Experimental And Theoretical Evidences Of P-Type Conductivity In Nickel Carbodiimide Nanoparticles With A Delafossite Structure Type

Nickel carbodiimide (NiCN2) 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(2)/g). This layered material crystallizes in the 2H structure type of delafossite (space group P6(3)/mmc), which is built upon infinite 2/infinity[NiN2] layers connected by linear carbodiimide ([N=C=N](2-)) 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 N2-. 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 CuGaO2 and CuCrO2 delafossite oxides and NiO, prompted us to test NiCN2 nanoparticles as a photocathode in p-type dye-sensitized solar cells.