Phase-Dependent Electrocatalytic H₂O₂ Selectivity of Fe-Based Spinels

Hydrogen peroxide (H₂O₂) production via the ORR two-electron pathway is a promising, decentralized, and environmentally friendly alternative to the energy-intensive traditional anthraquinone oxidation process. Here, we present the phase-dependent electrochemical assessment of the hydrogen peroxide (H₂O₂) selectivity for MnFe₂O₄, NiFe₂O₄, and CoFe₂O₄, conducted via solvothermal (SP) and solid-state (SS) synthetic routes. The XRD results indicated that spinel ferrites produced via the solvothermal method (SP-) display a single, consistent phase, while the materials synthesized through the solid-state method (SS-) show multiple phases. Scanning electron microscopy (SEM) images reveal that (SS-) spinel ferrites exhibited particles with a major size, but both synthetic methods yield particles with irregular shapes and aggregates. Interestingly, electrochemical characterization between groups revealed that a lower cathodic potential is required to generate current for (SP-) spinel ferrites than for SS counterparts, indicating better catalytic activity for the ORR two-electron pathway (H₂O₂ generation). Within groups, SP-NiFe₂O₄ exhibits the highest selectivity for H₂O₂ production, attributed to the coactive Ni²⁺ and Fe²⁺ sites that promote the 2e^- ORR pathway. Our findings indicate that achieving a structurally pure, single-phase spinel crystal is essential for maximizing H₂O₂ production for Fe-based spinels. We demonstrate that a straightforward solvothermal route is the most effective method for obtaining single-phase Fe-based spinel ferrites, thereby providing a practical synthetic platform for designing catalysts with an advanced H₂O₂-selective activity.