Transpiration-mimicking wood-based microfluidic aluminum-air batteries: Green power sources for miniaturized applications

Capillary microfluidics on porous substrates emerges as an innovative platform for constructing miniaturized electronics. However, maintaining a steady flow within microfluidics remains challenging, thus limiting their practical applications. Inspired by plant transpiration, this work presents a novel wood-based microfluidic Al-air battery (μAAB) configuration driven by a photothermal evaporator (biomimetic “leaf”). Except for the Al anode, the μAAB features an all-wood design, utilizing the well-aligned microchannels of the natural wood for electrolyte transportation, partially charred wood as photothermal evaporator for flow regulating, and wood-derived self-standing carbon cathode for the oxygen reduction reaction. These components are assembled through mortise-and-tenon joints, and the resulting μAAB exhibits a remarkable peak power density of 230 mW cm−3. The superior performance stems from the boosted mass transfer, maximized electrochemical interface and minimized depletion boundary layer provided by the 3D channeled structure of the wood-derived cathode. A steady discharge for over 11 h (200 mA cm−3) is obtained via the continuous electrolyte flow which is facilitated by the photothermal evaporator in the μAAB. This work not only presents a novel concept for miniaturized microfluidic power sources but also highlights the potential of 3D wood-based microfluidics combined with solar energy utilization.