Carbon support corrosion

Pt particle agglomeration is due to carbon support corrosion. Electrochemical carbon corrosion is known to occur above 0.9 V. It has been suggested that loss of carbon causes Pt particle agglomeration and electrical isolation, leading to loss in activity. 

Modeling of Membrane-Electrode-Assembly Degradation in Proton-Exchange-Membrane Fuel Cells - Local H2 Starvation and Start-Stop Induced Carbon-Support Corrosion... 

In this chapter, we will review the fundamental models that we developed to predict cathode carbon-support corrosion induced by local H2 starvation and start-stop in a PEM fuel cell, and show how we used them to understand experiments and provide guidelines for developing strategies to mitigate carbon corrosion. We will discuss the kinetic model,12 coupled kinetic and transport model,14 and pseudo-capacitance model15 sequentially in the three sections that follow. Given the measured electrode kinetics for the electrochemical reactions appearing in Fig. 1, we will describe a model, compare the model results with available experimental data, and then present... 

As COR and OER occur simultaneously in the cathode, their kinetics are particularly important in evaluating carbon-support corrosion. The kinetics of OER is material-specific, dependent on catalyst composition and electrode fabrication.35,37 -39 A number of OER kinetics studies were done on Pt metal electrodes.37-39 However, there is a lack of OER kinetics data on electrodes made of Pt nano-particles dispersed on carbon supports. Figure 2 shows the measured OER current density with respect to the overpotential defined by Eq. (6).35 The 02 concentration was measured at the exit of a 50-cm2 cell using a gas chromatograph (GC). The 02 evolution rate (= 02 concentration x cathode flow rate) was then converted to the OER current density, assuming 4e /02 molecule. Diluted H2 (10%) and a thicker membrane (50 p,m) were used in the measurement to minimize H2 crossover from anode to cathode, because H2 would react with 02 evolved at the cathode and incur inaccuracy in the measured OER current density. Figure 2 indicates that the OER... 

As shown in Fig. 14, the cathode potential changes abruptly across the H2/air-front. This fact warrants the inclusion of the pseudocapacitance into the previous steady-state kinetic model.12 It is clear that the electrode s pseudo-capacitance can supply protons in transient events and thereby reduce the cathode carbon-support corrosion rate in the case of fast moving H2/air- ronts. Figure 18... 

Recent kinetic studies indicate that carbon corrosion can be significant under normal transient operation.56,57,60-62 The rate of voltage change, common in the automotive application, enhances cathode carbon-support corrosion.16 Hence, further model improvement shall be focused on finding the carbon corrosion kinetics associated with voltage cycling. Currently, the relationship between fuel cell performance decay and accumulated carbon-support loss is only empirical.22 More effort has to be made to incorporate mechanisms that can accurately quantify voltage decay with carbon-support loss.31,32... 

Li W, Lane AM (2009) Investigation of Pt catalytic effects on carbon support corrosion of the cathode catalyst in PEM fuel cells using DEMS spectra. Electrochem Commun 11 1187-1190... 

Durable and reliable operation for several thousand hours are considered crucial for the successfully commercialization of DAFC. The factors that determine a PEM fuel cell s lifetime (as platinum-particle dissolution and sintering, carbon-support corrosion, and membrane thinning) is currently studied by many researchers in order of increase the lifetime without increasing cost or losing performance [83-85]. The relative contribution of each component s degradation to the degradation of the entire fuel cell is not completely understood yet. 

To reach the requirements of performance and durability for both automotive and stationary PEFC appUcations [20], catalyst durability has become an important issue both for of academic and industrial R D. Cathode degradation in operating PEFCs mainly occurs tmder transient conditions, leading both to Pt dissolu-tion/degradation and carbon-support corrosion. At typical operational pH conditions and above 0.9 V, two main mechanisms lead to Pt degradation (i) diffusion of dissolved Pt species... 

Under normal fuel cell operating conditions, the highest oxidative potentials in the cathode range between 0.6 V (vs. RHE) at high-current density and 0.95 V (vs. RHE) at open circuit (the anode potential remains always near 0 V vs. RHE), so that carbon-support corrosion is negligible. However, under start/stop conditions or in the case of localized hydrogen starvation, the cathode potential significantly exceeds 1 V versus RHE and the associated rapid carbon-support corrosion leads to... 

Fig. 11.6 Fuel cell perfoimance loss as a function of the extent of carbon-support corrosion. Conditions H2/air (s = 2/2) performance at 80°C, 100%RH, 150 kPaats (Reproduced from H.A. Gasteiger et al. [3] by permission from Springer)...

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