Redox-Active Octaiodophenoxy Cobalt Phthalocyanine for Elevating Oxygen Reduction Reaction

Fuel cells and metal-air batteries have emerged as the most efficient energy devices for various applications. These devices are aided by the oxygen reduction reaction (ORR) in the cathodic chamber of the half-cell. The effective catalysts for ORR can be engineered via integration of suitable metal to an organic moiety with acceptor-donor groups, which facilitates easy electron transfer and overcomes the sluggish reaction kinetics. Here, low-cost, earth-abundant, nonprecious octa-substituted 4-iodophenoxy cobalt(II) phthalocyanine (Co(II)OOIPc) is designed for electrocatalytic ORR application. The synthesized molecule is screened by using fundamental and advanced characterization techniques. The organic hybrid of Co(II)OOIPc with Ketjen black (Co(II)OOIPc+KB) is fabricated and evaluated as electrocatalyst for ORR. The optimized hybrid of Co(II)OOIPc+KB (3.5:1.5 (mg)) ratio fostered a positive shift in onset potential (E_onset) and half-wave potential (E_1/2) of +0.878 V and +0.752 V vs RHE respectively, which is appreciable compared to pristine Co(II)OOIPc catalyst and closer to benchmark Pt/C catalyst in 0.1 M KOH electrolyte at a 10 mV s^-1 scan rate. The improvement in the ORR performance and durability of Co(II)OOIPc+KB catalyst could be ascribed to the facile incorporation of KB nanocarbon particles with the complex which shifts the d-band center. The combined synergistic effects introduced due to the efficient electronic-conductive properties of KB and π-π stacking interactions of KB and phthalocyanine create large availability of active sites which yields enhanced electrocatalytic ORR performance. Further, the Co(II)OOIPc+KB hybrid catalyst inferred 4 electrons transfer pathway during ORR, with a lower Tafel slope of 66 mV/dec and a higher double layer capacitance, C_dl of 10.57 mF cm^-2. Noticeably, this cost-effective, modified hybrid electrocatalyst is highly durable, is stable toward ORR due to favorable π-π* interactions, and promises as an efficient electrocatalyst for sustainable energy generation.