Electrochemical behavior and electrocatalytic properties towards hydrogen peroxide, dioxygen and nitrate of the polyanions [(Ni(II)OH₂)₂(Fe(III))₂(X₂W₁₅O₅₆)₂]¹⁴¯ (X = P(V) or As(V)): A comparative study

In this study, the electrochemical behavior and the electrocatalytic properties towards the reduction of hydrogen peroxide, dioxygen and nitrate are compared for the two mixed sandwich-type complexes Ni₂Fe₂P₄ and Ni₂Fe₂As₄. In media of pH 3, Ni₂Fe₂P₄ displayed two waves corresponding to the reduction of the two Fe(III) centers within the complex followed by four W(VI) based-waves. Compared to Ni₂Fe₂P₄, Ni₂Fe₂As₄ displayed only one Fe-based wave and three W-waves. In other words, the two Fe(III) waves and the first two W(VI) waves observed for Ni₂Fe₂P₄ merge into one Fe-based wave and one W-wave in Ni₂Fe₂As₄. This is probably related to a slight difference in acidity between the two complexes. In other words, Ni₂Fe₂P₄ is slightly more basic than Ni₂Fe₂As₄. This difference in acidity is also reflected in the position of the potentials. Compared to Ni₂Fe₂P₄, the peak potentials of Ni₂Fe₂As₄ are slightly shifted towards positive values, and the shift is more pronounced for the W-based waves than for the Fe-waves. The remarkable stability of the two complexes (roughly from pH 0 to 7) permitted to evaluate their catalytic behavior towards H₂O₂, O₂ and NO₃. For the electrocatalytic reduction of H₂O₂, it is noticed that Ni₂Fe₂As₄ is more efficient than Ni₂Fe₂P₄. However, for O₂ and NO¯₃ it is observed that Ni₂Fe₂P₄ is more efficient than Ni₂Fe₂As₄.status: publishe