Tailoring the Redox Activity of Cr‐Mn‐Fe Mixed Oxide for High‐performance Alkaline Water Splitting

In this study, we demonstrate that the optimized incorporation of Cr into Mn‐Fe containing mixed oxides effectively tailors the redox activity of the Mn and Fe centers for enhanced alkaline water splitting. This incorporation of Cr is precisely achieved through a facile controlled co‐precipitation route yielding compositionally tuned Cr‐Mn‐Fe mixed oxides. The structural characteristics of the synthesized materials were verified via XRD, FTIR, and Raman spectroscopy. XRD analysis revealed that the synthesized materials are primarily composed of rhombohedral α‐Fe 2 O 3 , while additional weak reflections in Cr‐containing samples suggest the possible presence of Cr 2 O 3 related secondary phases. Morphological evolution from dense agglomerated grains (F1N) to porous nanostructures (F4N) enhances electroactive surface exposure, while XPS confirms mixed‐valence states of Fe 2+ /Fe 3+ , Mn 2+ /Mn 3+ , and Cr 3+ , facilitating synergistic redox coupling. Electrochemical evaluations in 1.0 m KOH reveal that the optimized F3N catalyst exhibits improved bifunctional activity, requiring remarkably low overpotentials of 0.28 V for the oxygen evolution reaction (OER) and 0.23 V for the hydrogen evolution reaction (HER) at 10 mA/cm 2 . The corresponding Tafel slopes of 37.64 mV/dec (OER) and 35.00 mV/dec (HER) indicate accelerated charge‐transfer kinetics. Furthermore, the F4N catalyst also demonstrates improved long‐term durability, retaining 90.87% of its catalytic current density under continuous operation.