Chaotic flow-based fuel cell built on counter-flow microfluidic network: Predicting the over-limiting current behavior

The membraneless microfluidic fuel cell (MFC) is a promising micro-scale power source with potentially wide applications. MFC commonly relies on the co-laminar microfluidic platform in which redox streams flow in parallel in a microchannel. The nature of this cell architecture limits the mass transport inside the cell, often resulting in low power density. To overcome the issues, we propose an innovative concept of chaotic flow-based fuel cell (CFFC), which is built on a counter-flow microfluidic platform with the flow channel patterned with micro-ridges. A CFD/electrochemical model is used to predict the performance and investigate the underlay mechanism of the CFFC. Two theoretical upper bounds, i.e., the limiting current and limiting fuel conversion for conventional MFC, are derived. Through the results, it is found that the generation of chaotic flow inside the patterned activation zone enables the CFFC to exceed the theoretical limitations and work with over-limiting current for high-power output. Meanwhile, the interfacial mixing and crossover is minimized by the counter-flow microfluidics, allowing for over-limiting fuel conversion to useful electricity output. The achievement of unprecedented operating regime demonstrated in this study open up a new direction towards optimization, operating and design of the MFC.