A circular stacking strategy for microfluidic fuel cells with volatile methanol fuel

Microfluidic fuel cell (MFC) stacking is a prerequisite to improve its power output for practical applications. Unlike the stacking of membrane-based fuel cells, MFC stacking generally involves complex fluidic management, such as anolyte and catholyte distribution, and spent electrolyte collection, which greatly increases the system’s complexity. In addition, the operational robustness of MFC stacks is generally sensitive to the electrolyte flow rate, which imposes stringent requirements on the precision of the electrolyte distributor and the stability of the environment where the MFC stack works. To deal with these issues, a circular MFC stacking strategy is proposed in this paper, which is especially suitable for volatile hydrocarbon fuels. In such an MFC stack, anolyte is no longer needed because fuel is stored outside the MFC in neat form, which evaporates into vapor form and diffuses into the MFC anodes, while oxidant is directly obtained from the ambient air. In this manner, only one electrolyte flow is needed for each single cell, which greatly simplifies the fluidic management system. Moreover, the stack performance is also found to be flow rate insensitive, ensuring a much improved operational robustness. Experimental results of a six-cell stack prototype (connected in series) have demonstrated an OCV of 5–5.5V, indicating a very effective electrolyte distribution and, therefore, fuel crossover suppression. A peak power density of 108.7mWcm−2 can be achieved at 60°C with 3M KOH as electrolyte. Moreover, stacking efficiency as high as 98.4% was obtained, which could be attributed to both the effective inhibition of shunt currents and the limited performance difference among the single cells.