High electrocatalytic activity and stability of PtAg supported on rutile TiO2 for methanol oxidation

Rutile TiO₂ is used as a support for the PtAg nanoparticles, and the catalytic activity and stability of PtAg/TiO₂ for the electrooxidation of methanol are investigated. The PtAg nanoparticles with a Pt:Ag atomic ratio of 1:1 are prepared by the chemical co-reduction of the precursors of Pt and Ag, and physical characterizations reveal that the PtAg nanoparticles are evenly dispersed on TiO₂. PtAg/TiO₂ shows significantly higher catalytic activity and stability than PtAg/C, Pt/TiO₂ and Pt/C for methanol oxidation in both alkaline and acidic solutions, indicating that rutile TiO₂ is superior to carbon black as supports and PtAg is superior to Pt in achieving high catalytic activity. Rutile TiO₂ is also shown to be superior to anatase TiO₂ as supports for the PtAg nanoparticles. The results of this study suggest high potential of rutile TiO₂ as a support material for electrocatalysts.     

Fabrication and characterization of gold nanoparticles and fullerene-C60 nanocomposite film at glassy carbon electrode as potential electro-catalyst towards the methanol oxidation

Development of low cost anodic materials and high efficient electro-kinetics of methanol in direct methanol fuel cell (DMFC) has been a promising approach. However it has not been successfully reached to market from laboratory due to its high cost and low kinetic oxidation. Both issues encounter from one of its main components, the catalyst. Therefore, present work focuses upon the development of new catalyst material and optimization of various most significant influencing parameters of a high performance DMFC. We have developed a nanocomposite material employing gold nanoparticles and fullerene-C₆₀ at glassy carbon electrode (AuNP@reduced-fullerene-C₆₀/GCE) as anode for high performance oxidation of methanol. Fullerene-C₆₀ was manually dropped on pre treated GCE and partially electro-reduced in KOH to make it more conductive. Gold nanoparticles (AuNPs) were deposited on reduced-fullerene-C₆₀ modified electrode using cyclic voltammetry (CV). Electrochemical characterization techniques such as CV, electrochemical impedance spectroscopy (EIS) and chronocoulometry were used to characterize modified electrode. Modified electrode was also characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) for morphological properties. The electrochemical behavior of methanol was performed in alkaline medium using CV and chronoamperometry methods. The results revealed good electrocatalytic performance and better stability than previously reported catalysts using AuNP@reduced-fullerene-C₆₀ catalyst, suggesting making promising anodic material for direct methanol oxidation fuel cell.     

One-pot synthesis of Pd20-xAux nanoparticles embedded in nitrogen doped graphene as high-performance electrocatalyst toward methanol oxidation

Mixed Pd–Au bimetallic nanoparticles embedded nitrogen doped graphene composites (PdAu/NG180) are explored for efficient electrocatalytic oxidation of methanol. A simple hydrothermal one-pot polyol method, involving simultaneous reduction of both Pd and Au, is utilized for the synthesis of Pd_20-xAu_x/NG180 (x wt % = 0, 5, 10 and 15). This method is of multiple advantages such as inexpensiveness, reagent-free and environment-friendly being surfactant free. The morphology, crystal structure and chemical composition of NG180, Pd/NG180 and Pd_20-xAu_x/NG180 catalysts are analyzed by XRD, FESEM-EDX, TEM, XPS and Raman spectroscopy methods. Electrocatalytic activities of PdAu/NG180 nanocomposites toward methanol oxidation reaction (MOR) in alkaline media are investigated by cyclic voltammetry, chronoamperometry and CO stripping measurements. Pd_20-xAu_x/NG180 exhibited an increase in the electroactive surface area of Pd to twice by the coexistence of Au. In cyclic voltammetry studies, Pd₁₀Au₁₀/NG180 catalyst exhibits highest peak current density for MOR and is 1.5 times highly efficient compared to Pd₂₀/NG180 with an enhanced shift in the onset potential by 140 mV to lower overpotentials. Besides, Pd₁₀Au₁₀/NG180 catalyst exhibited enhanced electroactive surface area and long-time durability in comparison to Pd₂₀/NG180 catalyst. The steady state current density for MOR observed with Pd₁₀Au₁₀/NG180 at the end of 4000 s (98 mA mg⁻¹_Pd) is higher than those observed with all the other catalysts at the end of mere 1000 s alone (97, 61, and 32 mA mg⁻¹_Pd). The promising high electrocatalytic activity of Pd₁₀Au₁₀/NG180 is well corroborated from CO stripping experiments that the specific adsorption of CO onto Pd₁₀Au₁₀/NG180 (0.71 C m⁻²) is merely half to that observed onto Pd₂₀/NG180 (1.49 C m⁻²).     

Synthesis and characterization of Pt nanoparticles on sulfur-modified carbon nanotubes for methanol oxidation

Pt nanoparticles supported on carbon nanotubes (Pt/CNTs) have been synthesized from sulfur-modified CNTs impregnated with H₂PtCl₆ as Pt precursor. The dispersion and size of Pt nanoparticles in the synthesized Pt/CNT nanocomposites are remarkably affected by the amount of sulfur modifier (S/CNT ratio). The results of X-ray diffraction and transmission electron microscopy indicate that an S/CNT ratio of 0.3 affords well dispersed Pt nanoparticles on CNTs with an average particle size of less than 3 nm and a narrow size distribution. Among different catalysts, the Pt/CNT nanocomposite synthesized at S/CNT ratio of 0.3 showed highest electrochemically active surface area (88.4 m² g⁻¹) and highest catalytic activity for methanol oxidation reaction. The mass-normalized methanol oxidation peak current observed for this catalyst (862.8 A g⁻¹) was ∼ 6.5 folds of that for Pt deposited on pristine CNTs (133.2 A g⁻¹) and ∼ 2.3 folds of a commercial Pt/C (381.2 A g⁻¹). The results clearly demonstrate the effectiveness of a relatively simple route for preparation of sulfur-modified CNTs as a precursor for the synthesis of Pt/CNTs, without the need for tedious pretreatment procedures to modify CNTs or complex equipments to achieve high dispersion of Pt nanoparticles on the support.     

Synthesis of mesoporous silica (SBA-16) nanoparticles using silica extracted from stem cane ash and its application in electrocatalytic oxidation of methanol

In this work, a new catalyst based on modified mesoporous silica SBA-16 is proposed and used for electrochemical oxidation of methanol. Mesoporous silica SBA-16 nanoparticles are synthesized hydrothermally under the acidic medium using SiO₂/F127/BuOH/HCl/H₂O gel. Pure SiO₂ powder is prepared from inexpensive and environmentally friendly silica source of stem cane ash (SCA). The synthesized SBA-16 is characterized using X-ray diffraction, scanning electronic microscopy, transmission electron microscopy, Brumauer–Emmett–Teller (BET) and FT-IR techniques. The synthesized SBA-16 is modified with Ni(II) by dispersion in a 0.1 M nickel chloride solution. A modified carbon paste electrode (CPE) is prepared by mixing of NiSBA-16 to carbon paste (NiSBA-16CPE). The electrocatalytic oxidation of methanol was studied on modified electrode by cyclic voltammetry and chronoamperometry. From cyclic voltammetry, it is observed that the oxidation current is extremely increased by using NiSBA-16CPE compared to the nonmodified CPE. The incorporation of Ni²⁺ into SBA-16 channels provides the active sites for catalysis of methanol oxidation. Also, the rate constant for the catalytic reaction (k) of methanol is obtained.     

Influence of carbon support properties on the electrocatalytic activity of PtRuCu nanoparticles for methanol and ethanol oxidation

This work set out to explore the influence of kind and surface condition of carbon supports on the electrocatalytic activity of trimetallic PtRuCu alloy nanoparticles. The structure, composition, particle size and catalyst loading were determined by XRD, EDX, XPS, TEM and ICP-AES analysis. XRD studies revealed that support physical characteristics and surface conditions have an important influence in lattice strain, while XPS pointed out that a strong electronic interaction exists between the particles and the carbon support. Electrochemical experiments showed that the activated carbon black supported PtRuCu catalyst exhibits the best performance for methanol and ethanol oxidation and the lowest poisoning rate. The superior catalytic activity of this electrode can be rationalized in terms of metal-support interaction, Pt utilization efficiency and electrical conductivity of the carbon support. Furthermore, the as-prepared electrode exhibits 13 and 7 times higher activity towards methanol and ethanol oxidation when compared with a PtRu/C commercial catalyst.     

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).     

Au nanoparticles supported on nanorod-like TiO2 as catalysts in the CO-PROX reaction under dark and light irradiation: Effect of acidic and alkaline synthesis conditions

Gold nanoparticles precipitated-deposited on titania nanostructures (1.0 wt% nominal loading) were studied in the preferential CO oxidation in excess of H₂ at room temperature and atmospheric pressure, both in dark and under simulated solar light irradiation. Titania supports were synthesized by means of two hydrothermal methods markedly acid and basic, giving rise to rutile nanorods and anatase deformed nanorods structures, respectively. Characterization techniques such as N₂ physisorption, XRD, XPS, DRUV-vis, HRTEM and XRF were performed in order to study the chemical, structural and optical properties of the catalysts. Well defined rutile nanorods structures were obtained from the acidic treatment allowing a regular distribution of gold nanoparticles and resulting quite active in the CO-PROX reaction. In particular the sample from the acidic synthetic approach calcined at 700 °C displayed the best results as it was highly selective to CO₂ under both dark and simulated solar light irradiation.     

Carbon paper supported Pt/Au catalysts prepared via Cu underpotential deposition-redox replacement and investigation of their electrocatalytic activity for methanol oxidation and oxygen reduction reactions

Through a simple and rapid method, carbon papers (CPs) were coated with Au and the resulting Au/CP substrates were used for the preparation of Pt/Au/CP by Cu underpotential deposition (Cu UPD) and redox replacement technique. A series of Pt_n/Au/CP catalysts (where n = number of UPD-redox replacement cycles) were synthesized and their electrochemical properties for methanol oxidation reaction (MOR), and oxygen reduction reaction (ORR) were investigated by electrochemical measurements. The Pt_n/Au/CP electrodes show higher electrocatalytic activity and enhanced poison tolerance for the MOR as compared to a commercial Pt/C on CP (Pt/C/CP). The highest mass specific activity and Pt utilization efficiency for MOR was observed on Pt₁/Au/CP with a thickness close to a monatomic Pt layer. Chronoamperometric tests in methanol solution revealed that Pt_n/Au/CPs have much higher CO tolerance compared to Pt/C/CP. Among the Pt_n/Au/CPs, CO tolerance decreases with increasing the amount of deposited Pt, indicating that the exposed Au atoms in close proximity to Pt plays a positive role against CO poisoning. Compared with the Pt/C/CP, all the Pt_n/Au/CP electrodes show more positive onset potentials and lower overpotentials for ORR. For instance, the onset potential of ORR is 150 mV more positive and the overpotential is ∼140 mV lower on Pt₄/Au/CP with respect to Pt/C/CP.     

Direct conversion of methane into methanol and ethanol via spherical Au@Cs2[closo-B12H12]and Pd@Cs2[closo-B12H12] nanoparticles

In this present study, novel aqueous-phase catalytic systems, namely spherical Au and Pd nanoparticles (NPs) capped with Cs₂ [closo-B₁₂H₁₂], were used to produce ethanol and methanol via direct oxidation of methane in the presence of H₂O₂ and O₂ under mild conditions. The ethanol selectivity surpassed 52.96% and 86.33% at 50 °C, and the productivity reached 8.86 and 25.18 mol·kgcat^–1·h^–1, respectively. Plausible methane–ethane–ethanol pathway involving free radial •OH radicals was proposed based on the electron paramagnetic resonance (EPR) result. According to the theoretical calculations, the surfaces of {111} plane of Au NPs and {100} plane of Pd NPs were capped with Cs₂ [closo-B₁₂H₁₂], and Au–B and Pd–B bonds were consequently formed, respectively. Moreover, the binding energies of Au NPs and Pd NPs capped with Cs₂ [closo-B₁₂H₁₂] were calculated to be −128.9 and −230.1 kcal mol⁻¹, respectively. Based on the theoretical calculations, higher binding energy indicates a larger amount of charge on the surfaces of the planes of NPs. A lower peak intensity can lead to the formation of a more stable catalyst with enhanced catalytic activity. Thus, the ethanol selectivity of the as-prepared catalyst was considerably higher than that for methanol.     

Platinum–ruthenium nanoparticles in poly(2,5-dimethoxyaniline)-poly(styrene sulfonic acid) via one-step synthesis route for methanol oxidation

Platinum–Ruthenium (Pt–Ru) nanoparticles were generated along with the simultaneous formation of poly(2,5-dimethoxyaniline) (PDMA) in the presence of poly(styrene sulfonic acid) (PSS) using a one-step UV-assisted method. The existence of Pt–Ru nanoparticles was verified through characterization by transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The latter two confirmed that the surface state of Ru in the Pt–Ru nanoparticles not only has metallic characteristics but is also present in oxidized form. The existence of PDMA in PSS was also identified using ultraviolet–visible (UV–vis) spectroscopy. Based on electrochemical measurements, PDMA–PSS–Pt–Ru exhibited a much higher electrocatalytic activity than PDMA–PSS–Pt and bulk Pt in methanol oxidation. Under the appropriate conditions, these particles can potentially serve as robust electrocatalysts in fuel cell applications.     

Novel Pd/β-MnO2 nanotubes composites as catalysts for methanol oxidation in alkaline solution

In this work, we demonstrated a completely new, simple and effective strategy for preparing catalysts by using β-MnO₂ nanotubes as the supporting materials, and the Pd nanoparticles were coated onto β-MnO₂ nanotubes through a simple reductive process firstly. The as-prepared materials were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and electrochemical measurements. The results indicated that the Pd nanoparticles were homogeneously dispersed and well separated from one another on the β-MnO₂ nanotubes surfaces, which makes it have a potential application in catalysts. In this study, we mainly tested the electrochemical performance of Pd/β-MnO₂ for methanol oxidation in alkaline solution. Further research to optimize the synthesis condition, particularly to develop β-MnO₂ nanotubes as supporting materials of other noble metal catalysts is currently in progress.     

Effect of in situ growth of NiSe2 on NiAl layered double hydroxide on its electrocatalytic properties for methanol and urea

With high energy density and low theoretical potential, the methanol oxidation (MOR) and urea oxidation (UOR) are often used as substitute reactions to the oxygen evolution reaction (OER). As one of the popular non-precious metal catalysts for the MOR/UOR research in recent years, nickel-based layered double hydroxides (LDHs) have abundant active sites and low cost, but suffer from poor catalytic activity and poor stability. In the present study, we prepared NiAl LDH and then grew NiSe₂ in situ on its surface at different temperatures, and the catalyst obtained at 450 °C (4NiAlSe-450) exhibited excellent MOR/UOR electrocatalytic performance with potentials of 1.37 V vs. RHE and 1.36 V vs. RHE at a current density of 10 mA cm⁻², respectively, which were much higher than those of NiAl LDH (1.42 V vs. RHE and 1.39 vs. RHE). Chronoamperometry curves of 4NiAlSe-450 at 1.5 V potential showed that the methanol/urea oxidation was stable for more than 3 h. The physicochemical properties of 4NiAlSe-450 were analyzed by using X-ray diffraction, X-ray photoelectron spectroscopy and other techniques, and the results showed that the NiSe₂ nanoparticles were successfully grown in situ on the calcined layered structure, and therefore the excellent MOR/UOR electrocatalytic performance of 4NiAlSe-450 may be due to the synergistic effect between the NiAl composite oxides and NiSe₂.     

Electrodeposition of Ni nanoparticles from deep eutectic solvent and aqueous solution as electrocatalyst for methanol oxidation in acidic media

Electrodeposited Nano-Ni films at pencil graphite electrode from aqueous acetate buffer and Ethaline solvent as an example of deep eutectic solvents (DESs) were estimated as electrocatalysts for electrooxidation of 1 M methanol in 1 M H₂SO₄. The electrodeposition process and the electrocatalytic behavior of Nano-Ni films were performed using the chronoamperometry and cyclic voltammetry techniques, respectively. Scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX), and x-ray diffraction (XRD) were used for the characterization of Ni deposits from the two different solvents. It was found that Ni/PGE deposit from Ethaline gives 6.01 mA cm^?2 current density at anodic peak potential of 0.67 V and onset potential of 0.31 V while, Ni/PGE deposit from acetate produces 5.6 mA cm^?2 current density at anodic peak potential of 0.65 V and onset potential of 0.37 V, suggesting the higher catalytic activity of Ni/PGE from DES towards methanol oxidation.     

Core shell like behavior of PdMo nanoparticles on multiwall carbon nanotubes and their methanol oxidation activity in alkaline medium

Core–shell like behavior has been shown by the nanoparticles comprised of Pd and Mo that have been synthesized on multiwall carbon nanotubes (Mo@Pd/MWCNT or Pd@Mo/MWCNT) by hydrothermal technique in different pH. The synthesized catalysts are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The formation mechanism of the core–shell like PdMo nanoparticles has been explained with the consequences of reduction potential and surface segregation properties of Pd and Mo. The activity of the catalysts towards methanol oxidation is investigated by cyclic voltammetry (CV), chronoamperometry and impedance spectroscopy. The primary electrochemical analysis indicates that the electrochemical activity of this Pd@Mo/MWCNT along with Mo@Pd/MWCNT is better than that of Pd/MWCNT.     

Electrochemical fabrication of novel platinum-poly(5-nitroindole) composite catalyst and its application for methanol oxidation in alkaline medium

A novel composite catalyst, Pt nanoparticles supported on poly(5-nitroindole) (Pt/PNI), has been successfully prepared by the electrochemical method and used for the electrooxidation of methanol in alkaline media. As-prepared Pt/PNI was characterized by SEM, EDX and electrochemical methods. The results of the catalytic activity for methanol oxidation showed that Pt/PNI had higher catalytic activity and stronger poisoning-tolerance than Pt/Pt, Pt/GC and the common Pt electrode. The effects of different parameters related to the methanol oxidation reaction kinetics, such as Pt loading, mass of PNI film, concentration of methanol and KOH, potential scan rate, have also been investigated. The present study showed a promising choice of Pt/PNI as composite catalyst for methanol electrooxidation in alkaline medium.     

Enhanced electrocatalytic activity and stability of Pd nanoparticles supported on TiO2-modified nitrogen-doped carbon for ethanol oxidation in alkaline media

TiO₂-modified nitrogen-doped carbon (TiO₂-NC), prepared by a polymerization-pyrolysis process, is used to support the Pd catalyst for ethanol oxidation reaction (EOR) in alkaline media. X-ray photoelectron spectroscopy characterization indicates that the incorporation of TiO₂ and nitrogen into the carbon matrix could improve the percentage of Pd⁰ in Pd/TiO₂-NC catalyst. Electrochemical characterization shows that the Pd/TiO₂-NC catalyst presents higher electrocatalytic activity and stability for EOR than the nitrogen-doped carbon-supported Pd (Pd/NC) catalyst and the carbon black-supported Pd (Pd/CB) catalyst, which can be mainly attributed to the high percentage of Pd⁰ in Pd/TiO₂-NC catalyst (65%) than those in Pd/NC (48%) and Pd/CB (31%) catalysts. The results indicate that the Pd/TiO₂-NC catalyst holds great potential as high-performance anode catalyst for direct ethanol fuel cells.     

Sonochemical reduction method for synthesis of TiO2Pd nanocomposites and investigation of anode and cathode catalyst for ethanol oxidation and oxygen reduction reaction in alkaline medium

The development of the superior Pt-free electrocatalyst for enhancing electrocatalytic activity and stability towards the EOR (ethanol oxidation reaction) and ORR (oxygen reduction reaction) are very important for the commercialization of fuel cells. In this work, the palladium nanoparticles (Pd NPs) deposited on titanium dioxide nanospheres (PdTiO₂) were successfully prepared by the sonochemical reduction method. Hence, the TiO₂ nanospheres were directly used as the templates for nucleation and growth of Pd NPs over their surface using PdCl₄⁻ as the Pd precursor, PVP (Polyvinylpyrrolidone) as the stabilizer, ascorbic acid (AA) as the reducing agent, and water as the solvent. The size of Pd NPs is remarkably controlled using the sequential reduction steps by adding an excess of PdCl₄⁻. The excellent electrocatalytic activity towards EOR and ORR is ascribed by the synergistic effect of the Pd nanoparticles and TiO₂ nanospheres support. This unique nanocomposite should be of great benefit to the construction of commercial fuel cell systems.