Activity, Performance, and Durability for the Reduction of Oxygen in PEM Fuel Cells, of Fe/N/C Electrocatalysts Obtained from the Pyrolysis of Metal-Organic-Framework and Iron Porphyrin Precursors

Fe/N/Ctype 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 degrees C, then in NH3 at 950 degrees 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 degrees C inH(2)/O-2 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 degrees 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 degrees 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. (C) 2015 Elsevier Ltd. All rights reserved.