Electrochemical behavior and electrocatalytic properties towards hydrogen peroxide, dioxygen and nitrate of the polyanions [(NiIIOH2)2(FeIII)2(X2W15O56)2]14- (X = PV or AsV): 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, O-2 and NO3-. For the electrocatalytic reduction of H2O2, it is noticed that Ni2Fe2As4 is more efficient than Ni2Fe2P4. However, for O-2 and NO3- it is observed that Ni2Fe2P4 is more efficient than Ni2Fe2As4. (C) 2010 Elsevier B.V. All rights reserved.