Models of carbon corrosion induced by oxygen and hydrogen coexistence on the negative electrode are presented. In proton exchange membrane fuel cells (PEMFCs), this phenomenon occurs under several situations, such as start-up, shutdown, and hydrogen starvation. In the absence of hydrogen, the source of protons on the negative electrode is the oxygen reduction reaction. The solution potential decreases and induces an overpotential, ηnormals1 , large enough to cause carbon corrosion on the positive electrode even at low temperatures. The carbon corrosion current is large enough to influence the lifetime of PEMFCs not only in the case of high oxygen partial pressure, such as observed during start-up, but also in the case of low partial pressures such as a result of the permeation of oxygen through the membrane. The influence of key parameters for carbon corrosion is investigated. It is clear that the oxygen reduction activity on the negative electrode, the thickness of the membrane, and the cell potential can affect the carbon corrosion on the positive electrode significantly.

Severe carbon loss phenomena, such as partial hydrogen starvation and start-up, have been investigated in previous works. Even for short times, these acute situations can be fatal, and some methods have been suggested to mitigate carbon oxidation and improve proton exchange membrane fuel cell ͑PEMFC͒ durability. By comparison, the rate of carbon loss is low during an ordinary PEMFC operation. Although less severe than for hydrogen starvation and start-up, the impact is still large enough so that the cell performance degrades markedly after a long-term operation. In this work, carbon loss during a PEMFC operation is investigated with a physical model. These results quantify the effects that cell voltage, activity for oxygen reduction, humidity, and temperature have on the rate of carbon loss. More rapid kinetics for oxygen reduction promotes carbon loss by lowering the solution potential at the fuel cell cathode.Carbon is used extensively as the support for catalysts in proton exchange membrane fuel cells ͑PEMFCs͒. Loss of carbon is a wellknown degradation phenomenon in PEMFC electrodes, and this electrochemical oxidation of carbon causes cell performance to decay. The relationship between carbon loss and cell performance was confirmed by Yu et al. 1 A reduction in carbon of only 5 wt % results in a large drop in cell voltage under a fuel cell operation at a constant current. Because Reiser et al. reported a "reverse current mechanism," 2 carbon losses under partial hydrogen starvation 3 and start-up 4 conditions have been discussed collectively as carbondegradation phenomena in PEMFCs, and the potentially fatal consequences have been noted. 5-12 Makharia et al. suggested that only 1 h under conditions of partial hydrogen starvation caused a loss of more than 5 wt % carbon. 13 Takeuchi and Fuller reported that under severe conditions, a large carbon loss ͑Ͼ1 wt %͒ was expected during the start-up of the fuel cell when air and hydrogen gases were exchanged in the fuel cell anode. 14 As the details of the reverse current mechanism have been elucidated, some methods to mitigate these effects for partial hydrogen starvation and start-up conditions have been proposed. Reducing the loading of a Pt catalyst on the fuel cell anode is an effective mitigation for both cases of carbon loss. 9,10,14,15 At start-up, careful control of the cell voltage also reduces carbon loss, and keeping the cell voltage low can prevent fatal damage for the fuel cell cathode. 14,16 These approaches help to improve the durability of PEMFC membrane electrode assemblies ͑MEAs͒ by eliminating the most severe conditions that cause fatal damage to fuel cell cathodes.Even if we can avoid these catastrophic situations mentioned above, low rates of carbon oxidation are still expected under an ordinary PEMFC operation, especially under high temperature conditions. Whereas a minimum operational life of 5000 h is required for transportation applications, 17 the rate of carbon loss may be 1-10 wt % per 1000 h, large enough to cause the decay of PEMFC perf...

Non‐fluorinated sulphonated polyphosphazene (SPOP) was synthesised and characterised for utilisation as an electrode binder. Polarisation curves were obtained at 80 °C and 95% RH in a H2/air fuel cell. SPOP has the proper properties for a cathode binder in a fuel cell, as its polarisation curve traced that of Nafion® binder for the same operating conditions.

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Carbon loss phenomena, such as partial hydrogen starvation and startup, have been investigated in previous works. Even for short times, these situations can be fatal and some mitigation was suggested to improve PEMFC durability. Small carbon loss occurs under ordinary PEMFC operation. Although this impact is less severe than for hydrogen starvation and startup, it is still large enough to cause the degradation of PEMFC cell performance after long-term operation. Carbon loss under PEMFC operation is investigated in this work with a physical model. These results suggest that high cell potential, high oxygen reduction activity, high humidity, and any imbalance of water vapor pressure in the cell affect the rate of carbon loss. The kinetics for oxygen reduction promotes carbon loss by reducing the solution potential at the fuel-cell cathode.