A hybrid nickel/iron-pyromellitic acid electrocatalyst for oxygen evolution reaction

The migration of protons during the oxygen evolution reaction (OER) is a key factor that affects the performance of OER catalysts. To enhance proton transportation, we designed a catalyst based on nickel/iron-pyromellitic acid (NiFe-PMA) prepared by the electrochemical deposition method. This catalyst exhibited a low overpotential of 188 mV at a current density of 10 mA·cm−2, a Tafel slope of 28.2 mV·dec−1, and long-term stability for 30 days with a current of 50 mA·cm−2. We characterized the NiFe-PMA catalyst using various techniques, including Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and inductively coupled plasma-optical emission spectrometry (ICP-OES). Our results showed that NiFe-PMA contains nickel, iron atoms, and both coordinated and uncoordinated carboxylate groups. Additionally, XPS data confirmed that carboxylate ligands could adjust the outer electronic structure of metal ions, resulting in the high valence state of Ni in NiFe-PMA. The result of XAS indicated that the nickel atoms present in the catalyst might be easier to maintain a higher chemical state. Further investigations using kinetic isotope effects (KIEs) and proton inventory revealed that the uncoordinated carboxylic protons played a crucial role in receiving protons during the OER, which promoted the proton transfer of the rate-determining step of the OER. Our novel electrocatalysts provide a new strategy for designing more active and cost-effective catalysts for the OER.