Passive direct formic acid microfabricated fuel cells

This paper reports on microscale silicon-based direct formic acid fuel cells (Si-DFAFCs) in which the fuel and the oxidant are supplied to the electrodes in a passive manner. Passive delivery of fuel and oxidant eliminates the need for ancillary components and associated parasitic losses. In this Si-DFAFC, an aqueous solution of formic acid is in direct contact with a Pd- or Pt-based anode and a Pt-based cathode is exposed to either a forced oxygen stream or quiescent air. In the presence of a forced oxygen flow on the cathode side the cell with Pd catalyst on the anode delivers a maximum power density of about 30 mW cm−2 at room temperature, limited mostly by mass transfer at the anode, while in an all-passive mode (quiescent air on the cathode side) a maximum power density of 12.3 mW cm−2 is obtained, limited by oxygen transport. This all-passive Si-DFAFC is fabricated using processes that are post-CMOS compatible, and thus can be integrated directly with envisioned MEMS applications, such as small sensors and actuators.