An air-breathing microfluidic fuel cell with a carbon felt flow-through anode

Abstract

Rapid development of portable electronic devices promotes the demand for high performance and durability of micro power sources. As a new kind of portable power sources, microfluidic fuel cells (MFFC) utilize the parallel laminar flow to separate the fuel and the oxidant naturally without a proton exchange membrane (PEM) in traditional PEM fuel cells. As a result, a series of problems related to the PEM such as high cost, complicated water management and degradation of membrane can be eliminated. Therefore, microfluidic fuel cells have been paid more and more attention recently and are gradually becoming one of the promising micro portable power sources. Previous studies on microfluidic fuel cells showed that due to a relatively high oxygen concentration and diffusivity of oxygen in the air, using an air-breathing cathode could alleviate the oxygen transfer limitation in traditional microfluidic fuel cells which used dissolved oxygen as oxidant. As a result, the performance could be improved by the air-breathing cathode. However, the mass transfer at the anode still limits the cell performance. To further enhance the microfluidic fuel cell performance, a porous flow-through anode could be used to achieve the convective transport of the fuel to the electrode, resulting in reduction of the concentration boundary layer thickness at the planar electrode surface. However, in most studies of microfluidic fuel cells with porous flow-through electrodes, the two-dimensional porous carbon paper was used at the anode. As a common electrode material, the three-dimensional porous carbon felt with large porosity and specific surface area is expected to further improve the microfluidic fuel cell performance. In this study, an air-breathing microfluidic fuel cell with a carbon felt flow-through anode was fabricated and compared with the microfluidic fuel cell with a carbon paper anode. The micro morphology of electrode surface was characterized by a scanning electron microscopy (SEM). The electrochemical and cell performances were tested in acidic and alkaline conditions. The mass transport and performance characteristics of the microfluidic fuel cell with the carbon felt flow-through anode were further studied in alkaline condition. The experimental results showed that catalysts were better-distributed on the carbon felt electrode surface than that on the carbon paper electrode surface. The electrochemical performance of carbon felt electrode was superior to carbon paper electrode both in acidic and alkaline conditions because of its inherent three-dimensional porous structure. In acidic condition, the optimal power density and maximum current density of the microfluidic fuel cell with carbon felt anode were 1.8 and 2.8 times than that of the microfluidic fuel cell with carbon paper anode density, respectively. In alkaline condition, the optimal power density and the maximum current density of microfluidic fuel cell with carbon felt anode were 35.1 mW/cm2 and 192.9 mA/cm2, which were 5.2 and 7 times than that of the microfluidic fuel cell with carbon paper anode. Moreover, the cell performance under alkaline condition increased with an increase in the fuel and electrolyte flow rate and then remained almost the same, while it increased at first and then decreased as the fuel concentration, electrolyte and supporting electrolyte concentration increased.