Proton fuel starvation

Liang, D. (2009) Study of the cell reversal process of large area proton exchange membrane fuel cells under fuel starvation. J. Power Sources, 194, 847-853. 

Air starvation is less well documented, and is believed to be less detrimental than fuel starvation. As the lack of oxygen needs to be replaced by other components to be reduced, this will generally lead to the reduction of protons to form hydrogen, which on itself leads to a negative cell voltage, as the proton reduction potential lies below the hydrogen oxidation potential [90]. 

The protons will pass through the membrane and combine with oxygen at the cathode in the normal reduction reaction to produce water (reverse of reaction equation (1.37)). A polarization of a complete fuel starvation (no hydrogen) with humidified nitrogen flowing on the anode, with the cell connected to a power supply, is presented in Figure 1.8 for an anode with a 4 mg Pt/cm loading of Pt black catalyst on the anode. 

Sun et al. (2007) and Hottinen et al. (2003) studied the humidity conditions and the effects of humidity on local fuel starvation and learned that when the fuel cell membrane was under-humidified the current densities increased monotonicaUy across the flow channel due to the progressive hydration of the membrane and increased proton conductivity of the Nafion membrane. In a cell operating with an over-hydrated membrane, the current distribution decreased monotonicaUy due to increased partial pressure and decreased as water content increased in the catalyst layer due to blockage of active sites or water flooding. Thus, water content within the membrane strongly affects the current distribution within the fuel cell and can aggravate localized fuel starvation. 

However, when a load is increased abruptly or when the concentration of the fuel decreases, a so-called fuel starvation occurs in which the amount of fuel required at the anode during power generation becomes insufficient. In such a case, for example, carbon in a carbon-supported catalyst medium reacts with water at the anode, and occasionally, also at the cathode, to produce protons as shown... 

The design and assembly of PEM fuel cell components, such as flow fields and manifolds, can have a significant influence on water management and feed flows, which will in mrn affect the durability of fuel ceU components. For example, an improper design of the flow fields can result in water blockage, and improper manifold design can induce poor cell-to-cell flow distribution, both of which may cause localized fuel starvation. This localized fuel starvation can then induce an increased local anode potential to levels at which carbon oxidation or even water electrolysis may occur to provide the required protons and electrons for the oxygen reduction reaction (ORR) at the cathode. These reactions will induce corrosion of the carbon support and will result in a permanent loss of electrochemically active area at the anode. 

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

Ohs, J.H., Sauter, U., Maass, S., and Stolten, D. (2011) Modeling hydrogen starvation conditions in proton-exchange membrane fuel cells. J. Power Sources, 196 (1), 255-263. 

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