The selective electrocatalytic reduction of nitrate to ammonia using Co(ii)-decorated TiO2 nanosheets

Abstract

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 (FE_NH3) 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 FE_NH3 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 (r_NH3) 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.