Cobalt Single Atoms in Hexagonal Boron Nitride Host for Efficient Electrochemical Nitrate Reduction

Stabilizing transition‐metal single atoms in chemically inert hexagonal boron nitride (hBN) remains a fundamental challenge due to the absence of intrinsic anchoring sites. Here, we report an in situ co‐pyrolysis strategy that simultaneously constructs hBN nanosheets and anchors atomically dispersed Co single atoms. Our first experimental demonstration shows that nitrate‐to‐ammonia electroreduction (NO 3 RR) performance of Co single atoms in hBN (Co 1 /hBN) is far superior to Co single atoms in N‐doped graphene (Co 1 /NG), with over sixfold enhancement in per‐site turnover frequency compared with carbon‐supported Co single atoms. The Co 1 /hBN catalyst delivers high Faradaic efficiency, yield rate, low Tafel slope, and definitive 15 N isotopic validation. Importantly, the structural adaptability of the polar hBN lattice significantly enhances nitrate adsorption, lowers the adsorption free energy of NO 3 − ‐derived intermediates, and strongly accelerates NO 3 RR kinetics relative to Co 1 /NG. Combined EXAFS and DFT analyses identify a Co–N 6 coordination environment, while DFT reveals that NO 3 − adsorption induces a support‐driven Co–N 6 → distorted Co–N 4 transformation, lowering the rate‐determining energy barrier to 0.43 eV. In contrast, Co 1 /NG retains a rigid Co–N 4 configuration with slower kinetics (0.62 eV). These findings highlight host‐induced coordination flexibility as a powerful design principle for high‐performance single‐atom electrocatalysts in nitrogen‐conversion reactions.