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

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 mu A mu M-1 and a low detection limit of 1.14 nM in the range of 0.01-10 mu M, 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.