oxidation

Pt nanoparticles decorated TiO₂ nanotubes (Pt/TiO₂NTs) modified electrode has been successfully synthesized by depositing Pt in TiO₂NTs, which were prepared by anodization of the Ti foil. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electrochemical methods were adopted to characterize their structures and properties. The Pt/TiO₂NTs electrode shows excellent electrocatalytic activity toward methanol oxidation reaction (MOR) in alkaline electrolyte without UV irradiation.     

Improved electrical conductivity of Ce0.9Gd0.1O1.95 and Ce0.9Sm0.1O1.95 by co-doping

Solid electrolytes are the most important and indispensable part of a solid oxide fuel cell (SOFC) where hydrogen is used as one of the fuels to obtain electricity. Ce_0.9Gd_0.1O_1.95 and Ce_0.9Sm_0.1O_1.95 were chosen to be the base electrolytes. The effects of MgO and Nd₂O₃ as co-dopants on the electrical conductivity were investigated, respectively. For 4 mol% Mg-doped Ce_0.9Gd_0.1O_1.95 or Ce_0.9Sm_0.1O_1.95, MgO phases were detected by FESEM micrographs, which showed a very low solubility of Mg²⁺ in ceria lattice. The existence of MgO phases was observed to have negligible effect on the grain conductivity, but improve the grain boundary conductivity measured by ac impedance spectroscopy. However, when Nd₂O₃ was used as a co-dopant, XRD patterns and FESEM both indicated a pure cubic phase. Ce_0.9Gd_0.05Nd_0.05O_1.95 and Ce_0.9Sm_0.05Nd_0.05O_1.95 were found to exhibit higher grain conductivity, comparing with single-doped ceria.     

Excellent dispersion and electrocatalytic properties of Pt nanoparticles supported on novel porous anatase TiO2 nanorods

We synthesize, for the first time, a new Pt based catalyst for direct methanol fuel cells using homemade novel porous anatase TiO₂ nanorods as a new catalyst support. Pt nanoparticles are prepared by an improved ethylene glycol reduction method and supported on the surface of TiO₂ with excellent dispersion and without any aggregates. The structure and elemental composition of the TiO₂ and Pt/TiO₂ catalyst are characterized by transmission electron micrography (TEM), nitrogen sorption, energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The electrocatalytic properties of the Pt/TiO₂ catalyst for methanol and carbon monoxide electro-oxidation reactions are investigated by cyclic voltammetry (CV) in an acidic medium. Apparent electrocatalytic activity for methanol electro-oxidation reaction, high carbon monoxide tolerance and good stability are all observed for the Pt/TiO₂ catalyst. These may be attributed to the excellent dispersion of the Pt nanoparticles and the special properties of the TiO₂ support. These results imply that this Pt/TiO₂ catalyst has promising potential applications in direct methanol fuel cells.     

Promoting effect of CeO2 in the electrocatalytic activity of rhodium for ethanol electro-oxidation

The promoting effect of ceria in the electrocatalytic activity of rhodium for ethanol electro-oxidation in alkali media has been studied. Rh/C, CeO₂/C and RhCeO₂/C catalysts were synthesized and characterized by TEM, XRD, XPS, TG-MS, H₂-TPR and XAS. The electrocatalytic activity was studied by Cyclic Voltammetry (CV) and chronoamperometry. The onset potential of oxidation on RhCeO₂/C was shifted negatively as compared to that on Rh/C, despite ceria itself does not show any electrocatalytic activity. The promoting effect of ceria has been attributed to the improved rhodium dispersion, and differences in the oxidation state of rhodium between Rh/C and RhCeO₂/C were not found. The carbon support reduces rhodium species to Rh⁰, and also partially reduces ceria, during the samples preparation, and the surface of the carbon support is oxidised.     

Promoting the current for methanol electro-oxidation by mixing Pt-based catalysts with CeO2 nanoparticles

Pt particles were prepared through microwave radiation reduction of chloroplatinic acid in ethylene glycol and then adsorbed on carbon nanotubes (CNTs). The thus prepared catalyst was denoted as CNTs-Pt. CeO₂ nanoparticles were prepared through molten salt method. Transmission electron microscopy (TEM), X-ray diffraction (XRD) and scanning electronic microscopy (SEM) were used to characterize the morphology and structure of CNTs-Pt and CeO₂. Cyclic voltammetry (CV), CO stripping and chronoamperometry methods were used to characterize the electrochemical behaviors of the catalysts. The results showed that CeO₂ nanoparticles and CNTs-Pt catalysts can be mixed homogeneously and the current of methanol oxidation can be greatly increased by the mixed CeO₂ nanoparticles. The reason for the increased activity was analyzed and ascribed to the promotion of CO electro-oxidation reaction kinetics by CeO₂. The method of mixing co-catalyzing materials with Pt-based catalysts is effective and can find wide application in electro-catalysis.     

Electrochemical growth and oxygen reduction property of Ag nanosheet arrays on a Ti/TiO2 electrode

A standing Ag nanosheet array was successfully deposited using an electrochemical method. The results demonstrated that the adsorption of polyvinylpyrrolidone (PVP) over the Ag (111) plane during deposition (1) inhibits the crystalline growth in the [111] direction, (2) stacks atomic faults in the fcc structure, and (3) forms a standing Ag nanosheet composed essentially of (111) planes. In an application, this Ag nanosheet array can be successfully used as an oxygen reduction catalyst. Based on Koutecky-Levich equation, the involved electron number at −0.2 V was 3.97.     

Pt/3D-graphene/FTO electrodes: Electrochemical preparation and their enhanced electrocatalytic activity

We report a facile, low-cost and green route to fabricate platinum nanoparticle (Pt NP) decorated three-dimensional (3D) graphene assembled on fluorine-doped tin oxide (FTO) electrodes (Pt/3D-G/FTO) with enhanced electrocatalytic activity. The fabrication process was accomplished by preparation of 3D graphene (3D-G/FTO) electrodes through electrochemical reduction of a graphene oxide suspension followed by electrodeposition of Pt NPs onto them. The Pt/3D-G/FTO electrode exhibits much higher catalytic activity and better stability for methanol oxidation compared with the electrodes prepared by electrodeposition of Pt NPs onto two-dimensional graphene sheets substrate (Pt/G/FTO) or bare FTO (Pt/FTO) under the same condition. These enhancements can be attributed to the high surface area, large void volume and high electrical conductivity as well as smaller size of Pt NPs in the hollows of the 3D architecture and a large amount of ridges on it.     

Improvement of methanol electro-oxidation activity of PtRu/C and PtNiCr/C catalysts by anodic treatment

The effect of an anodic treatment on the methanol oxidation activity of PtRu/C (50:50 at.%) and PtNiCr/C (Pt:Ni:Cr = 28:36:36 at.%) catalysts was investigated for various potential limits of 0.9, 1.1, 1.3 and 1.4 V (vs. reference hydrogen electrode, RHE). NaBH₄ reduced catalysts were further reduced at 900 °C for 5 min in an argon balanced hydrogen flow stream. Improved alloying was obtained by the hydrogen reduction procedure as confirmed by X-ray diffraction results. In the PtRu/C catalyst, a decrease of irreversible Ru (hydrous) oxide formation was observed when the anodic treatment was performed at 1.1 V (vs. RHE) or higher potentials. In chronoamperometry testing performed for 60 min at 0.6 V (vs. RHE), the highest activity of the PtRu/C catalyst was observed when anodic treatment was performed at 1.3 V (vs. RHE). The current density increased from 1.71 to 4.06 A g_cat.⁻¹ after the anodic treatment. In the PtNiCr/C catalyst, dissolution of Ni and Cr was observed when potentials ≥1.3 V (vs. RHE) were applied during the anodic treatment. In MOR activity tests, the current density of the PtNiCr/C catalyst dramatically increased by more than 13.5 times (from 0.182 to 2.47 A g_cat.⁻¹) when an anodic treatment was performed at 1.4 V. On an A g_{noble metal}⁻¹ basis, the current density of PtNiCr-1.4V is slightly higher than the best anodically treated PtRu-1.3V catalyst, suggesting the PtNiCr catalyst is a promising candidate to replace the PtRu catalysts.     

Investigation of PtCoCr/C catalysts for methanol electro-oxidation identified by a thin film combinatorial method

The ternary Pt-Co-Cr system was investigated for suitability as a methanol electro-oxidation reaction (MOR) catalyst by combinatorial synthesis and high-throughput screening method. A PtCoCr thin film library was prepared by a multi-target sputtering technique while parallel characterization was performed using a multichannel multielectrode analyzer. The highest MOR activity was observed in the Pt₃₀Co₃₀Cr₄₀ composition after a conditioning process. The high MOR activity of the thin film Pt₃₀Co₃₀Cr₄₀ composition was verified in a powder version of the alloy. In 20 h chronoamperometry tests, the MOR activity of the Pt₃₀Co₃₀Cr₄₀ powder catalyst alloy was , which was 160% higher than the value of the PtRu/C catalyst, suggesting that PtCoCr alloys are promising candidates as Ru-free MOR catalysts. The effect of the conditioning process was also investigated, revealing that dissolution and oxidation of surface Co and Cr occurs during conditioning. After conditioning, the activity of 900 °C reduced Pt₃₀Co₃₀Cr₄₀ catalyst dramatically increased by 26.8 times from at 600 s of the chronoamperometry tests.     

Facile synthesis of nanometer-sized NiFe layered double hydroxide/nitrogen-doped graphite foam hybrids for enhanced electrocatalytic oxygen evolution reactions

We report a self-standing NiFe layered double hydroxide/nitrogen doped graphite foam (NiFe LDH/NGF) electrode for the oxygen evolution reaction (OER) prepared via a facile electrodeposition method. The electrode showed high electrocatalytic activity towards OER, exhibiting a low onset overpotential of 0.239 V and a small Tafel slope of 57.9 mV dec^?1 in basic electrolytes, as well as a good stability during the long-term cycling test. The outstanding electrocatalytic activity is mainly attributed to the synergy between the abundant catalytically active sites through good dispersion of NiFe LDH across NGF and fluent electron transport arising from NGF.     

Investigation on gaseous and electrochemical hydrogen storage performances of as-cast and milled Ti1.1Fe0.9Ni0.1 and Ti1.09Mg0.01Fe0.9Ni0.1 alloys

The AB-type Ti_1.1Fe_0.9Ni_0.1 (Mg₀ for short) and Ti_1.09Mg_0.01Fe_0.9Ni_0.1 (Mg_0.01 for short) alloys were fabricated by vacuum induction melting and mechanical milling. The effects of partly substituting Ti with Mg and/or mechanical milling on the structure, morphology, gaseous thermodynamics and kinetics, and electrochemical performances were studied. The results reveal that the as-cast Mg₀ alloy contains the main phase TiFe and a small number of TiNi₃ and Ti₂Ni phases. Substituting Ti with Mg and/or mechanical milling results in the disappearance of the secondary phases. The discharge capacities of the as-cast Mg₀ and Mg_0.01 alloys are 12.6 and 8.8 mAh g^?1, which increase to 52.6 and 80.4 mAh g^?1 after 5 h of mechanical milling. By milling the as-cast alloy powders with carbonyl nickel powders, they are greatly enhanced to 191.6 mAh g^?1 for the Mg₀+7.5 wt% Ni alloy and 205.9 mAh g^?1 for the Mg_0.01+5 wt% Ni alloy at the current density of 60 mA g^?1, respectively. The values of dehydrogenation enthalpy (ΔH_des) and dehydrogenation activation energy (E^des_(a)) are very small, meaning that the thermal stability and the desorption kinetics of the hydrides are not the key influence factors for the discharge capacity. The reduction of the particle size and the generation of the new surfaces without oxide layers have slight improvements on the discharge capacity, while the enhancement of the charge transfer ability of the surfaces of the alloy particles can significantly promote the electrochemical reaction of the alloy electrodes.     

Ethanol oxidation on carbon supported (PtSn)alloy/SnO2 and (PtSnPd)alloy/SnO2 catalysts with a fixed Pt/SnO2 atomic ratio: Effect of the alloy phase characteristics

To evaluate the effect of the alloy phase characteristics on the ethanol oxidation activity, carbon supported (PtSnPd)_alloy/SnO₂ catalysts were prepared and their electrocatalytic activity compared with that of carbon supported (PtSn)_alloy/SnO₂. Pt-Sn-Pd/C samples in the atomic ratio (1:1:0.3) and (1:1:1) were characterized by energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). XRD analysis shows the presence of fcc Pt reflexions, shifted to lower angles, and SnO₂ reflexions. By comparison with the XRD patterns of carbon supported Pt-Sn (1:1) and Pt-Pd (3:1) samples, prepared by the same method, the formation of ternary PtSnPd alloys is postulated. The crystallite size of the ternary catalysts is smaller than that of both binary Pt-Sn/C (1:1) and Pt-Pd/C (3:1) catalysts. Chronoamperometry experiments and tests in direct ethanol fuel cells of the as-prepared catalysts shows that the activity for ethanol oxidation of (PtSn)_alloy/SnO₂ is higher than that of (PtSnPd)_alloy/SnO₂. This result, obtained with the same Pt/SnO₂ atomic ratio in all the samples, indicates the critical role of the alloy phase characteristics of these catalysts on their activity for ethanol oxidation.     

Perovskite-type oxides La1−xSrxMnO3 for cathode catalysts in direct ethylene glycol alkaline fuel cells

Carbon-supported La_1−xSr_xMnO₃ (LSM/C) was prepared by reversible homogeneous precipitation method, and its catalytic activities for oxygen reduction under the existence of ethylene glycol (EG) were investigated by using rotating disk electrode. LSM/C exhibited the high activity for oxygen reduction irrespective with the presence of EG, indicating that EG is not oxidized by LSM/C at the cathode side in the present system. Consequently, LSM/C can serve as a cathode catalyst in alkaline direct alcohol fuel cells with no crossover problem. Performance test for fuel cells operation also supported these results and showed cathodic polarization curves were not affected by the concentration of EG supplied to anode even at 5 mol dm⁻³.     

Electro-oxidation of methanol on SnO2-promoted Pd/MWCNTs catalysts in alkaline solution

The methanol electro-oxidation (MEO) on Pd–SnO₂/MWCNTs catalysts prepared by microwave-assisted polyol reduction method has been investigated. The structure, morphology and electro-catalytic performances of the catalysts were characterized with XRD, TEM and cyclic voltammetry (CV). The results showed that the highly dispersed Pd nano-particles (PdNPs) with a narrow size distribution on MWCNTs were successfully synthesized. The catalytic activity of Pd–SnO₂/MWCNTs for MEO was up to 778.8 mA/mg Pd in 0.1 M KOH solution containing 1 M methanol, which was significant higher than that of Pd/C (414.2 mA/mg Pd) or Pd–SnO₂/C (566.7 mA/mg Pd). Moreover, the MEO on Pd–SnO₂/MWCNTs electrode displayed an irreversible behavior under a diffusion control giving an exchange current density (j⁰) of 3.76 × 10⁻⁴ A cm⁻² and a Tafel slope of 149 mV dec⁻¹ (α = 0.56) at 25 °C, which indicates that Pd–SnO₂/MWCNTs catalyst has a high electro-catalytic performance for the MEO in alkaline media.