Leveraging the well-documented integrate circuit (IC) processing and microfabrication techniques, over the years many interesting Si-based micromachined fuel cell prototypes have been demonstrated. However, most of the reported structures of micro fuel cells heavily rely on the approaches and materials employed in the traditional macroscopic counterparts. The combination of “traditional” and “microfabrication-friendly” materials prevents various cell components from a seamless integration, thus limiting the power output of the microfabricated fuel cell. It is therefore the objectives of this thesis to systematically address the issues of compatibility and integration of various fuel cell components, in particular the catalyst, the electrode and the current collectors, on the same silico...[ Read more ]

Leveraging the well-documented integrate circuit (IC) processing and microfabrication techniques, over the years many interesting Si-based micromachined fuel cell prototypes have been demonstrated. However, most of the reported structures of micro fuel cells heavily rely on the approaches and materials employed in the traditional macroscopic counterparts. The combination of “traditional” and “microfabrication-friendly” materials prevents various cell components from a seamless integration, thus limiting the power output of the microfabricated fuel cell. It is therefore the objectives of this thesis to systematically address the issues of compatibility and integration of various fuel cell components, in particular the catalyst, the electrode and the current collectors, on the same silicon-based platform, and to develop synthesis approaches of electrocatalysts that would facilitate the system integration.

The study of high-aspect-ratio Si pillars to replace carbon-based materials as electrocatalyst supports was first investigated. In particular, a novel lithography-free process to produce Si microcolumns of high surface area was developed. The dimension of Si pillars can be controlled by altering operating conditions of forming the polysilicon masking layer and the etching duration in an inductively coupled plasma-deep reactive ion etching (ICP-DRIE) reactor. Following the study of Si supports, electrochemical approaches to synthesize nanoscale Pt and PtRu catalyst particles supported on Si microelectrodes with controlled morphology and atomic composition were investigated. It was revealed that round-shaped Pt particles prepared at a low deposition overpotential exhibit a higher catalytic activity in comparison with the dendrite-like catalysts prepared at a high deposition overpotential. It was also noted that the electrodeposited PtRu electrode containing a Ru content of 24 atom % using the metallic precursor of 1:2 molar ratio of Pt to Ru demonstrates the highest electrochemical activity and cell polarization characteristics.

Additionally, the surface of uncatalyzed Si microelectrode can be coated with a thin layer of conductive polypyrrole (PPy)/Nafion^® film using electropolymerization method to improve the incorporation of electrocatalysts and enhance electrochemical active surface area of the catalyzed micro electrode. It was found that the optimized film of porous nature offers high electron and proton conductivity and is an attractive catalysts support. The investigation concludes that the strategy for the synthesis of non-carbon based supporting materials as well as nanoscale electrocatalysts by use of microfabrication-compatible methods has been successfully developed, and the realization of such catalyzed microelectrodes is a promising step toward the monolithic integration of a Si-based microfabricated fuel cell.