Nickel(II) Porphyrin Complex-Derived Electrocatalysts for Oxygen Evolution

The oxygen evolution reaction (OER) is a critical bottleneck in electrocatalytic water splitting due to its inherently sluggish kinetics and the high overpotential required to drive the reaction, which significantly limits overall energy efficiency. Although nickel tetraphenylporphyrin (NiTPP) shows potential as an OER catalyst, its performance in pristine form is often insufficient for practical applications. To overcome these limitations, this work introduces a strategic approach involving the controlled carbonization of the NiTPP precursor to synthesize a highly active and durable catalyst. By pyrolyzing NiTPP under a controlled atmosphere and at various temperatures (400 °C, 600 °C, and 800 °C), we embedded catalytically active nickel species within a conductive carbon matrix derived from the porphyrin ligand. Utilizing the synergistic effects between the active metal sites and the graphitic support, the resulting material exhibits improved charge transport and exposes a greater number of active sites. Electrochemical evaluations demonstrate that the NiTPP-800 sample, obtained by carbonization at 800 °C, exhibits superior performance. It delivers a low overpotential of only 347 mV at a current density of 20 mA cm^-2 and a low Tafel slope of 86 mV dec^-1 in 1 M KOH, surpassing that of the uncarbonized and lower-temperature carbonized samples. The catalyst also exhibits outstanding long-term stability, maintaining its performance for over 1000 CV cycles.