Polymeric cobalt phthalocyanine on nickel foam as an efficient electrocatalyst for oxygen evolution reaction

Abstract

Renewable energy is of prime importance for sustainable development. Hydrogen is considered as clean as well as an efficient energy source. In addition to H2 as fuel, polymer electrolyte membrane fuel cell requires oxygen as an oxidant. Electrocatalytic or photocatalytic water splitting processes yield H2 and O2. Compared to hydrogen evolution reaction (HER), the oxygen evolution reaction (OER) in water electrolysis is a very sluggish and slow process. Even precious and costly catalysts have demonstrated higher overpotential for OER. To overcome the issues related to overpotential as well as cost and durability, bio-inspired macrocycles and polymers based on phthalocyanine are being explored extensively because of their unique and versatile properties. In this effort, a novel cobalt phthalocyanine polymer (poly-CoTPzPyCPc) was synthesised and employed as a low-cost and efficient organic-based catalyst for OER. The characterized polymeric catalyst was coated on Ni foam and the fabricated electrodes were evaluated for OER in 0.1 M KOH. The electrodes Ni-foam, Ni/poly-CoTPzPyCPc, Ni/IrO2, and Ni/poly-CoTPzPyCPc + IrO2 exhibited an onset potential for OER at 1.57, 1.53, 1.47 and 1.43 V Vs. RHE, respectively. The Ni/poly-CoTPzPyCPc exhibited an overpotential of 365 mV (±2 mV) at a current density of 10 mA cm−2. Furthermore, the composite of poly-CoTPzPyCPc with IrO2, displayed surprisingly superior OER activity. The composite achieved a current density of 10 mA cm−2 at lower overpotential of 274 mV (±2 mV) than the polymeric phthalocyanine and benchmark IrO2 catalyst which showed an overpotential of 324 mV at the same current density. The Tafel slope value was found to be 89, 67, 34 and 31 mV/dec for pure Ni foam, Ni/poly-CoTPzPyCPc, Ni/IrO2 and Ni/poly-CoTPzPyCPc + IrO2, respectively. The stability studies performed on poly-CoTPzPyCPc + IrO2 composite catalyst revealed that the proposed catalyst is stable and can be successfully employed for OER in water electrolysis. The developed composite catalyst has a small amount loading of precious catalyst with simple organic based catalyst to achieve efficiency better than benchmark catalyst for OER.