H2 starvation

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

Figure 1 shows the schematic of a PEM fuel cell where there is an H2/02 front dividing the cell into two portions one is H2-rich and generates electric power as a power source, and the other is H2-ffee and becomes a load driven by the power source. The existence of the H2/02 front results from two scenarios (a) start-stop events frequently seen in automotive application and (b) local H2 starvation caused by local blockage of the H2 fuel supply, e.g., part of anode flow-field is filled with liquid water. As shown in Fig. 1,... 

Figure 1. The schematic of a PEMFC having the H2/O2 front in the anode and major electrochemical reactions considered in the analysis. The H2/O2 front divides the fuel cell into the power source and the load. In the load portion, anode flow-field (FF) is occupied by air (or O2+N2) in the case of start-stop, while it is filled with liquid water in the case of local H2 starvation.

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... 

In the fully developed H2 starvation region, where H2 is completely depleted, the cathode electrode potential reaches its maximum value as determined by the mixed potential of all electrochemical reactions involved at the cathode, namely, COR and OER. The reaction current therein is determined by 02 crossover (ixthrough membrane to anode, where only ORR takes place in the absence of H2. Charge balance yields... 

Catalyst, Catalyst-Support, and Membrane Material Impact on Maximum Catalyst-Support Corrosion Rate Under Fully Developed H2 Starvation Conditions. Here, Advanced-Support is a Hypothetical Support with a 30-Fold Lower Corrosion Rate than Graphitized Vulcan Carbon and Membrane-X Refers to a Hypothetical Membrane with a 10-Fold Lower 02 Permeability. 

We use the coupled kinetic and transport model to predict when local H2 starvation occurs and how it affects carbon corrosion rate. 

Figure 12 shows the time scales at which the carbon corrosion current reaches 50% of its maximum value at the center of the H2-starved region. Local H2 starvation takes place within 2—40 s... 

Since the time scales for establishing local H2 starvation events are on the order of seconds or 10 s of seconds,11,14 pseudo-capacitive effects will not be important. 

Thus far, most work on this phenomenon has been with whole cells or crude extract activities, and thus little enzymatic detail is available. The ADH activity is not present in cells grown in abundant H2 without the alcohol [26,27], suggesting regulation H2 starvation in the absence of alcohol may also induce the ADH. Several alcohols can cause cells to produce the active enzyme. 

Gu W, Carter RN, Yu PT, Gasteigta- HA (2007) Start/stop and local H2 starvation mechanisms of carbon corrosion model vs. experiment. ECS Trans ll(l) 963-973... 

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