Deciphering the Space Charge Effect of the CoNiLDH/FeOOH n-n Heterojunction for Efficient Electrocatalytic Oxygen Evolution.

Space charge transfer is an effective strategy to regulate the electron density of narrow bandgap semiconductors for enhancing electrocatalytic activity. Herein, the CoNiLDH/FeOOH n-n heterojunction hollow nanocages structure is constructed. The hollow structure provides abundant catalytic active sites and enhances mass transfer. The space charge region in the n-n heterojunction significantly promotes the adsorption of OH and electron transfer; and the built-in electric field accelerates the electron transport, optimizes the electronic structure during the catalytic reaction process, and ensures the stability of surface charged active center sites in the heterojunction. Thus, CoNiLDH/FeOOH delivers an excellent oxygen evolution reaction (OER) overpotential of 250 mV to achieve a current density of 10 mA cm with a small Tafel slope of 60 mV dec , and superior electrocatalytic durability for 210 h at a high current density. Density functional theory calculations further verify that the space charge effect and built-in electric field in the n-n heterojunction of CoNiLDH/FeOOH can improve the electron transfer and lower the adsorption energy of OH and the reaction energy barrier of the rate-determining step. This work provides a new fundamental understanding of the space charge effect of semiconductor heterojunction during the electrocatalytic process for developing more efficient OER electrocatalysts.