Two-phase mass transfer in a vapor-fed microfluidic fuel cell

Microfluidic fuel cells (MFCs) fed with methanol vapor are highly competitive in the field of high-efficient energy sources. However, the lack of a two-phase mass transfer theory within the porous electrode restricts the performance and scalability of this potential power option. Herein, a two-dimensional vapor-fed MFC model for twophase mass transfer based on the mixed wettability of each porous layer is proposed. The effects of two-phase mass transfer on the reactant transport, electrochemical reaction, ion conduction, and cell performance are deeply discussed. This model provides a plausible theoretical explanation for maintaining adequate ion conductivity in catalyst layer and the transport limitations for methanol and oxygen at each electrode. The low fuel concentrations under high current densities lead to concentration polarization, indicating that the inefficient mass transfer at the anode dominates the cell performance. Under a peak power density of 35 mW cm-2, the vapor-fed MFC's fuel utilization can reach up to 56%. For scaling up vapor-fed MFCs, the horizontal electrolyte channel and uniformly distributed evaporation surface are ideal for optimizing anode utilization and output power. The proposed model covers a gap in the theory of two-phase mass transfer within vapor-fed MFCs and facilitates its practical implementation for improved electrochemical performance.