Pt support of multidimensional active sites and radial channels formed by SnO2 flower-like crystals for methanol and ethanol oxidation

SnO₂ nanoflowers and nanorods have been synthesized by the hydrothermal method without using any capping agent. Both types of SnO₂ nanostructures are selected as a support of Pt catalyst for methanol and ethanol electrooxidation. The synthesized SnO₂ nanostructures and SnO₂ supported platinum (Pt/SnO₂) catalysts are characterized by X-ray diffraction, scanning electron microscope and high resolution transmission electron microscope. The electrocatalytic properties of the Pt/SnO₂ and Pt/C catalysts for methanol and ethanol oxidation have been investigated systematically by typical electrochemical methods. The influence of SnO₂ morphology on its electrocatalytic activity is comparatively investigated. The Pt/SnO₂ flower-shaped catalyst shows higher electrocatalytic activity and better long-term cycle stability compared with other electrocatalysts owing to the multidimensional active sites and radial channels of liquid diffusion.     

Design and preparation of CNT@SnO2 core-shell composites with thin shell and its application for ethanol oxidation

A novel electrocatalyst structure of carbon nanotubes (CNT) coated with thin SnO₂ and Pt (Pt/(CNT@SnO₂)) is reported. The CNT@SnO₂ composites with a thin shell (about 2 nm) are prepared by a simple chemical-solution method. The Pt/(CNT@SnO₂) catalyst is prepared by first microwave heating H₂PtCl₆ in NaOH ethylene glycol solution and then depositing Pt nanoparticles onto CNT@SnO₂ composites. High-resolution transmission electron microscopy and X-ray diffraction show that crystalline SnO₂ of about 2 nm thickness is coated uniformly on the surface of the CNTs. Pt nanoparticles of about 3.2 nm in diameter are homogenously dispersed on the SnO₂ surface. Electrochemical studies were carried out using cyclic voltammetry and chronoamperometry. The results showed that Pt/(CNT@SnO₂) catalysts have much higher catalytic activity and CO-tolerance for ethanol electro-oxidation than that of Pt/CNT.     

Electrochemically synthesized polypyrrole/MWCNTs-Al2O3 ternary nanocomposites supported Pt nanoparticles toward methanol oxidation

As known, a good support enhances the activity and durability of any catalyst. In the current study, polypyrrole (PPY)/nanocomposite (MWCNTs and Al₂O₃) films were fabricated by electrochemical polymerization of pyrrole solution with a certain amount of nanoparticles on titanium substrates and were used as new support materials for Pt catalyst. The modified electrodes were characterized by Fourier transform infrared (FT-IR) spectroscopy, field-emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis (EDX) techniques. High catalytic activity and long-time stability toward methanol oxidation of Pt/PPY–MWNTs-αAl₂O₃ catalyst have also been verified by cyclic voltammetry results and chronoamperometric response measurements. This catalyst exhibits a vehemently high current density (345.03 mA cm^?2) and low peak potential (0.74 v) for methanol oxidation. Other electrochemical measurements (electrochemical impedance spectroscopy (EIS), CO stripping voltammetry and Tafel test) clearly confirmed that Pt/PPY–MWNTs-αAl₂O₃/Ti electrode has a better performance toward methanol oxidation compared to the other electrodes and that can be used as a promising electrode material for application in direct methanol fuel cells (DMFCs).     

Platinum-antimony doped tin oxide nanoparticles supported on carbon black as anode catalysts for direct methanol fuel cells

Antimony doped tin oxide supported on carbon black (ATO/C) has been synthesized using an in situ co-precipitation method, and platinum-ATO/C nanoparticles have been prepared using a consecutive polyol process to enhance the catalyst activity for the methanol oxidation reaction. The Pt-ATO/C electrocatalyst is characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microcopy (SEM), energy dispersive X-ray spectroscopy (EDS) and cyclic voltammetry. The Pt-ATO/C catalyst exhibits a relatively high activity for the methanol oxidation reaction compared to Pt-SnO₂/C or commercial Pt/C catalyst. This activity can be attributed to the high electrical conductivities of the Sb-doped SnO₂, which induces the electronic effects with Pt catalysts. Pt-ATO/C is a promising methanol oxidation catalyst with high activity for the reaction in direct methanol fuel cells.     

Influence of metallic oxides on ethanol oxidation

An improvement in ethanol oxidation electrocatalysis is possible with multifunctional Pt-based combinations. Thus, the addition to Pt of Sn, Ir or Ni enhances the ethanol oxidation reaction (EO) and shifts the onset oxidation potential to lower values. It has been suggested that metallic oxides in the vicinity of Pt have the capacity of promoting the oxidation of residues coming from alcohol oxidative adsorption. In order to get a deeper knowledge on the ethanol oxidation catalysis, supported catalysts prepared either by thermal decomposition of polymeric precursors (PP) or by microwave assisted poliol reduction (MW) methodology are studied to determine the role of the catalyst components and its oxides on the improvement of ethanol oxidation. The catalysts are physically and electrochemically characterized. According to the synthesis method, the amount of SnO₂ in the catalyst varies. Faceted particle structures for the microwave-synthesized catalysts are observed. By employing electrochemical techniques it is concluded that the catalyst with the highest amount of SnO₂ has the best catalytic behaviour for EO.     

Heterostructure core PdSn–SnO2 decorated by Pt as efficient electrocatalysts for ethanol oxidation

To enhance the performance of heterostructure electrocatalysts for fuel cell and other applications, carbon-supported Pt decorating PdSn–SnO₂ nanoparticles are prepared and characterized by X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy. The electrochemical results show higher ethanol oxidation activity of heterostructured catalysts than that of Pt@PdSn/C, PtSn/C and PdSn–SnO₂/C catalysts. This result demonstrates significant potential for utilizing heterostructure-core synthesis in the preparation of novel core–shell catalysts.     

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.     

Carbon-supported PdSn–SnO2 catalyst for ethanol electro-oxidation in alkaline media

Carbon-supported PdSn–SnO₂ with high electrical catalytic activity for ethanol oxidation in alkaline solution was synthesized using an impregnation reduction method. XRD analysis of the as-prepared PdSn–SnO₂/C revealed that the Pd diffraction peaks shifted to lower 2θ values with respect to the corresponding peaks of the Pd/C catalyst, indicating that Sn doping could shrink the Pd crystalline lattice. XPS measurements confirmed the existence of Sn and SnO₂ in the PdSn–SnO₂/C catalysts. The prepared PdSn–SnO₂/C catalysts presented a remarkably higher electrocatalytic activity than that of the Pd–Sn/C and Pd/C catalysts. This was mainly because the easy adsorption-dissociation of OH_ads over the SnO₂ surface changed the electronic effect and accelerated the adsorption of ethanol on the surface of Pd, thus enhancing the overall ethanol oxidation kinetics and contributing to a significant improvement in the catalytic activity.     

Solvent effect in the synthesis of nanostructured Pt–Sn/CNT as electrocatalysts for the electrooxidation of ethanol

Pt and Pt–Sn nanoparticles were synthesized and supported onto carbon nanotubes (CNT), the electrocatalytic activity towards the ethanol oxidation reaction was analyzed. The effect of the solvent employed for the synthesis was evaluated. Metal nanoparticles synthesis was made using water (Pt–Sn/CNT-W) or ethanol (Pt–Sn/CNT-E) as a solvent. Pt–Sn/CNT-W material presented only Pt–Sn alloy nanoparticles homogeneously distributed on the carbon nanotubes support. Pt–Sn/CNT-E sample showed non well-dispersed nanoparticles forming agglomerates along the CNTs surface with predominantly Sn⁴⁺ superficial species (SnO₂) as show the XPS, FTIR and electrochemical results. These surface arrangements had important effects on the electrocatalytic properties. Pt–Sn/CNT-W shows higher ethanol electrooxidation activity than the Pt–Sn/CNT-E, which is attributed to: a) the double catalytic effect and the intrinsic electronic mechanism favored by the presence of Sn; b) the good particle dispersion of the bimetallic active phase on the CNT and; c) the absence of SnO₂ species.     

Electrodeposition of Pt–Ru and Pt–Ru–Ni nanoclusters on multi-walled carbon nanotubes for direct methanol fuel cell

A full-electrochemical method is developed to deposit three dimension structure (3D) flowerlike platinum-ruthenium (PtRu) and platinum-ruthenium-nickel (PtRuNi) alloy nanoparticle clusters on multi-walled carbon nanotubes (MWCNTs) through a three-step process. The structure and elemental composition of the PtRu/MWCNTs and PtRuNi/MWCNTs catalysts are characterized by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray polycrystalline diffraction (XRD), IRIS advantage inductively coupled plasma atomic emission spectroscopy (ICP-AES), and X-ray photoelectron spectroscopy (XPS). The presence of Pt(0), Ru(0), Ni(0), Ni(OH)₂, NiOOH, RuO₂ and NiO is deduced from XPS data. Electrocatalytic properties of the resulting PtRu/MWCNTs and PtRuNi/MWCNTs nanocomposites for oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) are investigated. Compared with the Pt/MWCNTs, PtNi/MWCNTs and PtRu/MWCNTs electrodes, an enhanced electrocatalytic activity and an appreciably improved resistance to CO poisoning are observed for the PtRuNi/MWCNTs electrode, which are attributed to the synergetic effect of bifunctional catalysis, three dimension structure, and oxygen functional groups which generated after electrochemical activation treatment on MWCNTs surface. The effect of electrodeposition conditions for the metal complexes on the composition and performance of the alloy nanoparticle clusters is also investigated. The optimized ratios for PtRu and PtRuNi alloy nanoparticle clusters are 8:2 and 8:1:1, respectively, in this experiment condition. The PtRuNi catalyst thus prepared exhibits excellent performance in the direct methanol fuel cells (DMFCs). The enhanced activity of the catalyst is surely throwing some light on the research and development of effective DMFCs catalysts.     

Comparison study of electrocatalytic activity of reduced graphene oxide supported Pt–Cu bimetallic or Pt nanoparticles for the electrooxidation of methanol and ethanol

Pt–Cu bimetallic nanoparticles supported on reduced graphene oxide (Pt–Cu/RGO) were synthesized through the simple one-step reduction of H₂PtCl₆ and CuSO₄ in the presence of graphene oxide (GO) at room-temperature. The Pt–Cu/RGO was characterized with UV–vis spectrophotometer, X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy and its catalytic behavior for the direct oxidation of methanol was investigated. Compared to Pt/RGO and Pt/C catalysts, Pt–Cu/RGO hybrids exhibited markedly superior catalytic activity for the electrocatalytic oxidation of methanol and ethanol. This improved catalytic activity can be attributed to the dendritic structure of the Pt–Cu bimetallic nanoparticles.     

Thin layer vs. nanoparticles: Effect of SnO2 addition to PtRhNi nanoframes for ethanol oxidation reaction

When designing catalysts for direct ethanol fuel cell applications (DEFC), four main parameters must be considered: shape, structure, size, and chemical composition. According to this knowledge, it is assumed that polyhedral hollow Pt-based nanoframes, with the addition of Rh and SnO₂ with a size below 50 nm, could be a promising nanocatalysts for the anode of DEFC. In this work, two different PtRhNi/SnO₂ nanoframes-based catalysts are obtained. First consists of PtRhNi nanoframes covered with small, about 3 nm, SnO₂ nanoparticles (PtRhNi/SnO₂ NPs); and second is the PtRhNi nanoframes covered with a thin and incomplete SnO₂ layer (PtRhNi/SnO₂ TL). Both nanocatalysts were tested toward ethanol oxidation reaction (EOR) and show higher activity in comparison to PtRhNi nanoframes without SnO₂ (PtRhNi NFs) addition and commercially used Pt nanoparticles. Especially, the electrochemical durability and stability of obtained nanocatalysts were tested. It was shown that both PtRhNi/SnO₂ nanoframes-based catalysts develop similar mass and specific activity, as well as nearly the same onset potential, but their stability is significantly different. It turns out, that catalyst based on PtRhNi nanoframes covered with a thin SnO₂ layer is susceptible to degradation, while the catalyst consisting of PtRhNi nanoframes covered with SnO₂ nanoparticles is much more durable and could be used as an efficient catalyst toward EOR.     

Effect of noble metal species and compositions on manganese dioxide-modified carbon nanotubes for enhancement of alcohol oxidation

By integrating the effects of alloying, chemical composition and support, a series of mono- and bi-metallic catalyst nanoparticles electrodeposited on α-manganese dioxide (MnO₂)-modified carbon nanotube (CNT) supports were synthesized to improve the efficiency of direct alcohol fuel cells. Small and dispersed nanoparticles on the CNT/MnO₂ surfaces with high electrochemically active surface area (ECSA) were successfully obtained in this work. The support materials were characterized by Fourier-transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD), while the as-prepared catalysts were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry (CV) and chronoamperometry (CA) were used to study the activity and stability of the catalysts, respectively. The results showed that a combination of Pt, Pd, Au and MnO₂ on the CNTs significantly affected the topography of the composite catalyst surfaces, and their electrochemical measurements showed excellent electrocatalytic activity toward the reaction. For methanol and ethanol oxidation in acid solution, CNT/MnO₂/1M3Pt (M = Pd or Au) catalysts revealed greater activity improvement compared to the other prepared catalysts. For the bimetallic CNT/MnO₂/xMyPt catalysts, the values of the forward peak current (I_f)) and the ratio of the forward peak current to the reverse peak current (I_f/I_b) were higher, while their onset potentials (E_o) were lower compared to those of the monometallic CNT/MnO₂/4Pt catalyst. Moreover, CO oxidation on these bimetallic catalysts was also confirmed to be poisoning resistant. These results indicate that our prepared catalyst showed excellent electrocatalytic performance, reliability, and stability. The catalytic activity improvement was based upon the unique integrated structural and functional properties and the synergistic effect of different compositions in the catalyst system.     

MoS2 nanoflower supported Pt nanoparticle as an efficient electrocatalyst for ethanol oxidation reaction

Developing highly active and stable ethanol oxidation electrocatalysts is crucial for direct ethanol fuel cells. Herein, platinum/molybdenum disulfide nanoflower (Pt/MoS₂) nanocomposite is synthesized through a facile method and is first applied as catalyst for ethanol oxidation reaction. In situ electrochemical nuclear magnetic resonance is carried out to investigate the electrocatalytic activity of Pt/MoS₂ and the detailed mechanism of ethanol oxidation reaction. Experimental results indicate that in situ electrochemical nuclear magnetic resonance possesses great advantages for real-time investigation of ethanol oxidation reaction, and Pt/MoS₂ is found to exhibit better electrocatalytic performances in terms of higher current density, better stability, and stronger anti-poisoning activity compared to commercial Pt/C and pure Pt catalysts in acid electrolyte, suggesting its potential for application in direct ethanol fuel cells. Density functional theory calculations indicate that MoS₂-supported Pt atom has a smaller energy barrier for the dissociation of ethanol compared to those of Pt and C-supported Pt atom, leading to the enhancement of catalytic activity. This work reveals the importance of the supporting materials for high performance direct ethanol fuel cells catalysts.     

Anodic oxidation of ethanol on core-shell structured Ru@PtPd/C catalyst in alkaline media

The direct ethanol fuel cell has been attracting increased attention due to its safety and the wider availability of ethanol as compared with methanol. The present work investigates the anodic oxidation of ethanol on a core-shell structured Ru@PtPd/C catalyst in alkaline media. The catalyst shows high activity toward the anodic oxidation of ethanol; with 18 wt.% ruthenium as the core and 12 wt.% PtPd (Pt:Pd = 1:0.2) as the active shell, its activity in terms of PtPd loading is 1.3, 3, 1.4, and 2.0 times as high as that of PtPd/C, PtRu/C, Pd/C, and Pt/C, respectively, indicating high utilization of Pt and Pd. The ratio of forward peak current density to backward peak current density (I_f/I_b) reaches 1.5, which is 1.9 times that of PtPd/C catalyst, revealing high poisoning tolerance to the intermediates in ethanol electrooxidation. In addition, the stability of Ru@PtPd/C is higher than that of Pt/C and PtPd/C, as evidenced by chronoamperometric evaluations. The catalyst is extensively characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy. The core-shell structure of the catalyst is revealed by XRD and TEM.     

Coating of multi-walled carbon nanotube with SnO2 films of controlled thickness and its application for Li-ion battery

Multi-walled carbon nanotubes (MWCNTs) coated with a smooth and uniform tin oxide (SnO₂) layers of different thickness were prepared by a novel thioglycolic acid assisted one-step wet chemical method. The coatings were characterized by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The thickness of the SnO₂ coatings can be easily controlled by changing the synthesis conditions, such as pH value of the solution and hydrolysis time. The electrochemical properties of the SnO₂/MWCNTs composites as anode materials for lithium batteries were studied by galvanostatic method. The composites showed high charge capacities and good durability against decay. This could be ascribed to the good dispersion, thin layer and small particle size of SnO₂ on MWCNTs.     

Enhanced ethanol oxidation on PbOx-containing electrode materials for fuel cell applications

The synthesis, characterization and utilization of lead oxide-based catalysts, deposited by the sol–gel method on carbon powder to be used as anode in direct ethanol fuel cells (DEFC) is described. For comparison, other materials, based on Ru and Ir (and mixtures of Ru, Ir or Pb) were tested in the same experimental conditions. X-ray diffraction analysis showed that the Pb was deposited on carbon powder as a mixture of PbO and PbO₂ molecular structures. The catalysts Pt-(RuO₂-PbO_x) and Pt-(RuO₂-IrO₂) exhibited significantly enhanced catalytic activity for the ethanol oxidation as compared to Pt/C commercial powder. Quasi-steady-state polarization curves showed that the composites Pt-(RuO₂-PbO_x)/C and Pt-(RuO₂-IrO₂)/C started the oxidation process in very low potentials (155 and 178 mV, respectively). So, the addition of metallic oxides by the sol–gel route to Pt is presented as a very interesting way to prepare materials with high catalytic activity for direct ethanol fuel cell systems. Current–time studies also showed the good performance of the Pt-(RuO₂-PbO_x) catalyst due to smaller poisoning of the material as the process advances.     

Preparation and characterization of Pt supported on graphene with enhanced electrocatalytic activity in fuel cell

Pt nanoparticles are deposited onto graphene sheets via synchronous reduction of H₂PtCl₆ and graphene oxide (GO) suspension using NaBH₄. Lyophilization is introduced to avoid irreversible aggregation of graphene (G) sheets, which happens during conventional drying process. Pt/G catalysts reveal a high catalytic activity for both methanol oxidation and oxygen reduction reaction compared to Pt supported on carbon black (Pt/C). The performance of Pt/G catalysts is further improved after heat treatment in N₂ atmosphere at 300 °C for 2 h, and the peak current density of methanol oxidation for Pt/G after heat treatment is almost 3.5 times higher than Pt/C. Transmission electron microscope (TEM) images show that the Pt particles are uniformly distributed on graphene sheets. X-ray photoelectron spectroscopy (XPS) results demonstrate that the interaction between Pt and graphene is enhanced during annealing. It suggests that graphene has provided a new way to improve electrocatalytic activity of catalyst for fuel cell.     

Ethanol electrooxidation on Pt/C and Pd/C catalysts promoted with oxide

This research aims to investigate Pd-based catalysts as a replacement for Pt-based catalysts for ethanol electrooxidation in alkaline media. The results show that Pd/C has a higher catalytic activity and better steady-state behaviour for ethanol oxidation than that of Pt/C. The effect of the addition of CeO₂ and NiO to the Pt/C and Pd/C electrocatalysts on ethanol oxidation is also studied in alkaline media. The electrocatalysts with a weight ratio of noble metal (Pt, Pd) to CeO₂ of 2:1 and a noble metal to NiO ration 6:1 show the highest catalytic activity for ethanol oxidation. The oxide promoted Pt/C and Pd/C electrocatalysts show a higher activity than the commercial E-TEK PtRu/C electrocatalyst for ethanol oxidation in alkaline media.     

Role of structural H2O in TiO2 nanotubes in enhancing Pt/C direct ethanol fuel cell anode electro-catalysts

TiO₂ nanotubes (TNTs) with different structural water were obtained by heat treatment under different temperatures. The role of the structural water in TNTs co-catalyzing ethanol oxidation with Pt/C catalyst was studied systematically. Electrochemical studies using cyclic voltammetry and CO stripping voltammetry indicated that more structural water in TNTs was favorable for improving the tolerance of Pt/C to poisoning species; while chronoamperometry curves and repeated cyclic voltammograms showed that slightly less structural water in TNTs actually led to higher catalytic activity and better stability of Pt/C catalysts for ethanol oxidation. This strange result has been analyzed and was ascribed to the appropriate balance of bi-functional mechanism and ethanol transfer in the catalyst layer with less structural water.