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Activity, Performance, and Durability for the Reduction of Oxygen in PEM Fuel Cells, of Fe/N/C Elect

Fe/N/C type catalysts have been produced by ballmilling ZIF-8 (a metal-organic-framework) and a chloroiron-tetramethoxyporphyrin (ClFeTMPP). The resulting material was first pyrolyzed in Ar at temperatures ranging from 850 to 1150 °C, then in NH3 at 950 °C in order to produce two series of catalysts: the Ar and the Ar + NH3 ones. They were labeled NC Por_x-T Ar or NC Por_x-T Ar + NH3, where x is the nominal Fe loading in wt% and T is the temperature of the first pyrolysis in Ar. At 80 °C in H2/O2 fuel cell, the most active and performing catalyst is NC Por_0.8-1050 Ar + NH3. All NC Por_0.8-T Ar + NH3 catalysts with T comprised between 850 and 1050 °C display the same instability behavior. The only catalyst showing an improvement in durability is NC Por_0.8-1150 Ar + NH3. It is proposed that the drastic change in durability upon increasing the first pyrolysis temperature, from 1050 to 1150 °C in Ar, is attributable to an important decrease in the heteroatom content (a drop of 32% for both N and O atoms) of the catalyst upon graphitization, reducing the hydrophilic character of its carbonaceous support and decreasing the possibility of water flooding its catalytic sites, particularly the sites located in micropores.

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