Comparison of Pt and Pd anode catalysts supported on nanocrystalline Ru–SnO2 for ethanol oxidation in fuel cell applications

The article presents promising catalysts, applicable for direct alcohol fuel cells (DAFC) for portable and mobile applications. The goal of this work is development of Pt and Pd catalysts deposited on interactive nanocrystalline Ru doped SnO₂ support with improved performance. The structure and the morphology of the prepared metal-oxide catalyst support and Pt and Pd based catalysts were examined using XRPD, SEM/EDX and TEM techniques. Electrocatalytic activities of the prepared Pt or Pd based catalysts were evaluated in both alkaline and acidic conditions. The ethanol oxidation reaction (EOR) was studied using conventional electrochemical techniques. The interactive nature of the novel Ru doped SnO₂ catalyst support was confirmed, resulting in the enhancement of the EOR kinetics, in comparison to commercially available catalysts. New and simplified synthetic route applied for preparation of interactive catalyst support was presented with the aim to enable easy scale-up of the catalyst production process. Obtained results on the novel catalysts promise great potential in improving the performance and durability of the DAFC.     

Frustrated Lewis pair engineering on ceria to improve methanol oxidation activity of Pt for direct methanol fuel cell applications

Practical application of direct methanol fuel cell (DMFC) technology is greatly hindered by the strong dependence of anodic methanol oxidation reaction (MOR) on precious Pt based catalyst and the unsatisfying performance of Pt. Therefore, increasing the utilization and the catalytic performance of Pt toward MOR in DMFC is urgent. Here in this work, CeO₂ is modified via a plasma-phosphating combing strategy and is invited as Frustrated Lewis Pair to assist the catalytic MOR process on Pt sites. Simultaneously, the plasma-phosphating combing strategy leads to negatively charged sites on CeO₂ surface, which can be functioned as host for Pt anchoring, facilitating the even dispersion of Pt nanocrystals. Besides, this strategy also has an effect on the Ce³⁺/Ce⁴⁺ ratio and vacancy oxygen ratio on CeO₂ surface, which are critical to the adsorbed OH generation and anti-CO poisoning ability, thus boosting the MOR catalytic activity of Pt. DMFC device therefore exhibits ca. 30% maximum power density enhancement compared with the commercial Pt/C based DMFC.     

Performance of sputter-deposited platinum cathodes with Nafion and carbon loading for direct methanol fuel cells

One of the difficulties for a direct methanol fuel cell (DMFC) is low catalyst utilization efficiency because a certain amount of Pt loading is inactive as the catalyst. Sputter-deposited Pt electrodes are expected to improve mass activities for oxygen reduction reaction (ORR) compared with those prepared by a conventional method. Meanwhile, mass activities of sputter-deposited Pt cathodes for the ORR decreased with an increase in amount of Pt loading. In this study, the loading of protonic and electronic conductors to improve mass activities of sputter-deposited Pt electrode were investigated as cathodes for DMFCs.     

Defect configuration of ceria for Pt anchoring toward efficient methanol oxidation

As a potential next-generation power source for portable electronic devices, commercialization process of direct methanol fuel cell (DMFC) technology is hindered by the high dependence of anode methanol oxidation reaction (MOR) on precious Pt catalyst. In order to improve the efficiency of Pt toward MOR catalysis, a Ni doping strategy is proposed for defect engineering on ceria substrate to achieve uniform dispersion of Pt nanoparticles. Besides, Ni could also act as electron donor for Pt and hence favor the removal of CO intermediate on Pt and act as a co-catalyst toward MOR. Superior MOR activity and great stability is therefore achieved for the as-prepared Pt/CeO₂@Ni catalyst with 3 times higher peak MOR current density compared with Pt/C catalyst. Due to the evenly anchored Pt and enhanced CO oxidation ability caused from Ni doped ceria substrate, Pt utilization of the Pt/CeO₂@Ni catalyst is calculated to be 3.24 times higher than that of the commercial Pt/C catalyst. By considering the significantly improved stability, the Pt/CeO₂@Ni catalyst has the potential for application in DMFC devices.     

High-efficiency carbon-supported platinum catalysts stabilized with sodium citrate for methanol oxidation

A high-efficiency platinum catalyst stabilized with sodium citrate for methanol oxidation is introduced in this paper, in which freshly prepared non-noble active cobalt is employed as reducer. According to X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements, the novel as-prepared nanoclusters Pt catalyst dispersed on carbon is composed of Pt nanoparticles, and the average particle size of the Pt nanoparticles is 2.0 nm. The catalyst with sodium citrate shows a very high electrochemically active surface area and significant increase electrocatalytic activity towards methanol oxidation, which indicates that it would be a better potential candidate for application in a direct methanol fuel cell (DMFC).     

Fabrication and evaluation of passive alkaline membraneless microfluidic DMFC

The fabrication and evaluation of a passive, air-breathing, membraneless microfluidic direct methanol fuel cell (ML-μDMFC) using a methanol-tolerant Ag/Pt/CP cathode is presented here. We previously proposed that due to its high tolerance to methanol and the good activity towards the oxygen reduction reaction in alkaline medium, this catalyst could be useful to reduce the methanol crossover effect in direct methanol fuel cells. Therefore, in order to demonstrate it, we designed and fabricated a microfluidic device that allowed the evaluation of the cathode in a high fuel concentration environment, using up to 5 M MeOH in 0.5 M KOH in passive mode. The results confirmed the high tolerance to MeOH and the ORR selectivity of the Ag/Pt/CP cathode, in contrast with a Pt/CP cathode, where performance decreased severely due to the methanol crossover. Employing the methanol-tolerant cathode, it was possible to obtain a power density of 2.4 mW cm⁻². Additionally, the durability studies revealed more stability for the ML-μDMFC using the bimetallic catalyst, compared with Pt/CP.     

Fabrication and characterization of gold nanoparticles and fullerene-C60 nanocomposite film at glassy carbon electrode as potential electro-catalyst towards the methanol oxidation

Development of low cost anodic materials and high efficient electro-kinetics of methanol in direct methanol fuel cell (DMFC) has been a promising approach. However it has not been successfully reached to market from laboratory due to its high cost and low kinetic oxidation. Both issues encounter from one of its main components, the catalyst. Therefore, present work focuses upon the development of new catalyst material and optimization of various most significant influencing parameters of a high performance DMFC. We have developed a nanocomposite material employing gold nanoparticles and fullerene-C₆₀ at glassy carbon electrode (AuNP@reduced-fullerene-C₆₀/GCE) as anode for high performance oxidation of methanol. Fullerene-C₆₀ was manually dropped on pre treated GCE and partially electro-reduced in KOH to make it more conductive. Gold nanoparticles (AuNPs) were deposited on reduced-fullerene-C₆₀ modified electrode using cyclic voltammetry (CV). Electrochemical characterization techniques such as CV, electrochemical impedance spectroscopy (EIS) and chronocoulometry were used to characterize modified electrode. Modified electrode was also characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) for morphological properties. The electrochemical behavior of methanol was performed in alkaline medium using CV and chronoamperometry methods. The results revealed good electrocatalytic performance and better stability than previously reported catalysts using AuNP@reduced-fullerene-C₆₀ catalyst, suggesting making promising anodic material for direct methanol oxidation fuel cell.     

Microfluidic direct methanol fuel cell by electrophoretic deposition of platinum/carbon nanotubes on electrode surface

Carbon nanotubes (CNTs) supported platinum (Pt) nanoparticles prepared via electrophoretic deposition are used as catalyst layer of a microfluidic direct methanol fuel cell (DMFC), to study the influence of catalyst layer materials and deposition methods on the cell performance. A Y‐shaped channel is designed and microfabricated. It is verified by cyclic voltammetric measurements that shows ca. 317.7% increase in the electrochemical active surface area for the electrode with CNTs over that without CNT. Scanning electron microscopy observations indicate the network formation within the electrode because of a 3‐D structure of CNTs, which could be beneficial to the increasing electrode kinetics and to the improvement in fuel utilization. Comparison between the DMFCs with and without CNTs as support shows that the proof‐of‐concept microfluidic DMFC with Pt/CNTs electrode is able to reach a maximum power density of 5.70 mW cm^?2 at 25 °C, while the DMFC with plain Pt electrode only has a maximum power density of 2.75 mW cm^?2. Copyright © 2015 John Wiley & Sons, Ltd.     

Performance of direct ammonia fuel cell with PtIr/C,PtRu/C,and Pt/C as anode electrocatalysts under mild conditions

While ammonia (NH₃) is an attractive alternative to pure hydrogen, its direct use in fuel cells is fraught with difficulties. A direct ammonia fuel cell (DAFC) with PtIr/C (Pt:Ir = 1:1), PtRu/C (Pt:Ru = 1:1), and Pt/C anode electrocatalyst was investigated at 25 °C and 100 kPa inlet gas pressure. Due to the synergistic and electronic effects of the PtIr alloy, their open-circuit voltages (OCVs) were rated as PtIr/C > PtRu/C > Pt/C, with the DAFC with PtIr/C anode achieving the highest OCV of 0.50 V and peak power density (PPD) of maximum 1.68 mW cm^?2. Meanwhile, an online Fourier transform infrared (FTIR) spectrometer detected an increase in ammonia permeation in the cathode exhaust gas, indicating a possibility of fuel permeation and cathode electrocatalyst degradation. The degradation of DAFC efficiency with rising cycle numbers may be due to ammonia cross-over and poisoning over the surface of the electrocatalyst.     

Application of N-doped carbon nanotube-supported Pt-Ru as electrocatalyst layer in passive direct methanol fuel cell

In this research, nitrogen-doped carbon nanotubes (N-CNT) were prepared through the low-temperature thermal method and used as the support material for the bimetallic catalyst PtRu and Pt nanoparticles. A passive single-cell direct methanol fuel cell (DMFC) was designed and fabricated to investigate and compare the performance of three discrete membrane electrode assemblies (MEA) with carbon black (CB), CNT, and N-CNT as the catalyst support, respectively. Adding N to the structure of CNTs remarkably improves the physical and electrochemical characteristics of the catalyst. More active sites and stronger interaction between support and metal particles lead to the formation of smaller metal clusters and higher surface area as well as superior electrochemical activity. Compared to PtRu/CB and PtRu/CNT, PtRu/N-CNT illustrate 32% and 12% higher surface area, 3 and 1.9 times higher MOR activity, and 62% and 18% higher power output (26.1 mW/cm²), respectively. Moreover, it is revealed that PtRu/N-CNT has long-term stability in the MOR. The research work presented in this paper exhibits the outstanding performance of Pt and PtRu supported on N-CNT in a passive single-cell DMFC.     

Platinum supported on hydroxyl-grafted poly (3,4-ethylenedioxythiophene)-modified RuCo,N-tridoped bamboo-like carbon nanotubes for direct methanol fuel cell

The development of highly active and efficient heterogeneous catalytic oxidation system has become an attractive research field. In this paper, a catalyst (RuCo/N-CNT@PEDOT-OH/Pt) from platinum nanoparticles (Pt NPs) supported on hydroxyl-grafted poly(3,4-ethylenedioxythiophene) (PEDOT–OH)-modified RuCo, N-tridoped bamboo-like carbon nanotubes (RuCo/N-CNT) are used for direct methanol fuel cell (DMFC). The electrocatalytic activity of RuCo/N-CNT@PEDOT-OH/Pt is systematically compared with RuCo/N-CNT/Pt (Pt NPs supported on RuCo/N-CNT without PEDOT-OH) in the methanol oxidation reaction (MOR). The growth mechanism of carbon nanotubes and the role of heteroatom doping in the electrocatalytic process is explored. The catalysts show excellent electrocatalytic performance with high stability for MOR. It is found that the mass activity (MA) of the RuCo/N-CNT@PEDOT-OH/Pt (1961.3 mA mg^?1_Pt) for MOR was higher than that of RuCo/N-CNT/Pt (1470.1 mA mg^?1_Pt) and the commercial Pt/C catalysts (281.0 mA mg^?1_Pt), indicating the positive effect of the PEDOT-OH in the electrocatalytic MOR. In addition, density functional theory (DFT) calculations verify the possible mechanism pathways of the obtained RuCo/N-CNT@PEDOT-OH/Pt catalyst. This presented catalyst offers new inspiration for designing efficient electrocatalysts for methanol oxidation.     

Sulfated zirconium oxide as electrode and electrolyte additive for direct methanol fuel cell applications

Sulfated zirconium oxide (S-ZrO₂) was used as electrode and electrolyte additive for direct methanol fuel cells (DMFCs). Composite Nafion electrolyte membranes and Pt electrocatalysts, both containing S-ZrO₂ at different content, were prepared. The morphology and catalytic activity of prepared catalysts were investigated by scanning electron microscopy, and voltammetric technique. Results indicated that Pt/S-ZrO₂ catalysts showed enhanced efficiency towards oxygen reduction reaction and increased methanol tolerance as compared to bare platinum. Pt/S-ZrO₂-based carbon cloth electrodes were prepared and assembled as cathode in a DMFC, with Nafion/S-ZrO₂ as composite electrolyte membrane. With respect to bare platinum and Nafion, higher values of current and power density were recorded at 110 °C. The use of S-ZrO₂ both as catalyst and electrolyte additive provided enhanced membrane/electrode interface stability, as revealed by EIS spectra recorded during cell operation.     

Engineering aspects of the direct methanol fuel cell system

The direct methanol fuel cell presents several interesting scientific and engineering problems. There are many engineering issues regarding eventual application concerning cell materials, feed and oxidant requirements, fuel utilisation and recovery, scale up, etc. This paper looks at several of these issues starting from the point of current, typical, cell performance. A small-scale flow cell and a large scale cell, both with a parallel channel flow bed design, are used. The structure of the direct methanol fuel cell (DMFC) is a composite of two porous electrocatalytic electrodes; Pt–Ru–C catalyst anode and Pt–C catalyst cathode, on either side of a solid polymer electrolyte (SPE) membrane. Flow visualisation on small scale and intermediate scale (100 cm²) cells has been used in the design of a new large-scale cell of 225 cm² active area. We discuss several important engineering factors in the successful design of large scale DMFCs including the use of vapour and liquid feeds, thermal management, gas management, methanol fuel management, hydrodynamics and mass transport.     

Three-dimensional porous PtCu as highly efficient electrocatalysts for methanol oxidation reaction

Exploring affordable, durable, and effective electrocatalysts for methanol oxidation reaction (MOR) is of great importance to the industrial application of direct methanol fuel cells. Herein, a three-dimensional (3D) porous PtCu catalyst is synthesized by a facile and effective galvanic replacement method, which exhibits high activity and durability for MOR. The modulated electronic and strain effects of the Pt atoms are verified by extensive characterizations, and the mass and specific activities of the prepared catalyst are roughly 3.8 and 9.9 times higher than those of the commercial Pt/C catalysts, respectively. The robust activity of the prepared catalyst is probably owing to the optimized affination between Pt and the adsorbed poisoning species (mainly CO) induced by the electronic and strain effects of the Pt, as well as the unique 3D porous nanostructure.     

Electrochemically synthesized polypyrrole/MWCNTs-Al2O3 ternary nanocomposites supported Pt nanoparticles toward methanol oxidation

As known, a good support enhances the activity and durability of any catalyst. In the current study, polypyrrole (PPY)/nanocomposite (MWCNTs and Al₂O₃) films were fabricated by electrochemical polymerization of pyrrole solution with a certain amount of nanoparticles on titanium substrates and were used as new support materials for Pt catalyst. The modified electrodes were characterized by Fourier transform infrared (FT-IR) spectroscopy, field-emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis (EDX) techniques. High catalytic activity and long-time stability toward methanol oxidation of Pt/PPY–MWNTs-αAl₂O₃ catalyst have also been verified by cyclic voltammetry results and chronoamperometric response measurements. This catalyst exhibits a vehemently high current density (345.03 mA cm^?2) and low peak potential (0.74 v) for methanol oxidation. Other electrochemical measurements (electrochemical impedance spectroscopy (EIS), CO stripping voltammetry and Tafel test) clearly confirmed that Pt/PPY–MWNTs-αAl₂O₃/Ti electrode has a better performance toward methanol oxidation compared to the other electrodes and that can be used as a promising electrode material for application in direct methanol fuel cells (DMFCs).     

Simplified model for the direct methanol fuel cell anode

A kinetic model for the anode of the direct methanol fuel cell (DMFC) is presented. The model is based on the generally accepted dual site mechanism of methanol oxidation, in aqueous solution, on well characterized Pt–Ru catalyst and it can predict the performance of the electrode as a function of cell temperature, anode potential and methanol concentration. In addition the model also generates data regarding the surface coverage of significant adsorbates involved in methanol oxidation on the dual site catalyst.     

A novel TiN coated CNTs nanocomposite CNTs@TiN supported Pt electrocatalyst with enhanced catalytic activity and durability for methanol oxidation reaction

The application of direct methanol fuel cells (DMFCs) is hampered by not only low activity but also poor stability and poor CO tolerance by the Pt catalyst. Herein, a novel titanium nitride coated multi-walled carbon nanotubes (CNTs@TiN) hybrid support was successfully synthesized by a facile solvothermal process followed by a nitriding process, and this hybrid support was used as Pt support for the oxidation of methanol. The structure, morphology and composition of the synthesized CNTs@TiN exhibits a uniform particle perfect coating with high purity and interpenetrating network structure. Notably, Pt/CNTs@TiN also showed excellent stability, experiencing only a slight performance loss after 5000 potential cycles. The onset potential (0.34 V) of CO oxidation on Pt/CNTs@TiN is obviously more negative than that on the Pt/TiN (0.38 V) and Pt/CNTs (0.48 V) in the first forward scan. In the Pt 4f XPS spectra, plentiful Pt atoms existed as Pt(II) in the Pt/CNTs and Pt/TiN catalysts, while a relatively smaller amount of Pt(II) was observed in the Pt/CNTs@TiN catalyst. The synthetic Pt/CNTs@TiN catalyst was studied with respect to its electrocatalytic activity and durability and CO tolerance toward methanol oxidation might be mainly attributed to the strongly coupled Pt–TiN and the fast electron-transport network structure. This work may provide more insight into developing novel catalyst supports of various transition metal nitrides coated CNTs for DMFCs with high activity and good durability and excellent CO tolerance.     

Evaluation of silver as a miniature direct methanol full cell electrode

Miniature direct methanol fuel cells (DMFCs) and direct hydrogen fuel cells are promising candidates for future polymer electrolyte membrane (PEM) based micro-power sources. Currently, most miniature DMFCs are developed using a silicon based microelectromechanical system (MEMS) technique, which requires complex and precise processing. Low temperature cofire ceramic (LTCC) technology offers an attractive alternative for a ceramics MEMS construction, allowing the integration of high density interconnect and embedded electronic components with microchannels and hermetic cavities from the meso- to the microscale. Silver is a major metallization source for LTCC, which can be fabricated in a range of configurations, from a solid hermetic layer to a porous open structure with microchannels that can easily be integrated into the structures. Silver based LTCC provides an ideal technology for the fabrication of an integrated fuel cell into a high density ceramic-based microelectronic assembly. A silver electrode was evaluated in a simulated DMFC operating environment and found to exhibit good corrosion resistance and chemical stability, essential properties for electrode systems. Potentiodynamic analysis of a catalyzed silver electrode (prepared by thermal decomposition of a Pt/Ru resinate) revealed excellent corrosion resistance under anodic and cathodic DMFC operating conditions. The Pt/Ru catalyst on the silver electrode enhanced the methanol oxidation reaction (MOR) as well as oxygen reduction reaction (ORR) as compared with similar reactions on carbon electrodes. The potential at which methanol is oxidized was lower than the silver oxidation potential, which served to protect the silver electrode. The determination of a contact angle of 30° on the silver electrode indicated wettability, which is deleterious for its application in DMFCs. Nevertheless, the results of good corrosion resistance derived from this investigation as well as the high electrical and thermal conductivities of silver all auger well for it usage as an electrode in DMFC.     

Electrochemical study of platinum deposited by electron beam evaporation for application as fuel cell electrodes

Platinum is the most used catalyst in electrodes for fuel cells due to its high catalytic activity. Polymer electrolyte and direct methanol fuel cells usually include Pt as catalyst in their electrodes. In order to diminish the cost of such electrodes, different Pt deposition methods that permit lowering the metal load whilst maintaining their electroactivity, are being investigated. In this work, the behaviour of electron beam Pt (e-beam Pt) deposited electrodes for fuel cells is studied. Three different Pt loadings have been investigated. The electrochemical behaviour by cyclic voltammetry in H₂SO₄, HClO₄ and in HClO₄ + MeOH before and after the Pt deposition on carbon cloth has been analysed. The Pt improves the electrochemical properties of the carbon support used. The electrochemical performance of e-beam Pt deposited electrodes was finally studied in a single direct methanol fuel cell (DMFC) and the obtained results indicate that this is a promising and adequate method to prepare fuel cell electrodes.     

直接液体甲醇燃料电池流场组织行为研究(Ⅰ) 传统对称流道电池的模型建立

建立了直接甲醇燃料电池垂直流道方向电池单元的二维稳态数学模型,考虑了电化学动力学、多组分传递和甲醇渗透影响.计算了流道布置密度、扩散层、催化层和质子交换膜等组件尺度对电池内物料传质特性、化学反应组织和电池输出性能的影响.研究发现,增加流道布置密度、增加催化层厚度能有效提高电极反应均匀性和电池性能.其中催化层和质子膜的厚度影响最为显著,在该文研究范围内分别可提高电池的平均电流密度131.0%和17.8%.而扩散层和质子交换膜厚度都存在一个最佳值,需要与以上流场板设计尺寸和膜电极尺寸匹配.