Electrodeposited NiFe-succinate for the oxygen evolution reaction in anion exchange membrane water electrolysis

Abstract

This study proposes Platinum Group Metal-free (PGM-free) electrocatalysts for the Oxygen Evolution Reaction (OER) to be used in Anion Exchange Membrane Water Electrolyzers (AEMWEs). NiFe-based electrodes were synthesized via an optimized electrodeposition process in the presence of succinic acid onto a low-cost 304 stainless steel (SS) mesh, resulting in an active and durable inorganic–organic complex. Morphological characterization confirmed the formation of high-surface-area electrodes, with a catalyst layer composed of Ni and Fe ions coordinated by organic carboxylic groups. X-ray Photoemission Spectroscopy (XPS) proved the formation of NiFe2O4 as the active species for OER, showing improved electrochemical performance compared to Ni-based and Fe-based electrodes. Notably, 240 mV and 306 mV were recorded as onset overpotential and overpotential at 10 mA cm−2, respectively, with a low Tafel slope of approximately 50 mV dec−1, using electrodes with total catalyst layer mass loading lower than 1 mg cm−2. Density Functional Theory (DFT) calculations were performed to gain more insight into the OER mechanism on NiFe2O4 species, obtaining simulated polarization curves in very good agreement with experimental data. Finally, the best-performing electrode was tested in a single-cell AEMWE, achieving a maximum current density of 1.86 A cm−2 at 2.2 V and 60 °C, and demonstrating good stability after a 40-h chronoamperometric test conducted at 2 V.