Pore-scale modeling of oxygen transport in the catalyst layer of air-breathing cathode in membraneless microfluidic fuel cells

Abstract

The air-breathing membraneless microfluidic fuel cell is one of the potential micro-fuel cells. Different from conventional membrane-based micro-fuel cells, its cathode catalyst layer directly contacts with flowing aqueous electrolyte. This makes it essential to well understand the oxygen transport, dissolve and reaction in cathode catalyst layer of the microfluidic fuel cell. For the first time, a pore-scale Lattice Boltzmann method model is developed for the cathode catalyst layer with an underneath electrolyte microchannel. The various nanostructured catalyst layers are numerically reconstructed. The effects of key components (ionomer and catalyst mass fractions) and geometric parameters (porosity, isotropy) on oxygen transport and reaction are investigated and discussed. The modeling results suggest that local oxygen concentration and reaction rate are closely correlated to nanostructure. Oxygen transfer can be enhanced by increasing the porosity yet ionomer is found to be extra resistance. The ionomer and catalyst mass fractions have complex effects on oxygen transfer and reaction. Vertical-anisotropic catalyst layers benefit oxygen transfer, thus ordered nanostructure of cathode catalyst layer holds great potentials to enhance performance. The electrolyte flow rate shows the minimum influence on oxygen transfer and reaction. The modeling results can provide insights into multiphysics interaction and characteristics of oxygen transport in air-breathing cathode and also be reference for flow in porous media involving electrochemical reactions.