Defective NiFe2 O4 Nanoparticles for Efficient Urea Electro-oxidation

Improved Urea Oxidation Performance via Interface Electron Redistributions of the NiFe(OH)x/MnO2/NF p-p Heterojunction

The development of highly efficient urea oxidation reaction (UOR) electrocatalysts is the key to simultaneously achieving green hydrogen production and the treatment of urea-containing wastewater. Ni-based electrocatalysts are expected to replace precious metal catalysts for UOR because of their high activity and low cost. However, the construction of Ni-based electrocatalysts that can synergistically enhance UOR still needs further in-depth study. In this study, highly active electrocatalysts of NiFe(OH)x/MnO2 p-p heterostructures are constructed on nickel foam (NF) by electrodeposition (NiFe(OH)x/MnO2/NF), illustrating the effect of electronic structure changes at heterogeneous interfaces on UOR and revealing the catalytic mechanism of UOR. The NiFe(OH)x/MnO2/NF only needs 1.364 V (vs Reversible Hydrogen Electrode, RHE) to reach 10 mA cm-2 for UOR. Structural characterizations and theoretical calculations indicate that energy gap leads to directed charge transfer and redistribution at the heterojunction interface, forming electron-rich (MnO2) and electron-poor (NiFe(OH)x) regions. This enhances the catalyst's adsorption of urea and reaction intermediates, reduces thermodynamic barriers during the UOR process, promotes the formation of Ni3+ phases at lower potentials, and thus improves UOR performance. This work provides a new idea for the development of Ni-based high-efficiency UOR electrocatalysts.

Metal-Organic Framework-Derived Fe/Co-based Bifunctional Electrode for H2 Production through Water and Urea Electrolysis

Hollow-structured Fe_x Co_2-x P, Fe_x Co_3-x O₄ , and Prussian blue analogue (FeCo-PBA) microbuilding arrays on Ni foam (NF) are derived from Co-based metal-organic frameworks (Co-MOF) using a simple room temperature and post-heat-treatment route. Among them, Fe_x Co_2-x P/NF shows excellent bifunctional catalytic activities by demonstrating very low oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) overpotentials of 255/114 mV at a current density of 20/10 mA cm^-2 respectively, whereas Fe_x Co_3-x O₄ /NF and FeCo-PBA/NF demand higher overpotentials. Remarkably, for water electrolysis, Fe_x Co_2-x P/NF requires only 1.61 V to obtain 10 mA cm^-2 . In contrast to water electrolysis, urea electrolysis reduces overpotential and simultaneously purifies the urea-rich wastewater. The urea oxidation reaction at the Fe_x Co_2-x P/NF anode needs just 1.345 V to achieve 20 mA cm^-2 , which is 140 mV less than the 1.48 V potential required for OER. Moreover, the generation of H₂ through urea electrolysis needs only 1.42 V to drive 10 mA cm^-2 .