Self-Pumping Membraneless Miniature Fuel Cell With an Air-Breathing Cathode

Abstract

Abstract-We introduce a simple and compact fuel-cell architecture consisting of only solid channels and demonstrate its validity by developing a miniature direct formic acid fuel cell (DFAFC). The proposed architecture generates electric power while pumping the fuel and removing byproduct CO 2 without any discrete pump, gas separator, or membrane electrode assembly (MEA). The fuel pump and gas separator are embedded in the channel, as reported before, by directionally growing and venting CO 2 byproduct bubbles formed inside the reaction microchannels using "virtual check valve" and microporous hydrophobic venting membrane. The new architecture further eliminates the MEA, along with the issues associated with it, by flowing one stream of fuel and electrolyte mixture in a single channel consisting of both an anode and an air-breathing cathode. The reported system obtains a supply of oxygen directly from quiescent air through a gas-diffusion cathode rather than using an oxygen tank. By eliminating all the ancillary parts, the so-called "packaging penalty," which has been hindering the miniaturization of fuel cells below the order of a centimeter, is avoided. This simple and self-standing fuel-cell unit produces 16.7 mW/cm 2 , a performance comparable to the existing bulkier DFAFCs that use external pumps, pressurized oxygen or MEA.[2011-0088]

Co-laminar flow cells for electrochemical energy conversion

“…As open cells depend on reactant flow, any commercial application involving CLFCs will inevitably require balance of plant items such as pumps and reactant storage. Even if future cells can eliminate such ancillary parts by relying on gravity induced flow, capillary action [118], [154], or even gaseous venting [155], [156]; the question of scale remains a significant barrier to commercialization as power sources. Since these cells are inherently limited in size by the co-laminar concept of reactant separation, it is crucial for these cells to be as effective as possible to achieve practical power outputs.…”

Miniature fuel-cell system complete with on-demand fuel and oxidant supply

“…3, was designed to integrate two main technologies-self-regulated fuel pumping and self-regulated oxygen supply-into one device. The top portion marked A, consisting of a fuel cartridge and a fuel channel, is essentially an air-breathing fuel-cell system developed in [23] and shown Fig. 2, which self-pumps the fuel in a self-regulating manner.…”

“…Furthermore, the complexity of integrating the moving ancillary components in a small space would make the miniature system expensive and unreliable. We have previously reported a self-pumping fuel cell that has an embedded ability to pump the liquid fuel within microfluidic channels, allowing one to miniaturize fuel cells (at least the anodic side) without the packaging penalty [22][23]. Unlike other passive fuel cells [9,13,24], the self-pumping fuel cell is an active fuel cell; it actively pumps to deliver fresh fuel from a reservoir, where fuel concentration is kept relatively constant.…”

“…Although the oxygen tank was eliminated, relying on oxygen 4 supply from air limited the application of the miniature fuel-cell system, because the system could not be stacked for higher power output. Figure 2: Simplified fuel-cell system previously developed from our group [23]. Oxygen is provided from the ambient air.…”

“…In pursuit of realizing a complete fuel-cell system, we then integrate the O 2 -generating mechanism with our previously proven air-breathing fuel-cell system [23]. This unique oxygen supply takes up a much smaller volume than the existing designs, which would require ancillary components, such as a pressurized oxygen tank with a regulator.…”