Miniature 250 μm Thick Fuel Cell with Monolithically Fabricated Silicon Electrodes

Abstract

A fabrication technique of miniature fuel cell electrodes was developed from Si wafers. The fuel channels, porous layer, and catalyst layer were formed in the Si wafer. The fuel channels were fabricated by photolithographic patterning and subsequent wet etching on the Si. The porous layer was formed by anodization of Si from the polymer electrolyte membrane side through the bottom of the fuel channels. Catalyst metals were deposited inside the porous layer by wet plating. The two electrodes were hot-pressed with a Nafion 112 sheet. Open-circuit voltage of 840 mV and maximum power density of 1.5 mW/cm 2 were observed by hydrogen feed.The increasing interest for portable electronic systems drives the research toward integrated regenerating power sources with small dimensions and miniaturized fuel cells are attractive. The microfabrication technology of Si is an important tool to reduce the fuel cell structure to micrometer sizes and have been employed by several research groups. 1-11 Those miniaturized fuel cells using various degrees of microfabrication techniques have been reported. Lee et al. 1 created flowfields on Si substrate and formed hydrogen feed fuel cell array on a Si wafer. Kelley et al. 4 created catalyst layer supporter on a Si chip and demonstrated that the miniaturized direct methanol fuel cell ͑DMFC͒ has almost same performance as state-of-the-art larger fuel cells. However, those miniaturized fuel cells uses conventional catalyst layers, in which Pt/Ru on activated carbon is splayed on the gold sputter deposited silicon electrodes or conventional membrane electrode assembly ͑MEA͒ is used, and treating powders such as activated carbon is not suitable for silicon batch fabrication process. To adapt the construction process to more Si processing steps, various approaches have been tried. In those studies, catalyst metals were deposited by physical vapor deposition ͑PVD͒ on porous layers formed by photolithographic patterning or anodization of Si. 5-8 Generally, it is difficult to deposit materials inside a porous layer by PVD and the catalyst deposits only on the surface of the porous layer and the performance of the catalyst will be poor. Therefore, a different approach to forming a catalyst layer should be developed. Recently, D'Ariggo et al. 9 proposed a novel Si-based electrode fabrication technique, although the power generation is not reported yet. In this technique, the fuel channels were formed inside the Si substrate by depositing an epitaxial Si layer after wet etching of a Si substrate, then the deposited epitaxial Si layer was anodized and the porous Si layer was obtained. Pt and Ru were electrodeposited into the porous layer and the catalyst layer was formed. Generally, resistivity of porous Si is high and it has been supposed to be difficult to use a porous Si layer as a catalyst support layer. However, porous Si has a large surface area up to 1700 m 2 /cm 3 which is comparable with that of activated carbon 12 and porous Si is attractive if it works as a catalyst support layer, becaus...

Template preparation of Pt–Ru and Pt nanowire array electrodes on a Ti/Si substrate for methanol electro-oxidation

“…The fundamentals of the DMFC system have been studied extensively [8][9][10][11][12]. Several groups have made micro fuel cells using micro-fabrication technologies using C/Si plane substrates [13][14][15][16][17][18].…”

Development of Batch and Flow Immobilized Catalytic Systems with High Catalytic Activity and Reusability

“…The silicon nanowire array, applied to silicon-based optoelectronics, fuel cells, solar cells and photoelectrodes, was obtained by the metal-assisted chemical etching of silicon wafers. [144][145][146][147][148][149][150][151][152][153] Copious nanospaces can be provided on the surface of a silicon wafer whose area is a square centimeters wide. The hybrid catalysts should be equipped with confined nano-size reaction fields surrounded by a lot of Pd nanoparticles with a square centimeter wide silicon wafer.…”

Nano-Porous Silicon-Based Mini Hydrogen Fuel Cells

“…The maximum power density of DMFC of 9.37 mW/cm 2 was obtained under using 2M methanol as fuel. The hybrid type of {porous silicon layer/ Nafion 112} hydrogen fuel cell has been developed (Hayase et al, 2004). The fuel channels were fabricated by photolithographic pattering and subsequent wet etching of silicon.…”