A platinum catalyst with hierarchical porosity supported on a honeycomb-like nitrogen-doped carbon for excellent oxygen reduction reaction performance
Advanced catalyst structures with good active site accessibility and strong metal-support interactions are crucial for oxygen reduction reaction (ORR) catalysis. A hierarchically porous Pt catalyst supported on honeycomb-like nitrogen-doped carbon (Pt/HNC-400, where 400 denotes the optimal dosage (mg) of the sacrificial SiO2 hard template used during synthesis) was fabricated by combining template-assisted pyrolysis and alcohol reduction. The fabrication involves the template-assisted pyrolysis of ZIF-67 (which provides the N-dopant through its 2-methylimidazole ligand) followed by HF etching to completely remove the SiO2, yielding a 3D interconnected porous carbon support. Compared to a commercial Pt/C, it had an exceptional ORR performance with a half-wave potential of 0.901 V (41 mV higher), a mass activity at 0.9 V that was 15.3 times higher, and significantly improved durability (a half-wave potential decay of 25 mV vs. 80 mV after 10,000 accelerated durability tests (ADTs)). Mechanistic investigations showed that this superior performance is due to the combined effects of the 3D porous structure, ultrafine Pt nanoparticles with strong metal-support interactions, and in-situ formed Co-Nx moieties from the pyrolysis of precursor ZIF-67. After 10,000 ADTs it was shown to have excellent structural integrity, retaining 87.4% of its initial electrochemically active surface area (102.7 m2 g−1). This study may assist the development of new high-performance ORR catalysts.