Nitrogen-doped WSe2 few-layer nanotubes for electrocatalytic nitrate reduction via Se vacancies

Abstract

Unlike pure transition metal dichalcogenides (TMDs) and chalcogen element-substituted TMDs, non-chalcogen element-doped TMDs could offer more extensive physicochemical properties. Moreover, the closed few-layer TMDs nanotubes (NTs) are unique considering the healing of the dangling bonds of the rim atoms of the layers invoked by the folding and seaming of the layers. Electrochemical conversion of nitrate group into ammonia represents a mild way to production of ammonia and economic utilization of NO3−-containing wastewater. Herein, nitrogen-doped tungsten diselenide (N-WSe2) few-layer NTs have been prepared, physically characterized, and synchronously modulated by controlling the N content. Se vacancies (Sev) are introduced into the N-WSe2 NTs, which results from the compensation of the charge imbalance when trivalent N3− ions are introduced in place of divalent Se2− ions. Accordingly, Sev serve as the enhanced active sites for electrocatalytic nitrate reduction reaction (NO3−RR), which is an effective avenue to the nitrate depollution in water and catalytic ammonia synthesis. An ammonium yield rate of 35.6 mg cm−2 h−1 at −1.0 VRHE and Faradaic efficiencies (FEs) of >93% are obtained, while the hydrogen evolution reaction (HER) is severely suppressed due to eliminating of the dangling bonds. Molecular orbital (MO) model in combination with density functional theory (DFT) theoretical computations reveals that the Sev effectively enhance adsorption and activation of NO3−, reduce the energy barrier of the rate-determining step (RDS), and facilitate the formation of intermediates in the elementary steps. These theoretical models and analyses also interpret the high selectivity of the N-WSe2 NTs for NO3−RR over HER.