Enhancing fuel transport in air-breathing microfluidic fuel cells by immersed fuel micro-jet

Air-breathing microfluidic fuel cells with flow-over planar anodes can facilitate system integration but suffer from the fuel concentration boundary layer over the anode, which significantly hinders the fuel transport and limit cell performance. A novel approach is proposed to actively replenish the fuel concentration boundary layer by immersed fuel micro-jet, where part of the fresh fuel is jetted perpendicular to the anode, enabling targeted fuel transfer enhancement. The immersed fuel micro-jet is visualized by fluorescence microscopy, and the micro-jet can reach and flow along the anode at optimal condition. The same cell architecture is tested in both the flow-over and micro-jet modes. The electrochemical measurement and preliminary modelling results indicate that the fuel transfer limitation can be largely mitigated by fuel micro-jet, and the cell performance is enhanced accordingly. The micro-jet located at the middle of flow channel can balance the trade-off between replenishment and benefitted anode area. The effect of total fuel flow rate and micro-jet/lateral flow rate ratio on the fuel transport and cell performance are also discussed in detail. As compared with the flow-over mode, the maximum performance improvement of 40.9% is achieved by the immersed fuel micro-jet, and the optimal power density reaches 119.3 mW cm−3.