Abstract

Abstract A built‐in electric field in electrocatalyst can significantly accumulate higher concentration of NO 3 − ions near electrocatalyst surface region, thus facilitating mass transfer for efficient nitrate removal at ultra‐low concentration and electroreduction reaction (NO 3 RR). A model electrocatalyst is created by stacking CuCl (111) and rutile TiO 2 (110) layers together, in which a built‐in electric field induced from the electron transfer from TiO 2 to CuCl (CuCl_BEF) is successfully formed . This built‐in electric field effectively triggers interfacial accumulation of NO 3 − ions around the electrocatalyst. The electric field also raises the energy of key reaction intermediate *NO to lower the energy barrier of the rate determining step. A NH 3 product selectivity of 98.6 %, a low NO 2 − production of <0.6 %, and mass‐specific ammonia production rate of 64.4 h −1 is achieved, which are all the best among studies reported at 100 mg L −1 of nitrate concentration to date.