In Situ Reconstructed Bi ⁰ ‐Guided Electron‐Deficient Co(OH) ₂ for Enhanced Electrocatalytic Nitrate Reduction to Ammonia

Abstract Electrocatalytic nitrate reduction into ammonia (NitRR) over Co‐based catalysts is attractive but still constrained by the competition with H* coupling to produce H ₂ . Additionally, the fundamental mechanism underlying the interfacial engineering associated with electronic state transformation for strengthening oriented NitRR remains elusive. Herein, a Co(OH) ₂ /Bi ₁₂ O ₁₇ Br ₂ heterostructure is fabricated using a one‐step wet chemistry method, performing remarkable reactivity for NH ₃ production own to the formation of electron‐deficiency Co sites induced by Bi ₁₂ O ₁₇ Br ₂ . Unexpectedly, the NitRR activity of Co(OH) ₂ /Bi ₁₂ O ₁₇ Br ₂ increases gradually in the initial stage and then keeps at a high level, which is uncovered as the reconstruction of Bi ₁₂ O ₁₇ Br ₂ into Bi ⁰ . Theoretical calculations suggest that the in situ reconstruction guides the electron‐deficiency of Co and the shift of d ‐band center of Co toward the Fermi level, thus promoting the adsorption and conversion of intermediates. The synergistic effect of the hydrolysis dissociation over Co(OH) ₂ and the inhibition of H* coupling over Bi ⁰ contributes to high selectivity and activity for NitRR. The reconstructed catalyst shows a high ammonia yield rate of 7343.3 µg h ⁻¹ mg ⁻¹ at −0.6 V versus RHE and nearly 100% Faradaic efficiency at −0.4 V versus RHE. This study provides insight into the strengthening mechanism of Co‐based catalysts for NitRR.