The effect of methanol on the stability of Pt/C and Pt–RuOx/C catalysts

The behavior of Pt/C and Pt–RuO_x/C electrodes subjected to a larger number of potential scans and constant potential for prolonged time periods was investigated in the absence and presence of methanol. The structural changes were analyzed on the basis of the modifications observed in the X-ray diffraction pattern of the catalysts. Carbon monoxide stripping experiments were performed before and after the potential scans, thus enabling analysis of the behavior of the electrochemically active surface area. The resulting solutions were examined by inductively coupled plasma mass spectrometry (ICP-MS). There was reduction in the electrochemically active surface area, as well as increase in crystallite size and dissolution of catalyst components after the potential scan tests. Catalyst degradation was more pronounced in the presence of methanol, and cyclic potential conditions accelerate the degradation mechanisms.     

Improving the performance of PtRu/C catalysts for methanol oxidation by sensitization and activation treatment

PtRu/C anode electrocatalysts for direct methanol fuel cells (DMFCs) have been prepared by electroless deposition with the pretreatment of Sn²⁺/Sn⁴⁺ sensitization and Pd activation. The as-prepared catalysts were composed of well dispersed PtRu alloy nanoparticles with relatively homogeneous size distribution, which were characterized by instrumental analyses, such as XRD, TEM, HRTEM and EDX. Electrochemical measurements demonstrated that the PtRu/C catalysts obtained with sensitizing and activating pretreatment exhibited an enhanced peak current density of 34% for methanol electrooxidation as compared to that synthesized without pretreatment.     

High conductivity and surface area of Ti0.7W0.3O2 mesoporous nanostructures support for Pt toward enhanced methanol oxidation in DMFCs

For the first time, a novel Pt catalyst supported on mesoporous Ti_0.7W_0.3O₂ nanoparticles, which exhibited superior advantages such as high conductivity (0.022 S/cm), large specific surface area (201.481 m²/g) and homogeneous morphology with 9 nm spherical-like particles, was prepared successfully via the rapid microwave-assisted polyol route. It is found that uniform 3 nm spherical-like Pt nano-forms were adhered homogeneous on the surface of Ti_0.7W_0.3O₂. Intriguingly, the electrochemical surface area of Pt catalyst supported on mesoporous Ti_0.7W_0.3O₂ was found to be around 90.05 m²/gPt, which is profoundly higher than ECSA value obtained from Pt/C (E-TEK) catalyst. Furthermore, as for methanol oxidation reaction measurement, the I_f/I_b ratio of the 20 wt % Pt/Ti_0.7W_0.3O₂ catalyst was found to be approximately 2.33, which 2.5-folds higher than that of the commercial Pt/C (E-TEK) catalyst. Importantly, the chronoamperometry data also revealed that the 20 wt % Pt/Ti_0.7W_0.3O₂ catalyst possessed the higher durability than the commercial 20 wt % Pt/C (E-TEK) catalyst. In addition, the successful synthesis of the 20 wt % Pt/Ti_0.7W_0.3O₂ catalyst not only offers an attractive catalyst for fuel cell using methanol but also opens application potentials for solar cells, as well as biosensors.     

The optimization performance of cross‐linked sodium alginate polymer electrolyte bio‐membranes in passive direct methanol/ethanol fuel cells

Consumption of methanol and ethanol as a fuel in the passive direct fuel cells technologies is suitable and more useful for the portable application compared with hydrogen as a preliminary fuel due to the ease of management, including design of cell, transportation, and storage. However, the cost production of commercial membrane is still far from the acceptable commercialization stage. Based to our previous works, the low cost of cross‐linked sodium alginate (SA) polymer electrolyte bio‐membrane shown the virtuous chemical, mechanical, and thermal characterization as polymer electrolyte membrane in the direct methanol fuel cells (DMFCs). This study will further the investigation of cross‐linked SA polymer electrolyte bio‐membrane performance in the passive DMFCs and the passive direct ethanol fuel cells (DEFCs). The experimental study investigates the influence of the membrane thickness, loading of catalysts, temperature, type of fuel, and fuel concentration in order to achieve the optimal working operation performances. The passive DMFCs is improved from 1.45 up to 13.5 mW cm^?2 for the maximum peak of power density, which is obtained by using 0.16 mm as an optimum thick of SA bio‐membrane that shown the highest selectivity 6.31 10⁴ S s cm^?3, 4 mg cm^?2 of Pt‐Ru as an optimum of anode catalyst loading, 2 mg cm^?2 of Pt at the cathode, 2M of methanol as an optimum fuel concentration, and an optimum temperature at 90°C. Under the same conditions of cells, the passive DEFCs are shown to be 10.2 mW cm^?2 in the maximum peak of power density with 2M ethanol. Based on our knowledge, this is the first work that reports the optimization works of performance SA‐based membrane in the passive DMFCs via experimental studies of single cells and the primary performance of passive DEFCs using the SA‐based membrane as polymer electrolyte membrane.     

Sulfonated poly(ether ether ketone)/clay-SO3H hybrid proton exchange membranes for direct methanol fuel cells

A new type of sulfonated clay (clay-SO₃H) was prepared by the ion exchange method with the sulfanilic acid as the surfactant agent. The grafted amount of sulfanilic acid in clay-SO₃H was 51.8 mequiv. (100 g)⁻¹, which was measured by thermogravimetric analysis (TGA). Sulfonated poly(ether ether ketone) (SPEEK)/clay-SO₃H hybrid membranes which composed of SPEEK and different weight contents of clay-SO₃H, were prepared by a solution casting and evaporation method. For comparison, the SPEEK/clay hybrid membranes were produced with the same method. The performances of hybrid membranes for direct methanol fuel cells (DMFCs) in terms of mechanical and thermal properties, water uptake, water retention, methanol permeability and proton conductivity were investigated. The mechanical and thermal properties of the SPEEK membranes had been improved by introduction of clay and clay-SO₃H, obviously. The water desorption coefficients of the SPEEK and hybrid membranes were studied at 80 °C. The results showed that the addition of the inorganic part into SPEEK membrane enhanced the water retention of the membrane. Both methanol permeability and proton conductivity of the hybrid membranes decreased in comparison to the pristine SPEEK membrane. However, it was worth noting that higher selectivity defined as ratio of proton conductivity to methanol permeability of the SPEEK/clay-SO₃H-1 hybrid membrane with 1 wt.% clay-SO₃H was obtained than that of the pristine SPEEK membrane. These results showed that the SPEEK/clay-SO₃H hybrid membrane with 1 wt.% clay-SO₃H had potential usage of a proton exchange membrane (PEM) for DMFCs.     

Laser-perforated anode gas diffusion layers for direct methanol fuel cells

Novel anode gas diffusion layers (AGDLs) with both hydrophobic and hydrophilic pathways are created to enhance transfer of both methanol and CO₂. Such AGDLs are created by perforating PTFE-treated AGDLs with laser, so that the original pores/pathways in the AGDL are hydrophobic and the laser perforations are hydrophilic, thus providing easy transport paths for both the liquid methanol solution and CO₂. One of the novel AGDLs has increased the cell performance by 32% over the non-perforated AGDL. Results of electrochemical impedance spectroscopy (EIS) show that the main reason for the performance enhancement is due to the reduction in mass transfer resistance. Additionally, there is a reduction in charge transfer resistances due to the enhanced methanol transfer to the catalyst layer. The results of linear sweep voltammetry (LSV) show that the perforations increase methanol crossover, thus if perforation density of the AGDL is too high, the cell performances are lower than that of the virgin AGDL.     

Evaluation of Quaternized polyvinyl alcohol/graphene oxide-based membrane towards improving the performance of air-breathing passive direct methanol fuel cells

Graphene oxide (GO) nanosheets are introduced to a Quaternized polyvinyl alcohol (QPVA) polymer matrix to obtain an anion exchange membranes (AEMs) for application of fuel cells. QPVA/GO nanocomposite membranes provide desirable properties such as low fuel uptake and permeability, excellent ionic conductivity, and cell performance, all of which are favorable for AEMs based on our previous works. Passive direct methanol fuel cells (DMFCs) are recognized as suitable technologies for use in portable devices. Nevertheless, the commercialization of DMFCs remains restricted due to a number of issues related to the conventional membrane; one of these issues is high fuel crossover problems due to high fuel uptake and permeability of Nafion membrane. This study aimed to expand the potential applications of QPVA/GO nanocomposite membranes in air-breathing passive DMFCs. The ionic conductivity, methanol uptakes (MUs), and permeabilities of self-synthesis QPVA/GO nanocomposites are examined to evaluate the ability to operate in methanol atmosphere. At 30°C, the ionic conductivity of the membranes reached 1.74 × 10⁻² S cm⁻¹. The MUs and permeabilities were as low as 35% and 7.6 × 10⁻⁷ cm² s⁻¹, respectively. The performance of air-breathing passive DMFCs bearing QPVA/GO nanocomposite membrane is much higher compared to conventional membranes. The maximum power density of air-breathing passive DMFCs was achieved 27.2 mW cm⁻² under the optimum condition of 2 M methanol + 4 M KOH at 70°C. Single-cells could be sustained for 1000 hours. This article is the first to optimize and highlight the performance air-breathing passive DMFCs by using a QPVA-based membrane.     

Methanol oxidation on carbon-supported Pt-Ru and TiO2 (Pt-Ru/TiO2/C) electrocatalyst prepared using polygonal barrel-sputtering method

Methanol oxidation performance of a carbon-supported Pt-Ru alloy catalyst used at the direct methanol fuel cell (DMFC) anode is improved by adding TiO₂. However, the methanol oxidation performance of the electrocatalyst described above must be enhanced further to realize practical application in DMFCs. In this study, we used our original surface-modifying technique termed the “polygonal barrel-sputtering method” to prepare a carbon-supported Pt-Ru and TiO₂ (Pt-Ru/TiO₂/C) electrocatalyst offering higher methanol oxidation performance. The obtained results show that the methanol oxidation performance of the prepared Pt-Ru/TiO₂/C is superior to that using wet process as the TiO₂ deposition method. Furthermore, for our sputtering method, the peak current of methanol oxidation on the Pt-Ru/TiO₂/C is enhanced by increasing the TiO₂ deposited amount up to 2.8 wt.%. These results suggest that a Pt-Ru/TiO₂ interface area is increased using the polygonal barrel-sputtering method, providing the high methanol oxidation performance of Pt-Ru/TiO₂/C.     

催化层与扩散层热压结合对DMFCs性能的影响

通过压汞法(MIP),交流阻抗法(EIS)研究了催化层和扩散层之间的结合条件对直接甲醇燃料电池(DMFCs)性能和稳定性的影响.结果表明,将采用转压法制备的膜电极与扩散层热压结合可以优化阴极扩散层的孔径结构,形成有利于水从阴极到阳极传输的返水结构,降低了传质阻抗,改善了在常压低化学计量比空气进料条件下阴极容易水淹的问题,显著提高了DMFCs单电池的性能和稳定性.     

DMFC甲醇渗透问题的研究进展

直接甲醇燃料电池（DMFC）是一种不需要燃料重整器而以甲醇直接进料的电化学装置。DMFCs的技术水平目前处于大规模商业化的准备阶段。鉴于DMFC商业化的主要障碍之一是甲醇渗透问题，全面解决甲醇渗透问题取决于许多因素，重点有以下几个方面：（1）改进电解质隔膜性能，（2）控制甲醇进料浓度，（3）改善电极催化活性，（4）改进MEA的结构及电池组装技术，（5）用其他醇取代甲醇，（6）用阴离子交换膜取代Nation膜开发碱性DMFC。提供一种质子传导率高，而又能显著降低甲醇渗透率的新型质子膜是上述诸因素中最有效的措施之一。