Effect of gas shutoff sequences on the degradation of proton exchange membrane fuel cells with dummy load during startup and shutdown cycles

In this paper, the effect of shutoff sequences of hydrogen and air on the degradation behaviours of proton exchange membrane fuel cells (PEMFCs) is investigated with two different shutdown procedures. After one of the gases is shut off, the dummy load is applied to consume the residual gas in the flow field. Theoretical analysis and experimental tests indicate that different gas shutoff sequences have great effect on the oxygen permeation rate across the membrane during introducing the dummy load, resulting in producing the H2/O2 interface at the anode in the next startup process. Electrochemical techniques, including the measurement of polarization curves, cyclic voltammetry, and cross-sectional scanning electron microscopy (SEM) of membrane electrode assemblies (MEAs) and transmission electron microscopy (TEM) of Pt/C catalyst are employed to evaluate the performance decay of PEMFCs after 1500 startup and shutdown cycles. The results show that the case if air is shut off firstly would significantly alleviate both the performance decay and the decrease in the electrochemically active surface area, resulting in an improvement in the durability of PEMFCs.

Graphical abstractSchematic images of two models, in case A air was shut off firstly and in case B hydrogen was shut off firstly with the formation process of the H2/O2 interface at the anode.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Catalyst layer degradation was reduced by shutting off air prior to hydrogen. ► Applying dummy load caused different oxygen permeation rates in shutdown processes. ► A theoretic model was used to analyse O2 permeation for different shutoff processes.