Metal-Organic Frameworks Offering Tunable Binary Active Sites toward Highly Efficient Urea Oxidation Electrolysis.

Area of Science:

• Materials Science
• Electrochemistry
• Environmental Science

Background:

• Electrocatalytic urea oxidation reaction (UOR) is crucial for degrading urea in wastewater into N$_{2}$ and CO$_{2}$.
• Sluggish kinetics and intermediate adsorption/desorption hinder efficient UOR.
• Rational design of catalytically active sites is essential to overcome these challenges.

Purpose of the Study:

• To demonstrate metal-organic frameworks (MOFs) as a platform for designing binary active sites to enhance UOR.
• To achieve remarkable electrocatalytic activity and efficient urea degradation using a tailored MOF.
• To provide insights into the synergistic roles of active sites in UOR.

Main Methods:

• Synthesis and characterization of a Ni/Mn-based MOF (NiMn$_{0.14}$-BDC).
• Electrocatalytic evaluation of the MOF for UOR, including voltage-current density measurements and turnover frequency (TOF) determination.
• Combination of experimental characterization and theoretical calculations to elucidate the reaction mechanism.

Main Results:

• The NiMn$_{0.14}$-BDC MOF demonstrated excellent UOR activity, requiring only 1.317 V to reach 10 mA cm$^{-2}$.
• A high TOF of 0.15 s$^{-1}$ was achieved at 1.4 V, leading to 81.87% urea degradation in 0.33 M urea solution.
• Synergistic effects between Ni and Mn sites were identified, influencing electronic structure and d-band center for improved intermediate evolution.

Conclusions:

• MOFs provide an effective platform for designing binary active sites to facilitate rate-determining steps in UOR.
• The NiMn$_{0.14}$-BDC MOF exhibits superior electrocatalytic performance for urea oxidation.
• This study offers valuable insights into active site engineering for highly efficient MOF-based electrocatalysts in UOR.