Experimental and Theoretical Evidences of p-Type Conductivity in Nickel Carbodiimide Nanoparticles with a Delafossite Structure Type

Abstract

Nickel carbodiimide (NiCN) was synthesized using a two-step precipitation-decomposition route leading to a brown powder with gypsum-flower-like morphology and a large specific surface area (75 m/g). This layered material crystallizes in the 2H structure type of delafossite (space group P6/mmc), which is built upon infinite /[NiN] layers connected by linear carbodiimide ([N═C═N]) bridges. An X-ray diffraction Rietveld refinement and thermal analyses pointed out some nickel deficiencies in the material, and band structure calculations carried out on the defect compound predicted p-type conductivity in relation to a slight amount of N. This p-type conductivity was demonstrated by electrochemical impedance spectroscopy measurements, and a flat band potential of 0.90 V vs SCE at pH 9.4 was measured. This value, which is more positive than those of CuGaO and CuCrO delafossite oxides and NiO, prompted us to test NiCN nanoparticles as a photocathode in p-type dye-sensitized solar cells.

Reversible High Capacity and Reaction Mechanism of Cr2(NCN)3 Negative Electrodes for Li‐Ion Batteries

“…The scanning electronic microscopy (SEM) image, shown in Figure b, reveals an intergrowth of flakes that look like desert rose petals with a size of several micrometers. As reported for other transition‐metal carbodiimide materials, Cr 2 (NCN) 3 also undergoes a minor initial weight loss (≈1.1%) in the 0–350 °C range followed by an abrupt loss (≈28%) at 400 °C, as shown from the thermogravimetric analysis (TGA) yellow plot in Figure b. The initial loss is mainly due to the departure of adsorbed water from the surface of the sample, whereas the second one corresponds to the decomposition into chromium oxide .…”

“…As reported for other transition‐metal carbodiimide materials, Cr 2 (NCN) 3 also undergoes a minor initial weight loss (≈1.1%) in the 0–350 °C range followed by an abrupt loss (≈28%) at 400 °C, as shown from the thermogravimetric analysis (TGA) yellow plot in Figure b. The initial loss is mainly due to the departure of adsorbed water from the surface of the sample, whereas the second one corresponds to the decomposition into chromium oxide . The final weight loss step from 500 to 700 °C can be attributed to the decomposition to form nanocrystalline chromium oxide as seen in the normal transition‐metal oxides …”

Cobalt Carbodiimide as Negative Electrode for Li‐Ion Batteries: Electrochemical Mechanism and Performance

“…The initial loss is associated with water or organic molecules desorption from the particles’ surface. The second abrupt loss is due to the decomposition of cobalt carbodiimide into cobalt oxide …”

A first principles study on structural, dynamical, and mechanical stability of newly predicted delafossite HCoO2 at high pressure

“…The good number of available properties of both polytypes of delafossite oxides suggests a strong structure–property relation in them. Jiang et al have recently studied the NiCN 2 compound in delafossite structure and found p‐type conductivity in this compound. Tiago et al predicted several Cu, Ag, and Au‐based ternary oxides in delafossite structures.…”