Bi-metallic and tri-metallic Pt-Sn/C, Pt-Ir/C, Pt-Ir-Sn/C catalysts for electro-oxidation of ethanol in direct ethanol fuel cell

In the present work, combination of bi-metallic and tri-metallic Pt, Ir, Sn electro-catalysts was prepared by impregnation reduction method on carbon Vulcan XC-72 to improve upon electro-oxidation of ethanol in direct ethanol fuel cell. The prepared electro-catalysts were characterized by means of scanning electron microscope (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) analyses. XRD and TEM analyses reveal that the prepared catalysts are of nano size (6-10 nm) range. It is shown that Pt lattice parameter decreases with the addition of Ir, and increases with the addition of Sn in Pt-Ir-Sn/C catalyst. The electro-catalytic activities characterized by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometry (CA) techniques reveal that the addition of small amount of Ir in Pt-Sn/C electro-catalyst exhibits higher activity towards ethanol oxidation than the Pt-Sn/C (20% Pt and 20% Sn by wt) electro-catalyst. The single direct ethanol fuel cell (DEFC) test at 90 °C, 1 bar with catalyst loading of 1 mg/cm² and 2 M ethanol as anode feed showed an enhancement of catalytic activity in following order: Pt-Ir-Sn/C (20% Pt, 5% Ir and 15% Sn by wt) > Pt-Ir-Sn/C (20% Pt, 10% Ir and 10% Sn by wt) > Pt-Sn/C (20% Pt and 20% Sn by wt) > Pt-Ir-Sn/C (10% Pt, 15% Ir and 15% Sn by wt) > Pt-Ir/C (20% Pt and 20% Ir by wt) >    Pt/C (40% Pt by wt). Pt-Ir-Sn/C (20% Pt, 5% Ir and 15% Sn by wt) exhibited highest performance among all the catalysts prepared with power density of 29 mW/cm² in DEFC operating at 90 °C.     

Acid-treated PtSn/C and PtSnCu/C electrocatalysts for ethanol electro-oxidation

PtSn/C with Pt:Sn atomic ratio of 50:50 and PtSnCu/C electrocatalysts with different Pt:Sn:Cu atomic ratios were prepared using NaBH₄ as reducing agent and carbon black Vulcan XC72 as support. In a second step, the electrocatalysts were treated with nitric acid to remove the less noble metals (chemical dealloying). The obtained materials were characterized by X-ray diffraction, EDX analysis, TEM images with EDX scan-line and cyclic voltammetry. The electro-oxidation of ethanol was studied by chronoamperometry and on single direct ethanol fuel cell (DEFC). The X-ray diffractograms of the as-synthesized electrocatalysts showed the typical face-centered cubic (FCC) structure of Pt alloys. After acid treatment the FCC structure was maintained and Sn and Cu atoms were removed from the nanoparticles surface. Chronoamperometry measurements showed a strong increase of performance of PtSn/C and PtSnCu/C electrocatalysts after acid treatment; however, under DEFC conditions at 100 °C, only acid-treated PtSn/C electrocatalyst showed superior performance compared to commercial PtSn/C from BASF.     

The effect of acetaldehyde and acetic acid on the direct ethanol fuel cell performance using PtSnO2/C electrocatalysts

PtSnO₂/C with Pt:SnO₂ molar ratios of 9:1, 3:1 and 1:1 prepared by an alcohol-reduction process were evaluated as anodicelectrocatalysts for direct ethanol fuel cell (DEFC). Acetaldehyde, acetic acid and mixtures of them with ethanol were also tested as fuels. Single cell tests showed that PtSnO₂/C electrocatalysts have a superior electrical performance for ethanol and acetaldehyde electro-oxidation when compared to commercial Pt₃Sn/C_(alloy) and Pt/C electrocatalysts. For all electrocatalysts, no electrical response was observed when acetic acid was used as a fuel. For ethanol electro-oxidation, the main product was acetaldehyde when Pt₃Sn/C_(alloy) and Pt/C electrocatalysts were employed. Besides, PtSnO₂/C electrocatalysts led to the formation of acetic acid as the major product. CO₂ was formed in small quantities for all electrocatalysts studied. A sharp drop in electrical performance was observed when using a mixture of ethanol and acetaldehyde as a fuel, however, the use of a mixture of ethanol and acetic acid as a fuel did not affect the DEFC performance.     

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.     

Effect of addition of rhenium to Pt-based anode catalysts in electro-oxidation of ethanol in direct ethanol PEM fuel cell

Breaking of C–C bond at low temperature to completely oxidize ethanol in direct ethanol fuel cell (DEFC) is the limiting factor for the development of DEFC as alternative source of power in portable electronic equipment. Binary and ternary Pt based catalysts with addition of Re, Pt–Re/C (20:20), Pt–Sn/C (20:20), Pt–Re–Sn/C (20:10:10) and Pt–Re–Sn/C (20:5:15) catalysts were prepared from their precursors by co-impregnation reduction method to study electro-oxidation of ethanol in DEFC. The electrocatalysts characterized by transmission electron microscope, scanning electron microscope, energy dispersive X-ray, and X-ray diffraction shows the formation of above mentioned bi- and tri-metallic catalyst with size ranges from 6 to 16 nm. Electrochemical analyses by cyclic voltammetry, linear sweep voltammetry and chronoamperometry show that Pt–Re–Sn/C (20:5:15) gives higher current density compared to that of Pt–Re/C (20:20) and Pt–Sn/C (20:20). The addition of Re to Pt–Sn/C is conducive to electro-oxidation of ethanol in DEFC. The power density obtained using Pt–Re–Sn/C(20% Pt, 5% Re, 15% Sn by wt) (30.5 mW/cm²) as anode catalyst in DEFC is higher than that for Pt–Re–Sn/C(20% Pt, 10% Re, 10% Sn by wt) (19.8 mW/cm²), Pt–Sn/C (20% Pt, 20% Sn by wt) (22.4 mW/cm²) and Pt–Re/C (20% Pt, 20% Re by wt) (9.8 mW/cm²) at 100 °C, 1 bar, with catalyst loading of 2 mg/cm² and 5 M ethanol as anode feed.     

PtM/C (M = Sn,Ru, Pd,W) based anode direct ethanol–PEMFCs: Structural characteristics and cell performance

In the present work, the role of the structural characteristics of Pt-based catalysts on the single direct ethanol proton exchange membrane fuel cell (PEMFC) performance is examined. Several PtM/C (M = Sn, Ru, Pd, W) catalysts were characterized by means of transmission electron microscopy (TEM) and X-ray diffraction (XRD) and then evaluated as anode catalysts in single direct ethanol fuel cells. XRD spectra showed that Pt lattice parameter decreases with the addition of Ru or Pd and increases with the addition of Sn or W. According to the obtained experimental results, PtSn catalysts presented better electrocatalytic activity towards ethanol electro-oxidation. Based on these results, PtSn/C catalysts with different Pt/Sn atomic ratio were tested and compared. The maximum power density values obtained were correlated with the structural characteristics of the catalysts. A volcano type behaviour between the fuel cell maximum power density and the corresponding atomic percentage of Sn (Sn%) was observed. It was also observed that Sn% affects almost linearly the Pt_xSn_y catalysts’ lattice parameter.     

Electrooxidations of ethanol,acetaldehyde and acetic acid using PtRuSn/C catalysts prepared by modified alcohol-reduction process

Well-dispersed ternary PtRuSn catalysts of various atomic ratios (60:30:10, 60:20:20 and 60:10:30) were deposited onto carbon using modified alcohol-reduction process for electrochemical oxidation of ethanol. The alloy phase structure and surface morphology for each variation of the PtRuSn/C catalysts were determined by XRD and HRTEM. In order to evaluate the contributions of Ru and Sn in the different stages of ethanol oxidation, electrochemical oxidations of adsorbed CO, ethanol, acetaldehyde and acetic acid were performed on each PtRuSn/C catalyst. The results indicated that the Ru-rich PtRuSn/C catalyst (60:30:10) exhibited the lowest onset potential for the electrooxidations of adsorbed CO, ethanol and acetaldehyde, revealing that the removal through oxidation of the intermediate C₁ and C₂ species from Pt sites is primarily attributed to the Ru and Pt₃Sn alloy structures. However, for the overall oxidation of ethanol, the Sn-rich PtRuSn/C catalyst (60:10:30) containing PtSn phase and SnO₂ structure is favorable for the activation of CC bond breaking, thereby generating higher current density (mass activity) at higher potentials. Moreover, in the electrooxidation of acetic acid, a remarkable improvement for oxidizing acetic acid to C₁ species was observed in the Sn-rich PtRuSn/C catalyst (60:10:30), while the Ru-rich PtRuSn/C catalyst (60:30:10) was almost incapable of breaking the CC bond to further oxidize acetic acid. The possible reasons for the different reactivities on the studied PtRuSn/C catalysts were discussed based on the removal of intermediates and activation of the CC bonds on the different surfaces.     

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.     

Ethanol oxidation using a metallic bilayer Rh/Pt deposited over Pt as electrocatalyst

This paper presents the preparation and characterization of a Rh/Pt bilayer electrodeposited on Pt and its behavior for ethanol oxidation in perchloric acid solution. The electrodes were characterized by atomic force microscopy (AFM) and cyclic voltammetry. The ethanol oxidation was studied on a Pt/Rh/Pt bilayer using cyclic voltammetry and chronoamperometry techniques. In this study, an increase of 268% in the current density peak for the ethanol oxidation and a displacement of 100 mV towards more negative values in the beginning of this process on the Pt/Rh/Pt are observed. The ethanol oxidation at constant potential (E = 0.5 V versus reversible hydrogen electrode (RHE)) showed an increase of 10 times in the current density compared to polycrystalline platinum.     

Carbon-supported PdM (M = Au and Sn) nanocatalysts for the electrooxidation of ethanol in high pH media

Carbon-supported Pd₄Au- and Pd_2.5Sn-alloyed nanoparticles were prepared by a chemical reduction method, and characterized by a wide array of experimental techniques including mass spectrometry, transmission electron microscopy, and X-ray diffraction spectroscopy. Ethanol electrooxidation on the as-synthesized catalysts and commercial Pt/C was then investigated and compared in alkaline media by cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy studies at room temperature. Voltammetric and chronoamperometric measurements showed higher current density and longer term stability in ethanol oxidation with the palladium alloy nanocatalysts than with the commercial one. Electrochemical impedance spectroscopy and Tafel plots were employed to examine the charge-transfer kinetics of ethanol electrooxidation. The results suggest that whereas the reaction kinetics might be somewhat more sluggish on the Pd-based alloy catalysts than on commercial Pt/C, the former appeared to have a higher tolerance to surface poisoning. Overall, the Pd-based alloy catalysts represent promising candidates for the electrocatalytic oxidation of ethanol, and Pd₄Au/C displays the best catalytic activity among the series for the ethanol oxidation in alkaline media.     

Multiwalled carbon nanotube-supported Pt/Sn and Pt/Sn/PMo12 electrocatalysts for methanol electro-oxidation

Carbon nanotube (CNT) containing electrocatalysts, Pt/Sn/PMo₁₂/CNT, Pt/Sn/CNT, and Pt/CNT, were prepared by a microwave-heated polyol process. The electrocatalysts were characterized by X-ray diffraction, energy dispersive spectroscopy, scanning and transmission electron microscopy, and cyclic voltammetry. We found that the addition of PMo₁₂ can help Pt-Sn nanoparticles to disperse very uniformly on the outer walls of CNTs. The Pt/Sn/PMo₁₂/CNT catalyst exhibited the lowest onset potential for electro-oxidation of adsorbed C intermediates, compared to the Pt/Sn/CNT and Pt/CNT catalysts. It also generated much higher current density for methanol oxidation at room temperature compared to Pt/Sn/CNT and Pt/CNT catalysts, which were prepared by the same method.     

Ethanol electro-oxidation on carbon-supported Pt,PtRu and Pt3Sn catalysts: A quantitative DEMS study

The electrocatalytic activity of commercial carbon supported PtRu/Vulcan and Pt₃Sn/Vulcan bimetallic catalysts (E-TEK, Inc.) for ethanol oxidation under well defined electrolyte transport conditions and their selectivity for complete oxidation were evaluated using cyclic voltammetry combined with on-line differential electrochemistry mass spectrometry (DEMS) measurements and compared to the activity/selectivity of standard Pt/Vulcan catalysts. The main reaction products CO₂, acetaldehyde and acetic acid were determined quantitatively, by appropriate calibration procedures, current efficiencies and product yields were calculated. Addition of Ru or Sn in binary Pt catalysts lowers the onset potential for ethanol electro-oxidation and leads to a subtle increase of the total activity of the Pt₃Sn/Vulcan catalyst. It does not improve, however, the selectivity for complete oxidation to CO₂, which is about 1% for all three catalysts under present reaction conditions—incomplete ethanol oxidation to acetaldehyde and acetic acid prevails on all three catalysts. The results demonstrate that the performance of the respective catalysts is limited by their ability for C–C bond breaking rather than by their activity for the oxidation of poisoning adsorbed intermediates such as CO_ad or CH_x,ad species.     

Study of ethanol electro-oxidation in acid environment on Pt3Sn/C anode catalysts prepared by a modified polymeric precursor method under controlled synthesis conditions

A carbon-supported binary Pt₃Sn catalyst has been prepared using a modified polymeric precursor method under controlled synthesis conditions. This material was characterized using X-ray diffraction (XRD), and the results indicate that 23% (of a possible 25%) of Sn is alloyed with Pt, forming a dominant Pt₃Sn phase. Transmission electron microscopy (TEM) shows good dispersion of the electrocatalyst and small particle sizes (3.6 nm ± 1 nm). The polarization curves for a direct ethanol fuel cell using Pt₃Sn/C as the anode demonstrated improved performance compared to that of a PtSn/C E-TEK, especially in the intrinsic resistance-controlled and mass transfer regions. This behavior is probably associated with the Pt₃Sn phase. The maximum power density for the Pt₃Sn/C electrocatalyst (58 mW cm⁻²) is nearly twice that of a PtSn/C E-TEK electrocatalyst (33 mW cm⁻²). This behavior is attributed to the presence of a mixed Pt₉Sn and Pt₃Sn alloy phase in the commercial catalysts.     

Heterogeneous Ir3Sn–CeO2/C as alternative Pt-free electrocatalysts for ethanol oxidation in acidic media

For reducing the Pt usage and driving down the cost of fuel cells, it is urgent to develop alternative Pt-free catalysts with high catalytic performance. In this study, an Ir₃Sn–CeO₂/C heterogeneous catalyst is designed as low-price, alternative Pt-free electrocatalyst towards ethanol oxidation reaction (EOR) in acidic conditions. Owing to the strong synergistic effect among Ir, Sn and CeO₂ components, Ir₃Sn–CeO₂/C heterogeneous catalyst exhibits higher catalytic activity and stability for EOR in comparison with commercial Pt/C, as-prepared Ir/C and Ir₃Sn/C. Additionally, kinetics and mechanisms of EOR are also investigated. It proves that ethanol electrooxidation on Ir₃Sn–CeO₂/C catalyst is a diffusion controlled irreversible process. Meanwhile, the H₂SO₄ and ethanol concentrations can affect the EOR activity. All results demonstrate Ir₃Sn–CeO₂/C heterogeneous catalyst is a promising Pt-free choice for EOR.     

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.     

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.     

Carbon supported Pt–Co (3:1) alloy as improved cathode electrocatalyst for direct ethanol fuel cells

In direct alcohol fuel cells, ethanol crossover causes a less serious effect compared to that of methanol because of both its smaller permeability through the Nafion^® membrane and its slower electrochemical oxidation kinetics on a Pt/C cathode. The main interest in direct ethanol fuel cells (DEFCs) is to find an anode catalyst with high activity for the oxidation of ethanol. However, due to the low activity of pure platinum for the oxygen reduction reaction (ORR), research on cathode electrocatalysts with improved ORR and the same or improved ethanol tolerance than that of Pt are also in progress. In this work, a commercial carbon supported Pt–Co (3:1) electrocatalyst (E-TEK) was investigated as cathode material in DEFCs and the activity compared to that of Pt. In the cathodic potential region (0.7–0.9 V versus RHE) Pt/C and Pt–Co/C showed the same activity for the oxidation of crossover ethanol. But the performance of Pt–Co/C as cathode material in DEFCs in the temperature range 60–100 °C is better than that of Pt/C both in terms of mass activity and specific activity, due to an improved activity of the alloy for oxygen reduction.     

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.     

PtxSn/C electrocatalysts synthesized by improved microemulsion method and their catalytic activity for ethanol oxidation

The Pt_xSn/C (x = 1, 2, 2.5, 3, 4) anodic catalysts for direct ethanol fuel cell (DEFC) have been prepared by an improved microemulsion method. Ethylene glycol is used as cosurfactant, and metal precursors are dissolved in it beforehand to prevent the hydrolysis of metal precursors. The composition, particle size and structure of these catalysts are characterized by energy dispersive X-ray spectrum (EDX), transmission electron microscope (TEM) and X-ray diffraction (XRD). The results show that the synthesized Pt₃Sn/C catalyst has part of Pt and Sn alloying. The average diameter is about 2.9 nm, and has a narrow size distribution and a good dispersivity. The electrochemical experiments indicate that the Pt₃Sn/C catalyst prepared in the neutral microemulsion has superior catalytic activity for ethanol oxidation. The Pt_xSn/C nanoparticle formation in the improved microemulsion is also discussed.     

Decoration of carbon-supported Pt catalysts with Sn to promote electro-oxidation of ethanol

Carbon-supported Pt/Sn catalysts were prepared by decorating carbon-supported Pt with Sn, by decorating carbon-supported Sn with Pt, and by co-deposition of Pt and Sn on carbon. All of the Pt/Sn catalysts exhibited greatly enhanced activities for ethanol oxidation relative to Pt alone, with the Sn decorated Pt catalyst showing the best performance. The latter catalyst was shown by XPS to contain no metallic Sn, emphasizing the importance of surface Sn oxide species in the activation of Pt for ethanol oxidation. Decoration of Sn with Pt is shown to be a feasible way to increase Pt utilization.