Phase-Dependent Electrocatalytic H ₂ O ₂ 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.