Metal organic framework-assisted in-situ synthesis of β-NiMnOOH nanosheets with abundant NiOOH active sites for efficient electro-oxidation of urea.

NiOOH has been considered as the active center for urea oxidation reaction (UOR), but it remains challenging to synthesize high-performance NiOOH-based catalysts. Herein, we realize the synthesis of a high-performance NiOOH-based catalyst through in-situ transformation from the NiMn-based metal-organic framework to NiMnOOH. X-ray photoelectron spectroscopy characterization shows that the Ni/Ni ratio in the NiMnOOH is 3.9 times as big as that in the Ni(OH), and in-situ Raman characterization further consolidates the presence of the NiOOH species in the NiMnOOH and as well unveils the faciliated Ni/Ni redox reaction. The abundant NiOOH species, the markedly facilitated Ni/Ni redox reaction and the Ni-Mn synergy contribute to the high intrinsic activity of the NiMnOOH towards UOR. The NiMnOOH exhibits an impressively low onset potential of 1.305 V vs reversible hydrogen electrode (RHE) and requires only a small potential of 1.34 V vs RHE to deliver a current density of 100 mA cm in 1.0 M KOH + 0.33 M urea. In addition, the NiMnOOH catalyst possesses good long-term working stability.