Effect of operating cell voltage on the NaCl poisoning mechanism in polymer electrolyte membrane fuel cells

The mechanism of NaCl poisoning in polymer electrolyte membrane fuel cells (PEMFCs) depends on the operating cell voltage. Both the Pt dissolution and the liberation of Cl₂ and CO₂ gases are monitored using an on-line mass spectrometer to differentiate between the different poisoning mechanisms. The changes in the particle size and composition of the catalyst are measured by high-resolution transmission electron microscopy and energy dispersive spectroscopy. At a cell voltage of 0.6 V the degradation of performance due to NaCl poisoning is primarily attributed to blockage of the active sites of the catalyst by the adsorption of Cl⁻. This reduced performance can be fully restored by removing Cl⁻ in the form of Cl₂ while slowing down the carbon corrosion reaction. However, NaCl poisoning at a high cell voltage of 0.9 V results in Cl⁻-induced dissolution of the Pt catalyst, which prevents performance recovery. Thus, it has been demonstrated that the NaCl poisoning mechanism and the reversibility of the performance loss depends largely on the operating cell voltage of the PEMFC.