Structure and electrochemical activity of nickel aluminium fluoride nanosheets during urea electro-oxidation in an alkaline solution

An electrocatalyst of potassium nickel aluminium hexafluoride (KNiAlF(6)) nanosheets has been prepared using solid-phase synthesis at 900 °C. X-ray diffraction, scanning electron microscopy, and conductivity studies confirmed the formation of KNiAlF(6) nanosheets having a cubic defect pyrochlore structure with an average thickness of 60–70 nm and conductivity of 1.297 × 10(3) S m(−1). The electrochemical catalytic activity of the KNiAlF(6) nanosheets was investigated for urea oxidation in alkaline solution. The results show that the KNiAlF(6) nanosheets exhibit a mass activity of ∼395 mA cm(−2) mg(−1) at 1.65 V vs. HRE, a reaction activation energy of 4.02 kJ mol(−1), Tafel slope of 22 mV dec(−1) and an oxidation onset potential of ∼1.35 V vs. HRE which is a significant enhancement for urea oxidation when compared with both bulk Ni(OH)(2) and nickel hydroxide-based catalysts published in the literature. Chronoamperometry and impedance analysis of the KNiAlF(6) nanosheets reveal lower charge transfer resistance and long-term stability during the prolonged urea electro-oxidation process, particularly at 60 °C. After an extended urea electrolysis process, the structure and morphology of the KNiAlF(6) nanosheets were significantly changed due to partial transformation to Ni(OH)(2) but the electrochemical activity was sustained. The enhanced electrochemical surface area and the replacement of nickel in the lattice by aluminium make KNiAlF(6) nanosheets highly active electrocatalysts for urea oxidation in alkaline solution.