Direct Pyrolytic Transformation of a Cocrystal of Pt(acac)₂ with Hexaaminotriphenylene into a Novel Composite ORR Electrocatalyst

A platinum-containing hexaaminotriphenylene (HATP, 2,3,6,7,10,11-hexaaminotriphenylene, [C18H12N6]) hybrid cocrystal material ([Pt(acac)2][HATP]) has been synthesized and used as a precursor that was pyrolyzed to produce an oxygen reduction reaction (ORR)-active electrocatalyst. The crystalline precursor, pyrolyzed in vacuo and monitored in situ with temperature-variable TEM, was found to form an amorphous carbon network intercalated with crystalline platinum nanoparticles (NPs). The thermal decomposition of the coordinated hexaaminotriphenylene ligand, with loss of the amino groups around 300 °C, is concomitant with the reduction of platinum centers from Pt2+ to Pt0, while the pyrolysis time and temperature control the ultimate size of the nanoparticles. Pt nanoparticle growth above 300 °C was found to be limited, likely as a result of the nanoparticles being trapped in a carbon network that formed from the HATP molecules during the pyrolytic process. Samples of the pyrolyzed material were investigated by RDE for ORR catalysis in an acidic medium and were found to have a modest electrochemical surface area (38.8 m2/gPt) and a mass-specific activity of 58.5 mA/cmPt2.