Iron oxide nanorods array in electrochemical detection of H₂O₂

Nanorod arrays (NRs) of β-FeOOH, γ-Fe₂O₃, and α-Fe₂O₃ were synthesized, and their electrocatalytic properties toward the reduction of H₂O₂ were investigated. In phosphate electrolyte, iron phosphate (FePO₄) was in situ deposited onto these iron oxides during pretreatment, and the interaction between iron oxides and the deposited FePO₄ played an important role in determining the electrocatalytic activity of the resultant electrodes. It was found that the redox reaction of FePO₄ is more facile on α-Fe₂O_3NR, and the resultant FePO₄ modified α-Fe₂O_3NR showed best electrocatalytic activity toward the reduction of H₂O₂. In addition, α-Fe₂O_3NR showed two reduction peaks in phosphate electrolyte containing 1.66 mM H₂O₂, one being pH-dependent and related to the electrocatalytic properties of FePO₄, and the other one being pH-independent and only related to the intrinsic electrocatalytic properties of α-Fe₂O_3NR. However, all iron oxides showed only one pH-independent reductive peak in non-phosphate electrolyte containing H₂O₂. The sensing mechanisms in both conditions are proposed. Under optimized condition, α-Fe₂O_3NR exhibited excellent sensing characteristics, including a high sensitivity of 181 μA mM^-1 cm^-2, a wide linear range up to 2.5 mM, a low detection limit of 1.3 μM, and high selectivity against some common biomolecules, which indicates its applicability as a reliable electrochemical H₂O₂ sensor.