Water Oxidation in the Presence of Iron-Doped Copper (Hydr)Oxide

This study explores the influence of Fe ion incorporation on the oxygen-evolution reaction (OER) in alkaline media, utilizing CuO-based materials. Instead of developing an efficient and stable OER catalyst, this research investigates two distinct CuO variants: one with Fe ions adhered to the surface and another with Fe ions integrated into the CuO lattice. By employing a variety of analytical techniques, the study demonstrates that the CuO variant with surface-bound Fe ions (referred to as compound 1) exhibits significantly enhanced OER performance compared to the variant with internally embedded Fe ions (referred to as compound 2). The Tafel plots obtained from multistep amperometry profiles for compounds 1 and 2, as well as pure CuO and FeO(OH), exhibit linear relationships in the log(j) vs overpotential plot, with Tafel slopes of 39.3, 41.5, 115.9, and 121.9 mV/decade, respectively. These Tafel slopes indicate that compounds 1 and 2 likely share a similar reaction mechanism, whereas CuO and FeO(OH) appear to follow distinct mechanisms. At 570 mV overpotential, the turnover frequencies of Fe ions for compounds 1 and 2, as well as for FeO(OH), calculated from electrode compositions and chronoamperometry data, are found to be 1.1, 0.2, and 5.7 × 10^-4 s^-1, respectively. Despite the differing distributions of Fe ions, both CuO variants exhibit similar Tafel slopes, suggesting that they follow comparable OER mechanisms. Additionally, cyclic voltammetric profiles, corrected for the electrochemically active surface area, indicate that FeO(OH) demonstrates notably higher activity than the other compounds. These findings deepen our understanding of Fe's role in CuO structures for OER processes and offer valuable insights for the design of more efficient electrocatalytic materials in alkaline environments.