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.     

The performance of Pt nanoparticles supported on Sb2O5.SnO2, on carbon and on physical mixtures of Sb2O5.SnO2 and carbon for ethanol electro-oxidation

Pt nanoparticles were supported on Sb₂O₅.SnO₂ (ATO), on carbon and on physical mixtures of ATO and carbon by an alcohol-reduction process using ethylene glycol as reducing agent. The obtained materials were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Their performance for ethanol oxidation was investigated at room temperature by chronoamperometry and in a direct ethanol fuel cell (DEFC) at 100 °C. Pt nanoparticles supported on a physical mixture of ATO and carbon showed a significant increase of performance for ethanol oxidation compared to Pt nanoparticles supported on ATO or on carbon.     

TiO2 nanotubes promoting Pt/C catalysts for ethanol electro-oxidation in acidic media

In this paper, TiO₂ nanotubes/Pt/C (TNT/Pt/C) catalysts for ethanol electro-oxidation were prepared by co-mixing method in solution. TEM and XRD showed that uniform anatase TiO₂ nanotubes were about 100 nm in length and 8 nm in diameter and the TGA results indicated that the amount of H₂O contained in TiO₂ nanotubes was much more than that in anatase TiO₂. The composite catalysts activities were measured by cyclic voltammetry (CV), chronoamperometry and CO stripping voltammetry at 25 °C in acidic solutions. The results demonstrated that the TNT can greatly enhance the catalytic activity of Pt for ethanol oxidation and increase the utilization rate of platinum. The CO stripping test showed that the TNT can shift the CO oxidation potential to lower direction than TiO₂ does, which is helpful for ethanol oxidation.     

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.     

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.     

Methanol oxidation reaction on PtSnO2 obtained by microwave-assisted chemical reduction

Methanol electro-oxidation was investigated on PtSnO₂/C based electrocatalyst in acidic solution. This study was focused on the use of this material as anodic active material for potential applications in direct methanol fuel cells. PtSnO₂/C nanoparticles were prepared using a microwave-assisted synthesis. Physic-chemical and electrochemical characterizations were carried out by XRD, TEM, EDS, cyclic voltammetry and chronoamperometric studies. TEM analysis revealed that PtSnO₂/C electrocatalyst is formed by well dispersed nanoparticles with average particle size around 2.2 nm. The results showed that synthesized PtSnO₂/C has better electrochemical characteristics than commercial PtRu/C for methanol oxidation. It was found that PtSnO₂/C showed less methanol oxidation reaction onset potential than PtRu/C. The investigation of some kinetic parameters like Tafel slope and charge transfer coefficient showed that PtSnO₂/C has a Pt based electrocatalyst performance associated to the bi-functional process able to oxidize CH₃OH and CO_ads, it is probably activated by the co-existence of SnO₂ phase.     

Wormholelike mesoporous carbons as the support for Pt2Sn1 towards ethanol electrooxidation: Effect of pore diameter

Pt₂Sn₁ nanoparticles supported on wormholelike mesoporous carbons (WMCs) with three different pore diameters, namely WMC-F7, WMC-F30, and WMC-F0 have been synthesized by adopting a modified pulse microwave-assisted polyol method. The pore diameters (D_p) of WMC-F7, WMC-F30, and WMC-F0 are 8.5 nm, 4.4 nm, and 3.1 nm respectively, while the particle size of Pt₂Sn₁ (D_Pt) on each support is identical (∼3 nm). Based on the experimental results, it has been found that the pore diameter plays an important role in the electrochemical activity of Pt₂Sn₁ catalysts towards ethanol electrooxidation reaction (EOR). Pt₂Sn₁/WMC-F7 catalyst exhibits the highest electrochemical surface area (ESA) and activity towards EOR. Moreover, Pt₂Sn₁/WMC-F7 gives the comparable activity to the Pt₂Sn₁ supported on the commercial XC-72 carbon. However, in the cases of WMC-F30 (D_Pt < Dp < 2 D_Pt) and WMC-F0 (Dp = D_Pt) as the supports, the corresponding catalysts obtain much lower ESA and EOR activity with respect to WMC-F7 (Dp > 2 D_Pt). This could be attributed to the easy accessibility of Pt₂Sn₁ nanoparticles in the case of WMC-F7 with Dp > 2 D_Pt for the easy fuel transportation, and consequently the EOR activity has been greatly improved.     

Cu1−xPdx/CeO2-impregnated cermet anodes for direct oxidation of methane in LaGaO3-electrolyte solid oxide fuel cells

A series of ceramic-metal composite anodes containing 1.0 wt.% Cu_1−xPd_x alloys (where x = 0, 0.15, 0.25, 0.4, 0.5, 0.75 and 1.0) were prepared by impregnation of the respective metal salts and 5.0 wt.% CeO₂ into a porous La_0.4Ce_0.6O_2−σ anode skeleton. The performance of these anodes was evaluated in both dry H₂ and CH₄ in the temperature range of 700-800 °C using the 300-μm thick La_0.8Sr_0.2Ga_0.83Mg_0.17O_3−σ (LSGM) electrolyte-supported solid oxide fuel cells (SOFCs). The addition of Pd to Cu significantly increased the performance of the single cells in dry CH₄, with the cell maximum power density changed from 66 mW cm⁻² for Cu_1.0Pd_0.0 to 345 mW cm⁻² for Cu_0.0Pd_1.0 at 800 °C. In H₂, however, the performance improvement was not as significant compared to that in CH₄. In addition, carbon formation was greatly suppressed in the Cu-Pd alloy-impregnated anodes compared to that with pure Pd after exposure to dry CH₄ at 800 °C, which led to different performance stability behaviors for these cells operating with dry CH₄.     

Continuous monitoring of CO2 yields from electrochemical oxidation of ethanol: Catalyst,current density and temperature effects

A very simple method for continuous quantification of carbon dioxide yields from electrochemical processes, using a commercial CO₂ detector, is presented. Application of this method to electrochemical oxidation of ethanol greatly decreases the time needed to evaluate catalyst behaviours and allows for efficient elucidation of the factors that influence CO₂ yields. A systematic study of the effects of current density and temperature on the performances of Pt and PtRu anode catalysts has been carried out. The amount of CO₂ produced at each current and temperature has been measured in real time. Yields of CO₂, the product of total oxidation of ethanol, are compared with the limited results reported in the literature for direct ethanol fuel cells.