Composition regulation of Ni-BDC MOF architecture to enhance electrocatalytic urea oxidation in alkaline solution†

Urea oxidation reaction (UOR) is a promising substitution for the oxygen evolution reaction (OER) on anode for highly efficient H₂ production. However, the sluggish kinetics and high oxidation potential of Ni^II → Ni^III severely limit the activity of Ni-based catalysts in the electrochemical UOR. Herein, composition regulation was adopted to enhance the electrocatalytic activity of a nickel-benzene dicarboxylate framework (Ni-BDC MOF)-derived electrode towards urea oxidation. In 1 M KOH with 0.33 M urea solution, the derived amorphous tri-metallic hydroxide layer on the surface of the NiMnCo MOF, induced by electro-activation, exhibited a low onset potential and a steeply rising current density with increasing applied potential. It achieved a benchmark current density of 10/100 mA cm⁻² at an anode potential of 1.28/1.33 V vs. RHE, respectively. In particular, a 500 mA cm⁻² current density was reached at an impressively low potential of 1.41 V vs. RHE. This exceptional performance is ascribed to the fact that the open framework provides a large electrochemical active surface, while the multicomponent synergy decreases the Ni^II → Ni^III oxidation potential, enhances electron transfer and promotes the UOR kinetics. This study suggests that rational composition regulation is a promising approach to improving the performance of Ni-based MOF materials towards electrocatalytic urea oxidation.