Synthesis and electrocatalytic mechanism of ultrafine MFe2O4 (M: Co, Ni, and Zn) nanocrystallites: M/Fe synergistic effects on the electrochemical detection of Cu(ii) and hydrogen evolution reaction performances

Abstract

Binary spinel oxides with synergistic effects between metal ions in electronic microstructures have attracted significant attention due to their vital importance in both fundamental studies and potential applications. Herein, we synthesized ultrafine MFe₂O₄ (M: Co, Ni, Zn) nanocrystallites with different M/Fe compositions via the one-pot hydrothermal method. The M/Fe synergistic effect on the electrochemical detection of Cu(II) and hydrogen evolution reaction (HER) activities are systematically investigated by experimental characterizations and density functional theory (DFT) calculations. When MFe₂O₄ is evaluated as modified electrodes for electrochemical sensors for Cu(II), NiFe₂O₄ shows a high sensitivity of 18.30 μA μM⁻¹ and a low detection limit of 1.14 nM in the range of 0.01–10 μM, superior to CoFe₂O₄ and ZnFe₂O₄, and successfully applied in real water environment. The adsorption–desorption mechanism of MFe₂O₄ with the synergistic effect between M/Fe and Fe(II)/Fe(III) cycles, is first proposed via DFT calculations and demonstrated that M cation regulation is an effective strategy to enhance electrochemical detection performance. Besides, NiFe₂O₄ also exhibits electrocatalytic activity for HER activities with an overpotential of 93 mV and a Tafel slope of 55.4 mV dec⁻¹. These results not only provide a facile strategy to adjust the electronic microstructures of uniform MFO materials but also pose an in-depth insight into the detection mechanism for Cu(II) and HER performances.