Active NiO outperforms other Ni-based catalysts for urea electrolysis

초록

Single- and multi-component nickel (Ni)-based oxide and oxyhydroxide catalysts have been developed for the urea oxidation reaction (UOR) in alkaline solutions. Herein, NiO catalysts synthesized via a facile process show excellent UOR activity in alkaline solutions, with 0.33- and 0.46-V lower E values for the UOR than for the oxygen evolution reaction (OER) at J values of 100 and 400 mA cm(-2), respectively. The bulk electrolysis of urea with the optimized NiO catalyst results in the stepwise formation of ammonia, nitrite, and nitrate, with a faradaic efficiency of similar to 100 % for nitrite formation at J = 400 mA cm(-2) in the initial stage. The NiO catalyst also shows a high electrocatalytic stability over 24 h, with insignificant changes in morphology, crystallinity, and elemental oxidation states. Although NiOOH is also capable of driving the UOR, it exhibits a higher E value and slower UOR kinetics under the same J as for NiO. The as-synthesized NiO catalyst is superior to most previously-reported single- and multi-component Ni-based catalysts in terms of E values and Tafel slopes. This is attributed to a high electrical conductivity, intrinsic activity, stability, and rich active sites. Various detailed surface characterization and electrochemical studies confirm the excellent UOR performance of the NiO.

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