On the performance of membraneless laminar flow-based fuel cells

This paper reports on the characterization and optimization of laminar flow-based fuel cells (LFFCs) for both performance and fuel utilization. The impact of different operating conditions (volumetric flow rate, fuel-to-electrolyte flow rate ratio, and oxygen concentration) and of different cell dimensions (electrode-to-electrode distances, and channel length) on the performance (both power density and fuel utilization) of individual LFFCs is investigated. A finite-element-method simulation, which accounts for all relevant transport processes and electrode reactions, was developed to explain the experimental results here. This model can be used to guide further LFFC optimizations with respect to cell design and operation conditions. Using formic acid as the fuel, we measured a peak power density of 55 mW cm−2. By hydrodynamically focusing the fuel to a thin stream on the anode we were able to reduce the fraction of fuel that passes through the channel without reacting, thereby increasing the fuel utilization per pass to a maximum of 38%. This paper concludes with a discussion on the various trade-offs between maximizing power density and optimizing fuel utilization per pass for individual LFFCs, in light of scaling out to a multichannel LFFC-based power source system.