An investigational method of improving the performance of a fuel cell that contains a polymer-electrolyte membrane (PEM) is based on the concept of roughening the surface of the PEM, prior to deposition of a thin layer of catalyst, in order to increase the PEM/catalyst interfacial area and thereby increase the degree of utilization of the catalyst. The roughening is done by means of laser ablation under carefully controlled conditions. Next, the roughened membrane surface is coated with the thin layer of catalyst (which is typically platinum), then sandwiched between two electrode/catalyst structures to form a membrane/electrode assembly.

Figure 1. This Scanning Electron Micrograph shows portions of a PEM before and after roughening by laser ablation.
The feasibility of the roughening technique was demonstrated in experiments in which proton-conducting membranes made of a perfluorosulfonic acid-based hydrophilic, proton-conducting polymer were ablated by use of femtosecond laser pulses. It was found that when proper combinations of the pulse intensity, pulse-repetition rate, and number of repetitions was chosen, the initially flat, smooth membrane surfaces became roughened to such an extent as to be converted to networks of nodules interconnected by filaments (see Figure 1).

Figure 2. These EIS Data were acquired in measurements at frequencies from 100 kHz down to 10 mHz on 0.4-mm-thick smooth and roughened PEMs that had lateral dimensions of 3 by 3 mm, were 0.4 mm thick, and were coated with Pt on both faces. The smaller imaginary components of impedance of the roughened specimens are attributed to greater capacitances, which, in turn, are attributed to greater surface areas. Roughened specimens 1 and 2 were subjected to different laser-ablation conditions.
In further experiments, electrochemical impedance spectroscopy (EIS) was performed on a pristine (smooth) membrane and on two laser-roughened membranes after the membranes were coated with platinum on both sides. Some preliminary EIS data were interpreted as showing that notwithstanding the potential for laser-induced damage, the bulk conductivities of the membranes were not diminished in the roughening process. Other preliminary EIS data (see Figure 2) were interpreted as signifying that the surface areas of the laser-roughened membranes were significantly greater than those of the smooth membrane. Moreover, elemental analyses showed that the sulfur-containing molecular groups necessary for proton conduction remained intact, even near the laser-roughened surfaces. These preliminary results can be taken as indications that laser-roughened PEMs should function well in fuel cells and, in particular, should exhibit current and power densities greater than those attainable by use of smooth membranes.

This work was done by Jay Whitacre of Caltech and Steve Yalisove of the University of Michigan for NASA’s Jet Propulsion Laboratory.

NPO-45075

Topics:
Assembling Catalysts Emissions Emissions control Fuel cells Lasers Manufacturing & Prototyping Manufacturing processes On-board energy sources Optics
This Brief includes a Technical Support Package (TSP).
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Laser Ablation Increases PEM/Catalyst Interfacial Area

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NASA Tech Briefs Magazine

This article first appeared in the March, 2009 issue of NASA Tech Briefs Magazine (Vol. 33 No. 3).

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Overview

The document is a technical support package from NASA's Jet Propulsion Laboratory (JPL) detailing research on the effects of laser ablation on proton exchange membranes (PEM) and their interaction with catalysts. The focus of the study is on enhancing the interfacial area between PEMs and catalysts to improve fuel cell performance.

Preliminary results indicate that by employing specific laser ablation conditions, a membrane surface with a promising morphology can be achieved. This modified surface shows an increase in net surface area compared to a smooth membrane, which is crucial for enhancing the efficiency of fuel cells. Notably, the electrochemical impedance spectroscopy (EIS) data reveal that the bulk conductivity of the membrane remains unaffected despite the modifications, which is significant as it suggests that the laser treatment does not compromise the membrane's overall performance.

The document highlights that the sulfur groups essential for proton conduction are preserved even in the modified areas of the membrane, indicating that the integrity of the membrane's conductive properties is maintained. This is a critical finding, as it suggests that the laser-modified membranes could yield superior current and power densities compared to existing state-of-the-art membranes.

Figures included in the document illustrate the surface morphology of the ultra-fast laser modified Nafion 117 membrane, showcasing the differences before and after modification. The research is part of NASA's Commercial Technology Program, aimed at disseminating aerospace-related developments with broader technological, scientific, or commercial applications.

For further inquiries or assistance, the document provides contact information for the Innovative Technology Assets Management at JPL, emphasizing the collaborative nature of this research and its potential implications for fuel cell technology.

Overall, the document presents a promising advancement in fuel cell technology through laser ablation, suggesting that this method could lead to more efficient and effective PEMs, thereby enhancing the performance of fuel cells in various applications.