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.     

Controllable synthesis of PtPd nanocubes on graphene as advanced catalysts for ethanol oxidation

PtPd nanocubes (NCs) were uniformly deposited on the reduced graphene oxides (RGOs) via a one-pot solvothermal reduction. These PtPd NCs were enclosed with (100) facet. Their size can be tuned from 11 to 27 nm by controlling their composition. Under the optimum atomic ratio of Pt/Pd (1:5), the as-prepared RGO-supported PtPd NCs show a superior catalytic efficiency of ethanol oxidation reaction (EOR) with a specific activity of 2.3 mA cm^?2 and a mass activity of 1.08 A mg^?1 Pt, far above those for the RGO-supported Pt nanoparticles (0.3 mA cm^?2 for specific activity and 0.018 A mg^?1 Pt for mass activity). Besides, these EOR catalysts exhibit a high CO-tolerance without significant current decay during steady-state polarization at 0.6 V over 4000 s. Their durability is also remarkable with only 8.9% loss of their electrochemical surface area (ECSA) after 10 000 cycles of voltammetric test.     

Effect of operating parameters and anode diffusion layer on the direct ethanol fuel cell performance

A parametric study was conducted on the performance of direct ethanol fuel cells. The membrane electrode assemblies employed were composed of a Nafion^® 117 membrane, a Pt/C cathode and a PtRu/C anode. The effect of cathode backpressure, cell temperature, ethanol solution flow rate, ethanol concentration, and oxygen flow rate were evaluated by measuring the cell voltage as a function of current density for each set of conditions. The effect of the anode diffusion media was also studied. It was found that the cell performance was enhanced by increasing the cell temperature and the cathode backpressure. On the contrary, the cell performance was virtually independent of oxygen and fuel solution flow rates. Performance variations were encountered only at very low flow rates. The effect of the ethanol concentration on the performance was as expected, mass transport loses observed at low concentrations and kinetic loses at high ethanol concentration due to fuel crossover. The open circuit voltage appeared to be independent of most operating parameters and was only significantly affected by the ethanol concentration. It was also established that the anode diffusion media had an important effect on the cell performance.     

NiPt sinter as a promising electrode for methanol electrocatalytic oxidation

Methanol is one of the chemical compounds utilized in fuel cells. The direct methanol fuel cell (DMFC) can be applied in many devices such as light electric vehicles and field equipment. Such a fuel cell is characterized by its high fuel energy density and low pollution. Despite many advantages of DMFCs, they are not commercially available, as the most efficient catalyst, which can be used in this process, has not been developed yet. Traditionally, it was platinum that was used in these fuel cells which is expensive and susceptible to CO poisoning. The solution to this is the use of bimetallic catalysts such as a NiPt system. In this study, we used a sintered NiPt electrode as the anode for the electrocatalytic oxidation of methanol. Based on our results, the sintered NiPt electrodes exhibited much higher activity in the oxidation of methanol, when compared with some conventional anodes.     

Thermodynamic analysis of solid oxide fuel cells operated with methanol and ethanol under direct utilization,steam reforming,dry reforming or partial oxidation conditions

There is increasing interest in developing solid oxide fuel cells (SOFC) for portable applications. For these devices it would be convenient to directly use a liquid fuel such as methanol and ethanol rather than hydrogen. The direct utilization of alcohol fuels in SOFC involves several processes, including the deposition of carbon, which can lead to irreversible deactivation of the fuel cell. Several publications have addressed the thermodynamic analysis of the reforming of methanol (MeOH) and ethanol (EtOH) in SOFC, but none have considered the direct utilization of these fuels. The equilibrium compositions, the carbon deposition boundaries, and the electromotive forces for the direct utilization and partial oxidation of methanol and ethanol in SOFC as a function of the fuel utilization are obtained in this study. In addition, the minimum amounts of H₂O, and CO₂ for direct and indirect reforming with MeOH and EtOH to avoid carbon formation are calculated.     

Review: Direct ethanol fuel cells

Direct ethanol fuel cells have attracted much attention recently in the search for alternative energy resources. As an emerging technology, direct ethanol fuel cells have many challenges that need to be addressed. Many improvements have been made to increase the performance of direct ethanol fuel cells, and there are great expectations for their potential. However, many improvements need to be made in order to enhance the potential of direct ethanol fuel cells in the future. This paper addresses the challenges and the developments of direct ethanol fuel cells at present. It also presents the applications of DEFC.     

Preparation and characterization of nano-sized Pt–Pd/C catalysts and comparison of their electro-activity toward methanol and ethanol oxidation

In the present work nano-sized Pt–Pd alloys have been prepared by polyol process on Vulcan XC72. The information on structural characteristics and surface chemistry of the nano-material was obtained using TEM, XRD and XPS.     

Catalysts for direct ethanol fuel cells

By comparing the performance of fuel cells operating on some low molecular weight alcohols, it resulted that ethanol may replace methanol in a direct alcohol fuel cell. To improve the performance of a direct ethanol fuel cell (DEFC), it is of great importance to develop anode catalysts for ethanol electro-oxidation more active than platinum alone. This paper presents an overview of catalysts tested as anode and cathode materials for DEFCs, with particular attention on the relationship between the chemical and physical characteristics of the catalysts (catalyst composition, degree of alloying, and presence of oxides) and their activity for the ethanol oxidation reaction.     

PtRh alloys on hybrid TiO2 – Carbon support as high efficiency catalyst for ethanol oxidation

High cost and poor stability of catalysts remain major obstacles for the commercialization of direct ethanol fuel cells (DEFCs). In this work, a Pt₉Rh/TiO₂C nanostructured catalyst is synthesized via an impregnation-reduction method followed by thermal annealing in N₂ at ambient pressure. X-ray powder diffraction (XRD) and scanning transmission electron microscopy (STEM) are used to characterize the corresponding physico-chemical properties of the as-prepared catalysts. The results reveal that PtRh nanoparticles are uniformly distributed on the TiO₂C hybrid support material. Cyclic voltammetry, linear scan voltammetry, CO-stripping voltammograms, chronoamperometry and chronopotentiometry methods are employed to investigate their catalytic performance for ethanol oxidation. The results show that the Pt₉Rh/TiO₂C produced a current density of 1039.5 mA mg_Pt^?1, which are 3.98, 8.31 and 2.43 times higher than Pt/TiO₂C, Pt/C and Pt₉Rh/C, respectively. Furthermore, the Pt₉Rh/TiO₂C also has greater resistance to CO-poisoning and displays better stability for ethanol oxidation than other catalysts. Pt₉Rh/TiO₂C therefore provides a promising material for ethanol oxidation in direct ethanol fuel cells.     

Investigation of AuNi/C anode catalyst for direct methanol fuel cells

AuNi nanoparticles supported on the activated carbon (AuNi/C) are synthesized by the impregnation method in the ethyleneglycol system using NH₂NH₂·H₂O as a reducing agent. The alloying of Au and Ni and the removal of unalloyed Ni in the AuNi/C composition are achieved by heat and acid treatments in sequence. Research results reveal that the average size and alloying degree of the AuNi nanoparticles in the AuNi/C catalyst increase with the enhancement of the annealing temperature. However, the Ni content of the AuNi/C catalyst firstly goes up and then down with the rising of heat treatment temperature due to the AuNi system phase-separates. Moreover, the electrocatalytic activity normalized by the electrochemically active surface area of each AuNi/C catalyst is far better than that of the Au/C catalyst, because of the bifunctional mechanism and the electrocatalytic activity of the NiOOH. In particular, the AuNi/C catalyst annealed at 400 °C exhibits the most excellent activity, due to its small AuNi particles and proper alloying degree. Furthermore, its mass-specific electrochemical activity is higher than that of the Au/C catalyst, although the mean diameter of the AuNi nanoparticles in this catalyst is larger than that of the Au nanoparticles.     

Direct utilization of methanol and ethanol in solid oxide fuel cells using Cu-Co(Ru)/Zr0.35Ce0.65O2−δ anodes

The direct utilization of methanol (MeOH) and ethanol (EtOH) was investigated on Cu-Co(Ru)/Zr_0.35Ce_0.65O₂ anodes for solid oxide fuel cells (SOFC) prepared by impregnation. Cells had similar performance and stability in H₂ and MeOH, while in EtOH the performance varied with time; that is, the power density initially increased, and then declined exponentially. This behavior was likely a consequence of carbon deposition that initially improved electronic conductivity to the anode functional layer, and subsequently blocked active sites. For all cells, the performance was recovered by re-exposing the anode to humidified hydrogen. In some cases, the cell performance exceeded the initial activity measured in hydrogen. Thus, the direct utilization of MeOH and EtOH did not irreversibly deactivate the Co(Ru)/Zr_0.35Ce_0.65O₂ anodes.     

Binary Pt–Pd and ternary Pt–Pd–Ru nanoelectrocatalysts for direct methanol fuel cells

Nano-sized binary and ternary alloys are synthesized by polyol process on Vulcan XC72-R support. Nanostructured binary Pt–Pd/C catalysts are prepared either by co-deposition or by depositing on each other. Ternary Pt–Pd–Ru/C catalysts are prepared by co-deposition. The structural characteristics of the nanocatalysts are examined by TEM and XRD. Their electrocatalytic activity toward methanol oxidation and CO stripping curves were measured by electrochemical measurements and compared with that of commercial Pt/C catalyst. The results show that the binary nanocatalyst prepared by depositing the Pt precursor colloids on Pd-Vulcan XC-72R are more active toward methanol oxidation than that of the co-deposited binary alloy nanocatalyst. The co-deposited ternary Pt–Pd–Ru/C nanocatalyst based membrane electrodes assembly shows higher power density compared to the binary nanocatalysts as well as commercial Pt/C catalyst in direct methanol fuel cell. Significantly higher catalytic activity of the nanocatalysts toward methanol oxidation compared to that of the commercial Pt/C is believed to be due to lower level of catalyst poisoning.     

Sawtooth-shaped nickel-based submicrowires and their electrocatalytic activity for methanol oxidation in alkaline media

Sawtooth-shaped nickel and nickel-cobalt submicrowires were fabricated by hydrazine reduction of their salt precursors under magnetic field. The sawtooth-shaped submicrowires exhibited better electrochemical property in electrooxidation of methanol in alkaline media than nickel nanoparticles and smooth submicrowires because the sawtooth-shaped structure benefited more from both geometry of nanowires and nano-size effect. Therefore, the sawtooth-shaped nickel-based submicrowires synthesized in this work have the potential for use as a non-precious electrode catalyst for alkaline fuel cells.     

Use of Pd–MnMoO4–graphene hybrids as efficient and CO poisoning tolerant electrocatalysts for methanol oxidation

40 wt%Pd-x wt%MnMoO₄/Graphene (GNS) (0 ≤ x ≤ 20) hybrids have been synthesized for use as efficient and CO poisoning tolerant anode materials in methanol fuel cells. Investigations revealed that the addition of MnMoO₄ increases the electrocatalytic activity of the base electrode (40 wt%Pd/GNS) towards the methanol oxidation reaction (MOR) in 1 M KOH significantly. The catalytic activity of the electrode is found to be the greatest with 8 wt%MnMoO₄. The addition of MnMoO₄ also improves CO poisoning tolerance of the base electrode by 11–73%. The MOR activity and CO poisoning tolerance of the 40 wt%Pd-8 wt%MnMoO₄/GNS hybrid electrode were superior to other electrodes of the investigation.