Flexible direct formate paper fuel cells with high performance and great durability

Paper-based microfluidic fuel cells are prominent in flexible electronics, including wearable and disposable devices, such as smart packages and point-of-care diagnostics. However, the performance is generally low, and the long-term durability is questionable. In this work, we propose a flexible paper-based fuel cell with a novel cell architecture that adopts a single flow for the delivery of both the fuel and the supporting electrolyte. During cell operation, the anode is immersed in a liquid fuel with a supporting electrolyte, while the cathode is exposed to the ambient air. The performance of this cell is increased by one order of magnitude compared to the conventional co-flow cell architecture due to the enhanced mass transfer. A maximum power density of ~20 mW/cm² and a maximum current density of 122.9 mA/cm² are achieved, which are the highest among all reported paper-based direct formate fuel cells. Furthermore, this cell can steadily discharge at 5 mA cm⁻² for more than 10 days continuously, while the morphology of the anode and the cathode before and after cell operation remains unchanged. Finally, this paper-based fuel cell can be efficiently fabricated by 3D printing, which is simple, low cost, and advantageous for paper-based fuel cell fabrication.