Zeolite supported Pd electrocatalyst nanoparticle characterization

A laboratory made 1.5 wt% Palladium (Pd) zeolite electrocatalyst is investigated using the Extended X-ray Adsorption Fine Structure (EXAFS) and Cyclic Voltammetry (CV) techniques to reveal Pd structure and resultant electrochemical performance. It was found that the electrochemical activity of hydrogen charger transfer in the hydride region increased for electrocatalyst with large-size particles made at high temperature of 400 °C, compared to those with small-size particles calcined and reduced at temperature below 360 °C, at which no major discrepancies were observed between catalysts of different sizes. Furthermore, Pd particle location has played an important role to enhance electrocatalyst performance. The Pd atom tends to remain at small cages, i.e. zeolite sodalite cages or hexagonal prisms at calcinations and reduction temperatures below 360 °C. When temperature increases to about 400 °C, the majority Pd atoms tend to migrate from zeolite small cages to supercages and zeolite external structures with enhanced electrochemical performance.     

Preparation and characterization of Pt supported on graphene with enhanced electrocatalytic activity in fuel cell

Pt nanoparticles are deposited onto graphene sheets via synchronous reduction of H₂PtCl₆ and graphene oxide (GO) suspension using NaBH₄. Lyophilization is introduced to avoid irreversible aggregation of graphene (G) sheets, which happens during conventional drying process. Pt/G catalysts reveal a high catalytic activity for both methanol oxidation and oxygen reduction reaction compared to Pt supported on carbon black (Pt/C). The performance of Pt/G catalysts is further improved after heat treatment in N₂ atmosphere at 300 °C for 2 h, and the peak current density of methanol oxidation for Pt/G after heat treatment is almost 3.5 times higher than Pt/C. Transmission electron microscope (TEM) images show that the Pt particles are uniformly distributed on graphene sheets. X-ray photoelectron spectroscopy (XPS) results demonstrate that the interaction between Pt and graphene is enhanced during annealing. It suggests that graphene has provided a new way to improve electrocatalytic activity of catalyst for fuel cell.     

Coal gas fuel utilization effects on electrolyte supported solide oxide fuel cell performance

Solid oxide fuel cells (SOFCs) transform the energy of the fuel instantly into electric energy with a large fuel option. Coal, which is a local energy source, is a preferred fuel despite its negative features because it is cheap and abundant. The use of coal and coal-based fuels in SOFCs has recently attracted considerable attention. In this study, performance analysis of the SOFC has been performed experimentally by using hydrogen, generator gas (contained 12% H₂), and water-gas (contained 50% H₂) in an electrolyte-supported SOFC (ES-SOFC). The numerical modelling of the fuel cell had been previously performed. In addition, the effect of inlet gas fuel flow rates on the ES- SOFC has been investigated numerically in this study. The temperature effect on the performance of ES-SOFC has been examined experimentally. It is seen that the performance of SOFCs fueled hydrogen is favorable than fueled water gas and generator gas. This is because of the higher hydrogen substance in the water gas measure against the other gas. In addition, it is seen that the increase in temperature increases the performance with positive effects on the reactions. It is also concluded that the performance of SOFC increases when inlet fuel flow rates increase.     

Synthesis and characterization of PtRuMo/C nanoparticle electrocatalyst for direct ethanol fuel cell

This research aims at enhancement of the performance of anodic catalysts for the direct ethanol fuel cell (DEFC). Two distinct DEFC nanoparticle electrocatalysts, PtRuMo/C and PtRu/C, were prepared and characterized, and one glassy carbon working electrode for each was employed to evaluate the catalytic performance. The cyclic-voltammetric, chronoamperometric, and amperometric current–time measurements were done in the solution 0.5 mol L⁻¹ CH₃CH₂OH and 0.5 mol L⁻¹ H₂SO₄. The composition, particle sizes, lattice parameters, morphology, and the oxidation states of the metals on nanoparticle catalyst surfaces were determined by energy dispersive analysis of X-ray (EDAX), X-ray diffraction (XRD), transmission electron micrographs (TEM) and X-ray photoelectron spectrometer (XPS), respectively. The results of XRD analysis showed that both PtRuMo/C and PtRu/C had a face-centered cubic (fcc) structure with smaller lattice parameters than that of pure platinum. The typical particle sizes were only about 2.5 nm. Both electrodes showed essentially the same onset potential as shown in the CV for ethanol electrooxidation. Despite their comparable active specific areas, PtRuMo/C was superior to PtRu/C in respect of the catalytic activity, durability and CO-tolerance. The effect of Mo in the PtRuMo/C nanoparticle catalyst was illustrated with a bifunctional mechanism, hydrogen-spillover effect and the modification on the Pt electronic states.     

Highly purified hydrogen production from ammonia for PEM fuel cell

Liquid ammonia is an attractive hydrogen carrier because of high storage capacity. According to ISO14687-2, an acceptable ammonia concentration in hydrogen for polymer electrolyte membrane (PEM) fuel cell vehicles is 0.1 ppm. When ammonia is used as the hydrogen carrier, about 1000 ppm of ammonia included in gas generated by ammonia decomposition at 773–823 K and 0.1 MPa has to be reduced to less than 0.1 ppm. Although several types of ammonia absorption materials are investigated as ammonia remover, the target value cannot be achieved by static adsorption methods. However, we have succeeded in that the ammonia concentration is reduced down to 0.01–0.02 ppm by using Li-exchange X-type zeolite (Li-X) as the absorbent and dynamic adsorption methods. Furthermore, Li-X is simply recycled by heating at 673 K. Therefore, Li-X is a durable and recyclable ammonia removal material for the highly purified hydrogen production from ammonia for PEM fuel cells.     

Highly stable Pt and PtPd hybrid catalysts supported on a nitrogen-modified carbon composite for fuel cell application

The durability and cost of fuel cell cathode catalysts are major technical barriers to the commercialization of fuel cells for vehicle applications. In this work, novel Pt and PtPd hybrid catalysts are developed that use a nitrogen-modified carbon composite (NMCC), which is itself active for the oxygen reduction reaction (ORR), instead of a conventional carbon black support. The fuel cell accelerated stress test (AST) for supports and catalysts demonstrated that the Pt₃Pd₁/NMCC and Pt/NMCC hybrid catalysts possess much higher stability than Pt/C catalysts in polymer electrolyte membrane (PEM) fuel cells. Moreover, the hybrid catalysts exhibit higher mass activity than the Pt/C catalysts. The origin of the hybrid catalysts’ improved performance relative to Pt/C is discussed in light of pore size distribution and surface area analysis, XRD, XPS, and TEM analyses and electrochemical measurements.     

Proton conducting composite membranes for fuel cell application

Composites were fabricated by blending SPSEBS (Sulfonated Poly Styrene Ethylene Butylene Poly Styrene) with Boron phosphate (BPO₄) for proton conducting applications in fuel cells. The effects of boron phosphate and its relative loading were analyzed in terms of IEC and proton conductivity. Water and methanol uptake of these membranes were also studied.The membranes were characterized by IR spectroscopy. Thermal stability was studied by TGA and DSC analyses. Surface morphology was done by Scanning Electron Microscopy (SEM). The XRD studies indicated the existence of a certain level of crystallinity in the SPSEBS, and the composite membranes. Mechanical strength of the membranes was measured by Universal Testing Machine (UTM). This paper presents the result of recent investigations to develop an optimised in-house membrane electrode assembly (MEA) preparation technique combining catalyst ink spraying and assembly hot pressing. Easy steps were chosen in this preparation technique aiming at simplification and cost reduction.     

Zeolite beta-filled chitosan membrane with low methanol permeability for direct methanol fuel cell

Zeolite beta particles with different sizes and narrow size distribution were hydrothermally synthesized and incorporated into chitosan (CS) matrix to prepare CS/zeolite beta hybrid membranes for direct methanol fuel cell (DMFC). It was found that the chitosan membrane filled by zeolite beta particles about 800 nm in size exhibited the lowest methanol permeability, which can be ascribed to their optimum free volume and methanol diffusion characteristics. To further improve the performances of CS/zeolite beta hybrid membranes, zeolite beta particles about 800 nm in size were sulfonated via three different approaches. The results indicated that the introduction of sulfonic groups could reduce the methanol permeability further as a result of the enhanced interfacial interaction between zeolite beta and chitosan matrix. Furthermore, in terms of the overall selectivity index, CS/zeolite beta hybrid membranes were comparable to Nafion^® 117 membrane at low methanol concentration (2 mol L⁻¹) and much better at high methanol concentration (12 mol L⁻¹).     

A novel cesium hydrogen sulfate-zeolite inorganic composite electrolyte membrane for polymer electrolyte membrane fuel cell application

A new type of CsHSO₄-HZSM-5 inorganic composite electrolyte membrane is prepared by mechanically mixing CsHSO₄ (CHS) and nanometer-scale HZSM-5 zeolite powders. The effects of HZSM-5 on the crystallite structure, proton conductivity, and thermal stability of the CsHSO₄ electrolyte are investigated. Incorporation of HZSM-5 is found to significantly increase the low-temperature proton conductivity of the CsHSO₄ electrolyte, extending its operating temperature down to 100 °C. The composite electrolyte with 40 mol% HZSM-5 shows the highest proton conductivity in the measured temperature range. The low-temperature activation energy of the composite with 40 mol% HZSM-5 is lower than that of the CHS-SiO₂ composite. The improvement of the proton conductivity can be attributed to the enhanced interfacial interaction between the two phases. And the small HZSM-5 particles lead to a change in the bulk properties of the ionic salts. The melting point of the CHS-HZSM-5 composite electrolyte is lower than that of the pure CHS electrolyte. The CHS-HZSM-5 composite electrolyte is suitable for polymer electrolyte membrane fuel cells operated at 100-200 °C.     

Methanol fuel processor and PEM fuel cell modeling for mobile application

The use of hydrocarbon fed fuel cell systems including a fuel processor can be an entry market for this emerging technology avoiding the problem of hydrogen infrastructure. This article presents a 1 kW low temperature PEM fuel cell system with fuel processor, the system is fueled by a mixture of methanol and water that is converted into hydrogen rich gas using a steam reformer. A complete system model including a fluidic fuel processor model containing evaporation, steam reformer, hydrogen filter, combustion, as well as a multi-domain fuel cell model is introduced. Experiments are performed with an IDATECH FCS1200™ fuel cell system. The results of modeling and experimentation show good results, namely with regard to fuel cell current and voltage as well as hydrogen production and pressure. The system is auto sufficient and shows an efficiency of 25.12%. The presented work is a step towards a complete system model, needed to develop a well adapted system control assuring optimized system efficiency.     

Thermally integrated fuel processor design for fuel cell applications

Effective thermal integration could enable the use of compact fuel processors with PEM fuel cell-based power systems. These systems have potential for deployment in distributed, stationary electricity generation using natural gas. This paper describes a concept wherein the latent heat of vaporization of H₂O is used to control the axial temperature gradient of a fuel processor consisting of an autothermal reformer (ATR) with water gas shift (WGS) and preferential oxidation (PROX) reactors to manage the CO exhaust concentration. A prototype was experimentally evaluated using methane fuel over a range of external heat addition and thermal inputs. The experiments confirmed that the axial temperature profile of the fuel processor can be controlled by managing only the vapor fraction of the premixed reactant stream. The optimal temperature profile is shown to result in high thermal efficiency and a CO concentration less than 40 ppm at the exit of the PROX reactor.     

A novel bifunctional electrocatalyst for unitized regenerative fuel cell

5 wt.% of platinum (Pt) nanoparticles are highly dispersed on the surface of IrO₂ by chemical reduction, and the catalyst is mixed with Pt black to be used as a novel bifunctional oxygen electrocatalyst for the unitized regenerative fuel cell (URFC). The novel cell has been evaluated in the hydrogen and oxygen fuel cell and water electrolysis modes, and compared to a similar cell with an oxygen electrode using conventional mixed Pt black and IrO₂ catalyst. With the novel oxygen electrode catalyst, the highest fuel cell power density is 1160 mW cm⁻² at 2600 mA cm⁻²; the overall performance is close to that with the commercial Pt supported on carbon catalyst and about 1.8 times higher than that with the conventional mixed Pt black and IrO₂ catalyst. Additionally, the cell performance for water electrolysis is also slightly improved, which is probably the result of lower interparticle catalyst resistance with 5 wt.% Pt on IrO₂ compared to no Pt on IrO₂.     

A three-dimensional two-phase flow model for a liquid-fed direct methanol fuel cell

A three-dimensional, two-phase, multi-component model has been developed for a liquid-fed DMFC. The modeling domain consists of the membrane, two catalyst layers, two diffusion layers, and two channels. Both liquid and gas phases are considered in the entire anode, including the channel, the diffusion layer and the catalyst layer; while at the cathode, two phases are considered in the gas diffusion layer and the catalyst layer but only single gas phase is considered in the channels. For electrochemical kinetics, the Tafel equation incorporating the effects of two phases is used at both the cathode and anode sides. At the anode side the presence of gas phase reduces the active catalyst areas, while at the cathode side the presence of liquid water reduces the active catalyst areas. The mixed potential effects due to methanol crossover are also included in the model. The results from the two-phase flow mode fit the experimental results better than those from the single-phase model. The modeling results show that the single-phase models over-predict methanol crossover. The modeling results also show that the porosity of the anode diffusion layer plays an important role in the DMFC performance. With low diffusion layer porosity, the produced carbon dioxide cannot be removed effectively from the catalyst layer, thus reducing the active catalyst area as well as blocking methanol from reaching the reaction zone. A similar effect exits in the cathode for the liquid water.     

Fabrication of hydrogen electrode supported cell for utilized regenerative solid oxide fuel cell application

A utilized regenerative solid oxide fuel cell (URSOFC) provides the dual function of performing energy storage and power generation, all in one unit. When functioning as an energy storage device, the URSOFC acts like a solid oxide electrolyzer cell (SOEC) in water electrolysis mode; whereby the electric energy is stored as (electrolyzied) hydrogen and oxygen gases. While hydrogen is useful as a transportation fuel and in other industrial applications, the URSOFC also acts as a solid oxide fuel cell (SOFC) in power generation mode to produce electricity when needed. The URSOFC would be a competitive technology in the upcoming hydrogen economy on the basis of its low cost, simple structure, and high efficiency. This paper reports on the design and manufacturing of its anode support cell using commercially available materials. Also reported are the resulting performance, both in electrolysis and fuel cell modes, as a function of its operating parameters such as temperature and current density. We found that the URSOFC performance improved with increasing temperature and its fuel cell mode had a better performance than its electrolysis mode due to a limited humidity inlet causing concentration polarization. In addition, there were great improvements in performance for both the SOFC and SOEC modes after the first test and could be attributed to an increase in porosity within the oxygen electrode, which was beneficial for the oxygen reaction.     

Alkaline anion-exchange polymer membrane with grid-plug microstructure for hydrogen fuel cell application

Porous polysulfone membrane, prepared by a phase-inversion technique, is filled with (3-acrylamidopropyl)trimethylammonium chloride and N,N′-methylenebisacrylamide via interfacial diffusion. The impregnated membrane is then subjected to UV-irradiation for polymerizing monomers that are entrapped in pore channels of the membrane. This in-situ polymerization engenders a grid-plug microstructure, where the grid is polysulfone and the plugs are an ion (OH⁻) conducting phase. As the plugs are extensively interconnected and non-tortuous throughout the membrane matrix, the ion-conducting phase sustains a power density as high as 55 mW cm⁻² at 60 °C. Thermal analysis indicates that the pore-filling condition affects the packing density of the plugs that in turn, impacts on ion transport flux.     

The analysis for the efficiency properties of the fuel cell engine

In this paper, the efficiency properties of the single fuel cell and the fuel cell stack have been analyzed theoretically, and the efficiency models of the fuel cell stack and fuel cell engine (FCE) are developed. Through experimental studies, we analyze the relationships between (1) the efficiency of the fuel cell stack and its current, (2) the efficiency of the fuel cell stack and its power, (3) the efficiency of the fuel cell stack and the hydrogen consumption ratio, (4) the efficiency of the FCE and the fuel cell stack current, (5) the efficiency of the FCE and its power, and (6) the efficiency of the FCE and the hydrogen consumption ratio. The factors which affect the efficiency of the fuel cell stack and that of the FCE are discussed. Finally, the efficiency models of the fuel cell stack and the FCE discussed in this paper are verified by test data. The results show that the simulation values fit well with the test data, and they can be applied in the fuel cell vehicle simulation studies.     

Optimization of fuel cell system operating conditions for fuel cell vehicles

Proton exchange membrane fuel cell (PEMFC) technology for use in fuel cell vehicles and other applications has been intensively developed in recent decades. Besides the fuel cell stack, air and fuel control and thermal and water management are major challenges in the development of the fuel cell for vehicle applications. The air supply system can have a major impact on overall system efficiency. In this paper a fuel cell system model for optimizing system operating conditions was developed which includes the transient dynamics of the air system with varying back pressure. Compared to the conventional fixed back pressure operation, the optimal operation discussed in this paper can achieve higher system efficiency over the full load range. Finally, the model is applied as part of a dynamic forward-looking vehicle model of a load-following direct hydrogen fuel cell vehicle to explore the energy economy optimization potential of fuel cell vehicles.     

Preparation and characterization of novel nickel–palladium electrodes supported by silicon microchannel plates for direct methanol fuel cells

A novel anode structure based on the three-dimensional silicon microchannel plates (Si-MCP) is proposed for direct methanol fuel cells (DMFCs). Ni–Pd nanoparticles produced by electroless plating onto the Si-MCP inner sidewalls and followed by annealing at 300 °C under argon serve as the catalyst. In order to evaluate the electroactivity of the nanocomposites, Ni–Pd/silicon composites synthesized by the same method are compared. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and electrochemical methods are employed to investigate the Ni–Pd/Si-MCP anode materials. As a result of the synergetic effects rendered by the MCP and Ni–Pd nanoparticles, the Ni–Pd/Si-MCP nanocomposites exhibit superior electrocatalytic properties towards methanol electro-oxidation in alkaline solutions, as manifested by the negative onset potential and strong current response to methanol even during long-term cyclical oxidation of methanol. This new structure possesses unique and significant advantages such as low cost and integratability with silicon-based devices.     

Chelating agent assisted heat treatment of carbon supported cobalt oxide nanoparticle for use as cathode catalyst of polymer electrolyte membrane fuel cell (PEMFC)

Cobalt-based catalysts for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cell (PEMFC) have been successfully incorporated cobalt oxide (Co₃O₄) onto Vulcan XC-72 carbon powder by thermal decomposition of Co-ethylenediamine complex (ethylenediamine, NH₂CH₂CH₂NH₂, denoted en) at 850 °C. The catalysts were prepared by adsorbing the cobalt complexes [Co(en)(H₂O)₄]³⁺, [Co(en)₂(H₂O)₂]³⁺ and [Co(en)₃]³⁺ on commercial XC-72 carbon black supports, loading amount of Co with respect to carbon black was about 2%, the resulting materials have been pyrolyzed under nitrogen atmosphere to create CoO_x/C catalysts, donated as E1, E2, and E3, respectively. The composite materials were characterized using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). Chemical compositions of prepared catalysts were determined using inductively-coupled plasma-atomic emission spectroscopy (ICP-AES). The catalytic activities for ORR have been analyzed by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The electrocatalytic activity for oxygen reduction of E2 is superior to that of E1 and E3. Membrane electrode assemblies (MEAs) containing the synthesized CoO_x/C cathode catalysts were fabricated and evaluated by single cell tests. The E2 cathode performed better than that of E1 and E3 cathode. This can be attributed to the enhanced activity for ORR, in agreement with the composition of the catalyst that CoO co-existed with Co₃O₄. The maximum power density 73 mW cm⁻² was obtained at 0.3 V with a current density of 240 mA cm⁻² for E2 and the normalized power density of E2 is larger than that that of commercial 20 wt.% Pt/C-ETEK.     

Polymer electrolyte fuel cell mini power unit for portable application

This paper describes the design, realisation and test of a power unit based on a polymer electrolyte fuel cell, operating at room temperature, for portable application. The device is composed of an home made air breathing fuel cell stack, a metal hydride tank for H₂ supply, a dc–dc converter for power output control and a fan for stack cooling. The stack is composed by 10 cells with an active surface of 25 cm² and produces a rated power of 15 W at 6 V and 2 A. The stack successfully runs with end-off fed hydrogen without appreciable performance degradation during the time. The final assembled system is able to generate 12 W at 9.5 V, and power a portable DVD player for 3 h in continuous. The power unit has collected about 100 h of operation without maintenance.