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

Saba A Aladeemy; Abdullah M Al-Mayouf; Mabrook S Amer; Nouf H Alotaibi; Mark T Weller; Mohamed A Ghanem

doi:10.1039/d0ra10814f

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

RSC Adv. 2021 Jan 14;11(5):3190-3201. doi: 10.1039/d0ra10814f. eCollection 2021 Jan 11.

Authors

Saba A Aladeemy^{1

2}, Abdullah M Al-Mayouf^{1

2}, Mabrook S Amer¹, Nouf H Alotaibi¹, Mark T Weller³, Mohamed A Ghanem¹

Affiliations

¹ Electrochemical Sciences Research Chair (ESRC), Chemistry Department, King Saud University 11451 Riyadh Saudi Arabia mghanem@ksu.edu.sa +96614675992 +966 114670405.
² K. A. CAR Energy Research and Innovation Center at Riyadh Saudi Arabia.
³ Chemistry Department, Cardiff University Cardiff CF10 3AT UK.

Abstract

An electrocatalyst of potassium nickel aluminium hexafluoride (KNiAlF₆) nanosheets has been prepared using solid-phase synthesis at 900 °C. X-ray diffraction, scanning electron microscopy, and conductivity studies confirmed the formation of KNiAlF₆ nanosheets having a cubic defect pyrochlore structure with an average thickness of 60-70 nm and conductivity of 1.297 × 10³ S m^-1. The electrochemical catalytic activity of the KNiAlF₆ nanosheets was investigated for urea oxidation in alkaline solution. The results show that the KNiAlF₆ 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 KNiAlF₆ 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 KNiAlF₆ 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 KNiAlF₆ nanosheets highly active electrocatalysts for urea oxidation in alkaline solution.