Heterostructured Co/Co3O4 anchored on N-doped carbon nanotubes as a highly efficient electrocatalyst for nitrate reduction to ammonia

Abstract

The electrochemical reduction of nitrate (NO₃⁻) to ammonia (NH₃) has emerged as an attractive approach for selectively reducing NO₃⁻ to highly value-added NH₃ and removing NO₃⁻ pollutants simultaneously. In this work, a heterostructured Co/Co₃O₄ electrocatalyst anchored on N-doped carbon nanotubes was prepared and applied for the NO₃⁻ reduction towards NH₃ under alkaline conditions. The catalyst achieves outstanding performance with up to 67% NH₃ faradaic efficiency at −1.2 V vs. Hg/HgO and 8.319 mg h⁻¹ mg_cat⁻¹ yield at −1.7 V vs. Hg/HgO. In addition, it also exhibits good long-term stability. ¹⁵N isotopic labelling experiments prove that the yielded NH₃ is derived from NO₃⁻ species. In situ electrochemical Raman spectra revealed that the structure of the as-prepared catalyst showed outstanding stability and identified possible intermediates during the electrocatalytic NO₃⁻ reduction reaction (NO₃RR).