Ryan Presents at ECS meeting and receives ECS Graduate Student Travel Grant

by TMD Lab  
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Novel Metallic Glass Micro Fuel Cell Architecture

Ryan C. Sekol, Golden Kumar, Marcelo Carmo, Sundeep Mukherjee, Forrest Gittleson, Nathan Hardesty-Dycke, Jan Schroers, André D. Taylor

Chemical & Environmental Engineering,

Mechanical Engineering & Materials Science,

Yale University, 9 Hillhouse Ave, New Haven, CT, USA

Previously, we described a silicon-based micro fuel cell (MFC) as well as the electrocatalytic properties of bulk metallic glass (BMG) nanowires. Here, we show a first demonstration of an all BMG MFC with a room temperature peak power density of 9.4 mW/cm2. BMGs are a subset of glass forming alloys that can be easily vitrified forming relatively large amorphous sections and can be patterned on multiple length scales. The absence of crystallites, grain boundaries, and dislocations in the amorphous structure of bulk metallic glass results in a homogeneous and isotropic material down to the atomic scale, which displays very high strength (100 times the toughness of silicon), hardness, elastic strain limit, and corrosion resistance. By showing a processing ability similar to plastics, we demonstrate the essential components of a MFC that includes the housing with serpentine flow field channels (for gas distribution and current collection) as well as uniquely patterned BMG catalyst layers. MFCs offer several advantages over conventional alternative power sources, such as high theoretical power density, low operating temperature, and a great potential for long-term operations [5]. Miniaturization for use in portable electronics remains a primary design challenge despite much work in this field. We selected a zirconium-based BMG (Zr35Ti30Cu8.25Be26.75) as the flow field for this study due to its high corrosion resistance, electrical conductivity, shock resistance, and low cost [6]. The Zr-BMG flow field was synthesized by hot embossing into a serpentine channel silicon design, producing a 4 mm x 4 mm active area with holes of 1 mm in diameter for gas feed (Fig. 1). The performance of this flow field design was tested with standard Pt/C ETEK catalyst and Nafion® 212 membrane in our in house MFC housing, producing a room temperature peak power density of 294.0 mW/cm2 (Fig. 2a). We have previously shown that Pt-BMG (Pt57.5Cu14.7Ni5.3P22.5) nanowires are highly active and durable electrocatalysts [2], which was an essential step toward this first demonstration of an all BMG MFC. We designed a new freestanding Pt-BMG catalyst layer for this study using a CMOS compatible technique. We highlight the surface of the catalyst as a 4 mm x 4 mm square with patterned Pt-BMG nanowires (250 nm diameter, 1.5 μm long). Si pillars are used to nano imprint the porous catalyst layer with uniformly distributed 110 μm diameter holes with 110 μm spacing (Fig. 3). Combined together, the Zr-BMG flow field and porous Pt-BMG catalyst layer with nanowires produces the first presented all BMG fuel cell (Fig. 2b). This architecture is the first reported all BMG micro fuel cell, including both the flow field and catalyst layer. The fabrication method is CMOS compatible and represents a breakthrough in the design of flow fields for MFCs. These BMGs are a new class of engineering materials with an unusual combination of strength, elasticity, hardness, and processability opening up a new range of possibilities for further enhancements of next generation MFCs and MEMs devices. This demonstration further highlights the ability to pattern the surface of BMG alloys along multiple length scales which is difficult to achieve with other materials. Ongoing efforts are being pursued to optimize these new BMG electrochemical devices and these results will be reported.