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Highlights: [•] Copper ionic liquid displayed partially reversible plating and stripping. [•] Ionic liquid reference electrode was evaluated with ferrocene and cobaltocene. [•] Strongly coordinating ligands suppressed copper dendrite formation. [•] Anions influenced copper particle size and morphology. [ABSTRACT FROM AUTHOR]

Abstract: Five new copper(II)-based ionic liquids and three crystalline compounds have been synthesized in order to further understand the role of the anion in determining their physicochemical properties. Materials were prepared with combinations of three different anions (2-ethylhexanoate (EHN), tetrafluoroborate (BF4), and triflate (OTf)) and six-coordinate Cu(II) cations. The complexes that contain at least one BF4 anion consistently displayed both the highest specific conductivity and electrochemical reversibility. The presence of one OTf anion (in combination with one EHN or BF4) facilitates the formation of crystalline materials. Single crystal X-ray diffraction studies were completed on two of the mixed anion compounds. The results show that both ethanolamine (EA) and diethanolamine (DEA) chelate to the Cu(II) centers in a highly distorted tetragonal geometry. The properties of the ionic liquid with the overall lowest viscosity and highest conductivity and electrochemical reversibility (Cu{NH2CH2CH2OH}6(BF4)2, 4) were studied as a function of temperature. The viscosity decreases with increasing temperature, but at 45°C (over three hours) there is a loss of two EA ligands to form a more viscous four-coordinate complex. Cyclic voltammetry of 4 reveals a quasi-reversible Cu(II)/Cu(I) reduction wave that shifts to more positive potentials with increasing temperature. [Copyright &y& Elsevier]

Abstract: 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 FeIII centers within the complex followed by four WVI based-waves. Compared to Ni2Fe2P4, Ni2Fe2As4 displayed only one Fe-based wave and three W-waves. In other words, the two FeIII waves and the first two WVI 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 . For the electrocatalytic reduction of H2O2, it is noticed that Ni2Fe2As4 is more efficient than Ni2Fe2P4. However, for O2 and it is observed that Ni2Fe2P4 is more efficient than Ni2Fe2As4. [ABSTRACT FROM AUTHOR]