Zero-dimensional thermodynamic and electrochemical modeling of a direct methanol fuel cell with dynamic methanol feeding control for portable applications

This paper presents the thermodynamic and electrochemical modeling of a Direct Methanol Fuel Cell (DMFC) system designed for portable power applications. A dynamic mixing tank model was developed to maintain a stable 1 M methanol concentration in the methanol–water mixture. The proposed design enhances overall system efficiency by recycling the water generated during fuel cell operation back to the mixing tank. The target methanol concentration is regulated by supplying pure methanol proportionally to the amount consumed within the fuel cell. A zero-dimensional modeling approach was applied to mathematically describe system behavior. The anode and cathode performances were modeled using the semi-empirical equations of Meyers and Newman. These equations were implemented in the Engineering Equation Solver (EES) environment to calculate key operating parameters such as flow rate, cell voltage, and current density. Time-dependent analyses were conducted to research the variation of methanol concentration in the mixing tank under different current loads. Results indicate that methanol concentration decreases more rapidly at higher current densities, highlighting the necessity of a dynamic fuel feeding algorithm. Accordingly, a mathematical model was improved to determine the methanol flow rate dynamically based on real-time methanol consumption inside the fuel cell. A maximum power density of 0.166 W cm⁻² was reached at a current density of 0.38 A cm⁻² and 30 °C, corresponding to an overall system efficiency of approximately 42%. Methanol flow rate calculations based on both Faraday’s law and energy balance methods yielded consistent results of 0.796 mL min⁻¹ and 0.753 mL min⁻¹, respectively. The findings demonstrate that precise and adaptive fuel management is essential for sustaining optimal DMFC performance in portable applications.