Fe-doping induced electronic structure reconstruction in Ni-based metal-organic framework for improved energy-saving hydrogen production via urea degradation

Urea-assisted water electrolysis provides an energy-saving strategy toward hydrogen evolution and wastewaterrelevant environmental crisis. Efficient bifunctional electrocatalyst for urea oxidization reaction (UOR) and hydrogen evolution reaction (HER) is the key to solve these challenges. Herein, we demonstrated a Fe-doped Nibased MOF nanosheet arrays (FeNi-MOF NSs) through one-step hydrothermal synthesis for efficient energysaving urea-assisted water electrolysis. When applied for UOR, such prepared FeNi-MOF NSs achieves a current density of 10 and 100 mA cm-2 at overpotentials of 131 and 155 mV, respectively. Based on both comprehensive experimental and theoretical investigations, the excellent UOR performance can be attributed to that the Fe-doping caused electronic structure reconstruction in MOF, which not only induced the formation of abundant high-valence Ni as active centers for UOR, but also created more electronic states with optimized adsorption energies of reactant and product molecules on the surface, benefiting the UOR kinetics. Based on the UOR and HER activities of FeNi-MOF NSs, a urea electrolyser has been assembled, which affords 10 mA cm-2 current density at a low cell voltage of 1.431 V with excellent stability during long-term electrolysis.

Automated summary

Urea-assisted water electrolysis is an energy-saving strategy for hydrogen production and wastewater treatment. The key to solving these challenges lies in efficient bifunctional electrocatalysts for urea oxidation reaction (UOR) and hydrogen evolution reaction (HER). In this study, Fe-doped Ni-based MOF nanosheet arrays (FeNi-MOF NSs) were synthesized through a one-step hydrothermal method for efficient urea-assisted water electrolysis. The FeNi-MOF NSs achieved high current densities of 10 and 100 mA cm-2 at overpotentials of 131 and 155 mV, respectively, in UOR. The excellent UOR performance was attributed to electronic structure reconstruction induced by Fe-doping in the MOF, which promoted the formation of abundant high-valence Ni active centers for UOR and created more electronic states with optimized adsorption energies for reactant and product molecules on the surface, benefiting the UOR kinetics. The FeNi-MOF NSs were also used for HER, and a urea electrolyzer was assembled with a low cell voltage and excellent stability during long-term electrolysis.