A theoretical model of macro kinetics for methanol oxidation in the porous anode of DMFC was developed.First

an intrinsic kinetics expression including the coverage ratios of CO and OH was derived from the dual site mechanism of methanol hydroxylation on Pt-Ru catalyst surface.Second

the balances for both material and charge in a differential volume of the porous anode were calculated to the model equations coupled for describing concentration and potential distributions in the anode.Then the generalized macro kinetics model was obtained with dimensionless variables and parameters.The physical characteristics of the porous anode

including the thickness of catalyst layer

specific area

effective diffusion and conductive coefficients

as well as the catalytic characteristics related to CO and OH coverage ratios as functions of the variable of thickness in particular

were included in this model.Furthermore

the expressions of effectiveness and polarization curve for the porous electrode were presented.The model was a boundary problem of a set of nonlinear second order differential equations

from which two equivalent differential equations can be obtained separately by decoupling.The model equation was solved by using Newman’s BAND (J) program while inserting a subroutine to calculate the coverage ratios at each note.Through comparing the model predicted values with experimental polarization data reported，it was found that the predictions agreed with the data satisfactorily under lower current densities

and were regularly lower than the data under higher current densities as CO2 bubbling became considerable.Detailed analysis of macro kinetics showed that crucial issues for improving performance of the porous anode should be to increase the activity of Pt set of the catalyst for methanol electro decomposition

and to optimize both micro- and macro-structures of the anode for mitigating the influence of two phase flow.This work may also provide an analysis tool for the performance of anodes in DEFC as well as DBFC.