Work

Nitrate-to-Ammonia Electroconversion at Neutral pH on Polycrystalline Vanadium Sulfide Derived from Vanadium Disulfide

Year: 2025

Type: article

Abstract: High Resolution Image Download MS PowerPoint Slide The electrochemical nitrate reduction reaction (NO 3 RR) offers a pathway to produce NH 3 for fuel and fertilizer from waste NO 3 – . In this work, a polycrystalline vanadium sulfide (VS x ), which is derived from solvothermally grown and annealed VS 2, is shown to exhibit excellent NO 3 RR activity (2.3 ± 0.6 mg·cm –2 geo.·h –1 @ −0.92 V RHE ) and Faradaic efficiency to NH 4 + (69 ± 6% at −0.69 V RHE ) in buffered neutral pH electrolyte containing 0.1 M NO 3 – . A variety of characterization techniques are leveraged to support the VS x assignment, including X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, selected area electron diffraction, and X-ray diffraction measurements. The VS 2 annealing step reduces the oxide character and generates VS x, which, based on the improved NO 3 RR activity, results in the creation of active sites for NO 3 – binding. To help shed light on NO 3 RR on VS x, VS 2 is used as a model system, and a grand-canonical density functional theory (GC-DFT) investigation of VS 2 shows strong evidence that S vacancies are active sites for NO 3 RR, where NO 3 – outcompetes H + for adsorption at the S-vacancy sites. Moreover, GC-DFT results highlight a thermodynamically favorable reaction to generate NH 4 + in an aqueous electrolyte at relevant cathodic potentials. As an annealed material, VS x may contain undersaturated V sites, which show an electronic structure similar to the theoretically calculated S-vacancy site of VS 2, and these sites may contribute to the observed increase in NO 3 RR activity and selectivity for NH 4 + on VS x versus unannealed VS 2 . Finally, kinetic isotope effect measurements suggest that the kinetic rate-limiting step of the NO 3 RR on VS x is not proton-coupled, indicating it may be the first electron transfer to adsorbed NO 3 *.

Source: ACS Applied Energy Materials

DOI: 10.1021/acsaem.5c01047