Local entropy generation analysis on passive high-concentration DMFCs (direct methanol fuel cell) with different cell structures

In this paper, the local entropy generation analysis has been conducted based on a two-dimensional, two-phase, non-isothermal DMFC (direct methanol fuel cell) model, the entropy generation contributed by the chemical reactions, heat transfer, mass diffusion, and viscous dissipation is investigated. Then, the performance of fuel cells with different methanol barrier layers and electrolyte membranes have been studied based on the local entropy generation analysis. Results indicate that the entropy generation during cell operation is mainly caused by the irreversible electrochemical reactions, and that the entropy generated by mass diffusion and viscous dissipation can be considered negligible. The entropy generated by heat transfer is about two magnitudes less than the entropy generated by the electrochemical reactions in the passive DMFCs operating near room temperature. The overall entropy generation rate in a DMFC can be decreased by increasing the thickness of the methanol barrier layer and decreasing the thickness of the electrolyte membrane.

Research highlights
► Less than 18% of the exergy input by methanol supply is converted to electricity due to irreversibilities in a direct methanol fuel cell (DMFC).
► The exergy destruction during DMFC operation is mainly caused by the irreversible electrochemical reactions.
► The exergy destruction due to heat transfer is about two orders of magnitudes smaller than the entropy generated by the electrochemical reactions.
► The exergy destructions caused by mass diffusion and viscous dissipation are negligible.
► The overall entropy generation rate in a DMFC can be decreased by using a thinner electrolyte membrane and a thicker methanol barrier layer.