Manipulating Trimetal Catalytic Activities for Efficient Urea Electrooxidation-Coupled Hydrogen Production at Ampere-Level Current Densities

Abstract

Replacing the oxygen evolution reaction (OER) with the urea oxidation reaction (UOR) in conjunction with the hydrogen evolution reaction (HER) offers a feasible and environmentally friendly approach for handling urea-rich wastewater and generating energy-saving hydrogen. However, the deactivation and detachment of active sites in powder electrocatalysts reported hitherto present significant challenges to achieving high efficiency and sustainability in energy-saving hydrogen production. Herein, a self-supported bimetallic nickel manganese metal-organic framework (NiMn-MOF) nanosheet and its derived heterostructure composed of NiMn-MOF decorated with ultrafine Pt nanocrystals (Pt_NC/NiMn-MOF) are rationally designed. By leveraging the synergistic effect of Mn and Ni, along with the strong electronic interaction between NiMn-MOF and Pt_NC at the interface, the optimized catalysts (NiMn-MOF and Pt_NC/NiMn-MOF) exhibit substantially reduced potentials of 1.459 and -0.129 V to reach 1000 mA cm^-2 during the UOR and HER. Theoretical calculations confirm that Mn-doping and the heterointerface between NiMn-MOF and Pt nanocrystals regulate the d-band center of the catalyst, which in turn enhances electron transfer and facilitates charge redistribution. This manipulation optimizes the adsorption/desorption energies of the reactants and intermediates in both the HER and UOR, thereby significantly reducing the energy barrier of the rate-determining step (RDS) and enhancing the electrocatalytic performance. Furthermore, the urea degradation rates of Pt_NC/NiMn-MOF (96.1%) and NiMn-MOF (90.3%) are significantly higher than those of Ni-MOF and the most reported advanced catalysts. This work provides valuable insights for designing catalysts applicable to urea-rich wastewater treatment and energy-saving hydrogen production.