The electrocatalytic nitrate-to-ammonia reduction reaction (NARR) is a promising route for zero-carbon ammonia synthesis as well as the recycling of nitrate waste, supporting the realization of agricultural nutrition supply and irrigation. TiO2 is a great potential NARR electrocatalyst candidate with ideal stability, yet it is hindered by limited selectivity for ammonia. In this regard, Co(ii) atoms with high faradaic efficiency toward NH3 (FENH3) are integrated into TiO2 nanosheets (NSs) (TiO2 NSs), affording a Co(ii)-decorated TiO2 NSs (Co/TiO2 NSs) catalyst. As an alternative to the value of 62.7% obtained using pristine TiO2 NSs, the as-prepared Co/TiO2 NSs catalyst exhibits a remarkable FENH3 increase up to 97.4% in 1.0 M neutral phosphate buffer solution (PBS) with 0.4 M NO3− at −0.72 V (vs. reversible hydrogen electrode, RHE), also outperforming other reported TiO2-based catalysts. And NH3 formation rates (rNH3) of 0.223 and 0.348 mmol cm−2 h−1 are also achieved at −0.72 and −1.12 V (vs. RHE), respectively. Furthermore, NARR also achieves a more favorable onset potential compared with the hydrogen evolution reaction (HER), reducing the energy input and displaying the promising future of NARR in coupling hydrogen production and storage.