Study of the self-degradation performance of a passive direct methanol fuel cell with an Fe-N-C catalyst

Fe-N-C catalysts are considered promising substitutes for Pt-based catalysts at the cathode in direct methanol fuel cells (DMFCs) owing to their great methanol tolerance. However, Fe-N-C-based DMFCs commonly suffer from a decreased performance under extremely high methanol concentrations and exhibit poor stability, while the underlying mechanism remains controversial. In this study, a self-degradation phenomenon in a passive Fe-N-C-based DMFC was investigated in detail. The DMFC with an optimized ionomer content and catalyst loading delivered an extremely high peak power density of 28.85 mW cm^-2 when fed with 3 M methanol solution, while the peak power density of the cell rapidly declined to 16.61 mW cm^-2 after standing for 10 days without any discharging operation. Several electrochemical measurements were designed and conducted to explore the mechanism for this phenomenon. The results of these measurements revealed that methanol molecules are chemically adsorbed on the surface of the Fe-N-C catalyst, and the bonding cannot be reversed using simple physical methods, leading to the isolation of active sites from oxygen. Herein, we provide a new perspective on passive Fe-N-C-based DMFCs that would be significant for the technological development of portable power devices.