Photoenhanced Electrochemical\nConversion of Nitrate\nto Ammonia Via Sulfur Vacancy-Rich Exfoliated MoS<sub>2</sub>

Nitrate ion is a common pollutant in surface and groundwater.\nHence,\nits catalytic conversion into ammonia at ambient conditions by electrochemical\nand photoelectrochemical pathways is an attractive alternative to\ncurrent ammonia production from the energy-intensive and high-carbon-featuring\nHaber-Bosch process. As such, developing highly active and product-selective\ncatalysts with good durability and cost-effectiveness is highly desired.\nIn this work, exfoliated MoS<sub>2‑x</sub> is reported as a\nhighly active and selective electrocatalyst and a photoelectrocatalyst\nfor nitrate reduction to ammonia. Exfoliation via the acid treatment\nof bulk MoS<sub>2</sub> results in exfoliated MoS<sub>2‑x</sub>, which is only a few layers thick and has a high degree of sulfur\nvacancies (ca. 12−13%). Electrochemical studies and electrolysis\nproduct analysis reveal promising nitrate reduction activity, which\nis found to be highly enhanced by the application of visible light\nillumination. The exfoliated MoS<sub>2‑x</sub> achieves a Faradaic\nefficiency of 69% with an ammonia yield rate of 5.56 mmol g<sub>cat</sub><sup>–1</sup> h<sup>–1</sup> in the absence of a light\nsource, which is enhanced to 80% with an ammonia yield of 7.48 mmol\ng<sub>cat</sub><sup>–1</sup> h<sup>–1</sup> upon visible\nlight illumination. DFT calculations support the binding of nitrate\nand other NO<sub><i>x</i></sub> species to the sulfur vacancies,\nresulting in the formation of *N, which is then reduced to ammonia.