Morphology effect of MnO2 promoter to the catalytic performance of Pt toward methanol electrooxidation reaction

Three MnO₂ samples with different well-defined morphologies including nanoplates, nanorods and corallines are prepared through a simple chemical precipitation method and used as the promoter/support for Pt electrocatalysts (denoted as Pt/MnO₂P, Pt/MnO₂-R and Pt/MnO₂C, respectively). The morphology effects of MnO₂ to the catalytic properties of Pt for methanol oxidation reaction (MOR) are intensively investigated. Results show that the catalytic properties of Pt are strongly dependent on the morphology of the promoter. Pt/MnO₂-R with MnO₂ nanorods as the promoter shows the highest catalytic properties among the MnO₂-promoted catalysts. The mass-specific activity and intrinsic activity of Pt in Pt/MnO₂-R catalyst is 0.51 A mg⁻¹_Pt and 11.54 A m⁻²_Pt, which is ca. 1.89 and 2.18 times that of commercial Pt/C catalysts (0.27 A mg⁻¹_Pt and 5.29 A m⁻²_Pt), respectively. Change in the electronic structure of Pt is responsible for the enhancement in the catalytic properties of Pt/MnO₂-R.     

HxMoO3-assisted deposition of platinum nanoparticles on MWNTs for electrocatalytic oxidation of methanol

Platinum nanoparticles were loaded on multi-walled carbon nanotubes (MWNTs) by using ethylene glycol as reductant and with the assistance of hydrogen molybdenum bronze (H_xMoO₃, 0 < x ≤ 2) for the electrocatalytic oxidation of methanol. In this approach, MWNTs were modified by H_xMoO₃ and used as the support for platinum nanoparticles. The XRD and TEM characterizations indicate that the average particle size of platinum supported by the modified MWNTs (Pt/H_xMoO₃-modified-MWNTs) is 3.4 nm, smaller than that (4.3 nm) of the platinum supported by the unmodified MWNTs (Pt/MWNTs). The voltammetric and chronoamperometric experiments show that Pt/H_xMoO₃-modified-MWNTs exhibits better electrocatalytic activity toward methanol oxidation than Pt/MWNTs, although the former has a less platinum loading (4.6 wt%) than the latter (6.0 wt%). The mechanism on the assistance of H_xMoO₃ to the platinum deposition was discussed.     

Testing of carbon supported Pd-Pt electrocatalysts for methanol electrooxidation in direct methanol fuel cells

In the present work, a detailed characterization of the electrochemical behavior of carbon supported Pd-Pt electrocatalysts toward CO and methanol electrooxidation in direct methanol fuel cells is reported. Technical electrodes containing an ionomer in their catalyst layer were prepared for this purpose. CO and methanol electrooxidation reactions were used as test reactions to compare the electrocatalytic behavior of bimetallic supported nanoparticles in acidic liquid electrolyte and in solid polymer electrolyte (real fuel cell operating conditions). Experimental results in both environments are consistent and show that the electrochemical behavior of carbon supported Pd-Pt depends on their composition, giving the best performance in direct methanol single fuel cell with a Pd:Pt atomic ratio of 25:75 in the catalyst.     

Nontrivial role of carbon nanofibers morphology in binderless Pt nanocatalyst supported electrode

Similar to conventional composite electrodes, developing binderless-based carbon nanostructured (CNs) electrodes for fuel cells requires particularly the optimisation of both the morphology and the density of the CNs. In this work, carbon nanofibers (CNFs) have been optimised and used as catalyst support for Pt nanoparticles (NPs). The nontrivial role of the CNFs on the catalytic behavior is clearly demonstrated. We have shown that for a similar amount, morphology and dispersion of the Pt NPs fabricated onto CNFs, the density of the latter and to a lesser extent their diameter are the main factors influencing the catalytic activity. For the particular case of CNFs considered in this work, an optimum activity toward methanol fuel cell reaction was obtained when Pt NPs were supported with CNFs synthesized with a C₂H₂/Ar ratio of 0.31.     

Hollow nanoporous Au/Pt core–shell catalysts with nanochannels and enhanced activities towards electro-oxidation of methanol and ethanol

In the work, hollow nanoporous Au/Pt core–shell (H-PtAu) catalysts with nanochannels were prepared with different sizes of gold nanoparticles of a narrow size distribution in the range of 1.8 ± 0.3, 3.2 ± 0.3 and 4.6 ± 0.5 nm. The hollow spheres were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM) and an energy-dispersive X-ray (EDX) analyzer. The electrochemical methods by cyclic voltammetric and chronoamperometry demonstrate that the catalytic performance of hollow nanoporous Au/Pt sphere electrocatalysts increases with the decrease of Au particles size in the samples. The nanoporous hollow structure of the electrocatalysts improves the efficiency for electro-oxidation of methanol and ethanol. More importantly, the nanoporous H-PtAu electrocatalysts have a higher catalytic activity and better steady-state performance for ethanol oxidation than methanol.     

A membraneless microscale fuel cell using non-noble catalysts in alkaline solution

This paper presents the development of a novel liquid-based microscale fuel cell using non-noble catalysts in an alkaline solution. The developed fuel cell is based on a membraneless structure. The operational complications of a proton exchange membrane lead the development of a fuel cell with the membraneless structure. Non-noble metals with relatively mild catalytic activity, nickel hydroxide and silver oxide, were employed as anode and cathode catalysts to minimize the effect of cross-reactions with the membraneless structure. Along with nickel hydroxide and silver oxide, methanol and hydrogen peroxide were used as a fuel at anode and an oxidant at cathode. With a fuel mixture flow rate of 200 μl min⁻¹, a maximum output power density of 28.73 μW cm⁻² was achieved. The developed fuel cell features no proton exchange membrane, inexpensive catalysts, and simple planar structure, which enables high design flexibility and easy integration of the microscale fuel cell into actual microfluidic systems and portable applications.     

甲醇发动机的点火正时和喷射正时优选的试验研究

缸内喷射、火花助燃甲醇发动机是在缸内形成一种层状分布的不均匀混合气，为获得优良的燃烧和排放性能，存在一个最佳的点火和喷射正时。此时着火延迟期最短，缸内混合气浓、稀分布最合理，平均火焰传播速度最快，热效率最高，效率和排放折衷最好。本文详细介绍了点火正时和喷射正时的优选过程及对缸内混合气浓度分布及燃烧过程的影响。     

生物柴油/甲醇混合燃料对柴油机性能与排放的影响研究

在一台4缸直喷式柴油机上研究了超低硫柴油、生物柴油及后者与甲醇的混合燃料对发动机性能、气体及微粒排放的影响。生物柴油由餐饮废油制取,除单独使用外和甲醇按体积比90：10和80：20混合后使用。在最大扭矩转速1800 r.m in-1时,在5个不同负荷下,比较了不同燃料热效率及CO、HC、NOx以及微粒质量浓度,微粒的总数量及平均几何粒径。结果表明,和超低硫柴油相比,生物柴油及其和甲醇的混合燃料的热效率增加,NOx和微粒质量、数量浓度的排放降低,但HC、CO和NO2排放升高;同时,随着甲醇混合比例的增加,HC、CO和NO2的排放成比例增加,微粒的质量浓度及数量浓度进一步降低,热效率及NOx几乎保持不变。     

Comparative LCA of methanol-fuelled SOFCs as auxiliary power systems on-board ships

Fuel cells own the potential for significant environmental improvements both in terms of air quality and climate protection. Through the use of renewable primary energies, local pollutant and greenhouse gas emissions can be significantly minimized over the full life cycle of the electricity generation process, so that marine industry accounts renewable energy as its future energy source. The aim of this paper is to evaluate the use of methanol in Solid Oxide Fuel Cells (SOFC), as auxiliary power systems for commercial vessels, through Life Cycle Assessment (LCA). The LCA methodology allows the assessment of the potential environmental impact along the whole life cycle of the process. The unit considered is a 20 kWel fuel cell system. In a first part of the study different fuel options have been compared (methanol, bio-methanol, natural gas, hydrogen from cracking, electrolysis and reforming), then the operation of the cell fed with methanol has been compared with the traditional auxiliary power system, i.e. a diesel engine. The environmental benefits of the use of fuel cells have been assessed considering different impact categories. The results of the analysis show that fuel production phase has a strong influence on the life cycle impacts and highlight that feeding with bio-methanol represents a highly attractive solution from a life cycle point of view. The comparison with the conventional auxiliary power system shows extremely lower impacts for SOFCs.     

Nano-sized Fe2O3–SO4 solid superacid composite Nafion membranes for direct methanol fuel cells

In this paper, Fe₂O₃–SO₄²⁻/Nafion^® composite membranes were prepared by a solution casting method. The physico-chemical properties of composite membranes were characterized by X-ray diffraction (XRD), SEM–EDX and thermogravimetric analysis (TGA). The water uptake ability, proton conductivity, and methanol permeability of the composite membranes were evaluated and compared with the recast Nafion^® membrane. The results showed that the proton conductivity and the water uptake of the composite membranes were slightly higher than that of the recast Nafion^® membrane. The composite membrane containing 5 wt.% Fe₂O₃–SO₄^2- showed superior ability to suppress methanol crossover, and it further improved the direct methanol fuel cell (DMFC) performances with both 1 M and 5 M methanol feeding, compared with the recast Nafion^® membrane. The preliminary 30 h lifetime test of the DMFC with the composite membrane with 5% Fe₂O₃–SO₄²⁻ indicated that the composite membrane is stable working at the real DMFC operating conditions at least during the test. These results suggest the applicability of the composite membranes in DMFCs.