Polymerized Phthalocyanine\nManganese/Graphene Composites\nfor Single-Atom Oxygen Reduction Catalysts

Oxygen reduction reaction (ORR) catalysts are a key research\narea\nof fuel cells and zinc-air batteries (ZABs). The planar fully conjugate\npoly(manganese phthalocyanine) (PPcMn) is synthesized. Thermogravimetry\n(TG) shows that PPcMn is not decomposed at 400 °C. The catalyst\nPPcMn/3D-G (three-dimensional graphene) is prepared. The solid-state\nultraviolet spectroscopy and Raman spectra indicate strong π–π\ninteractions between PPcMn and 3D-G. X-ray photoelectron spectroscopy\n(XPS) demonstrates that PPcMn on the surface of 3D-G does not decompose\nduring heat treatment (HT). The combination of TG and XPS proves that\nthe active center of the catalyst is a single-atom Mn–N<sub>4</sub> structure. In 0.1 M KOH, the half-wave potential (<i>E</i><sub>1/2</sub>) of PPcMn/3D-G is 0.863 V vs RHE. The potential\ngap (Δ<i>E</i> = <i>E</i><sub><i>j</i> = 10</sub> – <i>E</i><sub>1/2</sub>) of PPcMn/3D-G is 0.77 V. Density functional theory (DFT) calculations\ndemonstrate that PPcMn has a low effect on the energy barriers for\nintermediates in the catalytic ORR process. PPcMn has a higher electron\ncloud density of the Mn–N<sub>4</sub> center, and the catalytic\nORR performance is enhanced. Zinc-air batteries (ZABs) using PPcMn/3D-G\nas a catalyst exhibit excellent performance. In the antioxidant test,\nPPcMn/3D-G does not produce hydroxyl radicals during the catalytic\nH<sub>2</sub>O<sub>2</sub> oxidation of poly[2,2-(<i>m</i>-phenylene)-5,5-bibenzimidazole] (mPBI) membranes. Therefore, PPcMn/3D-G\nis an excellent ORR single-atom electrocatalyst for fuel cells.