Counter-flow formic acid microfluidic fuel cell with high fuel utilization exceeding 90%

Microfluidic fuel cell (MFC) is a promising energy source for portable applications, which draws lots of R&D attention. However, MFCs fed with hydrocarbon fuel like formic acid suffers low fuel utilization problem because of sluggish kinetics, complicate reaction condition and dilemma on cell control. In this work, a formic acid MFC based on counter-flow design is proposed. This counter-flow structure is verified a promising design for high Graetz number operation, which is especially beneficial for high fuel utilization manipulation of MFC. A breakthrough in fuel utilization is achieved and the highest fuel utilization of 91.4% is obtained at 1 μL min−1. It is revealed that counter-flow MFC is capable for low flow rate operation, which is significant for reduce the pump energy consumption and improve the energy efficiency of MFC system. Each potential loss involved in counter-flow MFC is categorized and it is found that potential loss caused by internal resistance hinders performance mostly.