A dual-functional three-dimensional herringbone-like electrode for a membraneless microfluidic fuel cell

Carbon fibers (CFs) due to their excellent electrochemical properties, large specific surface area as well as good flexibility have received much attention for flexible energy harvesting devices. A dual-functional three-dimensional (3D) herringbone-like electrode is fabricated for a membraneless microfluidic fuel cell (MMFC) in this study. CFs are braided together into a 3D herringbone-like pattern. The porous structure and the inter-fiber gaps of the braided carbon fiber provide flow channels for aqueous fuel and oxidant. Palladium (Pd) catalysts are electrochemically deposited on the surface of the braided carbon fiber, which makes it simultaneously serve as the electrode for the MMFC. Through ultrasonic treatment in concentrated acid, the surface concentration of oxygenated groups increases and impurities on the fiber surface are removed, resulting in modification of the carbon fiber surface from hydrophobic to hydrophilic. Benefitting from the superior electrical conductivity and plenty of exposed active sites of the 3D herringbone-like electrode, the MMFC produces a peak power density of 29.9 mW cm−2 and a limiting current density of 83.3 mA cm−2 normalized to the effective projected area of the electrode. Importantly, the proposed fuel cell shows considerable promising as miniature power sources to power portable micro-analytical devices or electrochemical sensors.