Manipulation of Built‐in Electric Field in Heterojunctions for Efficient Electrocatalytic Nitrate Reduction to Ammonia

Heterojunction interface engineering can modulate the electronic structure of catalysts, playing a crucial role in enhancing catalytic activity. Rational regulation of the built‐in electric field can optimize the electronic structure of interfacial active sites and design efficient electrocatalysts for NO 3 RR. Herein, we develop a compact heterostructure composed of Cd‐doped In 2 S 3 /CdS nanosheets over CoO x nanoparticles (Cd‐In 2 S 3 /CdS/CoO x ) toward efficient ammonia electrosynthesis, in which the Cd‐doped In 2 S 3 /CdS heterojunction generates a built‐in electric field that promotes interfacial electron transfer and modulates the electronic microenvironment, thereby enhancing the electron injection of active sites on CoO x . Various spectroscopic analyses and theoretical calculations revealed that the unique architecture with built‐in electric fields strengthens the Co‐N orbital interaction between the Co site and *NOH, lowering the energy barrier of the rate‐determining step, thereby improving the reaction kinetics of the hydrogenation process. Consequently, the Cd‐In 2 S 3 /CdS/CoO x achieves exceptional performance with 98.48% Faradaic efficiency and a high NH 3 yield of 45.22 mg h −1 mg cat −1 . This study proposes an effective strategy that elucidates how doping engineering enhances the built‐in electric field of heterojunctions and optimizes the electronic structure of interfacial active sites, thereby improving NO 3 RR performance.