Preparation of Pt/C electrocatalysts using an incipient precipitation method

Highly loaded and dispersed Pt/C catalysts, used as cathodic electrocatalysts in low temperature fuel cells, were prepared using a new method involving the slow addition of a Pt precursor to a solution containing dispersed carbon powder and a reducing agent. During this process, the added Pt precursor was reduced instantaneously into fine particles and adsorbed onto the carbon surface in the solution. A Pt loading of 55 wt% was obtained, which was close to the nominal amount of Pt, 60 wt%, added in the preparation step. The average particle size of Pt was about 4.2 nm, according to X-ray diffraction. The surface area of the Pt measured by cyclic voltammetry was about 61.4 m²/(g of Pt). The activity of the prepared Pt/C, as an electrode of polymer electrolyte membrane fuel cell, was increased by 34.8% and 15.0%, according to the half- and single-cell tests, respectively, compared to the activity of one prepared using a conventional precipitation method.     

Properties of Pt-based electrocatalysts containing selectively deposited Sn as the anode for polymer electrolyte membrane fuel cells

Sn-promoted Pt-based catalysts were prepared by the chemical vapor deposition (CVD) of Sn on commercial Pt/C and PtRu/C catalysts using Sn(CH₃)₄ as an Sn precursor. The prepared catalysts showed higher CO tolerance than those prepared by adding Sn using an impregnation (IMP) method. This result was obtained because Sn added by CVD was selectively deposited on the Pt and Ru surfaces, instead of on a carbon support, such that the interfacial contact between Pt and Sn was greater in the Sn-CVD catalyst than in the others, as confirmed by in-situ infrared and X-ray photoelectron spectroscopic observations of the catalysts.     

Effect of functional groups of carbon nanotubes on the cyclization mechanism of polyacrylonitrile (PAN)

The cyclization mechanism of polyacrylonitrile (PAN) in PAN/functionalized carbon nanotube (CNT) composites was examined. The surface functionalization of CNTs was carried out by using diazonium reagents with 4-substituted aniline. The results strongly suggest that the type of functional groups on the CNTs strongly influences the cyclization mechanism of PAN during the stabilization process. The nitrile of PAN in F–Ph–CNT/PAN composite was cyclized through the free radical reaction during thermal stabilization whereas nitrile of PAN in COOH–Ph–CNT/PAN composite underwent cyclization via the ionic reaction due to the acid groups on the surfaces of the CNTs. The fluoro functional groups on the CNTs can act as effective external initiators for nitrile cyclization in homo PAN, in contrast to acid functional groups. Consequently, a lower cyclization temperature (265 °C) and enthalpy value (688 J/g) of F–Ph–CNT were shown compared to those of homo PAN.     

Dynamic behavior of cracked pipe conveying fluid with moving mass based on timoshenko beam theory

In this paper we studied about the effect of the open crack and the moving mass on the dynamic behavior of simply supported pipe conveying fluid. The equation of motion is derived by using Lagrange’s equation and analyzed by numerical method. The crack section is represented by a local flexibility matrix connecting two undamaged pipe segments i.e. the crack is modeled as a rotational spring. The influences of the crack severity, the position of the crack, the moving mass and its velocity, the velocity of fluid, and the coupling of these factors on the vibration mode, the frequency, and the mid-span displacement of the simply supported pipe are depicted.     

Free vibration analysis of Euler-Bernoulli beam with double cracks

In this paper, the influence of two open cracks on the dynamic behavior of a double cracked simply supported beam is investigated both analytically and experimentally. The equation of motion is derived by using the Hamilton’s principle and analyzed by numerical method. The simply supported beam is modeled by the Euler-Bemoulli beam theory. The crack sections are represented by a local flexibility matrix connecting three undamaged beam segments. The influences of the crack depth and the position of each crack on the vibration mode and the natural frequencies of a simply supported beam are analytically clarified for the single and double cracked simply supported beam. The theoretical results are also validated by a comparison with experimental measurements.     

In situ synthesis of thermochemically reduced graphene oxide conducting nanocomposites

Highly conductive reduced graphene oxide (GO) polymer nanocomposites are synthesized by a well-organized in situ thermochemical synthesis technique. The surface functionalization of GO was carried out with aryl diazonium salt including 4-iodoaniline to form phenyl functionalized GO (I-Ph-GO). The thermochemically developed reduced GO (R-I-Ph-GO) has five times higher electrical conductivity (42,000 S/m) than typical reduced GO (R-GO). We also demonstrate a R-I-Ph-GO/polyimide (PI) composites having more than 10(4) times higher conductivity (~1 S/m) compared to a R-GO/PI composites. The electrical resistances of PI composites with R-I-Ph-GO were dramatically dropped under ~3% tensile strain. The R-I-Ph-GO/PI composites with electrically sensitive response caused by mechanical strain are expected to have broad implications for nanoelectromechanical systems.     

Sensor-less control of methanol concentration based on estimation of methanol consumption rates for direct methanol fuel cell systems

Adequate control over the concentration of methanol is critically needed in operating direct methanol fuel cell (DMFC) systems, because performance and energy efficiency of the systems are primarily dependent on the concentration of methanol feed. For this purpose, we have built a sensor-less control logic that can operate based on the estimation of the rates of methanol consumption in a DMFC. The rates of methanol consumption are measured in a cell and the resulting data are fed as an input to the control program to calculate the amount of methanol required to maintain the concentration of methanol at a set value under the given operating conditions of a cell. The sensor-less control has been applied to a DMFC system employed with a large-size single cell and the concentration of methanol is found to be controlled stably to target concentrations even though there are some deviations from the target values.     

Development and characteristics of a 400 W-class direct methanol fuel cell stack

In this study, a 400 W-class direct methanol fuel cell (DMFC) stack is developed for large size portable applications and its operating behaviors under the various conditions are monitored. The DMFC stack comprising of 42-cells is assembled with graphite bipolar plates and membrane–electrode assemblies (MEAs) having an active area of 138 cm² per each. The stack is operated by varying the concentrations of methanol, stoichiometry (λ), and the electric load. In addition, other associated factors, such as voltage and temperature distributions along the individual unit cells, pressure drops inside the stack, voltage behaviors in response to the dynamic change of the electric load and the pHs of the effluent solutions from the outlets of both electrodes, are also studied in a detailed manner. The stack produces a power of 400 W under an operating condition of feeding 0.8 M methanol and 34 l/min air at 1 atm, and uniform distributions of temperature and voltage prevail in all the 42 unit cells. A long-term operation coupled with performance restoration processes shows that a typical single cell used in this stack is able to run with a good stability for more than 500 h without any substantial degradation in the performance.     

Synthesis of branched carbon nanotubes by carbonization of solid polyvinylidene fluoride fibers

Branched carbon nanotubes (b-CNTs) were synthesized by carbonization of polyvinylidene fluoride (PVDF) fibers containing a Pt catalyst. The solid fibrous polymer converted into carbon nanotubes with simultaneous growth of branches on the surface of the tubes during carbonization. The Pt particles were expected to decompose PVDF polymer inside the tubes into volatile carbonaceous species leaving a hollow center, and also to act as catalytic sites for the growth of carbon branches. The resulting b-CNTs had a high degree of graphitization and a large electrochemical surface area, and also showed a possibility as a supporting material for electrocatalysts.     

A direct methanol fuel cell system to power a humanoid robot

In this study, a direct methanol fuel cell (DMFC) system, which is the first of its kind, has been developed to power a humanoid robot. The DMFC system consists of a stack, a balance of plant (BOP), a power management unit (PMU), and a back-up battery. The stack has 42 unit cells and is able to produce about 400 W at 19.3 V. The robot is 125 cm tall, weighs 56 kg, and consumes 210 W during normal operation. The robot is integrated with the DMFC system that powers the robot in a stable manner for more than 2 h. The power consumption by the robot during various motions is studied, and load sharing between the fuel cell and the back-up battery is also observed. The loss of methanol feed due to crossover and evaporation amounts to 32.0% and the efficiency of the DMFC system in terms of net electric power is 22.0%.