Transport characteristics and formation mechanism of voltage inconsistency in 200-cell PEMFC stack: Numerical reconstruction and experimental investigation

Due to the difficulty in directly observing and resolving internal mass transport in multi-cell proton exchange membrane fuel cell (PEMFC) stacks, current studies on stack voltage inconsistency remain largely confined to macroscopic performance analysis. Consequently, the mechanisms responsible for voltage inconsistency remain insufficiently understood. To address this gap, this study develops a framework integrating offline pressure testing, pressure boundary extraction, and grouped numerical reconstruction to investigate internal transport processes and clarify the formation mechanism of voltage inconsistency in large-scale multi-cell stacks. In this framework, pressure data measured at different stack positions are used as boundary conditions to reconstruct the transport behavior of representative cells and analyze stack mass transport characteristics. The reconstructed results are then combined with sensitivity analysis of the experimental data to identify the dominant factors governing stack voltage nonuniformity. Finally, numerical simulations are performed to reproduce the development of low-voltage cells and further verify the proposed mechanism. The results show that the maximum oxygen concentration difference among cells at different stack positions is only 0.4 mol/m 3 , indicating that oxygen distribution differences alone are insufficient to cause significant performance variations. Correlation analysis further indicates that liquid water accumulation at the bottom of the stack is the dominant factor responsible for voltage reduction in the bottom cells. Water-rich simulations demonstrate that increased liquid-water loading in the bottom cells can obstruct oxygen transport and cause voltage decay. This study provides an effective numerical reconstruction method for resolving internal transport processes in multi-cell PEMFC stacks and offers guidance for improving stack cell-voltage consistency.