A Bifunctional Electrocatalyst based on Ni-porphyrin/Vapor-Grown Carbon Fibres for Oxygen Reduction and Evolution Reactions in Alkaline Media

Looking for affordable and competent bifunctional electrocatalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is imperative for widespread fuel cells and metal-air batteries. Metalloporphyrins have gained considerable attention owing to remarkable catalytic characteristics. Herein, we investigate the catalytic performance of a composite catalyst comprising nickel- 5,10,15,20-tetra(p-thioanisole) porphyrin complex (Ni-TPSMe-P) and vapor grown carbon fibres (VGCFs) towards both the OER and ORR. A simple approach is adopted to synthesis the targeted Ni-TPSMe-P. Several spectroscopic techniques, including NMR, FT-11t, UV-Vis and MS are used to confirm the formation of the target catalyst structurally. Also, kinetic parameters such as overpotential (eta), Tafel slope, onset potential, the average number of electrons transferred and peroxides yield are used to evaluate the catalytic activity towards the OER, and ORR . The composite catalyst demonstrates OER activity at a current density of 10 mA cm(-2) with an overpotential of 400 mV and Tafel slope of 130 mV dec(-1). In addition, the composite catalyst shows high catalytic activity towards the ORR with an average number of electrons of 3.60, onset potential of 0.82 V and peroxide yield of 22%. The bifunctional index (BI) is used to evaluate the bifunctional activity towards the OER and ORR, which is found to be 0.92 V. These outcomes suggest that, the synthesized nickel porphyrin has an outstanding bifunctional characteristic towards the OER and ORR, which is an important merit for energy conversion systems, such as metalair battery and regenerative fuel cells.