Stand-alone external power-free microfluidic fuel cell system harnessing osmotic pump for long-term operation

External pumps (e.g. syringe pump) that operate microfluidic fuel cell (MFFC) devices are inefficient because the amount of electricity required to run such pumps easily exceeds that generated by the MFFC. Herein, we propose a suitable small, lightweight, and external power-free osmosis-driven pump embedded with an MFFC system, capable of steady-flow generation. Methanol and vanadium are used as fuel, and the electrodes are made of carbon paper. We do not utilize sputtering equipment, commonly used for electrode fabrication. To incorporate the carbon paper-based electrode into the MFFC, the cross section of the microchannel is uniquely designed into a bridge-shaped channel, and its electrochemical and fluid dynamic influences are analyzed through experiments and simulations. The total weight of our MFFC system is less than 20g, the size is approximately 5cm, and the power density generated is approximately 0.3 mW cm(-2). The presented methods will contribute to the development of standalone MFFCs operable for prolonged durations (similar to 1 d), thereby enhancing the possibility of MFFC commercialization.