Bare and Pt-loaded LaCo1-xFexO3 perovskites as catalysts for CO-PROX reaction

Perovskites based on cobalt and iron LaCo_1-xFe_xO₃ (x = 0, 0.1 and 1) and their behavior in the presence of platinum yPt/LaCo_1-xFe_xO₃ (y = 0.1, 0.5 and 2.5% wt.) were evaluated as catalysts in the preferential oxidation of carbon monoxide (CO-PROX). Perovskites (general formula ABO₃) are alternative materials to conventional transition metal oxides, expanding the tunable redox properties according to the combination of elements. In CO-PROX, Co₃O₄ and Pt/Fe₃O₄ are well-studied systems. The superficial Co^3+/Co²⁺ redox pair is highly active. Still, the Co₃O₄ is easily reduced at low temperatures under the reducing conditions of CO-PROX, forming less active phases enriched in Co²⁺ and Co⁰. On the other hand, Fe₃O₄ is not active but becomes highly reactive when associated with Pt through the redox mechanism intermediated by the Fe³⁺/Fe²⁺ pair created at the metal interface. Supported by in situ characterization under reducing conditions and complementary ex situ analyses, we found that the LaCoO₃ resembles the Co₃O₄, and the addition of Fe forming LaCo_0·9Fe_0·1O₃ induced higher stability of the perovskite structure under reducing conditions. The presence of Pt significantly impacted the stabilization of the active sites under CO-PROX conditions depending on the perovskite composition. Finally, the Pt/LaFeO₃ catalyst combined the high activity of the Pt/Fe₃O₄ system with the thermal stability of the perovskite structure.     

Synthesis of bimetallic iron ferrite Co0.5Zn0.5Fe2O4 as a superior catalyst for oxygen reduction reaction to replace noble metal catalysts in microbial fuel cell

A low-cost electrochemically active oxygen reduction reaction (ORR) catalyst is obligatory for making microbial fuel cells (MFCs) sustainable and economically viable. In this endeavour, a highly active surface modified ferrite, with Co and Zn bimetal in the ratio of 1:1 (w/w), Co_0.5Zn_0.5Fe₂O₄ was synthesised using simple sol-gel auto combustion method. Physical characterisation methods revealed a successful synthesis of nano-scaled Co_0.5Zn_0.5Fe₂O₄. For determination of ORR kinetics of cathode, using Co_0.5Zn_0.5Fe₂O₄ catalyst, electrochemical studies viz. cyclic voltammetry and electrochemical impedance spectroscopy were conducted, which demonstrated excellent reduction current response with less charge transfer resistance. These electrochemical properties were observed to be comparable with the results obtained for cathode using 10% Pt/C as a catalyst on the cathode. The MFC using Co_0.5Zn_0.5Fe₂O₄ catalysed cathode could produce a maximum power density of 21.3 ± 0.5 W/m³ (176.9 ± 4.2 mW/m²) with a coulombic efficiency of 43.3%, which was found to be substantially higher than MFC using no catalyst on the cathode 1.8 ± 0.2 W/m³ (15.2 ± 1.3 mW/m²). Also, the specific power recovery per unit cost for MFC with Co_0.5Zn_0.5Fe₂O₄ catalysed cathode was found to be 4 times higher as compared to Pt/C based MFC. This exceptionally low-cost cathode catalyst has enough merit to replace costly cathode catalyst, like platinum, for scaling up of the MFCs.     

Pt electrodeposited on CeZrO4/MCNT as a new alternative catalyst for enhancement of ethanol oxidation

Electrocatalytic preparation of Pt-based nanocomposites has been investigated for improvement of direct ethanol fuel cells (DEFCs). In this study, new alternative catalysts of Pt-decorated cerium zirconium oxide-modified multiwalled carbon nanotubes (Pt/CeZrO₄/MCNT) were successively prepared to improve the activity of the ethanol oxidation reaction (EOR). The prepared CeZrO₄ with a face-centered cubic (fcc) structure compatibly dispersed onto MCNT provides abundant active Pt sites for highly active catalysts. The fcc-structured Pt was also satisfactorily decorated onto CeZrO₄/MCNT, resulting in highly active Pt. The Ce⁴⁺/Ce³⁺ redox property can promote oxygen vacancies to improve the electrochemical activity for oxidation of carbonaceous species. An increase in roughness and a stabilized catalyst structure can also be produced by inserting Zr⁴⁺ into the ceria metal oxide. The prepared Pt/20%CeZrO₄/MCNT catalysts present excellent electrochemical active surface area, mass activity, CO tolerance and high electron kinetic transfer with low resistance and high stability over commercial PtRu/C toward EOR. This promising catalyst material could be introduced to enhance the anodic oxidation reaction in DEFCs.     

Tailoring performance of Co–Pt/MgO–Al2O3 bimetallic aerogel catalyst for methane oxidative carbon dioxide reforming: Effect of Pt/Co ratio

Co–Pt/MgO–Al₂O₃ bimetallic aerogel catalysts were synthesized via a sol-gel combined with supercritical drying method. The catalysts were characterized by XRD, BET, HRTEM, STEM-HAADF, XPS, H₂-TPR, H₂-TPD, TG/DSC, FESEM and their catalytic performances in CH₄ oxidative CO₂ reforming were evaluated. The H₂ spillover effect between Pt and Co enhanced the reducibility of the catalyst, while the strong metal-support interaction (SMSI) effect in the bimetallic aerogel catalysts confined the agglomeration of metal particles. Pt/Co ratio played a key role on the existence of surface metal species, leading to different catalytic performances. The optimal Pt/Co ratio was Pt/Co = 0.02 w/w, on which a 50% higher activity in terms of CH₄ conversion than monometallic Co or Pt aerogel catalysts was obtained. Whereas the impregnated catalyst with an identical composition showed a much lower activity. The Co–Pt aerogel catalysts also showed high resistance to inactive carbon formation. The oxidation temperature of the carbon species deposited on the spent Co–Pt aerogel catalyst was only 275 °C and no filamentous or graphitic carbon was identified, disclosing that the formation of inactive carbon was inhibited due to the synergy between Co and Pt and the SMSI effect.     

Partial oxidation of ethanol on supported Pt catalysts

This work studied the effect of the nature of the support on the performance of Pt/Al₂O₃, Pt/ZrO₂, Pt/CeO₂ and Pt/Ce_0.50Zr_0.50O₂ catalysts on partial oxidation of ethanol. The reducibility and oxygen transfer capacity were evaluated by temperature-programmed reduction (TPR) and oxygen storage capacity (OSC) experiments. The results showed that the support plays an important role on the products distribution of the partial oxidation of ethanol. Acetic acid was the main product on Pt/Al₂O₃ catalyst whereas methane and acetaldehyde were the only products detected on Pt/ZrO₂, Pt/CeO₂ and Pt/Ce_0.50Zr_0.50O₂ catalysts.The products distribution obtained on Pt/ZrO₂, Pt/CeO₂ and Pt/Ce_0.50Zr_0.50O₂ catalysts was related to their redox properties. The OSC experiments showed that the oxygen exchange capacity was higher on Pt/CeO₂ and Pt/Ce_0.50Zr_0.50O₂ catalysts. A high oxygen storage capacity favored the formation of acetate species, which could be decomposed to CH₄ and/or oxidized to CO₂ via carbonate species. On the other hand, the lower oxygen exchange capacity of Pt/ZrO₂ catalyst led to a higher ethoxy species formation. These species can be dehydrogenated and desorb as acetaldehyde. Then, the higher selectivity to acetaldehyde observed on Pt/ZrO₂ catalyst could be assigned to its low oxygen storage/release capacity.In the case of Pt/Al₂O₃ catalyst, the production of acetic acid could be related to its acidic properties, since this material did not show redox properties, as revealed by OSC analysis.     

Fast synthesis and electrocatalytic activity of M@Pt (M = Ru,Fe3O4, Pd) core–shell nanostructures for the oxidation of ethanol and methanol

We report the fast synthesis and electrochemical evaluation of M@Pt core–shell nanostructures (M = Ru, Fe₃O₄, Pd) as well as Pt-alone nanoparticles for the ethanol and methanol oxidation reactions (EOR and MOR, respectively) in H₂SO₄ solution. The cores were obtained in 60 s. The Pt shells were deposited afterward on the cores also in 60 s. The reducing agent was NaBH₄. XRD results showed that crystalline Pd, Fe₃O₄ and Pt materials were obtained from this rapid process, while Ru was formed as a quasi-amorphous structure. The average particle sizes of the core–shell nanostructures determined with the Scherrer equation, ranged from 7.35 to 9.29 nm. The electrochemical characterization revealed a catalytic activity of the novel Fe₃O₄@Pt anode as high as that of Ru@Pt for the EOR, and higher than the activity of Pt-alone. However, the Fe₃O₄@Pt catalysts showed a lower activity for the MOR than Ru@Pt and Pt-alone. Durability tests indicated a high electrochemical stability of the Fe₃O₄@Pt and Ru@Pt nanostructures.     

Platinum/vivianite bifunction catalysts for DMFC

Bi-functional catalysts are used to solve the poisoning problem caused by carbon monoxide (CO) which is the intermediate of direct methanol fuel cells (DMFCs). Flower-like vivianite (Fe₃(PO₄)₂·8H₂O) spheres with diameter around 10 μm are originally used as supports of Pt to form bifunction catalysts. The cyclic voltammetry in 1 M H₂SO₄ indicates that the electrochemical surface area (ECSA) of Pt reduced on as-prepared vivianite (Pt/Vi) was 105, greater than 91 m² g⁻¹ for the commercial Pt/C. Besides, Pt/Vi reveals the less CO poisoning effects, including the greater mass activity in methanol oxidation and the lower onset potential in CO-stripping than Pt/C. These excellent performances on electrolyzes are related to the chemical state of Fe³⁺ and the coexistence of Pt⁰ and Pt²⁺ in Pt/Vi. The former activates the water and yields Fe-OH_ads at lower potential and the latter may offer an easy way of electron transition.     

The nanometer magnetic solid base catalyst for production of biodiesel

Nanometer magnetic solid base catalysts were prepared by loading CaO on Fe₃O₄ with Na₂CO₃ and NaOH as precipitator, respectively. The optimum conditions for preparation of this catalyst were investigated. The influence of the proportion of Ca²⁺ to Fe₃O₄ on the catalytic performance has been studied. The catalyst with highest catalytic activity has been obtained when the proportion of Ca²⁺ to Fe₃O₄ is 7:1; the catalytic activity of the catalyst calcined from Ca(OH)₂ to Fe₃O₄ is better than that calcined from CaCO₃ to Fe₃O₄; under the conditions of methanol/oil molar ratio of 15:1, catalyst dosage of 2 wt% and temperature of 70 °C, the biodiesel yield reaches to 95% in 80 min, even to 99% finally. The catalytic activity and recovery rate of the nanometer magnetic solid base catalysts are much better than those of CaO. Calcination temperature was determined by differential thermogravimetric analysis. Ca₂Fe₂O₅, a kind of new metal multiple oxide, was found in the catalyst through X-ray diffraction. At the end, these catalysts were characterized by scanning electronic microscope (SEM), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM).     

Cu/Fe3O4 catalyst for water gas shift reaction: Insight into the effect of Fe2+ and Fe3+ distribution in Fe3O4

Two precursors, namely, p-CFO-T (tetragonal) and p-CFO-C (cubic), were fabricated by a sol-gel method via citric acid and poly(vinyl alcohol) complexation, respectively. After H₂-reduction, the two were converted to Cu/Fe₃O₄ catalysts of different complexions, which are named as CFO-CA and CFO-PVA, respectively. The distribution of Fe²⁺ and Fe³⁺ in the Cu/Fe₃O₄ catalysts was studied by Raman and XPS techniques. It was disclosed that the distribution of Fe²⁺ and Fe³⁺ in Fe₃O₄ has an effect on Cu–Fe₃O₄ interaction and catalyst surface basicity. Compared to CFO-PVA, CFO-CA has a larger amount of Fe³⁺, which mostly sits at the octahedral sites, leading to stronger Cu–Fe₃O₄ interaction, and a larger amount of catalyst surface sites that are of weak basicity. As a result, the critical elementary steps of WGS reaction, viz. water dissociation, –COOH decomposition and CO₂ desorption are promoted as reflected in the lower E_a and higher catalytic activity of CFO-CA.     

Catalytic activity,stability and impedance behavior of PtRu/C,PtPd/C and PtSn/C bimetallic catalysts toward methanol and formic acid oxidation

PtRu, PtPd and PtSn with weight ratios of (2:1) on carbon black (Vulcan XC-72) supported bimetallic catalysts were prepared by using microwave method via chemically reduction of H₂PtCl₆·6H₂O, RuCl₃, PdCl₂ and SnCl₂·2H₂O precursors with ethylene glycol (EG). These prepared catalysts were systematically investigated and obtained results were compared with commercial Pt black, PtRu black catalysts and with each other. The catalysts were characterized with XRD, ICP-MS, EDS and TEM. The electrocatalytic activities, stability and impedance of the catalysts were investigated in sulfuric acid/methanol and sulfuric acid/formic acid mixtures using electrochemical measurements. The results showed that PtSn/C catalyst showed comparable activity and durability with commercial Pt/C catalyst toward methanol oxidation. The synthesized PtRu/C catalyst was found to completely oxidize methanol and it showed more catalytic activity than commercial PtRu catalyst. Bimetallic PtPd/C catalyst gave better activity than both commercial Pt black and synthesized Pt/C catalyst for oxidation of formic acid. Higher electrochemical active surface areas were obtained with supported bimetallic catalysts.     

Catalytic transfer hydrogenation of furfural to furfuryl alcohol over Fe3O4 modified Ru/Carbon nanotubes catalysts

In this study, magnetic Fe₃O₄ modified Ru/Carbon nanotubes (CNTs) catalysts were used to achieve the catalytic transfer hydrogenation of furfural (FF) to furfuryl alcohol (FFA), with alcohols as the solvent and hydrogen donors. According to the result of the catalyst characterization, Fe₃O₄ promoted the formation of Ru⁰ species. The effects of Fe₃O₄ loading and different hydrogen donors on the catalytic transfer hydrogenation of FF were tested, and the reaction parameters and catalyst stability were also analyzed. It is found that Fe₃O₄ effectively enhanced the activity of Ru/CNTs in catalytic transfer hydrogenation of FF, the catalytic activity was optimized at the Fe₃O₄ loading of 5 wt%, and the optimal hydrogen donor was i-propanol. Moreover, the Ru–Fe₃O₄/CNTs could be easily collected for further use and possessed excellent stability. The mechanism of the catalytic transfer hydrogenation of FF using Ru–Fe₃O₄/CNTs was discussed, and the corresponding catalyst activity groups included metal Ru sites and RuO_x-Fe₃O₄ Lewis acid sites, which account for the excellent catalytic activity of transfer hydrogenation.     

Preparation and physical/electrochemical characterization of Pt/poly(vinylferrocenium) electrocatalyst for methanol oxidation

Preparation and characterization of a platinum (Pt)-based catalyst using a redox polymer, poly(vinylferrocenium) (PVF⁺), as the support material was described. Pt was obtained from aqueous solution of K₂PtCl₄ in the complex form. Pt particles were reduced by chemical and electrochemical means. Chemical reduction was performed using aqueous hydrazine solution and electrochemical reduction was carried out in H₂SO₄ solution. The Pt/PVF⁺ catalyst system showed catalytic activity towards methanol oxidation. Cyclic voltammetry was used for the electrochemical characterization of the catalyst system. Scanning electron microscopy (SEM) images and energy dispersive X-ray spectrum (EDS) of the catalyst system were also recorded. The system was tested in a single fuel cell configuration at ambient temperature and atmospheric pressure. The open circuit voltage (OCV) was 680 mV for the system and the maximum power density was 0.31 mW cm⁻² at a current density of 0.63 mA cm⁻². Catalytic activity of Pt/PVF⁺ system towards methanol oxidation was comparable with the related catalysts in the literature.     

CO2 reforming of methane over Pt-Ni/Al2O3 catalysts: Effects of catalyst composition, and water and oxygen addition to the feed

A series of Pt-Ni bimetallic catalysts supported on δ-Al₂O₃ to be used in carbon dioxide reforming of methane was prepared and tested with the objective of optimizing the Ni/Pt metal composition to obtain high activity and stability. Selected catalyst samples, before and after reaction, were characterized by XRD, XPS, TGA/DTA and SEM-EDS. The activity results showed that the catalytic performance of bimetallic Pt-Ni samples strongly depended on the metal loadings and Ni/Pt loading ratio. Among all the catalysts, 0.3%Pt-10%Ni/Al₂O₃, which has the lowest Ni/Pt ratio, exhibited the highest catalytic activity and stability. The combined characterization and catalyst performance tests results reveal that low Ni/Pt molar loading ratio of 0.3%Pt-10%Ni/Al₂O₃ sample led to a relatively easy reduction of nickel oxide species and smaller nano-sized nickel particles having better dispersion caused by the intimate interaction between Pt and Ni sites in the closed vicinity. The changes in the catalysts’ activity and stability under the presence of an additional oxygen source were determined through addition of small amounts of either oxygen or water vapor to the feed stream. The results of the combined dry reforming and partial oxidation tests strongly indicated a change in surface reaction mechanism depending on the Pt load and Ni/Pt ratio of the catalysts. 0.3Pt-10Ni was capable of operating under a variety of feed conditions without significant deactivation suggesting that the catalyst is very promising for synthesis gas production for gas-to-liquid technology.     

The effect of Ni:Pt ratio on oxidative steam reforming performance of Pt–Ni/Al2O3 catalyst

Oxidative steam reforming of propane was tested over four Pt–Ni/δ-Al₂O₃ bimetallic catalysts aiming to investigate the effect of metal loadings and Ni:Pt loading ratio on catalyst performance. A trimetallic Pt–Ni–Au/δ-Al₂O₃ catalyst was additionally studied aiming to understand the effect of Au presence. Reaction temperature, carbon to oxygen ratio, and residence time were taken as the reaction parameters. The effect of C/O₂ ratio on the hydrogen production and H₂/CO selectivity was found dependent on the Pt and Ni loadings. The results underlined the importance of C/O₂ ratio as an optimization parameter for product distribution. The highest hydrogen production and H₂/CO ratio levels were obtained for the highest C/O₂ ratio tested. An optimum Ni:Pt weight ratio was found around 50 due to suppressed methanation and enhanced hydrogen production activities of these catalysts. The presence of gold in the trimetallic catalyst caused poor activity and selectivity in comparison to bimetallic catalysts.     

Na-intercalated carbon nanotubes-supported platinum nanoparticles as new highly effective catalysts for preferential CO oxidation in H2-rich stream

Na⁺-intercalated carbon nanotubes (Na-CNTs) were obtained by impregnation of CNTs with sodium acetate followed by annealing at high temperatures under argon. Stable Na-CNTs-supported Pt catalysts (Pt/Na-CNT catalysts) were then prepared for hydrogen purification via preferential CO oxidation in a H₂-rich stream (CO-PROX). Characteristic studies show that the content of Na⁺ species in CNTs is increased with increased annealing temperature and the Pt nanoparticles with an average size of 2–3 nm are uniformly dispersed on the surfaces of Na-CNTs. An optimized Pt/Na-CNT catalyst with 5 wt% Pt loading can completely remove CO from 40 °C to 200 °C. This catalyst also exhibits long-term stability for 1000 h at 100 °C in feed gas containing 1% CO, 1% O₂, 50% H₂, 15% CO₂, and 10% H₂O balanced with N₂. The electron transfer between the Pt nanoparticles and Na⁺ species plays an important role in enhancing the CO-PROX performance of the catalyst.     

Further performance enhancement of a DME-fueled solid oxide fuel cell by applying anode functional catalyst

In order to increase the coking resistance of SOFCs operating on DME fuel, a Pt/Al₂O₃–Ni/MgO mixture catalyst was investigated for internal partial oxidation of DME. Catalytic test demonstrated the mixture catalyst has higher activity for DME partial oxidation and lower CH₄ selectivity than the individual Pt/Al₂O₃ and Ni/MgO catalysts. O₂-TPO analysis demonstrated that the mixture catalyst also had much higher coke resistance than sintered Ni-YSZ anode, especially at high O₂ to DME ratio. Raman spectroscopy of the carbon-deposited catalysts demonstrates that the graphitization degree of carbon is reduced with introducing O₂ into DME, and the carbon deposited on the mixture catalyst is almost in amorphous structure. Two operation modes of the mixture catalyst for indirect internal partial oxidation of DME, i.e, directly depositing on the anode surface and locating in the anode chamber were tried. The performance of the cells operating on DME fuel through both operation modes was studied by I–V polarization test and EIS characterization. The cells delivered attractive peak power density of around 750 mW cm⁻² by operating on DME-O₂ mixture gas, modestly lower than 1012–1065 mW cm⁻² operating on pure hydrogen fuel at 700 °C. The direct deposition of Pt/Al₂O₃–Ni/MgO onto anode surface to perform as a functional layer and a DME to O₂ ratio of 2:1 in the mixture gas is preferred to minimize coke formation and maximize power output for the cell to operate on DME fuel.     

Effect of metal particle size and Nafion content on performance of MEA using Ir-V/C as anode catalyst

Ir and Ir-V nanoparticles were synthesized in ethylene glycol using IrCl₃ and NH₄VO₃ as the Ir and V precursors, respectively. These nanoparticles were evaluated as anode catalysts in proton exchange membrane fuel cells (PEMFCs). A thermal treatment of the catalysts at 200 °C in a reducing atmosphere leads to very high electrocatalytic activity for the hydrogen oxidation reaction. The fuel cell performance reveals an optimal Nafion ionomer content of 25% in the catalyst layer used for the MEA fabrication. The electrocatalytic effects related to the change in the electrocatalyst structure are discussed based on the data obtained by X-ray diffraction (XRD) and transmission electron microscopy (TEM). In addition, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques are used in-situ to assess the kinetics of hydrogen oxidation on the surface of these catalysts. A maximum power density of 1016.6 mW cm⁻² was obtained at 0.598 V and 70 °C with an anode catalyst loading of 0.4 mg (Ir) cm⁻². This performance is 50.7% higher than that for commercially available Pt/C catalysts under the same conditions. In addition, we also tested the anode catalyst with a low loading of 0.1 mg (Ir) cm⁻², the maximum power density is 33.8% higher than that of the commercial Pt/C catalyst with a loading of 0.4 mg (Pt) cm⁻².     

Hydrogen production through autothermal reforming of CH4: Efficiency and action mode of noble (M = Pt,Pd) and non-noble (M = Re,Mo, Sn) metal additives in the composition of Ni-M/Ce0.5Zr0.5O2/Al2O3 catalysts

Hydrogen production through autothermal reforming of methane (ATR of CH₄) over promoted Ni catalysts was studied. The control of the ability to self-activation and activity of Ni-M/Ce_0.5Zr_0.5O₂/Al₂O₃ catalysts was achieved by tuning their reducibility through the application of different types (M = Pt, Pd, Re, Mo or Sn) and content (molar ratio M/Ni = 0.003, 0.01 or 0.03) of additive. The comparison of the efficiency and action mode of noble (M = Pt, Pd) and non-noble (M = Re, Mo, Sn) metal additives in the composition of Ni-M/Ce_0.5Zr_0.5O₂/Al₂O₃ catalysts was performed using X-ray fluorescence analysis, N₂ adsorption, X-ray diffraction, high-resolution transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction with hydrogen, and thermal analysis. The composition-characteristics-activity correlations were determined. It was shown that the introduction of a promoter does not affect the textural and structural properties of catalysts but influences their reducibility and performance in ATR of CH₄. At the similar dispersion of NiO active component (11 ± 2 nm), the Ni²⁺ reduction is intensified in the following order of additives: Mo < Sn < Re ≤ Pd < Pt. It was found that for the activation of Ni and Ni–Sn catalysts before ATR of CH₄ tests, the pre-reduction is required. On the contrary, the introduction of Pt, Pd and Re additives leads to the self-activation of catalysts under the reaction conditions and an increase of the H₂ yield due to the enhanced reducibility of Ni²⁺. The efficient and stable catalyst for hydrogen production has been developed: in ATR of CH₄ at 850 °C over an optimum 10Ni-0.9Re/Ce_0.5Zr_0.5O₂/Al₂O₃ catalyst the H₂ yield of 70% is attained. The designed catalyst has enhanced stability against oxidation and sintering of Ni active component as well as high resistance to coking.     

A novel binary Pt3Tex/C nanocatalyst for ethanol electro-oxidation

The Pt₃Te_x/C nanocatalyst was prepared and its catalytic performance for ethanol oxidation was investigated for the first time. The Pt₃Te/C nanoparticles were characterized by an X-ray diffractometer (XRD), transmission electron microscope (TEM) and energy dispersive X-ray spectroscopy equipped with TEM (TEM-EDX). The Pt₃Te/C catalyst has a typical fcc structure of platinum alloys with the presence of Te. Its particle size is about 2.8 nm. Among the synthesized catalysts with different atomic ratios, the Pt₃Te/C catalyst has the highest anodic peak current density. The cyclic voltammograms (CV) show that the anodic peak current density for the Pt₃Te/C, commercial PtRu/C and Pt/C catalysts reaches 1002, 832 and 533 A g⁻¹, respectively. On the current–time curve, the anodic current on the Pt₃Te/C catalyst was higher than those for the catalysts reported. So, these findings show that the Pt₃Te/C catalyst has uniform nanoparticles and the best activity among the synthesized catalysts, and it is better than commercial PtRu/C and Pt/C catalysts for ethanol oxidation at room temperature.     

Worm-like Pt nanoparticles anchored on graphene with S,N co-doping and Fe3O4 functionalization for boosting the electrooxidation of methanol

Making use of synergy and introducing defects can effectively regulate the electronic structure of carbon nanomaterials, which is of great importance for achieving desired electrochemical performance. Herein, we report a facile protocol for preparing S, N-doped graphene with simultaneous ferroferric oxide functionalization (Fe₃O₄-SNG), which is then used as support to anchor Pt nanoparticles for catalyzing the anodic reaction of direct methanol fuel cells (DMFCs), the promising portable power sources that have small environmental footprint, compact system design, and higher volumetric energy density compared with existing technologies. The functionalization by Fe₃O₄ as well as S and N doping increases the defect level in graphene, and also affect the subsequent growth of Pt particles, leading to formation of Pt nanoparticles with worm-like morphology on the surface of Fe₃O₄-SNG support (Pt/Fe₃O₄-SNG). The electrochemical evaluations show that the worm-like Pt nanoparticles anchored on Fe₃O₄-SNG have larger electrochemically active surface areas and enhanced specific activities for methanol oxidation reaction (MOR) due to their strong electronic interaction with the supports, which also promotes the oxidative removal of the intermediate poisoning products formed during methanol electrooxidation, thereby improving the long-term stability of the Pt catalyst.