Numerical simulation of the performance of air-breathing direct formic acid microfluidic fuel cells

This work numerically investigated the effects of various factors on the performance of air-breathing direct formic acid microfluidic fuel cells. An MFC with a microchannel width of 1.5 mm, depth of 0.05 mm, and electrode spacing of 0.3 mm was used in the simulation. An MFC which was a 1.5-mm-wide, 0.05-mm-deep microchannel installed with two 0.3-mm-apart electrodes was used in the simulation. The mixture of formic acid at concentrations of 0.3, 0.5, and 1.0 M and 0.5-M sulphuric acid served as fuel, while a 0.5-M sulphuric acid stream served as the electrolyte introduced at inlet flow rates of 0.05, 0.1, and 0.5 mL/min. First, a three-dimensional MFC model was built using COMSOL Multiphysics 5.1 to simulate the fuel cell performance. Subsequently, I-V curves obtained from simulations and from published experimental data under similar operating conditions were compared to ensure the validity of the simulation. Transport phenomena were formulated with a continuity equation, momentum equation, species transport equation, and charge equation. Additionally, the flow through porous media in the gas diffusion layer was described using the Brinkman equation, whereas the Butler-Volmer equation was applied to obtain I-V and P-I curves. The current density distribution resulting from internal current loss and reactant concentration on both electrodes was also determined in this work.