Durable carbon-shell-encapsulated Pt/C catalysts synthesized by direct pyrolysis of Pt-pyrrole complexes for the oxygen reduction reaction

Abstract

Owing to the robust protection of carbon layers, Pt catalysts sheltered by carbon layers (Pt@C/C) show superior durability towards the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFs). Herein, we report a convenient method for synthesizing the Pt@C/C catalyst by the thermal treatment of carbon-supported Pt-pyrrole complexes which have a specific mole ratio of Pt and pyrrole of ∼2.2. The obtained Pt nanoparticles (∼3 nm) were well distributed and encapsulated by nitrogen-doped carbon layers. Notably, the pyrolyzing temperature has critical effects on the ORR activity of the Pt@C/C catalysts, with the Pt@C/C catalyst obtained at 700 °C (Pt@C/C700) exhibiting the best performance and far exceeding that of commercial Pt/C during potential cycling. TEM results show that the performance robustness of Pt@C/C700 is ascribed to the protection of ultra-thin carbon shells. In the cell test, the performance of the membrane-electrode-assembly with the Pt@C/C700 as the ORR catalyst was largely retained after the accelerated stress test, with a loss of only 12 mV at 0.8 A/cm2. The improved stability of Pt@C/C700 can result from the carbon shell's stabilizing effect which physically isolated the Pt nanoparticles from the harsh environment and prevented their degradation. This facile preparation method is promising for the mass production of Pt@C/C catalysts with enhanced durability for the ORR.