Paper-based microfluidic fuel cells: Is commercial filter paper a good-enough choice of substrate?

Paper-based microfluidic fuel cell (PMFC) is a green and low-cost power source for point-of-care applications. However, the current reliance on commercial filter paper strongly limits its power density. This work improves the PMFC performance by developing a homemade paper with thick and loosely-packed cellulose fibers. With similar areal density, the homemade paper obtains 4 times of peak power density compared with filter paper due to enhanced ionic conduction and mass transport, which is mainly attributed to its larger thickness and porosity after electrolyte uptake. Moreover, by tailoring key papermaking parameters such as hot-pressing pressure, cellulose loading and pulp stirring time, the homemade paper is further optimized together with the structure-performance relationship revealed. Results indicate that higher hot-pressing pressure leads to lower wet thickness and porosity, decreasing the cell performance. Larger cellulose loading also reduces wet porosity so weakens the capillary flow, but this is compensated by enhanced ionic conduction due to the increment of wet thickness. As for pulp stirring time, a higher value will reduce wet thickness and porosity, while a lower value will generate large pores that lead to catalyst loss. In summary, more advanced paper material should be developed for future PMFCs.