Triphenylamine-Substituted Ni(II) Porphyrins for Urea Electro-oxidation

Porphyrin-based molecular catalysts possess a typical aromatic macrocyclic structure regarding their metal centers and coordination frameworks, allowing for the development of promising electrocatalysts through precise selection of the metal and porphyrin ligand. However, reports on metalloporphyrins as catalysts for the electrocatalytic urea oxidation reaction (UOR) remain scarce. With these considerations in mind, the triphenylamine-Ni(II) porphyrin (NiPor-TPA) was synthesized through the solvothermal approach from 5,10,15,20-tetrakis [4-(diphenylamino)phenyl]porphyrin and nickel(II) acetate in this work. Experimental results reveal that the introduction of Ni species can serve as active sites and activate urea oxidation efficiently, and thus the prepared catalysts deliver better electrocatalytic activity than the metal-free TPA. The NiPor-TPA electrode delivers the lowest potential of 1.34 V versus reversible hydrogen electrode (RHE) at 10 mA cm^-2 for UOR with a Tafel slope of 44.6 mV dec^-1. This work proposes a new porphyrin-based molecular catalyst for effectively boosting electrocatalytic UOR activity. The π-conjugated macroring structure and the excellent electrocatalytic properties both make NiPor-TPA one of the burgeoning electrocatalytic UORs.