FeCo2O4/rGO shows higher selectivity and lower detection limit than CoFe2O4/rGO due to Fe3+ in octahedral sites. Both nanocomposites demonstrate excellent performance for non-enzymatic H2O2 detection in commercial bleach.

Two inverse spinel-based nanocomposites, FeCo₂O₄/rGO (FCO/rGO) and CoFe₂O₄/rGO (CFO/rGO), were synthesized and evaluated as non-enzymatic hydrogen peroxide sensors. Mössbauer and XPS analyses revealed distinct cation distributions: FCO presented mixed Co²⁺/Co³ ⁺ valence and a higher proportion of Fe³ ⁺ in octahedral coordination compared to CFO. These structural differences governed the electrocatalytic behavior. Reduced graphene oxide enhanced charge transfer, leading to optimal sensitivities of 0.1368 μA μM⁻¹ (LOD = 0.037 μM) for FCoO/rGO at 0.200 V and 0.2281 μA μM⁻¹ (LOD = 0.118 μM) for CFO/rGO at 0.300 V. The Fe³ ⁺ occupancy in octahedral sites was identified as a key factor for catalytic efficiency. Both sensors exhibited excellent selectivity and successfully quantified H₂O₂ in real samples. These findings establish a direct correlation between cation distribution and electrochemical performance, providing insights for the rational design of ternary spinel/rGO electrocatalysts. T.P. Brito, J.E. Prieto, J.F. Marco, C. Yáñez, D. Ruiz-León, S. Bollo, Journal of Alloys and Compounds 1047, 184877 (2025), DOI: 10.1016/j.jallcom.2025.184877.