Zerong Li

Electrocatalytic nitrate reduction reaction (NO3RR) affords a bifunctional character in the carbon-free ammonia synthesis and remission of nitrate pollution in water. Here, we fabricated the Co3O4 nanosheet array with cobalt vacancies on carbon cloth (vCo-Co3O4/CC) by in situ etching aluminum-doped Co3O4/CC, which exhibits an excellent Faradaic efficiency of 97.2% and a large NH3 yield as high as 517.5 μmol h–1 cm–2, better than the pristine Co3O4/CC. Theoretical calculative results imply that the cobalt vacancies can tune the local electronic environment around Co sites of Co3O4, increasing the charge and reducing the electron cloud density of Co sites, which is thus conducive to adsorption of NO3– on Co sites for greatly enhanced nitrate reduction. Furthermore, the vCo-Co3O4 (311) facet presents excellent NO3RR activity with a low energy barrier of about 0.63 eV on a potential-determining step, which is much smaller than pristine Co3O4 (1.3 eV).

Abstract Electrochemical nitrate (NO 3 − ) reduction reaction (NO 3 − RR) is a potential sustainable route for large‐scale ambient ammonia (NH 3 ) synthesis and regulating the nitrogen cycle. However, as this reaction involves multi‐electron transfer steps, it urgently needs efficient electrocatalysts on promoting NH 3 selectivity. Herein, a rational design of Co nanoparticles anchored on TiO 2 nanobelt array on titanium plate (Co@TiO 2 /TP) is presented as a high‐efficiency electrocatalyst for NO 3 − RR. Density theory calculations demonstrate that the constructed Schottky heterostructures coupling metallic Co with semiconductor TiO 2 develop a built‐in electric field, which can accelerate the rate determining step and facilitate NO 3 − adsorption, ensuring the selective conversion to NH 3 . Expectantly, the Co@TiO 2 /TP electrocatalyst attains an excellent Faradaic efficiency of 96.7% and a high NH 3 yield of 800.0 µmol h −1 cm −2 under neutral solution. More importantly, Co@TiO 2 /TP heterostructure catalyst also presents a remarkable stability in 50‐h electrolysis test.

Oxygen vacancy-enriched Co 3 O 4 nanosheet arrays enable ambient electrosynthesis of NH 3 via nitrate reduction, achieving a faradaic efficiency of 96.9% and a NH 3 yield of 12 157 μg h −1 cm −2 in 0.1 M NaOH with 0.1 M NO 3 − .

Abstract Ammonia (NH 3 ) is an indispensable feedstock for fertilizer production and one of the most ideal green hydrogen rich fuel. Electrochemical nitrate (NO 3 − ) reduction reaction (NO 3 − RR) is being explored as a promising strategy for green to synthesize industrial‐scale NH 3 , which has nonetheless involved complex multi‐reaction process. This work presents a Pd‐doped Co 3 O 4 nanoarray on titanium mesh (Pd‐Co 3 O 4 /TM) electrode for highly efficient and selective electrocatalytic NO 3 − RR to NH 3 at low onset potential. The well‐designed Pd‐Co 3 O 4 /TM delivers a large NH 3 yield of 745.6 µmol h −1 cm −2 and an extremely high Faradaic efficiency (FE) of 98.7% at −0.3 V with strong stability. These calculations further indicate that the doping Co 3 O 4 with Pd improves the adsorption characteristic of Pd‐Co 3 O 4 and optimizes the free energies for intermediates, thereby facilitating the kinetics of the reaction. Furthermore, assembling this catalyst in a Zn‐NO 3 − battery realizes a power density of 3.9 mW cm −2 and an excellent FE of 98.8% for NH 3 .