Ronald S. Besser

Novel microfabrication approaches for directly patterning PEM fuel cell membranes

We have successfully developed miniature hydrogen-air proton exchange membrane (PEM) fuel cells (FC) on silicon and poly-dimethylsiloxane (PDMS) base substrates using conventional and non-conventional microfabrication technologies. Prototype base substrates were fabricated by using well-known micromachining technologies, such as photolithography, deep reactive ion etching, and soft lithography. Sputtering, a physical vapor deposition method, was used to deposit catalysts and electrodes directly on the surface of the Nafion PEM. This paper describes the novel microfabrication approaches employed to selectively deposit electrodes and catalyst materials on the membrane with improved morphology and structure of electrodes. The aim was to reduce precious metal catalyst loadings, ohmic (iR) losses, and to improve structural support for the thin-film FC with concurrent reduction in fabrication complexity.

Experimental study of hydrocarbon hydrogenation and dehydrogenation reactions in silicon microfabricated reactors of two different geometries

Miniaturization is fast gaining importance and relevance in chemical processes that are conventionally carried out on a lab-scale or larger. Miniaturized chemical-reaction systems, or microreactors, are devices that behave as continuous flow systems and whose dimensions are in sub-millimeter range. Microreactors were successfully fabricated using wet silicon bulk micromachining and deep reactive ion etching (DRIE) techniques, were used to characterize reactions involving heterogeneous catalysis, and demonstrated their feasibility as efficient tools in catalyst and process development. In this study, the relatively simple reactions of cyclohexene hydrogenation and de-hydrogenation over a platinum catalyst were studied, reactions which are models for important classes of reactions of significance in petroleum industry. The conversion, selectivity and yield for products cyclohexane and benzene, were measured as a function of temperature and reactant flow rates. The experiments were done in microreactors of characteristic dimensions of 100 and 5 μm. The results are shown which compare the performance of these two types of reactors.

Evaluation of multi-attribute decision making systems applied during the concept design of new microplasma devices

Various multi-attribute decision making (MADM) systems can be implemented to narrow a field of new concept designs down to those with high likelihoods of surpassing state-of-the-art technologies. This research investigated the conceptual design phase of new microplasma devices in order to create metrics that evaluate the efficiency, effectiveness, and overall utility of representative MADM systems studied in previous engineering design applications. Device attributes and concept alternatives for the microplasma devices were identified from open-ended expert surveys. Efficiency metrics were defined based on the number of manual user inputs. Published device literature and testing were used to gauge how closely device concepts satisfied multi-attribute criteria, forming the basis of an effectiveness metric. A weighted average of the efficiency and effectiveness defined a MADM systems overall utility. Varying the effectiveness weight provided further insight into the conditions under which particular MADM approaches exhibited higher utility values. The MADM systems found to possess the highest overall quantified utilities were based on Pughs controlled convergence, Utility Based Axiomatic Framework, and Grey Relational Analysis. The MADM method with the lowest overall utility was the analytical hierarchy process. These findings indicate that consensus building and utility-based MADM systems are especially helpful to engineering design teams during the early design phases of novel technologies when resources are constrained or historical data is limited.

Nanotechnology Innovations for Low-Temperature Fuel Cells for Micro Autonomous Systems

The requirement for longer and uninterrupted operation by micro autonomous systems calls for alternatives to the incumbent battery technology. The proton exchange membrane fuel cell (PEMFC) presents a comparative advantage over battery technology due to their higher energy density and ability to operate continuously without the need for recharging. The cost of expensive catalyst materials utilized by the PEMFCs has so far impeded this technology. The dramatic success of the electronics industry in making cheaper and more efficient products has created new pathways for PEMFC advancement. This chapter discusses the integration of nano/microfabrication practices and techniques to fuel cell systems design. A new technique with the ability to produce high-aspect ratio features of sub-micrometer critical dimension and larger by leveraging the tools of electron beam lithography and advanced dry etching from the established techniques of nano/microtechnology is also discussed. This capability opens the possibility of creating a variety of novel architectures for fuel cells and other electrochemical devices (including sensors, electrolyzers, and electrochemical reactors, among others) and the promise of cost reduction through the model of microelectronics technology that leverages integration of components, rapid batch processing, automation, and economies of scale.

Microcavity Plasma Devices

Traditionally plasma systems have required high operating power, low operating pressure and are relatively large in size, limiting the technology to mostly immobile, large-scale industrial applications. In recent years, microplasma devices have emerged due especially to improvements in microchip fabrication technology. Microplasmas improve on plasma performance, allow for atmospheric operation, permit portability and significantly reduce both the cost of manufacturing and the cost of electrical power. These developments allow for technological improvements in fields such as displays, medicine, alternate energy and chemical analysis. This review will first introduce the concept of man-made plasmas and the distinctive characteristics of microplasmas, then discuss some of the most recent patents of microplasmas with specific regard to devices possessing a microcavity. These patents relate to device types, fabrication improvements and the various applications of microplasma technology.

Microfluidic system incorporating layer-by-layer nanofabricated capsules

A microfluidic system was designed, fabricated and implemented to study the behavior of polyelectrolyte capsules flowing in microscale channels. The silicon component of the system contains microchannels that leads into constrictions, which were fabricated using lithography techniques. Polyelectrolyte microcapsules were also fabricated with well-known layer-by-layer assembly technique, on a spherical template. Once the template was removed, the resulting hollow capsules were introduced into the system. The behavior of the capsules at the constrictions was visualized and the properties of the capsules were investigated. Capsules recovered from the system appear to have a undergone a plastic deformation.

Patterning the Cathode Catalyst Layer - Membrane Interface of a PEMFC for Elevated Power Density

Proton exchange membrane fuel cells (PEMFC’s) are attractive alternatives to conventional energy sources for transportation, stationary, and portable devices due to their efficiency and the high energy density of input fuel. Despite continued improvement, widespread adoption is still limited by the cost of the fuel cell stack, exacerbated by the cost of the precious catalyst materials used in the construction of the fuel cell. It is therefore of interest to minimize the amount of catalyst used for electrochemical energy conversion in a PEMFC without sacrificing performance. 2

Flexible microreactor system for chemical research at moderate temperatures

Miniaturization is fast gaining attention in chemical processes that are conventionally carried out on a lab-scale or larger. Major progress and landmarks has been made during the last five years. A microreactor system has been developed for fast catalyst development and process optimization. This paper focuses on the issues of microreactor system design and characterization for fast and accurate reaction analysis.