Computational modeling of air-breathing microfluidic fuel cells with flow-over and flow-through anodes

• A 3D computational model for air-breathing microfluidic fuel cells is developed.
• An in-house air-breathing microfluidic fuel cell with a flow-through anode is tested.
• Fuel transport to the flow-over anode is limited by the concentration boundary layer.
• Flow-through anodes can enhance fuel transport and improve electrode utilization.
• Flow-through anodes enable lower fuel crossover current densities at low flow rates.

A three-dimensional computational model for air-breathing microfluidic fuel cells (AMFCs) with flow-over and flow-through anodes is developed. The coupled multiphysics phenomena of fluid flow, species transport and electrochemical reactions are resolved numerically. The model has been validated against experimental data using an in-house AMFC prototype with a flow-through anode. Characteristics of fuel transfer and fuel crossover for both types of anodes are investigated. The model results reveal that the fuel transport to the flow-over anode is intrinsically limited by the fuel concentration boundary layer. Conversely, fuel transport for the flow-through anode is convectively enhanced by the permeate flow, and no concentration boundary layer is observed. An unexpected additional advantage of the flow-through anode configuration is lower parasitic (crossover) current density than the flow-over case at practical low flow rates. Cell performance of the flow-through case is found to be limited by reaction kinetics. The present model provides insights into the fuel transport and fuel crossover in air-breathing microfluidic fuel cells and provides guidance for further design and operation optimization.

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