Enhancement of mass transfer through under-rib convection in polymer electrolyte fuel cell with dimensionless moduli analysis

The significance of under-rib convection in the flow field development of polymer electrolyte fuel cells (PEFCs) is increasingly recognized. This study quantitatively evaluates the interplay between mass transfer and reaction processes in adjacent channels, affected by under-rib convection. A comprehensive analysis identifies that oxygen mole fraction and current density profiles in the channel-rib direction are governed by five dimensionless moduli. The effectiveness factor, defined as the ratio of the integral average under-rib current density to that without mass transfer resistance, elucidates the potential for current density enhancement due to under-rib convection. Experimental results demonstrate a significant increase in the under-rib current density from 0.15 to 0.32 A cm⁻ 2 as the pressure difference between adjacent channels rises from 0 to 929 Pa at 0.60 V and 0.52 relative humidity. This corresponds to an increase in the effectiveness factor from 0.37 to 0.77 and a Péclet number increase from 0 to 34.8. Model predictions indicate that the maximum net power density is achieved at a Péclet number of 60, balancing under-rib convection benefits and pumping pressure. Validated by experimental results, the model aids in reaction kinetics analysis and polarization prediction, offering significant insights and practical guidelines for electrochemical reactor optimization. • Under-rib convection affecting transport-reaction interactions is evaluated. • Dimensionless moduli determine the channel-rib oxygen and reaction profiles. • Polarization behaviors with varied pressure differences were measured and reproduced. • An optimal pressure difference maximizing the net power density is obtained. • The model demonstrates capability in kinetics analysis and polarization prediction.