In Situ Reconstructed Bi0‐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.