Carbon-Oxyanion Atomically Steering Direct Urea Oxidation on NiOOH at Industrial Current Densities

Abstract

Developing cost-effective electrocatalysts for the urea oxidation reaction (UOR) requires overcoming fundamental limitations of Ni-based systems: sluggish Ni2+/Ni3+ redox kinetics, competing oxygen evolution, and structural instability. Herein, we demonstrate an organic acid-assisted electrochemical reconstruction strategy to synthesize carbon-based oxyanion atomically modified beta-NiOOH nanosheets (Activated NiC2O4/NF) from nickel oxalate precursors. The in situ embedded oxyanions (-COx) confer triple functionality: 1) enabling direct urea oxidation at ultralow potentials (1.253 V@10 mA cm(-2), 1.357 V@2000 mA cm(-2) in 6 m KOH + 0.33 m urea) bypassing NiOOH pre-formation; 2) suppressing competing OER via a 0.23 eV thermodynamic penalty on the deprotonation evolution step; 3) enhancing lattice oxygen stability by increasing the oxygen vacancy formation energy. This synergy delivers record stability (3000 h@100 mA cm(-2)) and near-unity N-product selectivity (>95 +/- 2% Faradaic efficiency). In a practical alkaline urea electrolyzer (6 m KOH + 0.33 M urea, 80 degrees C), it achieves 2000 mA cm(-2) at 2.089 V, surpassing state-of-the-art systems. Operando studies and DFT calculations reveal that in situ-generated oxyanions not only promote UOR via an NH3 intermediate-assisted pathway but also inhibit the oxygen evolution reaction by suppressing deprotonation evolution at the active sites. This work establishes a paradigm for anionic-modification engineering in high-current-density electrocatalysis.