A steady-state, isothermal, one dimensional model of a proton exchange membrane fuel cell (PEMFC), with a polybenzimidazole (PBI) membrane, was developed. The electrode kinetics were represented by the Butler-Volmer equation, mass transport was described by the multi-component Stefan-Maxwell equations and Darcy's law and the ionic and electronic resistances described by Ohm's law. The model incorporated the effects of temperature and pressure on the open circuit potential, the exchange current density and diffusion coefficients, together with the effect of water transport across the membrane on the conductivity of the PBI membrane. The polarisation curves predicted by the model were validated against experimental data for a PEMFC operating in the temperature range of 125-200°C. There was good agreement between experimental and model data of the effect of temperature and oxygen/air pressure on cell performance. The model was used to simulate the effect of catalyst loading and the Pt/carbon ratio on cell performance and, in the latter case, a 40 wt.% Pt/C ratio gave the highest peak power density.Notations A act Active area of catalyst particles (m 2 ) A D Anode diffusion region (No units) A M Anode microporous region (No units) A R Anode reaction region (No units) A F Anode flow region (No units) a Height of catalyst (m) b Width of catalyst (m) c i Molar density/concentration of component i (mol m -3 ) C D Cathode diffusion region (No units) C R Cathode reaction/catalyst region (No units) c Depth of catalyst (No units) D ij Stefan-Maxwell diffusivities (m 2 s -1 ) D eff ij Effective Stefan-Maxwell diffusivities (m 2 s -1 ) D ij Symmetric diffusivities (m 2 s -1 ) E Potential (V) E 0 0 Standard state reference potential (V) F Faraday constant (A s mol -1 ) G Gibbs free energy (J mol -1 ) H Enthalpy (J mol -1 ) I Cell current density (A m -2 ) j e Electronic current (A m -2 ) j i Ionic/proton current (A m -2 ) j o Exchange current density (A m -2 ) j o b Exchange current density at electrode b (A m -2 ) j o a Exchange current density in anode (A m -2 ) j b V Current density source term in cathode (A m -3 ) j a V Current density source term in anode (A m -3 ) j c V Current density source term in cathode (A m -3 ) J i Diffusion flux (kg m -2 s -1 ) k Permeability of the porous media (m 2 ) L Catalyst loading (g m -2 ) M Membrane region (No units) M cat Mass of the catalyst (g) M i Mass of species i (kg mol -1 ) n Number of electrons (No units) N i Total flux of species i (kg m -2 s -1 ) p Total pressure (m -1 kg s -2 )

A steady-state, isothermal, one-dimensional model of a direct methanol proton exchange membrane fuel cell (PEMFC), with a polybenzimidazole (PBI) membrane, was developed. The electrode kinetics were represented by the Butler–Volmer equation, mass transport was described by the multicomponent Stefan–Maxwell equations and Darcy's law, and the ionic and electronic resistances described by Ohm's law. The model incorporated the effects of temperature and pressure on the open circuit potential, the exchange current density, and diffusion coefficients, together with the effect of water transport across the membrane on the conductivity of the PBI membrane. The influence of methanol crossover on the cathode polarization is included in the model. The polarization curves predicted by the model were validated against experimental data for a direct methanol fuel cell (DMFC) operating in the temperature range of 125–175 °C. There was good agreement between experimental and model data for the effect of temperature and oxygen/air pressure on cell performance. The fuel cell performance was relatively poor, at only 16 mW cm−2 peak power density using low concentrations of methanol in the vapor phase.