Polymerized Phthalocyanine Manganese/Graphene Composites for Single-Atom Oxygen Reduction Catalysts

Oxygen reduction reaction (ORR) catalysts are a key research area of fuel cells and zinc-air batteries (ZABs). The planar fully conjugate poly(manganese phthalocyanine) (PPcMn) is synthesized. Thermogravimetry (TG) shows that PPcMn is not decomposed at 400 °C. The catalyst PPcMn/3D-G (three-dimensional graphene) is prepared. The solid-state ultraviolet spectroscopy and Raman spectra indicate strong π–π interactions between PPcMn and 3D-G. X-ray photoelectron spectroscopy (XPS) demonstrates that PPcMn on the surface of 3D-G does not decompose during heat treatment (HT). The combination of TG and XPS proves that the active center of the catalyst is a single-atom Mn–N₄ structure. In 0.1 M KOH, the half-wave potential (E_1/2) of PPcMn/3D-G is 0.863 V vs RHE. The potential gap (ΔE = E_j = 10 – E_1/2) of PPcMn/3D-G is 0.77 V. Density functional theory (DFT) calculations demonstrate that PPcMn has a low effect on the energy barriers for intermediates in the catalytic ORR process. PPcMn has a higher electron cloud density of the Mn–N₄ center, and the catalytic ORR performance is enhanced. Zinc-air batteries (ZABs) using PPcMn/3D-G as a catalyst exhibit excellent performance. In the antioxidant test, PPcMn/3D-G does not produce hydroxyl radicals during the catalytic H₂O₂ oxidation of poly[2,2-(m-phenylene)-5,5-bibenzimidazole] (mPBI) membranes. Therefore, PPcMn/3D-G is an excellent ORR single-atom electrocatalyst for fuel cells.