Computation and numerical modeling of fuel concentration distribution and current density on performance of the microfluidic fuel cell

Abstract

This study numerically investigates current density and fuel concentration on the performance of microfluidic fuel cells that breathe air as an oxidant. The microfluidic fuel cells having a microchannel width of 1.0 mm and 50 μm in-depth with an electrode spacing of 0.3 mm. The concentration formic acid of 0.3 M, 0.5 M, and 1.0 M mixed with 0.5 M sulfuric acid (supporting electrolyte) in aqueous solution was used as fuel and another inlet a stream of 0.5 M sulfuric acid as an electrolyte which were varied at an inlet flow rate of 0.3, 0.5, and 0.7 mL/min. First, a three-dimensional microfluidic fuel cell model was established using COMSOL Multiphysics 5.1 to simulate the fuel cell performance. Subsequently, both V-I curves obtained from simulation and published experimental data under similar operating condition were compared to assure the validity of the simulation. The transport phenomena in the microfluidic fuel cells were formulated with continuity equation, momentum equation, species transport equation, and charge equation. The porous media flow in the gas diffusion layer was described by Brinkman equation. The Butler-Volmer equations were applied to get the V-I curves. The maximum power density of the fuel cell at 0.7 mL/min fed with 0.3 M, 0.5 M, and 1.0 M formic acid for the measured was approximately 27 mW/cm2, 30 mW/cm2, and 36 mW/cm2, respectively, while for the simulation was approximately 21.64, 29.82, and 36.57 mW/cm2, respectively.