Microscale mass transfer structure in the anode catalyst layer (CL) can significantly alter the performance of a direct methanol fuel cell (DMFC) because it changes both the oxidation rate and crossover flux of methanol. The microscale mass transfer structure can be modified by changing the loading of the pore former (PF). An empirical model was developed for the microstrucural design and optimization of anode CL by incorporating the PF into the anode CL. The optimal loading of PF is 100 g/m(2) according to the calculated results. Experimental results confirmed the accuracy of the calculations, and the passive DMFC performs 37% better by incorporating the optimal loading of PF into the anode CL as compared to the conventional anode CL. The validity of the proposed empirical model can also be proven by comparing the calculated polarization results with the previously reported experimental data. (C) 2012 American Institute of Chemical Engineers AIChE J, 59: 780-786, 2013