The sizes and distributions of active metals were shown by TEM and XRD analysis in Figs. 5 and 6, respectively. With the TEM images only, it was diHcult to measure the exact particle sizes. But the di'erences in the sizes and distributions of them were clearly visualized. Combined with XRD data, the particle sizes and the inter-particle distances were calculated mathematically in Table 3 and showed a goodcorrelation.WhilethediameterofPtparticles,d,hada narrowsizedistributionfrom1.4to2:1 nm,theinter-particle distance, X, showed more broad values from 1.3 to 6:9 nm. These results were correlated with the performance of air breathing-type DMFC single cell to Gnd out the optimum conditions of catalysts.