Effects of Cathode Inlet Relative Humidity on PEMFC Durability during Startup–Shutdown Cycling

Abstract

This work investigated the effect of cathode inlet relative humidity ͑RH͒ on the durability of proton exchange membrane fuel cells ͑PEMFCs͒ during startup-shutdown cycling via single-cell experiments. Electrochemical techniques, including measurements of polarization curves, electrochemical impedance spectroscopy ͑EIS͒, cyclic voltammetry ͑CV͒, and linear sweep voltammetry, were performed to examine the effect of cathode inlet RH on the degradation of PEMFCs. The performance was better for PEMFCs cycled at a lower cathode inlet RH than for those cycled at a higher cathode inlet RH on the order of 0 Ͼ 50 Ͼ 100%. The CV and EIS results showed that as the cathode inlet RH increased, the loss of electrochemically active surface area and the increase in the charge-transfer resistance ͑R ct ͒ were faster during the startup-shutdown cycling. However, changes in ohmic resistance ͑R ohm ͒ and hydrogen crossover current density were not detectable, revealing that severe membrane degradation did not occur regardless of the cathode inlet RH during startup-shutdown cycles.Polymer electrolyte membrane fuel cells ͑PEMFCs͒ continue to be considered as the most feasible power source, particularly for automotive applications, due to their high efficiency, relatively low operating temperature, fast startup, and low noxious emissions. Even with these significant advantages, which can have positive impacts in economic and environmental areas, there are several obstacles that still impede their successful commercialization. In addition to cost effectiveness, long-term durability is one key issue in fuel cell vehicles. According to the U.S. Department of Energy durability targets, an estimated 5000 h of continuous operation for fuel cell vehicle is required by 2015. 1 Therefore, optimization of the system operating conditions as well as the membrane electrode assembly ͑MEA͒ and its subcomponents must be implemented to improve performance and durability in fuel cell systems.It is commonly believed that operating conditions, including temperature, pressure, reactant stoichiometry, and gas relative humidity ͑RH͒, can influence cell performance. 2-4 Particularly, RH may play a significant role in the operation of PEMFCs, greatly influencing MEA performance. Many studies have been carried out to investigate the RH effect on PEMFCs. 3-8 Using X-ray diffraction, Borup et al. 4 showed that low RH decreased Pt particle growth but promoted corrosion of the carbon support after potential cycling. Xu et al. 3 investigated surface oxidation of the Pt cathode at different RHs via cyclic voltammetry ͑CV͒. They concluded that an increase in RH from 20 to 72% significantly facilitated the degree of Pt oxidation, which may influence the oxygen reduction kinetics. Recently, Xu et al. 6 also reported the RH effect on membrane degradation in PEMFCs at a constant voltage by showing a higher membrane degradation rate at 60% RH than at either 20 or 100% for given conditions. They further proposed the degradation mechanism of the membrane in terms of oxygen r...

Advanced reliability analysis of Polymer Electrolyte Membrane Fuel Cells using Petri-Net analysis and fuel cell modelling techniques

“…The results of the Petri-Net model using a SSC degradation module was tested using a polarisation curve model as in Figure 9. The model shows a good replication of the polarisation curve drop observed by Kim, et al [19] in Figure 7, with the same logic being carried through the entirety of the Petri-Net model. Each failure mode interaction has a voltage degradation value assigned to it, with some acting reversibly dependent upon the state of the system, and some acting as a counter (irreversible).…”

“…Kim, et al [19] conducted extensive experimentation to reveal the relationship between SSC and degradation of fuel cell performance. Their results show that after 1500 instances of SSC, a drop in performance of 0.08 V was observed (Figure 7).…”

Degradation aspects of water formation and transport in Proton Exchange Membrane Fuel Cell: A review

“…The dissolution of Pt particles from the active surface area of the catalyst layer due to the increase in the RH of the reactant gases was reported previously in [245,343]. Uchimura et al [245] found that the active surface area of the catalyst reduces dramatically by around 50% when RH increases from 30 to 100%.…”

“…One possible explanation for this is that the high current density they operated at (> 1 A cm -2 ) has generated excessive water facilitating chromium particles to be carried away by the back diffusion stream to the anode. Similarly, the Pt migration detected in [343] was found to be more severe at the cathode layer than the anode. When the cell was operated with three different levels of cathode inlet RH (e.g.…”

“…The measurements carried out by Stevens et al [244] showed significant increase in the carbon combustion rate for XC72 and BP2000 type carbon support when the cell operation changed from dry to wet conditions. The carbon corrosion of the cathode catalyst layer in [343] was enhanced noticeably when the cathode inlet RH increased from 0 to 100%. The gradual decrease in the catalyst thickness (~70% reduction, e.g.…”