Liquid fuel cells operated at room-temperature are promising candidates for the next-generation of power sources for microelectronic devices. Enabling high-concentrated or even neat fuel operation of fuel cells, which is currently limited by adverse fuel crossover through membrane, could significantly improve the cell current density, reversible potential and energy density. Herein, microfluidic tools are proposed to solve the crossover problem. A three-dimensional numerical model for air-breathing microfluidic fuel cell (MFC) fed with concentrated formic acid is developed. The model couples CFD with electrochemical kinetics to account for the complex interactions inside the cell. Maxwell-Stefan equations are used to describe the nonlinear behaviors in the electrolyte. Based on the model analysis, the feasibility of concentrated fuel operation has been proved. Nonlinear diffusion characteristics, mass transport and performance of MFC cell are analyzed. (C) 2013 Elsevier Ltd. All rights reserved.