Pd-Ni electrocatalysts for efficient ethanol oxidation reaction in alkaline electrolyte

Pd_xNi_y/C catalysts with high ethanol oxidation reaction (EOR) activity in alkaline solution have been prepared through a solution phase-based nanocapsule method. XRD and TEM show Pd_xNi_y nanoparticles with a small average diameter (2.4-3.2 nm) and narrow size distribution (1-6 nm) were homogeneously dispersed on carbon black XC-72 support. The EOR onset potential on Pd₄Ni₅/C (−801 mV vs. Hg/HgO) was observed shifted 180 mV more negative than that of Pd/C. Its exchange current density was 33 times higher than that of Pd/C (41.3 × 10⁻⁷ A/cm²vs. 1.24 × 10⁻⁷ A/cm²). After a 10,000-s chronoamperometry test at −0.5 V (vs Hg/HgO), the EOR mass activity of Pd₂Ni₃/C survived at 1.71 mA/mg, while that of Pd/C had dropped to 0, indicating Pd_xNi_y/C catalysts have a better ’detoxification’ ability for EOR than Pd/C. We propose that surface Ni could promote refreshing Pd active sites, thus enhancing the overall ethanol oxidation kinetics. The nanocapsule method is able to not only control over the diameter and size distribution of Pd-Ni particles, but also facilitate the formation of more efficient contacts between Pd and Ni on the catalyst surface, which is the key to improving the EOR activity.     

Effect of carbon nanofibers microstructure on electrocatalytic activities of Pd electrocatalysts for ethanol oxidation in alkaline medium

Pd electrocatalysts supported on three types of carbon nanofibers (CNFs), viz. platelet CNFs (p-CNFs), fish-bone CNFs (f-CNFs) and tubular CNFs (t-CNFs) are prepared and the effect of CNFs microstructure on the activities of the electrocatalysts for ethanol oxidation reaction (EOR) is investigated. The information on structural characteristics is obtained by high resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. Electrochemical techniques are employed to characterize the microstructure effect of CNFs on the catalytic activities of catalysts. HRTEM images indicate the microstructure of CNFs has a powerful influence on the distribution of Pd particles. The results of the electrochemical characterization also indicate that the structure of CNFs significantly influences the catalytic activities of the electrocatalysts and p-CNFs supported Pd electrocatalyst has the best performance for ethanol oxidation in an alkaline medium because p-CNFs has the highest ratio of edge atoms to basal atoms and correspondingly the fastest electrode kinetics and strongest Pd–CNFs interaction.     

Surface structure and electronic properties of Pt-Fe/C nanocatalysts and their relation with catalytic activity for oxygen reduction

In this work, physical and catalytic properties of Pt-Fe/C nanocatalysts of nominal compositions Pt:Fe 70:30 and 50:50, prepared by a polyol process using a long-chain diol as reducer (hexadecanediol) and oleic acid and oleylamine as stabilizers, are reported. As-prepared materials have very small particle size (2.2 nm), narrow particle size distribution, and homogeneous dispersion on the carbon support. The average compositions determined by energy dispersive X-ray analysis are Pt₇₅Fe₂₅/C and Pt₆₀Fe₄₀/C. Data for samples submitted to heat treatment in hydrogen atmosphere to induce Pt surface segregation are also presented. X-ray diffraction and transmission electronic microscopy are used to examine all as-prepared and heat-treated catalysts. Electronic properties are analyzed based on in situ dispersive X-ray absorption spectroscopy data. Measurements of electrocatalytic activity for oxygen reduction show that all Pt-Fe/C have electrocatalytic activities superior to that of Pt/C. Nanocatalysts with a Pt-rich surface have an enhanced performance for the reduction of oxygen but measurements carried out in methanol containing solutions show that Pt-enriched surfaces have an inferior methanol tolerance.     

Shape control of exposed planes in ceria-zirconia based electrocatalysts for methanol oxidation

Nano CeO₂–ZrO₂ composites with different shapes are synthesized by using hydrothermal and deposition-precipitation methods, and used to obtain Pt/CeO₂–ZrO₂/RGO catalysts, where reduced graphene oxide(RGO) acts as a carrier. X-ray Diffrattometry (XRD), Raman spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS) detection methods are used to characterize morphology, phase composition, exposed planes and oxygen defects of the catalyst. The obtained CeO₂–ZrO₂ supports are in the form of nanorods, nanospheres, and nanocubes, which mainly expose (110), (111), and (100) planes, respectively. Electrocatalytic methanol oxidation tests onto the Pt/CeO₂–ZrO₂/RGO catalysts show that the electrochemically active surface area and the peak current density of nanorods are the largest ones among the three catalysts, reaching 61.4 m²/g and 230 A/g. In addition, the long-term discharge stability and CO poisoning resistance of the nanorod-shaped Pt/CeO₂–ZrO₂/RGO catalyst are the highest ones among the examined catalysts.     

Preparation, characterization and application of Pt-Ru-Sn/C trimetallic electrocatalysts for ethanol oxidation in direct fuel cell

This work aimed to develop a method for the preparation of carbon-supported platinum nanocatalysts modified with Ruthenium and Tin, which were then evaluated for ethanol eletrooxidation in direct fuel cells. The Pechini method was employed to obtain these catalysts. This method consists in the decomposition of a polymeric precursor of metal salts. Nanocatalysts containing different Pt/Ru/Sn molar ratios were prepared by keeping the carbon/metal ratio at a constant value of 60/40%. The obtained nanoparticles were physico-chemically characterized by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), and Energy Dispersive X-ray Spectroscopy (EDX). Crystallite size of around 7.0 nm and 5.8 nm were achieved for the bimetallic and trimetallic nanocatalysts, respectively. The experimental composition was close to the nominal one, but the metal particles were not evenly distributed on the carbon surface. Electrochemical characterization of the nanoparticles was accomplished by cyclic voltammetry (CV) and chronoamperometry. High Performance Liquid Chromatography (HPLC) was carried out after ethanol electrolysis for determining the products generated. Acetaldehyde was the main electrolysis product and traces of CO₂ and acetic acid were also detected. Addition of Ru and Sn to the pure Pt nanoelectrocatalyst significantly improved its performance in ethanol oxidation. The onset potential for ethanol electrooxidation was 0.2 V vs. RHE, in the case of the trimetallic nanocatalyst Pt_0.8Ru_0.1Sn_0.1/C, which was lower than that obtained for the pure Pt catalyst (0.45 V vs. RHE).     

Carbon nanotubes as catalyst supports for ethanol oxidation

Multiwalled carbon nanotubes were obtained by chemical vapor deposition of xylene–ferrocene and employed as supports for PtSn alloy nanoparticles synthesized by the polyol method. The same metal alloy catalyst was also supported on Vulcan XC-72R to compare the influence of the substrate on the catalyst behavior for ethanol oxidation.     

Amorphous CoSn alloys decorated by Pt as high efficiency electrocatalysts for ethanol oxidation

This study examines the electro-catalytic behaviour of Pt decorating amorphous alloys in the electro-oxidation of ethanol. Pt decorated CoSn nanoparticles on carbon (denoted as Pt-CoSn/C) are prepared using a two-stage chemical synthesis (sol-gel preparation and Steady-state replacement method). The structure of Pt-CoSn/C nanoparticles is confirmed by the transmission electron microscopy (TEM) and X-ray diffraction (XRD). Under the same quantity of platinum, the Pt-CoSn/C nanoparticles have higher activity in alcohol oxidation than the Pt/C, PtRu/C and PtSn/C nanoparticles in cyclic voltammetry tests. The structure of Pt decorating amorphous CoSn alloys notably decreases the usage of Pt and enhances its catalytic activity at the same time.     

Sn-modified carbon-supported Pt nanoparticles synthesized using spontaneous deposition as electrocatalysts for direct alcohol fuel cells

Sn-modified carbon-supported Pt nanoparticles (Sn(Pt)/C electrocatalysts) were prepared by spontaneous deposition. Sn species were deposited on Pt/C by immersion in 2.0 × 10⁻⁴ M SnCl₂ + 0.1 M HClO₄ for different times, which allowed achieving an adequate control of the coverage (θ). Cyclic voltammetry (CV) in 0.5 M H₂SO₄ was carried out to determine θ and to evaluate the Sn(Pt)/C performance. The activity towards the oxidation reactions of methanol (MOR) and ethanol (EOR) was analyzed using CV in 0.5 M H₂SO₄ + 1.0 M alcohol. A promotional effect for the MOR and the EOR after the partial coverage by the Sn species was shown, as indicated by the significant reduction of the overpotential and the higher oxidation currents in both cases. This activation was explained by the formation of hydroxylated species on the tin deposits, thus facilitating the removal of the adsorbed intermediates. The best performance was achieved for θ ≈ 0.3 in the case of the MOR and for θ ≈ 0.5 in the case of the EOR. The reaction pathway for both alcohols was analyzed according to the obtained kinetic parameters, which significantly depended on the coverage.     

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.     

Nanostructured Pt and Pt-Sn catalysts supported on oxidized carbon nanotubes for ethanol and ethylene glycol electro-oxidation

Pt and Pt-Sn catalysts supported on oxidized carbon nanotubes were prepared by multiple potentiostatic pulses and tested for ethanol and ethylene glycol electro-oxidation in sulfuric acid. The composed nanostructured materials were characterized via SEM, TEM, EDX and XRD analysis. Small metal nanoparticles (4-6 nm) forming 3-D nanostructured agglomerates (25-100 nm) distributed over the carbon substrate were formed. XRD results showed that the bimetallic electrocatalysts consisted of a Pt single-phase material, suggesting the formation of solid solutions over the entire composition range. The tin content in the alloys was between 10 and 40 at. %.Cyclic voltammetry and chronoamperometry measurements at room temperature showed that at potentials below 0.5 V, the bimetallic catalyst with 40 at. % Sn exhibited the highest activity for ethanol and ethylene glycol oxidation, whereas at potentials above 0.5 V, the alloy with 25 at. % Sn displayed better performance. This behavior can be explained by the synergistic effect between the facilitation of alcohol oxidation via oxygen-containing species adsorbed on Sn atoms, the alteration of the electronic structure of Pt atoms that weakens CO and intermediates adsorption, and the adequate Pt ensembles size. Besides, the increment of the lattice parameter and the presence of grain boundaries can enhance the adsorption of the alcohols and favor the splitting of the C-C bond.     

Pd nanoparticles on self-doping-defects mesoporous carbon supports for highly active ethanol oxidation and ethylene glycol oxidation

The high activity electrocatalysts with low cost are crucial for large-scale direct alcohol fuel cells (DAFCs) applications. In this study, the “self-doping-defects” mesoporous carbon (SDMC) as support of uniformly-dispersed Pd nanoparticles (Pd/SDMC) was prepared for high active electrooxidation by a simple route without additional surfactant and acid treatment. According to the mutually corroborated experimental and theoretical calculation results, our route can significantly increase the carbon defect, which is conducive to the anchoring and uniform distribution of Pd nanoparticles. Meanwhile, the uniquely and hierarchically mesoporous nanostructure of SDMC provides abundant pathways for mass transport in the electrooxidation reaction. Benefitting from the above advantages, Pd/SDMC exhibits superior activity than commercial Pd/C and previously reported carbon-based electrocatalysts. The mass activities and specific activities of Pd/SDMC toward ethanol oxidation reaction (EOR) are 3404.3 mA mg⁻¹, 4.48 mA cm⁻², respectively. The mass activities and specific activities of Pd/SDMC for ethylene glycol oxidation reaction (EGOR) are 4002 mA mg⁻¹, 5.26 mA cm⁻², respectively. We believe that the facile strategy to synthesis mesoporous carbon with “self-doping” defects would promote large-scale DAFCs applications in the future.     

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.     

Preparation and activity of carbon-supported porous platinum as electrocatalyst for methanol oxidation

In this paper, we reported a novel electrocatalyst, Vulcan XC-72-supported porous platinum nano-particles (Pt_p/C) for methanol oxidation. In the preparation of Pt_p/C, platinum precursor was first adsorbed on carbon and then reduced by l-ascorbic acid in ethylene glycol solution. The structure and morphology of Pt_p/C and its activity toward methanol oxidation were characterized by transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) measurement, X-ray diffraction (XRD), energy-dispersion spectrometer (EDS), cyclic voltammetry (CV), and chronoamperometry (CA), with a comparison of the electrocatalyst prepared with sodium borohydride as reducer (Pt_s/C). It is found that both electrocatalysts have similar particle size but have different surface morphology of platinum and thus exhibit different electrocatalytic activity toward methanol oxidation. The platinum particle size of both electrocatalysts is 3–5 nm, but the corresponding BET surface areas are different significantly, 131.6 m² g⁻¹ and 87.7 m² g⁻¹ for Pt_p/C and Pt_s/C, respectively, indicative of the porous structure of platinum particles in Pt_p/C. The peak current for methanol oxidation on CV is 167 mA mg⁻¹ and 44 mA mg⁻¹ for Pt_p/C and Pt_s/C, respectively, indicative of the high electrocataytic activity of Pt_p/C toward methanol oxidation. The result from CA shows that Pt_p/C has good stability as the electrocatalyst for methanol oxidation.     

Preparation and electrocatalytic characteristics of the Pt-based anode catalysts for ethanol oxidation in acid and alkaline media

The current study reports the preparation and investigation of several Pt-based anode catalysts loaded on reduced graphene oxide (rGO) as electrocatalysts in both acid and alkaline media for ethanol electrooxidation. The synthesized catalysts are evaluated by the method of XRD, Raman spectroscopy, XPS and TEM. Electrocatalytic properties of these catalysts for ethanol oxidation were investigated by cyclic voltammetry and chronoamperometry. It was found that the as-prepared nanocatalysts doped by metals and oxide metals showed the improvement of catalytic performance compared to Pt-only supported on graphene catalyst. The results indicated that the presence of Al favoured Pt nanoparticles dispersing on the surface of rGO sheets. Indeed, the PAG catalyst exhibits the highest mass activity for the ethanol oxidation of 1194 mA mg^?1_Pt in acid medium and 3691 mA mg^?1_Pt in alkaline medium. In addition, the PAG catalyst also shows good antipoisoning ability for ethanol electrooxidation in both media. This catalyst could be a potential catalyst for direct ethanol fuel cell (DEFC).     

A comparative study of tungsten-modified PtRu electrocatalysts for methanol oxidation

The carbon supported PtRu nanocatalyst is modified by two kinds of tungsten compounds, i.e., tungsten oxide (WO_x) and phosphotungstic acid (H₃PW₁₂O₄₀, PW₁₂), respectively, and the catalytic performances of the modified catalysts for methanol oxidation are evaluated. The results show that tungsten oxide and phosphotungstic acid exhibit different promoting effects on the catalytic performance of the PtRu nanocatalyst for methanol oxidation. The WO_x-modified PtRu nanocatalyst has a considerably high catalytic activity, which is attributed to the uniform distribution of PtRu nanoparticles on the carbon support and the strong metal-support interaction (SMSI) between the hypo-d-tungsten and the hyper-d-platinum. The PW₁₂-modified PtRu nanocatalyst has a good poison resistance, which is ascribed to the protective effect of the self-assembled PW₁₂ layer on the catalyst surface.     

PtCu nanoframes as ultra-high performance electrocatalysts for methanol oxidation

Despite tremendous progress has been achieved in the past two decades, the lack of high-performance catalysts suitable for long-term operation remains a great challenge in realizing the commercial application of direct methanol fuel cell technology. Here, we reported a simple approach for one-pot synthesis of PtCu alloy nanoframes along with their exciting electro-catalytic performance for methanol oxidation. PtCu alloys with highly-open nanoframe structures have been achieved in presence of a structure-directing agent like polyvinyl pyrrolidone (PVP) and reducing solvent like sodium borohydride. Such PtCu alloy nanoframes show tremendous improvement in the methanol electrooxidation with a highest mass activity of 1.64 A mg_Pt ⁻¹ (much lower onset potential compared to Pt alone), which is believed to be much higher compared to that of the commercial Pt/C catalyst and most of the literature reports, indicating a better alloy formation and highly active sites created by highly open nanoframes structures.     

Preparation and characterization of carbon-supported sub-monolayer palladium decorated gold nanoparticles for the electro-oxidation of ethanol in alkaline media

Carbon-supported gold nanoparticles (Au/C) are successfully decorated with mono- or sub-monolayer palladium atoms with different Pd/Au atomic ratios by a chemically epitaxial seeded growth method. TEM, UV–vis spectrometry and XRD techniques are used to characterize the particle size, dispersion, palladium coverage on gold seeds and crystal structures of the prepared catalysts. Cyclic voltammetric tests show that the Pd-decorated Au/C (denoted by Pd@Au/C) have higher specific activities than that of Pd/C for the oxidation of ethanol in alkaline media. This suggests that the Pd utilization is improved with such a surface-alloyed nanostructure. In addition, stable chronoamperometric responses are achieved with the so-prepared electrocatalysts during ethanol oxidation.     

Synthesis of NiPt alloy nanoparticles by galvanic replacement method for direct ethanol fuel cell

The alloy of NiPt nanoparticles was successfully synthesized by galvanic replacement method in which Ni nanoparticles used as the templates and H₂PtCl₆ solution as additional reagent. The preparation conditions of Ni nanoparticle were optimized. The effect of platinum contents on the structure, morphology, magnetic and electrocatalyst of NiPt was investigated. The phase analysis by XRD showed the presence of Ni and Pt crystalline phases on the alloy. The TEM images indicated that the NiPt nanoparticles had porous crystalline structure with grain size in the range of 25 nm–30 nm. Besides, composition analysis by EDX showed that the ratios of Ni and Pt were changed with a change of the amount of H₂PtCl₆ using for the galvanic reaction. The magnetic properties of NiPt nanoparticles change significantly with a change of Pt composition. The NiPt nanoparticles exhibit ferromagnetic behavior depending on the amount of Pt composition. In particular, saturation magnetization decreases from 6.5 emu/g to 4.0 emu/g with the decrease of Ni:Pt ratio from 57.0:3.6 to 57.0:8.1 respectively. With lower Ni:Pt ratio (57.0:18.0), the NiPt nanoparticles exhibits superparamagnetic properties. The magnetic properties were attributed to the formation of NiPt alloy in which the electrons transfer from Pt atoms to d band of Ni. The cyclic voltammetry measurement showed that NiPt nanoparticles exhibit better ethanol oxidation in alkali medium comparing with pure Platinum.     

Enhanced activity of Pt nanoparticle catalysts supported on manganese oxide-carbon nanotubes for ethanol oxidation

Pt nanoparticles deposited on manganese oxide-carbon nanotubes (Pt/MnO_x-CNTs) are prepared by a microwave-assisted polyol method. Their structure characterizations are carried out by Fourier transform infrared spectrometry (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS) measurements, indicating that MnO_x nanoparticles cover the surface of CNTs and then Pt nanoparticles are uniformly dispersed on MnO_x-CNTs with the average particle size of about 2.2 nm. Ethanol oxidation peak current on Pt/MnO_x-CNTs (1141.4 mA mg⁻¹ Pt) is 1.82 times higher than that on Pt/CNTs (626.4 mA mg⁻¹ Pt) and 1.28 times higher than that on PtRu/C (JM) (888.6 mA mg⁻¹ Pt). The Pt/MnO_x-CNT catalyst presents not only excellent electrocatalytic activity and very high stability for ethanol oxidation, but also high tolerance to the poisonous carbonaceous intermediates generated during ethanol oxidation compared to Pt/CNT catalyst. This is attributed to the excellent proton conductivity of MnO_x and the synergistic effect between Pt and MnO_x. The optimum mass ratio of MnO_x to CNTs is 1:1 in the Pt/MnO_x-CNT catalysts.     

PtSnCe/C electrocatalysts for ethanol oxidation: DEFC and FTIR “in-situ” studies

The ethanol oxidation reaction (EOR) was investigated using PtSnCe/C electrocatalysts in different mass ratios (72:23:5, 68:22:10 and 64:21:15) that were prepared by the polymeric precursor method. Transmission electron microscopy (TEM) showed that the particles ranged in size from approximately 2 to 5 nm. Changes in the net parameters observed for Pt suggest the incorporation of Sn and Ce into the Pt crystalline network with the formation of an alloy between Pt, Sn and/or Ce. Among the PtSnCe catalysts investigated, the 68:22:10 composition showed the highest activity toward ethanol oxidation, and the current-time curves obtained in the presence of ethanol in acidic media showed a current density 50% higher than that observed for commercial PtSn/C (E-Tek). During the experiments performed on single direct ethanol fuel cells, the power density for the PtSnCe/C 68:22:10 anode was nearly 40% higher than the one obtained using the commercial catalyst. Data from Fourier transform infrared (FTIR) spectroscopy showed that the observed behavior for ethanol oxidation may be explained in terms of a double mechanism. The presence of Sn and Ce seems to favor CO oxidation, since they produce an oxygen-containing species to oxidize acetaldehyde to acetic acid.