An ethynyl-linked Fe/Co heterometallic phthalocyanine conjugated polymer for the oxygen reduction reaction

Abstract

The Sonogashira–Hagihara coupling reaction is utilized to fabricate ethynyl-linked phthalocyanine (Pc) 2D conjugated polymers (CPs), affording the unprecedented heterometallic compound Fe_0.5Co_0.5Pc-CP and homometallic analogues MPc-CPs (M = Fe, Co) for comparison. It is confirmed that Fe and Co ions are well-defined/distributed with one metal ion encircled by four neighboring ions of the second metal in close proximity in the heterometallic conjugated polymer. Compared to the homometallic analogues, the bimetallic polymer Fe_0.5Co_0.5Pc-CP is more highly efficient for the oxygen reduction reaction (ORR), indicating that the interaction of Fe and Co ions may provide a synergistic effect on the activity. Fe_0.5Co_0.5Pc-CP exhibits similar ORR catalytic activity and superior stability compared to commercial Pt/C in alkaline media. Density functional theory calculations reveal that a fast 2 × 2e⁻ synergistic catalytic reaction pathway is essential for the excellent ORR in Fe_0.5Co_0.5Pc-CP.