Tetraphenolphthalein Cobalt(II) Phthalocyanine Polymer Modified with Multiwalled Carbon Nanotubes as an Efficient Catalyst for the Oxygen Reduction Reaction

Oxygen reduction reaction (ORR) is the main reaction at the cathode of a fuel cell that utilizes Pt/C as the benchmark catalyst. Due to sluggish activity, high cost, rare abundance, and durability issues, Pt/C must be replaced by nonprecious, stable, and easily synthesizable materials. This work involves the synthesis of novel, simple, low-cost, and environmentally friendly phenolphthalein-bearing cobalt(II) phthalocyanine polymer, poly(Co II TPpPc) dyad, as an efficient catalyst for ORR. The results of analytical characterizations reveal the formation of the poly(Co II TPpPc) polymer in the pure state. To further enhance the catalytic response of poly(Co II TPpPc), a hybrid composite is prepared using poly(Co II TPpPc) and multiwalled carbon nanotubes (MWCNTs) that increase the surface area and conductivity. The poly(Co II TPpPc) and hybrid composite are separately deposited on the electrode surfaces. The electron microscopy images confirm the uniform distribution of the poly(Co II TPpPc) molecules on the electrode surface and MWCNTs. The poly(Co II TPpPc) and hybrid composite electrodes are evaluated for ORR, and the hybrid composite exhibits better onset potential at 0.803 V versus reversible hydrogen reference electrode for ORR according to linear sweep voltammograms (LSVs). The obtained data are superior compared to those of other carbon-based redox-active materials reported previously and nearer to those of the benchmark catalyst (Pt/C). The rotating disc electrode measurement of the hybrid composite electrode confirms the total number of electrons involved in ORR to be four. Furthermore, the hybrid composite electrode exhibits an excellent stability for 100 LSV scans. The synergistic effect of poly(Co II TPpPc) and MWCNTs leads to the surprisingly high ORR activity due to the improved surface area, conductivity, and interfacial confined surface.