Solar-Boosted Paper-Based Microfluidic Fuel Cells for Miniaturized Power Sources

Paper-based microfluidics emerges as an innovative platform for constructing miniaturized electrochemical devices, which mainly benefit from the spontaneous capillary action of paper. Nevertheless, the capillary-driven flow dynamics on paper are determined exclusively by the intrinsic properties of paper and fluidics, thus lacking the controllability that conventional pump-based microfluidics can provide. Herein, an approach to regulating the capillary flow on paper is introduced by conjugating the outlets of microfluidic channels with a photothermal module for water evaporation. The capillary flow rate on paper can be handily regulated from 4 to 37 µL min⁻¹ under controllable illumination conditions. As a proof-of-concept, prototypical paper-based microfluidic fuel cells integrated with the photothermal module are constructed. Their peak power density can be boosted from 0.3 up to 2.1 mW cm⁻² under the simulated sunlight irradiation. The influence of capillary flow rate on the fuel cell performance is further validated using multiphysics simulations. The present work not only provides a practically feasible method to boost the performance of paper-based microfluidic fuel cells using solar energy, but also opens a new avenue for modulating the performance of paper-based microfluidics, which has long been a challenge in this field.