Electrochemical Properties of CuCrO₂ Prepared by Chemical Route

Co-precipitation was used for the preparation of delafossite CuCrO₂ from nitrates under an inert N₂ flow. The diffractograms show a pure phase, crystallizing in a rhombohedral delafossite structure (S G: R \(\overline{3}\) $\overline{3}$ m). Stability up to 900°C, indicating high electrostatic energy, is demonstrated by the thermogravimetric analysis (TGA). The formation of CuCrO₂ is corroborated by x-ray photoelectron spectroscopy (XPS) analysis with valence states Cu⁺ and Cr³⁺. The forbidden band (2.49 eV) is assigned to the transition Cu⁺: d_{xz → hybridized}O²⁻: 2p/Cu⁺: d_z2/s linearly bonded in CuO₂³⁻ entities. The thermal dependence of the electrical conductivity follows an exponential law: {σ = σ_o exp(−0.13 eV/kT) (Ω-cm)^− 1} where the electrical conductivity comes from low polaron hopping (LPH) among mixed states of Cu^2+/+ in the basal (0 0 n) planes. The doping is due to Cu₂O units, the conduction of which gives a hole mobility of ~ 10⁻⁴ cm² V⁻¹ s⁻¹. The semiconductor behavior of CuCrO₂ is supported by the interfacial capacitance versus potential (C⁻² − E); the negative slope indicates p-type conduction, with a flat band potential (E_fb) of 0.16 V_SCE. The valence band (5.03 eV/0.28 V_SCE) is formed by O(2p)–Cr(3d) states. The electrochemical impedance spectroscopy plot shows an arc assigned to a capacitive comportment with a deviation from a pure capacitance and a dominant bulk contribution (R_b = 69 kΩ cm²). The center is positioned below the abscissa with a constant phase element.