Facile soft solution synthesis of delafossite structured Cu(Cr_1-xFe_x)O₂ (x = 0, 0.5, and 1) materials and their supercapacitor application

The investigation of metal oxides with delafossite-type crystal structure for electrochemical energy storage applications is an emerging area. Interestingly, the ternary oxides Cu(Cr_1-xFe_x)O₂ (0 ≤ x ≤ 1) with delafossite-type layered crystal structure are promising transparent p-type semiconductor and thermoelectric materials with excellent potential for electrochemical applications. However, the synthesis of single-phase Cu(Cr_1-xFe_x)O₂ (0 ≤ x ≤ 1) is challenging due to the limited stability of Cu⁺ oxidation state in ambient condition. In the present study, we have successfully synthesized polycrystalline Cu(Cr_1-xFe_x)O₂ (x = 0, 0.5, and 1) using a new polymer complex gel technique. The polymer complex gel method can produce homogeneous metal oxide with multiple cations. This is because the metal ions are very near (< few nm) to each other in the precursor. Furthermore, the solid solutions Cu(Cr_1-xFe_x)O₂ (x = 0, 0.5, and 1) have been synthesized successfully for the first time using this solution processing technique. Typically, a homogeneous solution containing stoichiometric metal ions and tartaric acid forms a gel-like substance upon evaporation. This gel is dried and followed by calcination at 900 °C in N₂ atmosphere to prepare polycrystalline powder of Cu(Cr_1-xFe_x)O₂ (x = 0, 0.5, and 1). The crystal structure and phase purity of all the samples were confirmed by powder X-ray diffraction (PXRD) technique. The as-prepared CuCr_0.5Fe_0.5O₂ electrode delivered excellent specific capacitance (Csp) and demonstrated notable electrochemical stability in galvanostatic charge–discharge (GCD) cycling, which may indicate enhancement of electrochemical performance of supercapacitor electrode materials due to synergistic effect of multiple metal ions. In conclusion, we have explored a new synthesis method and investigated electrochemical properties of new material with novel crystal structure and excellent potential for electrochemical supercapacitor applications.