William Chun

Performance of Direct Methanol Fuel Cells with Sputter‐Deposited Anode Catalyst Layers

Performance of direct methanol fuel cells with sputter-deposited Pt-Ru anodes was investigated. The thin film catalyst layers w ere characterized using X-ray diffraction, energy dispersive X-ray analysis, Rutherford backscattering spectroscopy, and X-ray photoelectron spectroscopy. Different catalyst loadings and membrane electrode assembly (MEA) fabrication processes were tested. The maximum power density achieved at 90°C was 100 mW/cm 2, and almost 75 mW/cm 2 was attained with a loading of only 0.03 mg/cm2. The results demonstrate that a catalyst utilization of at least 2300 mW/mg can be achieved at current densities ranging from 260 to 380 mA/cm2. The application of the sputter-deposition method for MEA fabrication is particularly attractive for commercialization of direct methanol fuel cell technology.

Recent advances in PEM liquid-feed direct methanol fuel cells

A direct methanol-air fuel cell operating at near atmospheric pressure, low-flow rate air, and at temperatures close to 60/spl deg/C would tremendously enlarge the scope of potential applications. While earlier studies have reported performance with oxygen, the present study focuses on characterizing the performance of a PEM liquid feed direct methanol-air cell consisting of components developed in house. These cells employ Pt-Ru catalyst in the anode, Pt at the cathode and Nafion 117 as the PEM. The effect of pressure, flow rate of air and temperature on cell performance has been studied. With air, the performance level is as high as 0.437 V at 300 mA/cm/sup 2/ (90/spl deg/C, 20 psig, and excess air flow) has been attained. Even more significant is the performance level at 60/spl deg/C, 1 atm and low flow rates of air (3-5 times stoichiometric), which is 0.4 V at 150 mA/cm/sup 2/. Individual electrode potentials for the methanol and air electrode have been separated and analyzed. Fuel crossover rates and the impact of fuel crossover on the performance of the air electrode have also been measured. The study identifies issues specific to the methanol-air fuel cell and provides a basis for improvement strategies.

Design and Operation of an Electrochemical Methanol Concentration Sensor for Direct Methanol Fuel Cell Systems

The development of a 150-Watt packaged power source based on liquid feed direct methanol fuel cells is being pursued currently at the Jet propulsion Laboratory for defense applications. In our studies we find that the concentration of methanol in the fuel circulation loop affects the electrical performance and efficiency the direct methanol fuel cell systems significantly. The practical operation of direct methanol fuel cell systems, therefore, requires accurate monitoring and control of methanol concentration. The present paper reports on the principle and demonstration of an in-house developed electrochemical sensor suitable for direct methanol fuel cell systems.

Recent advances in direct methanol fuel cells

The direct methanol fuel cell is based on the electro-oxidation of an aqueous solution of methanol in a polymer electrolyte membrane fuel cell without the use of a fuel processor. The electro-oxidation of methanol occurs on platinum-ruthenium catalyst at the anode and the reduction of oxygen occurs on platinum catalyst at the cathode. After the initial concept development at the Jet Propulsion Laboratory (JPL), there has been considerable development of methanol fuel cell (DMFC) technology at the JPL and at various other institutions under programs sponsored by DOD and DOE. Significant improvements in power density, efficiency, and life have been demonstrated at the cell and stack level. These advances in the performance of direct methanol fuel cells are sufficiently attractive for the design of complete power systems. Portable power sources, in the range of 50-150 W, based on this technology are currently being considered for various military applications. The development of a 150 W direct methanol fuel cell power system is being pursued at the Jet Propulsion Laboratory (JPL) under DARPA funding. This paper summarizes some of the progress in the development of cells, stacks and systems.

Direct methanol fuel cell for portable applications

A five cell direct methanol fuel cell stack has been developed at the Jet Propulsion Laboratory. Currently, direct methanol fuel cell technology is being incorporated into a system for portable applications. Electrochemical performance and its dependence on flow rate and temperature for a five cell stack are presented. Water transport data, and water transport mechanisms for direct methanol fuel cells are discussed. Stack response to pulse loads has been characterized. Implications of stack performance and operating conditions on system design have been addressed.

Comparison of Airborne Passive and Active L-Band System (PALS) Brightness Temperature Measurements to SMOS Observations During the SMAP Validation Experiment 2012 (SMAPVEX12)

In this letter, it is shown that spaceborne observations made by the European Space Agencys Soil Moisture and Ocean Salinity (SMOS) satellite agreed closely with the Passive Active L-band System (PALS) brightness temperature acquisitions during the Soil Moisture Active Passive (SMAP) Validation Experiment 2012. The difference between the SMOS and PALS measurements was less than 5 K and 6 K for vertical and horizontal polarizations, respectively, over the relatively homogeneous agricultural areas. These values are less than the SMOS subpixel variability determined from the PALS measurement. This result demonstrated that the measurements obtained in the experiment are scalable to spaceborne brightness temperature observations, are representative of the expected SMAP observations, and will be of value in the development of soil moisture algorithms for spaceborne missions.

An onboard processor and adaptive scanning controller for the Second-Generation Precipitation Radar

Technology for the 14- and 35-GHz Second-Generation Precipitation Radar (PR-2) is currently being developed by the National Aeronautics and Space Administration Jet Propulsion Laboratory to support the development of future spaceborne radar missions. PR-2 will rely on high-performance onboard processing techniques in order to improve the observation capabilities (swath width, spatial resolution, and precision) of a low-Earth orbiting rainfall radar. Using field-programmable gate arrays (FPGAs), we have developed a prototype spaceborne processor and controller module that will support advanced capabilities in the PR-2 such as autotargeting of rain and compression of rainfall science data. In this paper, we describe the new technology components designed for the onboard processor, including an FPGA-based 40 /spl times/ 10/sup 9/ op/s pulse-compression receiver/filter with a range sidelobe performance of -72 dB, and an adaptive scanning controller which yields a six-fold increase in the number of radar looks over areas of precipitation.

Design and demonstration of an advanced on-board processor for the second-generation precipitation radar

The Next-Generation Precipitation Radar (PR-2) prototyped by NASA/JPL will depend heavily on high-performance digital processing to collect meaningful echo data.

Commercialization of a direct methanol fuel cell system

This paper describes a major breakthrough in energy technology developed at the Jet Propulsion Laboratory that can be used in a wide variety of portable, remote and transportation applications without polluting the environment. The status, performance, and design considerations of the JPL non-polluting, Direct Methanol, Fuel Cell system for consumer equipment and transportation applications are reported herein. This new fuel cell technology utilizes the direct oxidation of a 3% aqueous liquid methanol solution as the fuel and air (O2) as the oxidant. The only products are CO2 and water. Therefore, because recharging can be accomplished by refueling with methanol, vehicles can enjoy unlimited range and extended use compared to battery operated devices requiring recharge time and power accessibility.

Submillimeter wave spectrometry for in-situ planetary science

Absorption and emission of gases in the submillimeter wavelengths is currently exploited for laboratory spectroscopy as well as remote astronomy and limb sounding. We are developing a field-ready submillimeter spectrometer that will enable in-situ sensing with a goal for characterization of biogenic gases and life tracers. Progress toward a field-ready instrument includes: the development of a brass board THz transceiver module; the development of the brass board RF/IF subsystem; an embedded computer and runtime software. Science experiments, including the study of laboratory simulations of Titan, will be performed while the final field instrument components are developed.