Operation Window of Integrated Methanol Steam Reformer/High-Temperature Proton Exchange Membrane Fuel Cells: A Three-Dimensional Numerical Study

Abstract Stack-integrated methanol steam reformer (MSR)/high-temperature proton exchange membrane fuel cell (HT-PEMFC) systems enable simultaneous hydrogen production and power generation within monolithic devices, significantly reducing system complexity and costs. However, in situ heat exchange between endothermic reforming layers and exothermic fuel cell layers creates complex thermal interactions under variable loads, posing a critical challenge to stable operation. Here, we systematically evaluate the adiabatic operational limits of a fully coupled stack-integrated MSR/HT-PEMFC using three-dimensional computational fluid dynamics. Although thermoneutral operation can be achieved at 0.4 A/cm 2 under isothermal conditions, adiabatic operation introduces temperature gradients exceeding 30 °C and elevates reformate carbon monoxide (CO) concentrations beyond 2000 × 10 −6 , which can irreversibly degrade fuel cell performance. Parametric analysis reveals a critical trade-off: reducing voltage or increasing methanol feed rates lowers CO levels by 38% but degrades system efficiency by 15%, highlighting an inherent safety–efficiency conflict in adiabatic systems. These findings underscore the necessity of coordinated voltage and methanol feed flow regulation, as well as strategic decoupling of MSR and PEMFC for practical implementation.