Surface reconstruction of defect-engineered MIL-88@Fe2O3 p-n heterojunction for enhanced electrocatalytic water and urea oxidation

Defective p-n heterojunction engineering has been under the spotlighted as a promising strategy for electrochemical oxygen evolution reaction (OER) and urea oxidation reaction (UOR). Still, it remains a great challenge how to use the space-charge region of p-n heterojunction to study the regulation mechanism of the p-n heterogeneous interface and vacancy defects on the incomplete self-reconstruction from pristine materials to (oxy) hydroxides. Herein, NH2-MIL-88b(Fe)/alpha-Fe2O3 p-n heterojunction with rich oxygen vacancies (denoted as p-n MIL-88@Fe2O3-OV) has been prepared using a simple one-step solvothermal method. The prepared catalyst exhibits promising electrocatalytic performance for OER and UOR, requiring low potentials of 1.50 and 1.35 V to reach the current density of 10 mA cm(-2), respectively. The combined in-situ/ex-situ experimental and theoretical investigations unveil that p-n heterojunction engineering can not only facilitate charge transfer from ntype alpha-Fe2O3 to p-type NH2-MIL-88b(Fe) (denoted as MIL-88) and generate abundant oxygen vacancies, but also appreciably trigger phase transformation of MIL-88 into active FeOOH. The reconstructed FeOOH/alpha-Fe2O3 heterojunction optimizes the bonding strength towards key oxygen-containing intermediates and boosts the intrinsic activity. This work provides new insight into the self-reconstruction effect in the p-n heterojunction for enhancing the OER and UOR catalytic activity.