Ni-Phthalocyanine Derived Electrocatalysts for Oxygen Reduction Reaction and Hydrogen Evolution Reaction: Active Sites Formation and Electrocatalytic Activity

Abstract

In this work, an electrocatalyst derived from a mixture of carbon black (Ketjenblack 600) and nickel phthalocyanine using a pyrolytic process is presented. The evolution of the active site during pyrolysis at different temperatures from room temperature to 1000 °C is evaluated through a series of advanced microscopic and spectroscopic tools. The electrocatalyst retains its atomically dispersed Ni–Nx structure until 600 °C, where coalescence occurs and nanoparticles are formed. Advanced synchrotron light source analysis (XANES + EXAFS) confirmed the absence of oxygen interaction with the atomically dispersed metal, showing overlapping in situ and ex situ spectra. Electrochemical characterization was also carried out. A comprehensive structure-to-property relationship is presented to correlate electrochemical features and microscopic/spectroscopic data. HER is enhanced by the presence of Ni nanoparticles with decreased overpotentials along with temperature increase. For ORR, the temperature is not beneficial for the electrocatalytic activity. The secondary active site (nitrogen-pyridinic) rather than Ni–Nx seems to be more efficient for faster kinetics and reduced peroxide production.