The fading behavior of direct methanol fuel cells under a start-run-stop operation

Stability tests of direct methanol fuel cells (DMFCs) were conducted under two different operational modes, start-run-stop (SRS) and long-running (LR) modes, to investigate the difference in performance decay of the cells. Frequency response analysis (FRA), cyclic voltammetry (CV), transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) were used to identify the causes of cell degradation. The cell performance test results showed that the fading behavior of the cell under the SRS operation was greater than that under the LR operation. The maximum power density was reduced approximately 20% and 32% of the initial value after operating under the LR and the SRS mode, respectively. This result was corresponded with the anode catalyst agglomeration data obtained from both XRD and TEM analysis. The increase of PtRu particle size under the SRS operation was higher than that under the LR operation. The FRA spectra showed that the anode reaction resistance increased from the initial value of 0.26 Ω cm2 to 0.30 Ω cm2 after life-testing under SRS mode for 45 h. A right-shift of the methanol oxidation peak and a 5.0% reduction of electrocatalyst surface area observed from the cyclic voltammograms also supported this finding. Finally the decay of cell performance was due to the Ru crossover, as verified by EDX results.