Harvey A. Frank

Advances in direct oxidation methanol fuel cells

Fuel cells that can operate directly on fuels such as methanol are attractive for low to medium power application in view of their low weight and volume relative to other power sources. A liquid feed direct methanol fuel cell has been developed based on a proton-exchange membrane electrolyte and Pt/Ru and Pt-catalyzed fuel and air/O2 electrodes, respectively. The cell has been shown to deliver significant power outputs at temperatures of 60 to 90 °C. The cell voltage is near 0.5 V at 300 mA/cm2 current density and an operating temperature of 90 °C. A deterrent to performance appears to be methanol crossover through the membrane to the oxygen electrode. Further improvements in performance appear possible by minimizing the methanol crossover rate.

LITHIUM BATTERIES FOR AEROSPACE APPLICATIONS: 2003 MARS EXPLORATION ROVER

Future NASA\ planetary exploration missions require batteries that can operate at extreme temperatures and with high specific energy and energy densities. Conventional aerospace rechargeable battery systems, such as Ni-Cd, Ni-H;! and Ag-Zn, are inadequate to meet these demands. Lithium ion rechargeable batteries are therefore being chosen as the baseline for these missions. The 2003 Mars Exploration Rover mission plans to deploy twin rovers onto Mars, with the objectives of understanding its geology, climate conditions and possibility of life on Mars. The spacecraft contain various batteries, i.e., primary batteries on the lander, thermal batteries on the back shell and rechargeable batteries on the Rovers. Significant among them are the Li ion rechargeable batteries, which are being utilized for the first time in a major NASA mission. The selection of the Li ion battery has been dictated by various factors, including mass and volume constraints, cycle life, and its ability to operate well at sub-zero temperatures (down to -30°C), at moderate rates. This paper describes the selection criteria, design and performance of the three battery systems on 2003 MER mission.

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.

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.

Direct methanol fuel cells-status, challenges and prospects

The status of direct methanol fuel cell technology with respect to power density, efficiency and integrated system operation have been summarized. The key challenge in improving power density is combining with operation at low air flow rates in order to maintain a water balance, and achieve attractive system mass and size. Improved catalysts and membranes with low methanol permeability are key to achieving these improvements. Challenges relating to miniature DMFC for battery replacement are discussed. Possibilities of reduction in catalyst and membrane cost suggest that premium power applications (100 W-5 kW) could be an early point of entry for DMFC into commercial markets.

Computer simulation of thermal modeling of primary lithium cells

Abstract The objective of this program was to gain a better understanding of the safety problems of primary LiSOCl 2 and LiSO 2 cells by carrying out detailed thermal modeling work. In particular, the transient heat generation rates during moderate and extremely high discharge rate tests of LiSOCl 2 cells were predicted and compared with those from the electrochemical heating. The difference between the two may be attributed to lithium corrosion and other chemical reactions. The present program was also evaluated in charging tests of LiSO 2 cells. In addition, the present methodology should be applicable, with minor modifications, to analyses of other primary cylindrical cells as well as rechargeable batteries.

Safety hazards associated with the charging of lithium/sulfur dioxide cells

Abstract A continuing research program to assess the responses of spirally wound, primary lithium/sulfur dioxide cells to charging, as functions of charging cur

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.

Chemical analysis of charged LiSO2 cells

Abstract The origin of hazardous behaviour of LiSO 2 cells is examined in both operational and chemical terms. The effect of charging was examined and determined to require extreme caution.

Reaction products on current or potential reversal in Li/SOCl2 cells

Abstract The products formed during abnormal operation due to current or potential reversal in Li/SOCl 2 cells have been identified by several complementary analytical techniques. In addition to the expected corrosion of cell components, the following compounds were found: Cl 2 , SO 2 , SO 2 Cl 2 , S 2 Cl 2 and SCl 2 . The presence of Cl 2 O and ClO 2 , reported earlier by others, has not been confirmed.