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Exfoliation of amorphous phthalocyanine conjugated polymers into ultrathin nanosheets for highly efficient oxygen reduction
- Liu, Wenping, Wang, Chiming, Zhang, Lijie, Pan, Houhe, Liu, Wenbo, Chen, Jun, Yang, Dongjiang, Xiang, Yanjuan, Wang, Kang, Jiang, Jianzhuang, Yao, Xiangdong
- Journal of materials chemistry A 2019 v.7 no.7 pp. 3112-3119
- atomic force microscopy, batteries, catalysts, cobalt, electric potential difference, electrochemistry, electronics, graphene, iron, nanosheets, oxygen, polymers, positional isomers, potassium hydroxide, transmission electron microscopy
- It is a significant challenge to develop a high-efficiency synthetic methodology to access fully conjugated 2D conjugated polymer (CP)/covalent organic framework (COF) nanosheets (NSs) that have great application potential for electronics and energy. Herein, we report the exfoliation of a series of amorphous ethynyl-linked phthalocyanine (Pc) CPs (MPc-CPs, M = Fe, Co, Fe₀.₅Co₀.₅) into ultrathin MPc-CP NSs. Random coupling between the four regioisomers (with D₄ₕ, D₂ₕ, C₂ᵥ and Cₛ symmetry) of the two tetra-β-substituted phthalocyanine precursors endows the resulting phthalocyanine conjugated polymers MPc-CPs with intrinsic structural defects and a disordered framework on individual layers. This in turn induces a diminished interlayer overlapping and a weakened interlayer π–π stacking interaction, facilitating the possible exfoliation of MPc-CPs into ultrathin 2D NSs with a yield of over 50%. The direction observation by transmission electron microscopy (TEM) and atomic force microscopy (AFM) demonstrates that the ultrathin MPc-CP NSs possess a smooth surface with a uniform thickness of 1–3 nm and a lateral size of hundreds of nanometers. The as-prepared bimetallic Fe₀.₅Co₀.₅Pc-CP NSs were further used to fabricate a heterostructure Fe₀.₅Co₀.₅Pc-CP NS@G with graphene NSs as an oxygen reduction reaction (ORR) catalyst, which exhibits an onset potential of 1006 mV and a half-wave potential of 927 mV in 0.1 M KOH, representing one of the best values in an alkaline medium. Moreover, the excellent ORR activity of the exfoliated tetrapyrrole-based conjugated NSs hybridized with graphene has also been demonstrated by a Zn–air battery device, showing an open circuit voltage of 1.34 V and a peak power density of ca. 180 mW cm⁻².